WO2025189249A1

WO2025189249A1 - Methods and systems for programming closed-loop neural stimulation therapy

Info

Publication number: WO2025189249A1
Application number: PCT/AU2025/050243
Authority: WO
Inventors: Robert Bruce GORMAN; Daniel John PARKER; Annie Hu
Original assignee: Saluda Medical Pty Ltd
Current assignee: Saluda Medical Pty Ltd
Priority date: 2024-03-14
Filing date: 2025-03-14
Publication date: 2025-09-18
Anticipated expiration: 2026-09-14

Abstract

Disclosed is a neural stimulation system comprising: an implantable closed-loop neural stimulation device for controllably delivering neural stimuli; a display; and a processor. The closed-loop neural stimulation device comprises a feedback controller configured to adjust a stimulus intensity parameter value so as to maintain a measured neural response intensity at a target value. The processor is configured to: render a graphical user interface on the display, the graphical user interface including one or more controls configured to adjust a target value; represent the target value on an element of the graphical user interface; and represent a predetermined target value on the element of the graphical user interface.

Description

METHODS AND SYSTEMS FOR PROGRAMMING CLOSED-LOOP NEURAL STIMULATION THERAPY [0001] The present application claims priority from Australian Provisional Patent Application No 2024900665 filed on 13 March 2024, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD [0002] The present invention relates to neuromodulation and in particular to programming closed- loop neural stimulation therapy for consistent analgesic effect. BACKGROUND OF THE INVENTION [0003] There are a range of situations in which it is desirable to apply neural stimuli in order to alter neural function, a process known as neuromodulation. For example, neuromodulation is used to treat a variety of disorders including chronic neuropathic pain, movement disorders, and voiding disorders. A neuromodulation device applies an electrical pulse (stimulus) to neural tissue (fibres, or neurons) in order to generate a therapeutic effect. In general, the electrical stimulus generated by a neuromodulation device evokes a neural response known as an action potential in a neural fibre which then has either an inhibitory or excitatory effects on neural networks. Inhibitory effects can be used to modulate an undesired process such as the transmission of pain, or excitatory effects may be used to cause a desired effect such as the contraction of a muscle. [0004] When used to relieve neuropathic pain originating in the trunk and limbs, the electrical pulse is applied to the dorsal column (DC) of the spinal cord, a procedure referred to as spinal cord stimulation (SCS). Such a device typically comprises an implanted electrical pulse generator, and a power source such as a battery that may be transcutaneously rechargeable by wireless means, such as inductive transfer. An electrode array is connected to the pulse generator, and is implanted adjacent the target neural fibre(s) in the spinal cord, typically in the dorsal epidural space above the dorsal column. An electrical pulse of sufficient intensity applied to the target neural fibres by a stimulus electrode causes the depolarisation of neurons in the fibres, which in turn generates an action potential in the fibres. Action potentials propagate along the fibres in an orthodromic direction (in afferent fibres this means towards the head, or rostral) and in an antidromic direction (in afferent fibres this means towards the cauda, or caudal) directions. Action potentials propagating along A^ (A-beta) fibres being stimulated in this way may inhibit the transmission of pain from a region of the body innervated by the target neural fibres (the dermatome) to the brain. To sustain the pain relief effects, stimuli are applied repeatedly, for example at a stimulus frequency in the range of 30 Hz - 100 Hz. [0005] For effective and comfortable neuromodulation, it is necessary to maintain stimulus intensity above a recruitment threshold. Stimuli below the recruitment threshold will fail to recruit sufficient neurons to generate action potentials with a therapeutic effect. In some neuromodulation applications, response from a single class of fibre is desired, but the stimulus waveforms employed can evoke action potentials in other classes of fibres which cause unwanted side effects. In pain relief, it is therefore desirable to apply stimuli with intensity below a discomfort threshold, above which uncomfortable or painful percepts arise due to over-recruitment of A^ fibres or recruitment of undesired fibre classes. When recruitment is too large, A^ fibres produce uncomfortable sensations. Stimulation at high intensity may even recruit Aδ (A-delta) fibres, which are sensory nerve fibres associated with acute pain, cold and heat sensation. It is therefore desirable to maintain stimulus intensity within a therapeutic range between the recruitment threshold and the discomfort threshold. [0006] The task of maintaining appropriate neural recruitment is made more difficult by electrode migration (change in position over time) or postural changes of the implant recipient (patient), either of which can significantly alter the neural recruitment arising from a given stimulus, and therefore the therapeutic range. There is room in the epidural space for the electrode array to move, and such array movement from migration or posture change alters the electrode-to-cord distance and thus the recruitment efficacy of a given stimulus. Moreover, the spinal cord itself moves within the cerebrospinal fluid (CSF) with respect to the dura. During postural changes, the amount of CSF or the distance between the spinal cord and the electrode can change significantly. This effect is so large that postural changes alone can cause a previously comfortable and effective stimulus regime to become either ineffectual or painful. [0007] Attempts have been made to address such problems by way of feedback or closed-loop control, such as using the methods set forth in International Patent Publication No. WO2012/155188 by the present applicant, the content of which is incorporated herein by reference. Feedback control seeks to compensate for relative nerve / electrode movement by controlling the intensity of the delivered stimuli so as to maintain neural recruitment at or near a target value. The intensity of a neural response evoked by a stimulus may be used as a feedback variable representative of the amount of neural recruitment. A signal representative of the neural response may be sensed by a measurement electrode in electrical communication with the recruited neural fibres, and processed to obtain the feedback variable. Based on the response intensity, the intensity of the applied stimulus may be adjusted to bring the response intensity closer to the target value. [0008] It is therefore desirable to accurately measure the intensity and other characteristics of a neural response evoked by the stimulus. The action potentials generated by the depolarisation of a large number of fibres by a stimulus sum to form a measurable signal known as an evoked compound action potential (ECAP). Accordingly, an ECAP is the sum of responses from a large number of single fibre action potentials. The ECAP generated from the depolarisation of a group of similar fibres may be measured at a measurement electrode as a positive peak potential, then a negative peak, followed by a second positive peak. This morphology is caused by the region of activation passing the measurement electrode as the action potentials propagate along the individual fibres. [0009] Approaches proposed for obtaining a neural response measurement are described by the present applicant in International Patent Publication No. WO2012/155183, the content of which is incorporated herein by reference. [0010] Closed-loop neural stimulation therapy is governed by a number of parameters to which values must be assigned to implement the therapy. The effectiveness of the therapy depends in large measure on the suitability of the assigned parameter values to the patient undergoing the therapy. As patients vary significantly in their physiological characteristics, a “one-size-fits-all” approach to parameter value assignment is likely to result in ineffective therapy for a large proportion of patients. An important preliminary task, once a neuromodulation device has been implanted in a patient, is therefore to assign values to the therapy parameters that maximise the effectiveness of the therapy the device will deliver to that particular patient. This task is known as programming or fitting the device. Programming generally involves applying certain test stimuli via the device, recording responses, and based on the recorded responses, determining the most effective parameter values for the patient. The resulting parameter values are then formed into a “program” that may be loaded to the device to govern subsequent therapy. Some of the recorded responses may be neural responses evoked by the test stimuli, which provide an objective source of information that may be analysed along with subjective responses elicited from the patient. In an effective programming system, the more responses that are analysed, the more effective the eventual assigned parameter values should be. [0011] However, programming may be costly and time-consuming if unnecessarily prolonged. There is therefore an incentive to minimise the number of test stimuli to be applied and the amount of information to be recorded and analysed in order to produce the assigned values of the therapy parameters. In particular, the size of the therapy parameter search space is such that testing every possible combination of therapy parameters is impractical. [0012] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present Background is solely for the purpose of providing a context for the present technology. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present technology as it existed before the priority date of each claim of the present disclosure. SUMMARY OF THE INVENTION [0013] The present invention seeks to provide methods and systems for programming closed-loop neural stimulation therapy, which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or at least provide an alternative. [0014] According to a first aspect of the present technology, there is provided a neural stimulation system comprising an implantable device for controllably delivering neural stimuli; a display; and a processor. The device comprises: a stimulus source configured to deliver neural stimuli to a neural pathway of a patient, the neural stimuli being configured to evoke neural responses from the neural pathway; measurement circuitry configured to capture signal windows from signals sensed on the neural pathway; and a control unit. The control unit configured to: control the stimulus source to deliver a neural stimulus according to a stimulus intensity parameter; measure an intensity of an evoked neural response in a captured signal window subsequent to the neural stimulus; and adjust, using a feedback controller, the stimulus intensity parameter so as to maintain the measured response intensity at or near a target response intensity value. The processor configured to: render a graphical user interface on the display, the graphical user interface including one or more controls configured to adjust a target value; represent the target value on an element of the graphical user interface; and represent a predetermined target value on the element of the graphical user interface. [0015] According to a first aspect of the present technology, there is provided a neural stimulation system comprising a closed-loop neural stimulation device; a display; and a processor. A processor configured to: render a graphical user interface on the display, the graphical user interface including one or more controls configured to adjust a target value; represent the target value on an element of the graphical user interface; and represent a predetermined target value on the element of the graphical user interface. [0016] According to a third aspect of the present technology, there is provided a method comprising: rendering a graphical user interface on a display, the graphical user interface including one or more controls configured to adjust a target value of a closed-loop neural stimulation device comprising a control unit configured to adjust, using a feedback controller, a stimulus intensity parameter of delivered neural stimuli so as to maintain an intensity of a measured neural response at or near a target response intensity value; representing the target value on an element of the graphical user interface; and representing a predetermined target value on the element of the graphical user interface. [0017] The present invention has been developed primarily for use in or with neuromodulation of the spinal cord and will be described hereinafter mostly with reference to this application. However, it will be appreciated that the present invention is not limited to this particular field of use, and may be applied in other neuromodulation contexts, including but not limited to sacral nerve stimulation, pudendal nerve stimulation, deep brain stimulation, stimulation of other parts of the peripheral and central nervous system. It will further be appreciated that the present invention may be applied for treatment of conditions other than chronic pain, including but not limited to movement disorders, Crohn’s disease, rheumatoid arthritis, diabetes, Reynaud’s phenomenon, incontinence/bladder disorders, faecal incontinence, non-obstructive urinary retention, constipation, chronic inflammatory conditions, migraine, stroke, or depression. BRIEF DESCRIPTION OF THE DRAWINGS [0018] Notwithstanding any other implementations which may fall within the scope of the present invention, implementations of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [0019] Fig. 1 schematically illustrates an implanted spinal cord stimulator, according to one implementation of the present technology; [0020] Fig.2 is a block diagram of the stimulator of Fig.1; [0021] Fig.3 is a schematic illustrating interaction of the implanted stimulator of Fig.1 with a nerve; [0022] Fig.4a illustrates an idealised activation plot for one posture of a patient undergoing neural stimulation; [0023] Fig.4b illustrates the variation in the activation plots with changing posture of the patient; [0024] Fig.5 is a schematic illustrating elements and inputs of a closed-loop neural stimulation (CLNS) system, according to one implementation of the present technology; [0025] Fig.6 illustrates the typical form of an electrically evoked compound action potential of a healthy subject; [0026] Fig.7 is a block diagram of a neural stimulation therapy system including the implanted stimulator of Fig.1 according to one implementation of the present technology; [0027] Fig.8 is an illustration of one implementation of a graphical user interface (GUI) presented on a remote controller; [0028] Fig.9a is an illustration of an element of the GUI of Fig.8 representing a current target value; [0029] Fig.9b is an illustration of an element of an alternative GUI representing a current target value; and [0030] Fig.10a is an illustration of the GUI element of Fig.9a representing a current target value and a predetermined target value according to one implementation of the present technology; [0031] Fig.10b is an illustration of the GUI element of Fig.9b representing a current target value and a predetermined target value according to one implementation of the present technology; [0032] Fig.11 is a flowchart illustrating a method of representing a predetermined target value of a normalised measure of dose (NMD) on a GUI element such as the GUI element of Fig.9a or Fig.9b, according to one implementation of the present technology; [0033] Fig.12 is an illustration of the GUI element of Fig.10a accompanied by an array of normalised measure of dose values; and [0034] Fig.13 is a flowchart illustrating a method of representing a predetermined target NMD value alongside a current target NMD value on a GUI element configured to represent target NMD values within a range on a uniform scale, according to one implementation of the present technology. DETAILED DESCRIPTION OF THE PRESENT TECHNOLOGY [0035] Fig. 1 schematically illustrates an implanted spinal cord stimulator 100 in a patient 108, according to one implementation of the present technology. Stimulator 100 comprises an electronics module 110 housed within a conductive case, implanted at a suitable location. In one implementation, stimulator 100 is implanted in the patient’s lower abdominal area or posterior superior gluteal region. In other implementations, the electronics module 110 is implanted in other locations, such as in a flank or sub-clavicularly. The electronics module 110 is configured to electrically connect to an electrode assembly, typically comprising an electrode array 150 implanted within the epidural space and connected to the module 110 by a suitable lead. The electrode array 150 may comprise one or more electrodes such as electrode pads on a paddle lead, circular (e.g., ring) electrodes surrounding the body of a percutaneous lead, conformable electrodes, cuff electrodes, segmented electrodes, or any other type of electrodes capable of forming unipolar, bipolar or multipolar electrode configurations for stimulation and measurement. The electrodes may pierce or affix directly to the tissue itself. [0036] Numerous aspects of the operation of implanted stimulator 100 may be programmable by an external computing device 192, which may be operable by a user such as a clinician or the patient 108. Moreover, implanted stimulator 100 serves a data gathering role, with gathered data being communicated to external device 192 via a transcutaneous communications channel 190. Communications channel 190 may be active on a substantially continuous basis, at periodic intervals, at non-periodic intervals, or upon request from the external device 192. External device 192 may thus provide a clinical interface configured to program the implanted stimulator 100 and recover data stored on the implanted stimulator 100. This configuration is achieved by program instructions collectively referred to as the Clinical Programming Application (CPA) and stored in an instruction memory of the clinical interface. [0037] Fig.2 is a block diagram of the stimulator 100. Electronics module 110 contains a battery 112 and a telemetry module 114. In implementations of the present technology, any suitable type of transcutaneous communications channel 190, such as infrared (IR), radiofrequency (RF), capacitive or inductive transfer, may be used by telemetry module 114 to transfer power or data to and from the electronics module 110 via communications channel 190. Module controller 116 has an associated memory 118 storing one or more of clinical data 120, clinical settings 121, control programs 122, and the like. Controller 116 is configured by control programs 122, sometimes referred to as firmware, to control a pulse generator 124 to generate stimuli, such as in the form of electrical pulses, in accordance with the clinical settings 121. Electrode selection module 126 switches the generated pulses to the selected electrode(s) of electrode array 150, for delivery of the pulses to the tissue surrounding the selected electrode(s). Measurement circuitry 128, which may comprise an amplifier or an analog-to-digital converter (ADC), is configured to process signals comprising neural responses sensed by measurement electrode(s) of the electrode array 150 as selected by electrode selection module 126. [0038] Fig.3 is a schematic illustrating interaction of the implanted stimulator 100 with a bundle of target nerve fibres 180 in the patient 108. In the implementation illustrated in Fig.3 the target fibres 180 may be located in the spinal cord, however in alternative implementations the stimulator 100 may be positioned adjacent any target neural tissue including a peripheral nerve, visceral nerve, sacral nerve, parasympathetic nerve or a brain structure. Electrode selection module 126 selects a stimulus electrode 2 of electrode array 150 through which to deliver a pulse from the pulse generator 124 to surrounding tissue including target fibres 180. A pulse may comprise one or more phases, e.g. a monophasic pulse comprises one phase, and a biphasic stimulus pulse 160 comprises two phases. Electrode selection module 126 also selects a return electrode 4 of the electrode array 150 for stimulus current return in each phase, to maintain a zero net charge transfer. An electrode may act as both a stimulus electrode and a return electrode over a complete multiphasic stimulus pulse. The use of two electrodes in this manner for delivering and returning current in each stimulus phase is referred to as bipolar stimulation. Alternative implementations may apply other forms of bipolar stimulation, or may use a greater number of stimulus or return electrodes. By contrast, in monopolar stimulation, current is returned through the conductive case of the stimulator 100, which may therefore be configured and function as an electrode though it is not physically part of the electrode array 150. The set of stimulus electrodes and return electrodes is referred to as the stimulus electrode configuration. Electrode selection module 126 is illustrated as connecting to a ground 130 of the pulse generator 124 to enable stimulus current return via the return electrode 4. However, other connections for current return may be used in other implementations. [0039] Delivery of an appropriate stimulus via electrodes 2 and 4 to the target fibres 180 evokes a neural response 170 comprising an evoked compound action potential (ECAP) which will propagate along the target fibres 180 as illustrated at a rate known as the conduction velocity. The ECAP may be evoked for therapeutic purposes, which in the case of a spinal cord stimulator for chronic pain may be to create paraesthesia at a desired location. To this end, the electrodes 2 and 4 are used to deliver stimuli periodically at any therapeutically suitable stimulus frequency, for example 30 Hz, although other frequencies may be used including frequencies as high as the kHz range. In alternative implementations, stimuli may be delivered in a non-periodic manner such as in bursts, or sporadically, as appropriate for the patient 108. To program the stimulator 100 to the patient 108, a clinician may cause the stimulator 100 to deliver stimuli of various configurations which seek to produce a sensation that may be experienced by the patient as paraesthesia. When a stimulus electrode configuration is found which evokes paraesthesia in a location and of a size which is congruent with the area of the patient’s body affected by pain and of a quality that is comfortable for the patient, the clinician or the patient nominates that configuration for ongoing use. The therapy parameters may be loaded into the memory 118 of the stimulator 100 as the clinical settings 121. [0040] Fig.6 illustrates the typical form of an ECAP 600 of a healthy subject, as sensed by a single measurement electrode referenced to the system ground 130. The shape and duration of the single- ended ECAP 600 shown in Fig.6 is predictable because it is a result of the ion currents produced by the ensemble of fibres depolarising and generating action potentials (APs) in response to stimulation. The evoked action potentials (EAPs) generated synchronously among a large number of fibres sum to form the ECAP 600. The ECAP 600 generated from the synchronous depolarisation of a group of similar fibres comprises a positive peak P1, then a negative peak N1, followed by a second positive peak P2. This shape is caused by the region of activation passing the measurement electrode as the action potentials propagate along the individual fibres. [0041] The ECAP may be recorded differentially using two measurement electrodes, as illustrated in Fig.3. Differential ECAP measurements are less subject to common-mode noise on the surrounding tissue than single-ended ECAP measurements. Depending on the polarity of recording, a differential ECAP may take an inverse form to that shown in Fig.6, i.e. a form having two negative peaks N1 and N2, and one positive peak P1. Alternatively, depending on the distance between the two measurement electrodes, a differential ECAP may resemble the time derivative of the ECAP 600, or more generally the difference between the ECAP 600 and a time-delayed copy thereof. [0042] The ECAP 600 may be characterised by any suitable characteristic(s) of which some are indicated in Fig.6. The amplitude of the positive peak P1 is Ap1 and occurs at time Tp1. The amplitude of the positive peak P2 is Ap₂ and occurs at time Tp₂. The amplitude of the negative peak P1 is An₁ and occurs at time Tn1. The peak-to-peak amplitude is Ap1 + An1. A recorded ECAP will typically have a maximum peak-to-peak amplitude in the range of microvolts and a duration of 2 to 3 ms. [0043] The stimulator 100 is further configured to measure the intensity of ECAPs 170 propagating along target fibres 180, whether such ECAPs are evoked by the stimulus from electrodes 2 and 4, or otherwise evoked. To this end, any electrodes of the array 150 may be selected by the electrode selection module 126 to serve as recording electrode 6 and reference electrode 8, whereby the electrode selection module 126 selectively connects the chosen electrodes to the inputs of the measurement circuitry 128. Thus, signals sensed by the measurement electrodes 6 and 8 subsequent to the respective stimuli are passed to the measurement circuitry 128, which may comprise a differential amplifier and an analog-to-digital converter (ADC), as illustrated in Fig.3. The recording electrode and the reference electrode are referred to as the measurement electrode configuration. The measurement circuitry 128 for example may operate in accordance with the teachings of the above- mentioned International Patent Publication No. WO2012/155183. [0044] Signals sensed by the measurement electrodes 6, 8 and processed by measurement circuitry 128 are further processed by an ECAP detector implemented within controller 116, configured by control programs 122, to obtain information regarding the effect of the applied stimulus upon the target fibres 180. In some implementations, the sensed signals are processed by the ECAP detector in a manner which measures and stores one or more characteristics from each evoked neural response or group of evoked neural responses contained in the sensed signal. In one such implementation, the characteristics comprise a peak-to-peak ECAP amplitude in microvolts (µV). For example, the sensed signals may be processed by the ECAP detector to determine the peak-to-peak ECAP amplitude in accordance with the teachings of International Patent Publication No. WO2015/074121 by the present applicant, the contents of which are incorporated herein by reference. Alternative implementations of the ECAP detector may measure and store an alternative characteristic from the neural response, or may measure and store two or more characteristics from the neural response. [0045] Stimulator 100 applies stimuli over a potentially long period such as days, weeks, or months and during this time may store characteristics of neural responses, clinical settings, target response intensity, and other operational parameters in memory 118. To effect suitable SCS therapy, stimulator 100 may deliver tens, hundreds or even thousands of stimuli per second, for many hours each day. Each neural response or group of responses generates one or more characteristics such as a measure of the intensity of the neural response. Stimulator 100 thus may produce such data at a rate of tens or hundreds of Hz, or even kHz, and over the course of hours or days this process results in large amounts of clinical data 120 which may be stored in the memory 118. Memory 118 is however necessarily of limited capacity and care is thus required to select compact data forms for storage into the memory 118, to ensure that the memory 118 is not exhausted before such time that the data is expected to be retrieved wirelessly by external device 192, which may occur only once or twice a day, or less. [0046] An activation plot, or growth curve, is an approximation to the relationship between stimulus intensity (e.g. an amplitude of the current pulse 160) and intensity of neural response 170 evoked by the stimulus (e.g. an ECAP amplitude). Fig.4a illustrates an idealised activation plot 402 for one posture of the patient 108. The activation plot 402 shows a linearly increasing ECAP amplitude for stimulus intensity values above a threshold 404 referred to as the ECAP threshold. The ECAP threshold exists because of the binary nature of fibre recruitment; if the field strength is too low, no fibres will be recruited. However, once the field strength exceeds a threshold, fibres begin to be recruited, and their individual evoked action potentials are independent of the strength of the field. The ECAP threshold 404 therefore reflects the field strength at which significant numbers of fibres begin to be recruited, and the increase in response intensity with stimulus intensity above the ECAP threshold reflects increasing numbers of fibres being recruited. Below the ECAP threshold 404, the ECAP amplitude may be taken to be zero. Above the ECAP threshold 404, the activation plot 402 has a positive, approximately constant slope indicating a linear relationship between stimulus intensity and the ECAP amplitude. Such a relationship may be modelled in piecewise linear form as: ^_{^ − ^^ ^^} (1) [0047] where s is the stimulus V T P is the slope of the activation plot (referred to herein as the patient sensitivity) above the ECAP threshold T. The sensitivity P and the ECAP threshold T are the key parameters of the activation plot 402. [0048] Fig.4a also illustrates a discomfort threshold 408, which is a stimulus intensity above which the patient 108 experiences uncomfortable or painful stimulation. The discomfort response intensity 422 is the response intensity when the stimulus intensity is equal to the discomfort threshold 408. Fig. 4a also illustrates a perception threshold 410. The perception threshold 410 corresponds to an ECAP amplitude that is barely perceptible by the patient. There are a number of factors which can influence the position of the perception threshold 410, including the posture of the patient. Perception threshold 410 may correspond to a stimulus intensity that is greater than the ECAP threshold 404, as illustrated in Fig.4a, if patient 108 does not perceive low levels of neural activation. Conversely, the perception threshold 410 may correspond to a stimulus intensity that is less than the ECAP threshold 404, if the patient has a high perception sensitivity to lower levels of neural activation than can be detected in an ECAP, or if the signal to noise ratio of the ECAP is low. [0049] For effective and comfortable operation of an implantable neuromodulation device such as the stimulator 100, it is desirable to maintain stimulus intensity within a therapeutic range. A stimulus intensity within a therapeutic range 412 is above the ECAP threshold 404 and below the discomfort threshold 408. In principle, it would be straightforward to measure these limits and ensure that stimulus intensity, which may be closely controlled, always falls within the therapeutic range 412. However, the activation plot, and therefore the therapeutic range 412, varies with the posture of the patient 108. [0050] Fig.4b illustrates the variation in the activation plots with changing posture of the patient. A change in posture of the patient may cause a change in impedance of the electrode-tissue interface or a change in the distance between electrodes and the spinal cord. While the activation plots for only three postures, 502, 504 and 506, are shown in Fig.4b, the activation plot for any given posture can lie between or outside the activation plots shown, on a continuously varying basis depending on posture. Consequently, as the patient’s posture changes, the ECAP threshold changes, as indicated by the ECAP thresholds 508, 510, and 512 for the respective activation plots 502, 504, and 506. Additionally, as the patient’s posture changes, the patient sensitivity also changes, as indicated by the varying slopes of activation plots 502, 504, and 506. In general, as the distance between the stimulus electrodes and the spinal cord increases, the ECAP threshold increases and the sensitivity decreases. The activation plots 502, 504, and 506 therefore correspond to increasing distance between stimulus electrodes and spinal cord, and decreasing patient sensitivity. [0051] To keep the applied stimulus intensity within the therapeutic range as patient posture varies, in some implementations an implantable neuromodulation device such as the stimulator 100 may adjust the applied stimulus intensity based on a feedback variable that is determined from one or more measured ECAP characteristics. In one implementation, the device may adjust the stimulus intensity to maintain the measured ECAP amplitude at or near a target response intensity. For example, the device may calculate an error between a target ECAP amplitude and a measured ECAP amplitude, and adjust the applied stimulus intensity to reduce the error as much as possible, such as by adding the scaled error to the current stimulus intensity. A neuromodulation device that operates by adjusting the applied stimulus intensity based on a measured ECAP characteristic is said to be operating in closed-loop mode and will also be referred to as a closed-loop neural stimulation (CLNS) device. By adjusting the applied stimulus intensity to maintain the measured ECAP amplitude at or near an appropriate target response intensity, such as a target ECAP amplitude 520 illustrated in Fig.4b, a CLNS device will generally keep the stimulus intensity within the therapeutic range as patient posture varies. [0052] A CLNS device comprises a stimulator that takes a stimulus intensity value and converts it into a neural stimulus comprising a sequence of electrical pulses according to a predefined stimulation pattern. The stimulation pattern is parametrised by multiple stimulus parameters including stimulus amplitude, pulse width, number of phases, order of phases, number of stimulus electrode poles (two for bipolar, three for tripolar etc.), and stimulus rate or frequency. At least one of the stimulus parameters, for example the stimulus amplitude, is controlled by the feedback loop. [0053] In an example CLNS system, the user sets a target response intensity, and the CLNS device performs proportional-integral-differential (PID) control. In some implementations, the differential contribution is disregarded and the CLNS device uses a first order integrating feedback loop. The stimulator produces stimulus in accordance with a stimulus intensity parameter, which evokes a neural response in the patient. The intensity of an evoked neural response (e.g. an ECAP) is measured by the CLNS device and compared to the target response intensity. [0054] The measured neural response intensity, and its deviation from the target response intensity, is used by the feedback loop to determine possible adjustments to the stimulus intensity parameter to maintain the neural response at or near the target response intensity. If the target response intensity is properly chosen, the patient receives consistently comfortable and therapeutic stimulation through posture changes and other perturbations to the stimulus / response behaviour. [0055] Fig.5 is a schematic illustrating elements and inputs of a closed-loop neural stimulation (CLNS) system 300, according to one implementation of the present technology. The system 300 comprises a stimulator 312 which converts a stimulus intensity parameter (for example a stimulus current amplitude) s, in concert with a set of predefined stimulus parameters, to a neural stimulus comprising a sequence of electrical pulses on the stimulus electrodes (not shown in Fig.5). According to one implementation, the predefined stimulus parameters comprise the number and order of phases, the number of stimulus electrode poles, the pulse width, and the stimulus rate or frequency. [0056] The generated stimulus crosses from the electrodes to the spinal cord, which is represented in Fig.5 by the dashed box 308. The box 309 represents the evocation of a neural response y by the stimulus as described above. The box 311 represents the evocation of an artefact signal a, which is dependent on stimulus intensity and other stimulus parameters, as well as the electrical environment of the measurement electrodes. Various sources of measurement noise n, as well as the artefact a, may add to the evoked response y at the summing element 313 to form the sensed signal r, including: electrical noise from external sources such as 50 Hz mains power; electrical disturbances produced by the body such as neural responses evoked not by the device but by other causes such as peripheral sensory input; EEG; EMG; and electrical noise from measurement circuitry 318. [0057] The neural recruitment arising from the stimulus is affected by mechanical changes, including posture changes, walking, breathing, heartbeat and so on. Mechanical changes may cause impedance changes, or changes in the location and orientation of the nerve fibres relative to the electrode array(s). As described above, the intensity of the evoked response provides a measure of the recruitment of the fibres being stimulated. In general, the more intense the stimulus, the more recruitment and the more intense the evoked response. An evoked response typically has a maximum amplitude in the range of microvolts, whereas the voltage resulting from the stimulus applied to evoke the response is typically several volts. [0058] Measurement circuitry 318, which may be identified with measurement circuitry 128, amplifies the sensed signal r (potentially including evoked neural response, artefact, and measurement noise), and samples the amplified sensed signal r to capture a “signal window” 319 comprising a predetermined number of samples of the amplified sensed signal r. The ECAP detector 320 processes the signal window 319 and outputs a measured neural response intensity V. In one implementation, the neural response intensity comprises a peak-to-peak ECAP amplitude. The measured response intensity V (an example of a feedback variable) is input into the feedback controller 310. The feedback controller 310 comprises a comparator 324 that compares the measured response intensity V to a target ECAP amplitude Vtgt as set by the target ECAP controller 304 and provides an indication of the difference between the measured response intensity V and the target ECAP amplitude V_tgt. This difference is the error value, e. [0059] The feedback controller 310 calculates an adjusted stimulus intensity parameter, s, with the aim of maintaining a measured response intensity V at or near the target ECAP amplitude Vtgt. Accordingly, the feedback controller 310 adjusts the stimulus intensity parameter s to minimise the error value, e. In one implementation, the controller 310 utilises a first order integrating function, using a gain element 336 and an integrator 338, in order to provide suitable adjustment to the stimulus intensity parameter s. According to such an implementation, the current stimulus intensity parameter s may be determined by the feedback controller 310 as ^_{^ = ∫ ^^^^^^^^ (2)} [0060] where K is the gain of the gain element 336 (the controller gain). This relation may also be represented as ^_{^^^ = ^^^^ (3)} [0061] where ^s is an adjustment to the current stimulus intensity parameter s. [0062] A target ECAP amplitude V_tgt is input to the feedback controller 310 via the target ECAP controller 304. In one implementation, the target ECAP controller 304 provides an indication of a specific target ECAP amplitude. In another implementation, the target ECAP controller 304 provides an indication to increase or to decrease the present target ECAP amplitude. The target ECAP controller 304 may comprise an input into the CLNS system 300, via which the patient or clinician can input a target ECAP amplitude, or indication thereof. The target ECAP controller 304 may comprise memory in which the target ECAP amplitude is stored, and from which the target ECAP amplitude is provided to the feedback controller 310. [0063] A clinical settings controller 302 provides clinical settings to the system 300, including the feedback controller 310 and the stimulus parameters for the stimulator 312 that are not under the control of the feedback controller 310. In one example, the clinical settings controller 302 may be configured to adjust the controller gain K of the feedback controller 310 to adapt the feedback loop to patient sensitivity. The clinical settings controller 302 may comprise an input into the CLNS system 300, via which the patient or clinician can adjust the clinical settings. The clinical settings controller 302 may comprise memory in which the clinical settings are stored, and are provided to components of the system 300. [0064] In some implementations, two clocks (not shown) are used, being a stimulus clock operating at the stimulus frequency (e.g.60 Hz) and a sample clock for sampling the sensed signal r (for example, operating at a sampling frequency of 16 kHz). As the ECAP detector 320 is linear, only the stimulus clock affects the dynamics of the CLNS system 300. On the next stimulus clock cycle, the stimulator 312 outputs a stimulus in accordance with the adjusted stimulus intensity s. Accordingly, there is a delay of one stimulus clock cycle before the stimulus intensity is updated in light of the error value e. [0065] Fig.7 is a block diagram of a neural stimulation system 700. The neural stimulation system 700 is centred on a neuromodulation device 710. In one example, the neuromodulation device 710 may be implemented as the stimulator 100 of Fig.1, implanted within a patient (not shown). The neuromodulation device 710 is connected wirelessly to a remote controller (RC) 720. The remote controller 720 is a portable computing device that provides the patient with control of their stimulation in the home environment by allowing control of the functionality of the neuromodulation device 710, including one or more of the following functions: enabling or disabling stimulation; adjustment of stimulus intensity or target response intensity; and selection of a stimulation control program from the control programs stored on the neuromodulation device 710. [0066] The charger 750 is configured to recharge a rechargeable power source of the neuromodulation device 710. The recharging is illustrated as wireless in Fig.7 but may be wired in alternative implementations. [0067] The neuromodulation device 710 is wirelessly connected to a Clinical System Transceiver (CST) 730. The wireless connection may be implemented as the transcutaneous communications channel 190 of Fig.1. The CST 730 acts as an intermediary between the neuromodulation device 710 and the Clinical Interface (CI) 740, to which the CST 730 is connected. A wired connection is shown in Fig.7, but in other implementations, the connection between the CST 730 and the CI 740 is wireless. [0068] The CI 740 may be implemented as the external computing device 192 of Fig.1. The CI 740 is configured to program the neuromodulation device 710 and recover data stored on the neuromodulation device 710. This configuration is achieved by program instructions collectively referred to as the Clinical Programming Application (CPA) and stored in an instruction memory of the CI 740. Assisted Programming System [0069] As mentioned above, obtaining patient feedback about their sensations is important during programming of closed-loop neural stimulation therapy, but mediation by trained clinical engineers is expensive and time-consuming. It would therefore be advantageous if patients could program their own implantable device themselves, or with some assistance from a clinician. However, interfaces for current programming systems are non-intuitive and generally unsuitable for direct use by patients because of their technical nature. The CPA disclosed herein comprises an Assisted Programming System (APS) that is as intuitive for non-technical users as possible while avoiding discomfort to the patient. [0070] In some implementations, the APS comprises two elements: the Assisted Programming Module (APM), which forms part of the CPA, and the Assisted Programming Firmware (APF), which forms part of the control programs 122 executed by the controller 116 of the device 710. The APF is configured to complement the operation of the APM by responding to commands issued by the APM to the device 710 via the CST 730 to deliver specified stimuli to the target neural tissue, and by returning, via the CST 730, data comprising measurements of neural responses to the delivered stimuli. The data obtained from the device 710 under the control of the APF is analysed by the APM to determine the clinical settings for the neural stimulation therapy to be delivered by the stimulator 100. [0071] In other implementations, all the processing of the APS according to the present technology is done by the APF. In other words, the data obtained from the patient is not passed to the APM, but is analysed by the controller 116 of the device 710, configured by the APF, to determine the clinical settings for the neural stimulation therapy to be delivered by the device 710. [0072] In implementations of the APS in which the APM analyses the data from the patient, the APS instructs the device 710 to capture and return signal windows to the CI 740 via the CST 730. In such implementations, the device 710 captures the signal windows using the measurement circuitry 128 and bypasses the ECAP detector 320, storing the data representing the raw signal windows temporarily in memory 118 before transmitting the data representing the captured signal windows to the APS for analysis. [0073] Following the programming, the APS may load the determined program onto the device 710 to govern subsequent neural stimulation therapy. In one implementation, the program comprises clinical settings 121, also referred to as therapy parameters, that are input to the neuromodulation device 710 by, or stored in, the clinical settings controller 302. The patient may subsequently control the device 710 to deliver the therapy according to the determined program using the remote controller 720 as described above. The determined program may also, or alternatively, be loaded into the CPA for validation and modification. Patient control of neural stimulation therapy [0074] As described above, in a closed-loop neural stimulation (CLNS) system, a characteristic value (for example, the intensity) of an evoked neural response is measured and compared with a target value for the characteristic to derive an error value. The error value is used to adjust the subsequent stimulus intensity so as to maintain the characteristic value at or near the target value. [0075] The target value may be manually predetermined during programming as a value that the patient feels to be comfortably analgesic. The predetermined target value may be saved as part of the therapy parameters, and the current target value provided by the target ECAP controller 304 may be initialised to the predetermined target value. However, as described above, the patient may be provided with the ability to adjust the target value away from the predetermined target value using the remote controller 720. [0076] Fig. 8 is an illustration of one implementation of a graphical user interface (GUI) 800 presented on the remote controller 720. The interface 800 comprises two activatable controls, an “up- control” 810 and a “down-control” 820. By activating the up-control 810, the patient or other user may increment the current target ECAP amplitude Vtgt (an example of a current target value) by a fixed increment ^Vtgt. By activating the down-control 820, the patient or other user may decrement the current target ECAP amplitude Vtgt by the same fixed increment ^Vtgt. The target ECAP amplitude is limited to the range [Vtgt(min), Vtgt(max)] where Vtgt(min) is a minimum target ECAP amplitude and V_tgt(max) is a maximum target ECAP amplitude, so only a certain number of successive activations of the up or down controls will have an effect on the target ECAP amplitude Vtgt. [0077] The minimum and maximum target ECAP amplitudes Vtgt(min) and Vtgt(max) may be predetermined, or set during programming, for example by the APS. In one implementation, the minimum target ECAP amplitude Vtgt(min) is a predetermined ECAP amplitude (for example, -20 microvolts (^V)) and the maximum target ECAP amplitude Vtgt(max) is set to the discomfort response intensity 422, i.e. the ECAP amplitude when the stimulus intensity is at the discomfort threshold 408. [0078] The target increment ^Vtgt may be determined from the minimum and maximum target ECAP amplitudes Vtgt(min) and Vtgt(max), for the formula: (4) [0079] where Nc is the number of “up-control” 810 activations (or “clicks”) necessary to adjust the target from V_tgt(min) to V_tgt(max). [0080] The remote controller interface may also contain a GUI element configured to graphically represent the current target ECAP amplitude Vtgt, as adjusted by the patient from time to time. In the interface 800, the GUI element 830 has this function. The GUI element 830 comprises a stack of bars, e.g. the bar 840. Each bar comprises a light-emitting diode (LED) configured to be lit, possibly in different colours or degrees of brightness. The GUI element 830 may represent target ECAP amplitudes on a uniform scale. In other words, each bar corresponds to an equally-sized sub-range of target ECAP amplitudes within the overall range from Vtgt(min) to Vtgt(max). The bars are notionally numbered from 1 to Nb, starting at the bottom, where Nb is the number of bars (in Fig.8, Nb is 7). The bar corresponding to the range that includes the current target ECAP amplitude Vtgt may be lit to represent the current target ECAP amplitude Vtgt. For example, the number n(Vtgt) of the bar corresponding to the range that includes the current target ECAP amplitude V_tgt may be determined using the following formula: ^_{^^^^^^^^^^^^^ ^^^^^^^^^^} (5) [0081] In , 1 to n(Vtgt)-1 are lit to represent the current target ECAP amplitude Vtgt more clearly. Fig. 9a is an illustration of a GUI element 900 in the form of a bar stack, similar to the GUI element 830, with Nb equal to 7. The bar 910 (the fourth bar from the bottom) is lit to represent a current target ECAP amplitude Vtgt of 40 ^V in an implementation in which Vtgt(min) is -20 and Vtgt(max) is 80, i.e. n(Vtgt) is 4. Bars 1 to 3 are also lit. [0082] Fig.9b is an illustration of an alternative GUI element 950 in the form of a virtual slider. The virtual slider 950 is suitable for an implementation in which the remote controller 720 has a touchscreen interface. On the virtual slider 950, the extreme left and right ends 980 and 990 of the line 960 represent the minimum and maximum target ECAP amplitudes Vtgt(min) and Vtgt(max) respectively, and the current target ECAP amplitude V_tgt is represented by the position of the indicator 970 (shown as a vertical line) along the line 960 such that the ratio of the length of the line segment 995 left of the indicator 970 to the total length of the line 960 is the same as the ratio of (Vtgt - Vtgt(min)) to (V_tgt(max) - V_tgt(min)). The virtual slider 950 also serves as a control element, in that a user may “drag” the indicator 970 along the line 960 to the right or left to adjust the current target ECAP amplitude Vtgt upwards to the upper limit Vtgt(max) or downwards to the lower limit Vtgt(min) respectively. In this implementation the virtual slider 950 subsumes the controls 810 and 820. [0083] A yet further alternative GUI element is a virtual dial in which linear position of the indicator 970 along the line 960 in the virtual slider 950 is replaced by angular position of an indicator around a circle. The indicator may be dragged around the circle to adjust the current target ECAP amplitude V_tgt. [0084] As mentioned above, patients may use the remote controller 720 to adjust their current target value. However, such adjustments may reduce the efficacy of the CLNS therapy compared to what they would receive if they kept the current target value at the predetermined target value. It would be advantageous for a programmed CLNS system to encourage the patient to maintain his or her CLNS therapy at the predetermined target value. Methods and systems according to the present technology are therefore configured to represent a predetermined target value on the GUI element on which the patient’s current target value is also represented. By this dual representation, the patient may be kept informed as to the relative values of their current target value and the predetermined target value. This in turn provides a straightforward way for the patient to maintain, using the activatable controls 810 and 820 on the remote controller GUI 800, their current target value at approximately the predetermined target value. [0085] Fig.10a is an illustration of a GUI element 1000 presented on the remote controller 720 according to one aspect of the present technology. The GUI element 1000 is a bar stack, which is the same as the bar stack 900 illustrated in Fig.9a, with bars 1 to 4 lit as in Fig.9a to represent the current target ECAP amplitude Vtgt. The bar stack 1000 has an additional bar 1010 (i.e. the bar numbered 6) lit to represent a predetermined target ECAP amplitude Vtgt(p). The additional bar 1010 is differently lit from the bars 1 to 4, for example being lit with different brightness, or in a different colour (as in Fig.10b), or intermittently (“flashing”). [0086] Fig.10b is an illustration of a GUI element 1050 presented on the remote controller 720 according to one aspect of the present technology. The GUI element 1050 is a virtual slider, which is the same as the virtual slider 950 illustrated in Fig.9b, with an indicator 1070 (corresponding to indicator 970) representing the current target ECAP amplitude Vtgt. The virtual slider 1050 contains an additional indicator 1080 to represent a predetermined target ECAP amplitude Vtgt(p). The additional indicator 1080 is rendered differently from the indicator 1070, for example being rendered dashed (as in Fig.10b), or in a different colour, or flashing. [0087] When, as generally described above, the characteristic value that is compared with the target value is neural response intensity, e.g. ECAP amplitude, that characteristic value is not normalised across patients. In other words, a target ECAP amplitude value of 40 ^V will provide widely differing analgesic effects between different patients. (This is why the target ECAP amplitude and the maximum target ECAP amplitude are generally predetermined for each patient during programming.) A target response intensity value is therefore generally unsatisfactory as a normalised measure of analgesic effect across patients. [0088] It would be advantageous for a programmed CLNS system to encourage the patient to maintain his or her therapy at a predetermined target value that is normalised across patients, i.e. that represents a consistent analgesic effect. The predetermined target value would then not need to be manually programmed for each patient, but could be set to a population value, saving programming time. It has been hypothesised [1] that there exists an ECAP-derived measure of “dose” that is normalised across all patients, i.e. delivery of a similar dose will have a similar analgesic effect on different patients, and on the same patient in different postures. According to that hypothesis, one example of such a normalised measure of dose (NMD) is defined as the current value of the stimulus intensity parameter s divided by a dose threshold s0. It has further been demonstrated [2] that such a definition of normalised dose is correlated with patient analgesic effect. [0089] Methods and systems according to the present technology are therefore configured to map a predetermined target NMD value to a predetermined target ECAP amplitude. The systems and methods of dual representation according to the present technology may be employed to display the resulting predetermined target ECAP amplitude alongside the current target ECAP amplitude. This in turn provides a straightforward way for the patient to maintain, using the activatable controls 810 and 820 on the remote controller GUI 800, their current target ECAP amplitude at approximately the predetermined target ECAP amplitude derived from the predetermined target NMD value, and therefore to receive a consistent analgesic effect. Since the mapping from NMD values to ECAP amplitudes is dependent on the activation plot, which in turn changes with posture (see Fig.4b), the predetermined target ECAP amplitude V_tgt(p) may be repeatedly updated, allowing patient to maintain the consistent analgesic effect as posture changes, with appropriate adjustments to the current target ECAP amplitude. [0090] Fig.11 is a flowchart illustrating a method 1100 of representing a predetermined target NMD value alongside a current target ECAP amplitude on a GUI element configured to represent target response intensity values within a range on a uniform scale, according to one implementation of the present technology. As mentioned above, the GUI element 830 of Fig.8 may be configured in this manner. The first two steps of the method 1100 may be implemented by the APS, whether wholly on the CI 740, wholly on the device 710, or in some combination of the two entities. The final step 1130 may be implemented by the device on which the GUI element is rendered, for example the remote controller 720. Alternatively, the entire method 1100 may be implemented by the device on which the GUI element is rendered. [0091] The method 1100 starts at step 1110, in which the APS delivers stimuli at respective stimulus intensity values si and makes respective measurements Vi of evoked neural response intensity to form _{a set of (stimulus intensity, response intensity) pairs ^^ = {(^^^, ^^^)}. Step 1110 uses the set S to} determine the current activation plot (AP), i.e. the relationship V(s) between response intensity V and stimulus intensity s, according to a predetermined model. Step 1110 involves fitting the model to the set S to estimate the parameters of the relationship V(s). In one implementation, the predetermined model is the piecewise linear model of equation (1). Conventional methods may be used to fit the _{piecewise linear model of equation (1) to the set S comprising at least two pairs (^^^, ^^^) to obtain the} current AP. One such method is disclosed in PCT International Publication no. WO2023/205858, the entire contents of which are incorporated by reference into the present disclosure. [0092] In an alternative implementation, the predetermined model is a continuous model comprising two separate linear portions, a sub-threshold linear portion and a supra-threshold linear portion, joined by a continuous curve. One such continuous model ^_{^(^^) = ^^^ + ^^^^௧^^ + ^^^^ ^^^} த ் ₍₆₎ [0093] where: ^ V0 is the zero-current measured response intensity (due to noise; can be positive or negative) ^ mart is the slope of the sub-threshold linear portion, due to artefact (can be positive or negative) ^ P is the sensitivity, i.e. the slope of the supra-threshold linear portion due to neural activation (so that P + m_art is the total slope of the supra-threshold linear portion) ^ T is a transition parameter that approximates the stimulus intensity at the transition between the sub-threshold linear portion and the supra-threshold linear portion ^ ^ is a curvature parameter that sets the sharpness of the transition between the two linear portions (the smaller the value, the sharper the transition). In some implementations the value of the curvature parameter ^ may be set between 0 and 1, or between 0.05 and 0.5, or between 0.1 and 0.4. _{[0094] Fitting a set S of (stimulus intensity, response intensity) pairs {(^^^, ^^^)} to the model of} equation (6) at step 1110 may be done in multiple steps. ^_{Fit a straight line to a subset of the measurement pairs (^^^, ^^^) at stimulus intensity parameter} values s_i that are undoubtedly below threshold. The zero-current response intensity V₀ and the slope mart are the d-axis intercept and slope of this fitted line. ^_{Fit a straight line to a subset of the measurement pairs (^^^, ^^^) at stimulus intensity parameter} values s_i that are close to the discomfort threshold s_max. Record the slope P(s_max) of this line, and the response intensity Vmax at the discomfort threshold smax. The slope of the fitted model at the discomfort threshold smax should be equal to P(smax), and the value V(smax) of the fitted model at the discomfort threshold s_max should be as close as possible to the measured V_max. ^ For a sequence of trial values Ti of the transition parameter T: ^ Estimate the sensitivity Pi based on trial threshold value Ti using the following = (7) ^ Evaluate V_max(i) at the discomfort threshold s_max using equation (6) with P_i , T_i, V₀, and mart. ^ The transition parameter T is the trial value Ti for which the Vmax(i) is closest in value to the measured V_max. [0095] Step 1120 then uses the AP determined at step 1110 to map a predetermined target NMD value D0 to a predetermined target ECAP amplitude Vtgt(D0). In one implementation, suitable for the definition of NMD as stimulus intensity divided by dose threshold s₀, step 1120 multiplies the predetermined target NMD value D0 by the dose threshold s0 to obtain a stimulus intensity value s(D0). The dose threshold s0 may be derived from the fitted AP from step 1110. Step 1120 then applies the fitted AP to the stimulus intensity value s(D0) to determine the predetermined target ECAP amplitude V_tgt(D₀). [0096] Some alternative derivations of the dose threshold s0 are as follows: ^ the transition parameter T; ^ a predetermined multiple of the transition parameter T; ^ the stimulus intensity of the fitted AP where the response intensity V is a predetermined increment above the baseline value V₀; ^ the stimulus intensity of the fitted AP where the response intensity V is an increment above the baseline value V0, where the increment is a predetermined multiple of the standard deviation of the measurement noise n; ^ the stimulus intensity of the fitted AP where the response intensity V is an increment above the baseline value V0 where the increment is some combination (e.g. a minimum) of a predetermined value and a predetermined multiple of the standard deviation of the measurement noise n. [0097] Step 1130 then represents the mapped predetermined target NMD value D0, i.e. the predetermined target ECAP amplitude V_tgt(D₀), on the GUI element alongside the current target ECAP amplitude Vtgt. In one implementation, in which the GUI element is the bar stack 830, step 1130 applies equation (5) to the predetermined target ECAP amplitude Vtgt(D0) to determine the number n(V_tgt(D₀)) of the bar to light on the GUI element 830 to represent the mapped predetermined target NMD value D0. Step 1130, in some implementations, represents the predetermined target ECAP amplitude Vtgt(D0) in a way that is distinguishable from the representation of the current target ECAP amplitude Vtgt. In one implementation, in which the GUI element is the bar stack 830, step 1130 lights the bar numbered n(Vtgt(D0)) in a different colour to the colour used to represent the current target ECAP amplitude Vtgt, or at a different degree of brightness. In another implementation, step 1130 lights the bar numbered n(Vtgt(D0)) intermittently, i.e. “flashing”, whereas the bars lit to represent the current target ECAP amplitude V_tgt are lit constantly, i.e “solid”. This difference of representation allows the patient to quickly perceive the relative values of the current target ECAP amplitude and the mapped predetermined target NMD value, enabling them to bring the two values into alignment by activation of appropriate controls on the remote controller 720. [0098] In some implementations, the method 1100 comprises a further step, similar to step 1120, in which the APS determines the maximum target ECAP amplitude Vtgt(max) from a predetermined maximum NMD value Dmax using the fitted AP before carrying out step 1130. In one implementation, suitable for the definition of NMD as stimulus intensity divided by dose threshold, this further step multiplies the predetermined maximum NMD value Dmax by the dose threshold s0 to obtain a stimulus intensity value s(Dmax). The optional step then applies the fitted AP to the stimulus intensity value s(D_max) to determine the maximum target ECAP amplitude V_tgt(max). The determined maximum target ECAP amplitude Vtgt(max) is then used by the representation step 1130. [0099] In some implementations, the method 1100 comprises a further step, similar to step 1120, in which the APS determines a recommended minimum target ECAP amplitude V_tgt(D_min) from a recommended minimum NMD value Dmin using the fitted AP before carrying out step 1130. In one implementation, suitable for the definition of NMD as stimulus intensity divided by dose threshold, this further step multiplies the recommended minimum NMD value D_min by the dose threshold s₀ to obtain a stimulus intensity value s(Dmin). The further step then applies the fitted AP to the stimulus intensity value s(Dmin) to determine the recommended minimum target ECAP amplitude Vtgt(Dmin). Step 1130 may then represent the mapped recommended minimum NMD value Dmin i.e. the recommended minimum target ECAP amplitude V_tgt(D_min), on the GUI element, alongside the representations of the mapped predetermined target NMD value D0 and the current target ECAP amplitude Vtgt. [0100] In some implementations, the method 1100 comprises a further step of displaying NMD values alongside the GUI element. In one such implementation, suitable for the implementation in which the GUI element 830 is a stack of bars as illustrated in Fig.10a, each bar is accompanied by a number representing an NMD value derived from the range of target ECAP amplitudes represented by the bar. Such an implementation is illustrated in Fig. 12, which shows a GUI element 1200 corresponding to the GUI element 1000 of Fig.10a alongside an array 1220 of NMD values, with one NMD value in the array 1220 corresponding to each bar. The NMD value Dn corresponding to the n-th bar (for n = 1, …, N_b) may be obtained as the stimulus intensity s_n corresponding to the target ECAP amplitude Vtgt(n) in the centre of the range of target ECAP amplitudes represented by the n-th bar, divided by the dose threshold s0. That is, ^^_^ = ^_^ ^_బ (8) [0101] where ^_{^(^^^) = ^^௧^௧(^) (9)} [0102] according to the AP determined in step 1110. For example, for the 6^th bar 1210, the corresponding NMD value D₆ is 1.48, as shown in Fig.12. [0103] The method 1100 may be carried out once during programming. In other implementations, the method 1100 may be carried out repeatedly while the patient is receiving CLNS therapy. In such implementations the subsequent iterations of the method 1100 are carried out on the device 710 and the remote controller 720. Such implementations allow the GUI to adapt its representation of the predetermined target NMD value D0 to different postures of the patient, which (as illustrated in Fig. 4b) result in different APs and therefore different mappings of the predetermined target NMD value D₀ to target ECAP amplitudes. In turn, this allows the patient, by activation of the controls 810 and 820 on the remote controller 720, to keep the current target ECAP amplitude in alignment with the mapped predetermined target NMD value D0. In this manner the patient is assisted to maintain their dose at the predetermined target NMD value D₀ through different postures, while allowing them to depart from it at need should their circumstances change. [0104] In some implementations, the GUI element 830 of Fig.8 is configured to represent target NMD values rather than target ECAP amplitudes on a uniform scale. In other words, each bar corresponds to an equally-sized sub-range of target NMD values within an overall range from a minimum target NMD value Dtgt(min) to a maximum target NMD value Dtgt(max). In such implementations, the controls 810 and 820 may be used to adjust a current target NMD value Dtgt. By activating the up-control 810, the patient or other user may increment the current target NMD value Dtgt by a fixed NMD increment ^Dtgt. By activating the down-control 820, the patient or other user may decrement the current target NMD value Dtgt by the same fixed NMD increment ^Dtgt. However, the CLNS device 710 operates as described above to maintain a measured ECAP amplitude V at or near a target ECAP amplitude Vtgt. The current target NMD value Dtgt may therefore be mapped to a current target ECAP amplitude V_tgt for use by the CLNS device 710. This mapping is the same operation as the mapping of the predetermined target NMD value D0 to the predetermined target ECAP amplitude Vtgt(D0) described above in relation to step 1120. The mapping may be carried out each time the current target NMD value Dtgt is adjusted using the controls 810 and 820. In addition, the mapping from NMD values to ECAP amplitudes changes with posture, so the mapping may be carried out repeatedly while the patient is receiving CLNS therapy. [0105] In such implementations, it remains advantageous to encourage the patient to maintain his or her CLNS therapy at a predetermined target value. Therefore, methods and systems according to such implementations of the present technology are therefore configured to represent a predetermined target NMD value Dtgt(p) on the GUI element 830 alongside the patient’s current target NMD value D_tgt. [0106] Fig.13 is a flowchart illustrating a method 1300 of representing a predetermined target NMD value alongside a current target NMD value on a GUI element configured to represent target NMD values within a range on a uniform scale, according to one implementation of the present technology. As mentioned above, the GUI element 830 of Fig.8 may be configured in this manner. The first two steps of the method 1300 may be implemented by the APS, whether wholly on the CI 740, wholly on the device 710, or in some combination of the two entities. The final step 1330 may be implemented by the device on which the GUI element is rendered, for example the remote controller 720. Alternatively, the entire method 1300 may be implemented by the device on which the GUI element is rendered. [0107] The method 1300 starts at step 1310 which is the same as step 1110 of the method 1100. Step 1320 then uses the AP determined at step 1310 to map a predetermined target ECAP amplitude Vtgt(p) to a predetermined target NMD value D_tgt(p). This mapping is the inverse of the mapping of the predetermined target NMD value D0 to the predetermined target ECAP amplitude Vtgt(D0) described above in relation to step 1120. In one implementation, step 1320 inverts the fitted AP from step 1310 to the find the stimulus intensity value s(V_tgt(p)) that corresponds to the predetermined target ECAP amplitude Vtgt(p). Step 1320 then divides the stimulus intensity value s(Vtgt(p)) by the dose threshold s0 to obtain the predetermined target NMD value Dtgt(p). The dose threshold s0 may be derived from the fitted AP from step 1310 as described above. [0108] Step 1330 then represents the mapped predetermined target ECAP amplitude value V_tgt(p), i.e. the predetermined target NMD value Dtgt(p), on the GUI element alongside the current target NMD value Dtgt. Step 1330 is similar to step 1130. Step 1330, in some implementations, represents the predetermined target NMD value D_tgt(p) in a way that is distinguishable from the representation of the current target NMD value Dtgt. In one implementation, in which the GUI element is the bar stack 830, step 1330 lights the bar corresponding to Dtgt(p) in a different colour to the colour used to represent the current target NMD value D_tgt, or at a different degree of brightness. In another implementation, step 1330 lights the bar corresponding to Dtgt(p) intermittently, i.e. “flashing”, whereas the bars lit to represent the current target NMD value Dtgt are lit constantly, i.e “solid”. This difference of representation allows the patient to quickly perceive the relative values of the current target NMD value and the predetermined target NMD value, enabling them to bring the two values into alignment by activation of appropriate controls on the remote controller 720. [0109] The mapping from ECAP amplitudes to NMD values, like the mapping from NMD values to ECAP amplitudes, changes with posture. The method 1300 may therefore be carried out repeatedly while the patient is receiving CLNS therapy. In such implementations the subsequent iterations of the method 1300 are carried out on the device 710 and the remote controller 720. Such implementations allow the GUI to adapt the predetermined target NMD value D_tgt(p) to different postures of the patient. In turn, this allows the patient, by activation of the controls 810 and 820 on the remote controller 720, to keep the current target NMD value Dtgt in alignment with the predetermined target NMD value D_tgt(p) as posture changes. [0110] In some implementations, the predetermined target NMD value D_tgt(p) is not obtained by mapping a predetermined target ECAP amplitude value Vtgt(p) using steps 1310 and 1320. Instead, the predetermined target NMD value Dtgt(p) may be a predetermined target NMD value D0 that is normalised across patients and does not vary with posture. In such implementations, the method 1300 need be carried out only once during programming. [0111] In some implementations, any of the GUI elements 1000, 1050, and 1200 may be presented on a display of the clinical interface (CI) 740 in addition to, or alternatively to, on the remote controller 720. In such implementations, representations of the controls 810 and 820 on the remote controller GUI 800 may also be presented on the display of the CI 740 alongside the GUI element 1000, 1050, or 1200. The representations on the CI 740 may be activated to adjust the current target value, and hence the appearance of the GUI elements 1000, 1050, and 1200, in the same manner as activations of the controls 810 and 820. Such implementations, taking place during the programming of the device 710, may be useful for training purposes, such as to educate the patient on the significance of the presented GUI element 1000, 1050, or 1200 in circumstances when the remote controller 720 is not ready to hand. INTERPRETATION [0112] The technology disclosed herein may be implemented in hardware (e.g., using digital signal processors, application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs)), or in software (e.g., using instructions tangibly stored on non-transitory computer-readable media for causing a data processing system to perform the steps described herein), or in a combination of hardware and software. The disclosed technology can also be implemented as computer-readable code on a computer-readable medium. The computer-readable medium can include any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer-readable medium include read-only memory ("ROM"), random-access memory ("RAM"), magnetic tape, optical data storage devices, flash storage devices, or any other suitable storage devices. The computer-readable medium can also be distributed over network-coupled computer systems so that the computer-readable code is stored or executed in a distributed fashion. The present technology is not limited to any particular programming language or operating system. Wireless [0113] In the context of the present disclosure, the term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. In the context of the present disclosure, the term “wired” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated signals propagating through a conductive medium. The term does not imply that the associated devices are coupled by electrically conductive wires. [0114] Wireless communication standards that can be accommodated include IEEE 802.11 wireless LANs and links, Bluetooth, and wireless Ethernet. The technology disclosed herein may be implemented using devices conforming to other network standards and for other applications, including, for example other WLAN standards and other wireless standards such as MICS. Processes [0115] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing”, “computing”, “comparing”, “estimating”, “calculating”, “determining”, “analysing” or the like, refer to the action or processes of a computer or computing system, or similar electronic computing device, that manipulate or transform data represented as physical, such as electronic, quantities into other data similarly represented as physical quantities, or to otherwise execute a predefined procedure suitable to effect the described actions. Processor [0116] In a similar manner, the term “processor” may refer to any device or portion of a device that processes electronic data, e.g., from registers or memory, to transform that electronic data into other electronic data that, e.g., may be stored in registers or memory. A “computer” or a “computing device” or a “computing machine” or a “computing platform” may include one or more processors. [0117] The methods described herein are, in one embodiment, performable by one or more processors that accept computer-readable (also called machine-readable) code containing a set of instructions that when executed by one or more of the processors cause the one or more processors to carry out at least one of the methods described herein. Any processor capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken are included within the meaning of the term “processor”. Thus, one example is a typical processing system that includes one or more processors. The processing system further may include a memory subsystem including main RAM or a static RAM, or ROM. Networked or Multiple Processors [0118] In alternative embodiments, the one or more processors operate as respective standalone device(s) or may be connected, e.g., networked to other processor(s), in a networked deployment. The one or more processors may operate in the capacity of a server or a client machine in server- client network environment, or as a peer machine in a peer-to-peer or distributed network environment. The one or more processors may form a web appliance, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. [0119] Note that while some diagram(s) only show(s) a single processor and a single memory that carries the computer-readable code, those in the art will understand that many of the components described above are included, but not explicitly shown or described in order not to obscure the inventive aspect. For example, while only a single machine may be illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methods discussed herein. Additional Implementations [0120] Thus, one implementation of each of the methods described herein is in the form of a computer-readable medium carrying a set of instructions, e.g., a computer program that are for execution on one or more processors. Thus, as will be appreciated by those skilled in the art, aspects of the present technology may be implemented as a method, an apparatus such as a special purpose apparatus, an apparatus such as a data processing system, or a computer-readable medium. The computer-readable medium carries computer-readable code including a set of instructions that when executed on one or more processors cause the processor or processors to implement a method. Accordingly, aspects of the present technology may take the form of a method, an entirely hardware implementation, an entirely software implementation or an implementation combining software and hardware aspects. Furthermore, the present technology may take the form of a carrier medium (e.g., a computer program product) carrying computer-readable program code embodied in the medium. Carrier Medium [0121] The software may further be transmitted or received over a network via a network interface device. While the carrier medium is shown in an example embodiment to be a single medium, the term “carrier medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) that store the one or more sets of instructions. A carrier medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Means For Carrying out a Method or Function [0122] Furthermore, some of the implementations are described herein as a method or combination of elements of a method that can be implemented by a processor of a processor device, computer system, or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus is an example of a means for carrying out the function performed by the element. [0123] Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software running on a special purpose machine that is programmed to carry out the operations described in the present disclosure, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the exemplary implementations. Implementations [0124] Reference throughout the present disclosure to “one implementation” or “an implementation” means that a particular feature, structure or characteristic described in connection with the implementation is included in at least one implementation of the present technology. Thus, appearances of the phrases “in one implementation” or “in an implementation” in various places throughout the present disclosure are not necessarily all referring to the same implementation, but may refer to different implementations. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more implementations. [0125] Similarly, it should be appreciated that in the above description of example implementations of the present technology, various features are sometimes grouped together in a single implementation, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single foregoing disclosed implementation. Thus, the claims following the Detailed Description of the Present Technology are hereby expressly incorporated into this Detailed Description of the Present Technology, with each claim standing on its own as a separate implementation of the present technology. [0126] Furthermore, while some implementations described herein include some, but not other features included in other implementations, combinations of features of different implementations are meant to be within the scope of the present technology, and form different implementations of the present technology, as would be understood by those in the art. For example, in the following claims, any of the claimed implementations can generally be used in any combination. [0127] As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word "about" or "approximately," even if the term does not expressly appear. The phrase "about" or "approximately" may be used when describing magnitude or position to indicate that the value or position described is within a reasonable expected range of values or positions. For example, a numeric value may have a value that is +/- 0.1% of the stated value (or range of values), +/- 1% of the stated value (or range of values), +/- 2% of the stated value (or range of values), +/- 5% of the stated value (or range of values), +/- 10% of the stated value (or range of values), etc. Any numerical values given herein should also be understood to include about or approximately that value, unless the context indicates otherwise. For example, if the value "10" is disclosed, then "about 10" is also disclosed. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. It is also understood that each value between two particular values is also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed. Different Instances of Objects [0128] As used herein, unless otherwise specified the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicates that different instances of like objects are being referred to, and is not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. Specific Details [0129] In the description provided herein, numerous specific details are set forth. However, it is understood that implementations of the present technology may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of the present technology. Terminology [0130] Throughout the present disclosure, the terms "a" and "an" mean "one or more", unless expressly specified otherwise. [0131] Throughout the present disclosure, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer, or step, or group of elements, integers, or steps, but not the exclusion of any other element, integer, or step, or group of elements, integers, or steps. [0132] Throughout the present disclosure, a statement that an element may be “at least one of” or “one or more of” a list of options is to be understood to mean that the element may be any one of the listed options, or may be any combination of two or more of the listed options. [0133] Throughout the present disclosure, the word “or” is to be read inclusively rather than exclusively, except where otherwise indicated. [0134] Neither the title nor any abstract of the present disclosure should be taken as limiting in any way the scope of the claimed invention. [0135] Where the preamble of a claim recites a purpose, benefit or possible use of the claimed invention, it does not necessarily limit the claimed invention to having only that purpose, benefit or possible use. [0136] In the present specification, terms such as "part", "component", "means", "section", or "segment" may refer to singular or plural items and are terms intended to refer to a set of properties, functions, or characteristics performed by one or more items having one or more parts. It is envisaged that where a "part", "component", "means", "section", "segment", or similar term is described as consisting of a single item, then a functionally equivalent object consisting of multiple items is considered to fall within the scope of the term; and similarly, where a "part", "component", "means", "section", "segment", or similar term is described as consisting of multiple items, a functionally equivalent object consisting of a single item is considered to fall within the scope of the term. The intended interpretation of such terms described in this paragraph should apply unless the contrary is expressly stated or the context requires otherwise. [0137] The term "connected" or a similar term, should not be interpreted as being limited to direct connections only. Thus, the scope of the expression “an item A connected to an item B” should not be limited to items or systems wherein an output of item A is directly connected to an input of item B. It means that there exists a path between an output of A and an input of B which may be a path including other items or means. "Connected", or a similar term, may mean either that two or more elements are in direct physical or causal contact, or that two or more elements are not in direct contact with each other yet still co-operate or interact with each other. [0138] It will be appreciated by persons skilled in the art that numerous variations or modifications may be made to the present technology as shown in the specific implementations without departing from the spirit or scope of the invention as broadly described. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present technology. The disclosed implementations are, therefore, to be considered in all respects as illustrative and not limiting or restrictive. [0139] The features described in relation to one or more aspects of the present technology are to be understood as applicable to other aspects of the present technology. More generally, combinations of the steps in the method(s) of the present technology or the features of the system(s) or device(s) of the present technology described elsewhere in the present disclosure, including in the claims, are to be understood as falling within the scope of the disclosure of the present disclosure. INDUSTRIAL APPLICABILITY [0140] It is apparent from the above that the arrangements described are applicable to the health care industries. EXAMPLES OF THE PRESENT TECHNOLOGY Example 1. A neural stimulation system comprising: an implantable device for controllably delivering neural stimuli, the device comprising: a stimulus source configured to provide neural stimuli to be delivered to a neural pathway of a patient in order to evoke neural responses from the neural pathway; measurement circuitry configured to capture signal windows from signals sensed on the neural pathway subsequent to respective neural stimuli; and a control unit configured to: control the stimulus source to provide a neural stimulus according to a stimulus intensity parameter; and measure an intensity of an evoked neural response in a captured signal window subsequent to the neural stimulus; a display; a processor configured to: instruct the control unit to deliver a plurality of neural stimuli according to respective stimulus intensity parameter values; instruct the control unit to measure the intensities of evoked neural responses in captured signal windows subsequent to respective delivered neural stimuli; determine a relationship between stimulus intensity parameter value and measured response intensity from the resulting plurality of (stimulus intensity parameter value, measured response intensity) pairs; and map a normalised measure of dose, using the determined relationship, to a target value; and a further processor configured to: render a graphical user interface on the display; and represent the target value on an element of the graphical user interface. Example 2. An automated method of controllably delivering neural stimuli to a neural pathway of a patient, the method comprising: delivering neural stimuli to the neural pathway of the patient in order to evoke neural responses from the neural pathway, the neural stimuli being delivered according to respective stimulus intensity parameter values; capturing signal windows from signals sensed on the neural pathway subsequent to respective neural stimuli; measuring intensities of neural responses evoked by the neural stimuli in respective signal windows; determining a relationship between stimulus intensity parameter value and measured response intensity from the resulting plurality of (stimulus intensity parameter value, measured response intensity) pairs; mapping a normalised measure of dose, using the determined relationship, to a target value; rendering a graphical user interface on a display; and representing the target value on an element of the graphical user interface. Example 3. A neural stimulation system comprising: an implantable closed-loop neural stimulation device for controllably delivering neural stimuli, the closed-loop neural stimulation device comprising a feedback controller configured to adjust a stimulus intensity parameter value so as to maintain a measured neural response intensity at a target value; a display; a processor configured to: determine a relationship between stimulus intensity parameter value and measured response intensity; map a normalised measure of dose, using the determined relationship, to a target value; and a further processor configured to: render a graphical user interface on the display; and represent the target value on an element of the graphical user interface. LABEL LIST stimulator 100 signal window 319 patient 108 ECAP detector 320 electronics module 110 comparator 324 battery 112 gain element 336 telemetry module 114 integrator 338 controller 116 activation plot 402 memory 118 ECAP threshold 404 clinical data 120 discomfort threshold 408 clinical settings 121 perception threshold 410 control programs 122 therapeutic range 412 pulse generator 124 discomfort response intensity 422 electrode selection module 126 activation plot 502 measurement circuitry 128 activation plot 504 ground 130 activation plot 506 array 150 ECAP threshold 508 biphasic stimulus pulse 160 ECAP threshold 510 ECAP 170 ECAP threshold 512 nerve 180 target ECAP amplitude 520 communications channel 190 ECAP 600 external computing device 192 neural stimulation system 700 CLNS system 300 device 710 clinical settings controller 302 remote controller 720 target ECAP controller 304 CST 730 box 308 CI 740 box 309 charger 750 controller 310 graphical user interface 800 box 311 up - control 810 stimulator 312 down - control 820 element 313 GUI element 830 measurement circuitry 318 bar 840 GUI element 900 indicator 1080 bar 910 method 1100 GUI element 950 step 1110 line 960 step 1120 indicator 970 step 1130 end 980 GUI element 1200 end 990 bar 1210 line segment 995 array 1220 GUI element 1000 method 1300 bar 1010 step 1310 GUI element 1050 step 1320 indicator 1070 step 1330 REFERENCES 1. Single, P.S. et al. Measures of Dosage for Spinal-Cord Electrical Stimulation: Review and Proposal. IEEE Trans. Neural. Syst. Rehabil. Eng.2023:31:4653-4660. 2. Leah Muller, MD, PhD, et al. First evidence of a biomarker-based dose-response relationship in chronic pain using physiologic closed-loop spinal cord stimulation. RAPM: Regional Anesthesia and Pain Medicine, 2024:0:1-7.

Claims

CLAIMS: 1. A neural stimulation system comprising: an implantable device for controllably delivering neural stimuli, the device comprising: a stimulus source configured to deliver neural stimuli to a neural pathway of a patient, the neural stimuli being configured to evoke neural responses from the neural pathway; measurement circuitry configured to capture signal windows from signals sensed on the neural pathway; and a control unit configured to: control the stimulus source to deliver a neural stimulus according to a stimulus intensity parameter; measure an intensity of an evoked neural response in a captured signal window subsequent to the neural stimulus; and adjust, using a feedback controller, the stimulus intensity parameter so as to maintain the measured response intensity at or near a target response intensity value; a display; and a processor configured to: render a graphical user interface on the display, the graphical user interface including one or more controls configured to adjust a target value; represent the target value on an element of the graphical user interface; and represent a predetermined target value on the element of the graphical user interface.

2. The neural stimulation system of claim 1, wherein a further processor is further configured to: instruct the control unit to control the stimulus source to deliver a plurality of neural stimuli according to respective stimulus intensity parameter values; instruct the control unit to measure the intensities of evoked neural responses in captured signal windows subsequent to respective delivered neural stimuli; and determine a relationship between stimulus intensity parameter value and measured response intensity from a resulting plurality of (stimulus intensity parameter value, measured response intensity) pairs.

3. The neural stimulation system of claim 2, wherein the target value is the target response intensity value and the predetermined target value is a predetermined target response intensity value.

4. The neural stimulation system of claim 3, wherein the further processor is further configured to map, using the determined relationship, a predetermined target normalised measure of dose (NMD) value to the predetermined target response intensity value.

5. The neural stimulation system of claim 2, wherein the target value is a target NMD value and the predetermined target value is a predetermined target NMD value.

6. The neural stimulation system of claim 5, wherein the further processor is further configured to map, using the determined relationship, the target NMD value to the target response intensity value.

7. The neural stimulation system of claim 5, wherein the further processor is further configured to map, using the determined relationship, a predetermined target response intensity value to the predetermined target NMD value.

8. The neural stimulation system of any one of claims 1 to 7, further comprising an external patient device in communication with the implantable device.

9. The neural stimulation system of claim 8, wherein the display and the processor form part of the external patient device.

10. The neural stimulation system of any one of claims 2 to 9, wherein the further processor forms part of the implantable device.

11. The neural stimulation system of any one of claims 2 to 9, further comprising an external programming device in communication with the implantable device.

12. The neural stimulation system of claim 11, wherein the further processor forms part of the external programming device.

13. The neural stimulation system of claim 11, wherein the display and the processor form part of the external programming device.

14. A neural stimulation system comprising: a closed-loop neural stimulation device for controllably delivering neural stimuli, the device comprising a control unit configured to adjust, using a feedback controller, a stimulus intensity parameter of delivered neural stimuli so as to maintain an intensity of a measured neural response at or near a target response intensity value; a display; and a processor configured to: render a graphical user interface on the display, the graphical user interface including one or more controls configured to adjust a target value; represent the target value on an element of the graphical user interface; and represent a predetermined target value on the element of the graphical user interface.

15. A method comprising: rendering a graphical user interface on a display, the graphical user interface including one or more controls configured to adjust a target value of a closed-loop neural stimulation device comprising a control unit configured to adjust, using a feedback controller, a stimulus intensity parameter of delivered neural stimuli so as to maintain an intensity of a measured neural response at or near a target response intensity value; representing the target value on an element of the graphical user interface; and representing a predetermined target value on the element of the graphical user interface.

16. The method of claim 15, further comprising: delivering, by the closed-loop neural stimulation device, a plurality of neural stimuli according to respective stimulus intensity parameter values; measuring, by the closed-loop neural stimulation device, the intensities of evoked neural responses in captured signal windows subsequent to respective delivered neural stimuli; and determining a relationship between stimulus intensity parameter value and measured response intensity from a resulting plurality of (stimulus intensity parameter value, measured response intensity) pairs.

17. The method of claim 16, wherein the target value is the target response intensity value and the predetermined target value is a predetermined target response intensity value.

18. The method of claim 17, further comprising mapping, using the determined relationship, a predetermined target normalised measure of dose (NMD) value to the predetermined target response intensity value.

19. The method of claim 16, wherein the target value is a target NMD value and the predetermined target value is a predetermined target NMD value.

20. The method of claim 19, further comprising mapping, using the determined relationship, the target NMD value to the target response intensity value.

21. The method of claim 19, further comprising mapping, using the determined relationship, a predetermined target response intensity value to the predetermined target NMD value.