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Transcutaneous electrical nerve stimulation (TENS) setup. (a) schematic representation of transcutaneous electrical nerve stimulation in the context of upper limb sensory restitution. This figure schematically illustrates how an electrode placed on the skin can generate a voltage field within the residual forearm's soft tissue. By placing the electrodes in the appropriate positions, the voltage field can elicit referred and clear sensations from the missing hand, corresponding to median and ulnar nerve innervations, as shown in transparent green and red. This allows for a certain amount of selectivity in the elicited response. (b) shows the exact electrode placements for each of the four subjects. The stimulation parameters (fixed amplitude, range of pulse widths) are also shown. The positions of the electrodes were patient specific.
Source publication
According to amputees, sensory feedback is amongst the most important features lacking from commercial prostheses. Although restoration of touch by means of implantable neural interfaces has been achieved, these approaches require surgical interventions, and their long-term usability still needs to be fully investigated. Here, we developed a non-in...
Contexts in source publication
Context 1
... placing electrodes on the skin (PALS neurostimulation electrodes, Axelgaard, US) in specific areas where the underlying nervous structures are close to the surface of the skin and easily accessible, it is possible to elicit activation of hand afferents, leading mainly to a paresthesia reported over the phantom limb (Fig. 8a). Initially the stimulating and return electrodes were round with a radius of 2.5 cm. In some cases (Subjects 1, 3 and 4), the round stimulation electrodes were cut with scissors to a more oval shape, which resulted in a smaller contact surface with the skin. Figure 8b shows the precise electrode positioning used for each of the four ...
Context 2
... some cases (Subjects 1, 3 and 4), the round stimulation electrodes were cut with scissors to a more oval shape, which resulted in a smaller contact surface with the skin. Figure 8b shows the precise electrode positioning used for each of the four subjects. The electrode placement and stimulation parameters were calibrated during an initial extensive exploration phase. ...
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The ability to perceive prosthetic grasping may enable amputees to better interact with external objects. This may require customized coding of multiple sensory feedback for each amputee. This study developed a protocol to determine optimal modulation ranges of sensations elicited by transcutaneous electrical nerve stimulation (TENS). These sensati...
Multimodal sensory feedback from upper-limb prostheses can increase their function and usability. Here we show that intuitive thermal perceptions during cold-object grasping with a prosthesis can be restored in a phantom hand through targeted nerve stimulation via a wearable thin-film thermoelectric device with high cooling power density and speed....
The restoration of sensory feedback in amputees plays a fundamental role in the prosthesis control and in the communication on the afferent channel between hand and brain. The literature shows that transcutaneous electrical nerve stimulation (TENS) can be a promising non-invasive technique to elicit sensory feedback in amputees, especially in the l...
Objective:
Evoked tactile sensation (ETS) elicited by transcutaneous electrical nerve stimulation (TENS) is promising to convey digit-specific sensory information to amputees naturally and non-invasively. Fitting ETS-based sensory feedback to amputees entails customizing coding of multiple sensory information for each stimulation site. This study...
Although peripheral nerve stimulation using intraneural electrodes has been shown to be an effective and reliable solution to restore sensory feedback after hand loss, there have been no reports on the characterization of multi-channel stimulation. A deeper understanding of how the simultaneous stimulation of multiple electrode channels affects the...
Citations
... Prior sensory restoration studies have not evaluated skin-surface electrode positions distally positioned from the wrist for people without limb loss as the end users. Some of the electrode positions evaluated in these studies are the residual limb's upper arm [18,19], elbow [16,20], or forearm [9,21]. Previous sensorized prosthesis studies have shown that stimulating the tricep area can provide information about object stiffness, shape, and surface topology [18,22]. ...
Objective: This study introduces distally-referred surface electrical nerve
stimulation (DR-SENS) and evaluates the effects of electrode placement,
polarity, and stimulation intensity on the location of elicited sensations in
able-bodied individuals. Approach: A two-phased human experiment was
used to characterize DR-SENS. In Experiment One, we explored 182 electrode
combinations to identify a subset of electrode position combinations that would
be most likely to elicit distally-referred sensations isolated to the index finger
without discomfort. In Experiment Two, we further examined this subset
of electrode combinations to determine the effect of stimulation intensity and
electrode position on perceived sensation location. Stimulation thresholds were
evaluated using parameter estimation by sequential testing and sensation locations
were characterized using psychometric intensity tests. Main Results: We found
that electrode positions distal to the wrist can consistently evoke distally referred
sensations with no significant polarity dependency. The finger-palm combination
had the most occurrences of distal sensations, and the different variations of this
combination did not have a significant effect on sensation location. Increasing
stimulation intensity significantly expanded the area of the sensation, moved
the most distal sensation distally, and moved the vertical centroid proximally.
Also, a large return electrode at the elbow mitigated all sensation at the return
electrode site while using symmetric stimulation waveforms. Furthermore, this
study showed that the most intense sensation for a given percept can be distally
referred. Lastly, for each participant, at least one of the finger-palm combinations
evaluated in this study worked at both perception threshold and maximum
comfortable stimulation intensities. Significance: These findings show that a
non-invasive surface electrical stimulation charge modulated haptic interface can
be used to elicit distally-referred sensations on able-bodied users. Furthermore,
these results inform the design of novel haptic interfaces and other applications
of surface electrical stimulation based haptic feedback on electrodes positioned
distally from the wrist.
... The tactile sensation elicited by peripheral nerve stimulation suggests that areas associated with anatomical representations of the missing limb are activated in the primary sensorimotor cortex (S1) (21). Although multiple groups have investigated the neural pathways involved in the tactile sensation of the hand, there has been less focus on determining the relationship between afferent inputs from the lower limb and higher neural circuitries, such as the spinal cord, cerebellum, and somatosensory cortex. ...
Lower limb loss is a major insult to the body’s nervous and musculoskeletal systems. Despite technological advances in prosthesis design, artificial limbs are not yet integrated into the body’s physiological systems. Therefore, lower limb amputees (LLAs) experience lower balance confidence, higher fear of falls, and impaired gait compared with their able-bodied peers (ABs). Previous studies have demonstrated that restored sensations perceived as originating directly from the missing limb via neural interfaces improve balance and performance in certain ambulatory tasks; however, the effects of such evoked sensations on neural circuitries involved in the locomotor activity are not well understood. In this work, we investigated the effects of plantar sensation elicited by peripheral nerve stimulation delivered by multicontact nerve cuff electrodes on gait symmetry and stability, speed perception, and motor adaptation. We found that restored plantar sensation increased stance time and propulsive force on the prosthetic side, improved gait symmetry, and yielded an enhanced perception of prosthetic limb movement. Our results show that the locomotor adaptation among LLAs with plantar sensation became similar to that of ABs. These findings suggest that our peripheral nerve–based approach to elicit plantar sensation directly affects central nervous pathways involved in locomotion and motor adaptation during walking. Our neuroprosthesis provided a unique model to investigate the role of somatosensation in the lower limb during walking and its effects on perceptual recalibration after a locomotor adaptation task. Furthermore, we demonstrated how plantar sensation in LLAs could effectively increase mobility, improve walking dynamics, and possibly reduce fall risks.
... More recently, the innovative use of electrical nerve stimulation to artificially restore sensory feedback after limb amputation has shown promising results [9,10]. The technique exploiting invasive neural interfaces (i.e., implantable electrodes) [11][12][13][14] and non-invasive transcutaneous stimulation (i.e., TENS) [15][16][17][18] has been successfully tested in upper and lower limb amputees. In addition, TENS preliminary showed good results with pain treatment in people with peripheral neuropathy [19] and affected by reduced peripheral sensitivity with impact on the motor control during movements (e.g., locomotion) [20]. ...
... Furthermore, the modulation of the intensity in electrical sensory feedback applications has shown promising results (e.g., grasping of an object with a prosthetic hand [16,52,53], or walking phase information relating to the pressure exerted by a lower limb prosthesis [13]). Second, it is important to evoke a somatotopic sensation that is inherently simple and intuitive, allowing for immediate and effortless understanding of the feedback [16], hence a medium weight was given to the location (w 3 = 0.25). ...
... Furthermore, the modulation of the intensity in electrical sensory feedback applications has shown promising results (e.g., grasping of an object with a prosthetic hand [16,52,53], or walking phase information relating to the pressure exerted by a lower limb prosthesis [13]). Second, it is important to evoke a somatotopic sensation that is inherently simple and intuitive, allowing for immediate and effortless understanding of the feedback [16], hence a medium weight was given to the location (w 3 = 0.25). Third, the type of sensation was introduced to avoid uncomfortable sensations but, since inducing natural (touch-like) sensory feedback with non-invasive interfaces is still a unresolved challenge [54][55][56], the lowest weight was assigned to it (w2 = 0.15). ...
Background
The identification of the electrical stimulation parameters for neuromodulation is a subject-specific and time-consuming procedure that presently mostly relies on the expertise of the user (e.g., clinician, experimenter, bioengineer). Since the parameters of stimulation change over time (due to displacement of electrodes, skin status, etc.), patients undergo recurrent, long calibration sessions, along with visits to the clinics, which are inefficient and expensive. To address this issue, we developed an automatized calibration system based on reinforcement learning (RL) allowing for accurate and efficient identification of the peripheral nerve stimulation parameters for somatosensory neuroprostheses.
Methods
We developed an RL algorithm to automatically select neurostimulation parameters for restoring sensory feedback with transcutaneous electrical nerve stimulation (TENS). First, the algorithm was trained offline on a dataset comprising 49 subjects. Then, the neurostimulation was then integrated with a graphical user interface (GUI) to create an intuitive AI-based mapping platform enabling the user to autonomously perform the sensation characterization procedure. We assessed the algorithm against the performance of both experienced and naïve and of a brute force algorithm (BFA), on 15 nerves from five subjects. Then, we validated the AI-based platform on six neuropathic nerves affected by distal sensory loss.
Results
Our automatized approach demonstrated the ability to find the optimal values of neurostimulation achieving reliable and comfortable elicited sensations. When compared to alternatives, RL outperformed the naïve and BFA, significantly decreasing the time for mapping and the number of delivered stimulation trains, while improving the overall quality. Furthermore, the RL algorithm showed performance comparable to trained experimenters. Finally, we exploited it successfully for eliciting sensory feedback in neuropathic patients.
Conclusions
Our findings demonstrated that the AI-based platform based on a RL algorithm can automatically and efficiently calibrate parameters for somatosensory nerve stimulation. This holds promise to avoid experts’ employment in similar scenarios, thanks to the merging between AI and neurotech. Our RL algorithm has the potential to be used in other neuromodulation fields requiring a mapping process of the stimulation parameters.
Trial registration: ClinicalTrial.gov (Identifier: NCT04217005)
... In their study, changes in the ipsilesional 187 motor theta and alpha power were significantly correlated with finger individuation 188 improvements [19]. Furthermore, in the field of neural prosthetics, several researchers 189 have studied neural markers during sensory retraining interventions, particularly in 190 tactile discrimination tasks [49][50][51][52]. For instance, Su et al. [51] found that alpha band 191 attenuation in the somatosensory cortex was correlated with tactile discrimination 192 performance. ...
A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, somatosensory interventions such as sensory electrical stimulation (SES) are not the standard of care, probably due to their unclear influence on neurorehabilitation.
We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with twenty-six healthy participants who explored a set of three visually identical virtual textures—haptically rendered by a robotic device and that differed in their spatial period— while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance —assessed by the probability of correct responses— before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8-13 Hz) associated with sensory processing.
We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced.
Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.
... Using peripheral nerve interfaces, researchers have elicited sensations that are referred to the phantom hand and consistent in location and quality over several months [8]- [10]. Combined with sensorized prosthetic hands, stimulation of peripheral nerve interfaces enabled people with amputation to sense the stiffness and shape of virtual objects more accurately [11], improve their performance in tasks involving grasp control [9], and improve their ability to modulate grip force [8], compared to conditions where they did not have additional feedback. Home use of a sensorized prosthesis increased daily prosthetic wear time [12], quality of life [12], and embodiment [12], [13]. ...
p>In four participants with upper limb loss, we characterized the quality and location of sensation elicited through electrical stimulation of regenerative peripheral nerve interfaces (RPNIs) over time (up to 54 months post implantation of wires). We also measured sensory perception and discomfort thresholds, sensitivity to changes in stimulation amplitude, and ability to differentiate objects of different stiffness and sizes.</p
... Using peripheral nerve interfaces, researchers have elicited sensations that are referred to the phantom hand and consistent in location and quality over several months [8]- [10]. Combined with sensorized prosthetic hands, stimulation of peripheral nerve interfaces enabled people with amputation to sense the stiffness and shape of virtual objects more accurately [11], improve their performance in tasks involving grasp control [9], and improve their ability to modulate grip force [8], compared to conditions where they did not have additional feedback. Home use of a sensorized prosthesis increased daily prosthetic wear time [12], quality of life [12], and embodiment [12], [13]. ...
p>In four participants with upper limb loss, we characterized the quality and location of sensation elicited through electrical stimulation of regenerative peripheral nerve interfaces (RPNIs) over time (up to 54 months post implantation of wires). We also measured sensory perception and discomfort thresholds, sensitivity to changes in stimulation amplitude, and ability to differentiate objects of different stiffness and sizes.</p
... The electro-tactile stimulation, also referred to transcutaneous electrical nerve stimulation (TENS), is considered as a plausible non-invasive way to restore somatosensory sensory feedback [54], [55], [56]. It uses surface electrodes to convey encoded electrical signals through the skin and indirectly activate underlying sensory nerves. ...
Dexterous prosthetic hand is an essential rehabilitation assistant device to improve the life quality of amputee patients. Despite the continuous emergence of commercial prostheses and laboratory prototypes, the rejection rate remains high caused by the poor neural interaction performance and excessive cognitive burden, especially for the usage of upper-arm prostheses controlled by above-the-elbow amputation stump. The progress in artificial perception, bidirectional neural interface and share control indicates a great potential to improve the manipulation efficiency of upper-limb prostheses. In this review, a comprehensive analysis of human-in-the-loop shared control studies is presented to provide researchers with a systematic technical route in upper-limb prostheses control. The latest avenues of research concerning myoelectric control, sensory feedback, perception, autonomous motion planning of multiple degree of freedom elbow-wrist, and share control are overviewed and discussed. The comprehensive assessments show that there remains inadequate technologies to achieve an anthropomorphic and efficient unified elbow-wrist-hand prostheses manipulation. By delineating the current shortcomings, the outcomes of this work highlight future investigation in the field of intuitive motion control, feedback of proprioception/touch and the natural interaction between human intent and machine autonomy.
... To address this, TENS has been introduced as intermediate solution between remapping and neural implants for non-invasive, somatotopic tactile feedback restoration. Indeed, it has been successfully tested on upper and lower limb amputees as low-cost, low-risk, temporally stable alternative to invasive interfaces [6], [10], [57]- [61]. However, mostly single-parameter stimulations have been implemented evoking low natural percepts and low informativeness. ...
... However, mostly single-parameter stimulations have been implemented evoking low natural percepts and low informativeness. For instance, object stiffness and size recognition were performed by modulating either only the pulse amplitude, as in Vargas et al. [59], [61] or only pulsewidth as in D'Anna et al. and Shin et al. [6], [62]. Few more complex, neuromorphic modulations have been implemented in TENS, without leading to significant improvements in sensation quality [47]. ...
... Moreover, the elicited sensations are characterized by a low intensity sensitivity (e.g. few encoded intensity levels) [6], [62], [63]. Neural stimulation codes, resembling more closely the cumulative asynchronous fibers activation during a sensory process (thus more natural neural activation), demonstrated higher naturalness and functionality in implants, therefore implementing these for TENS holds promise to increase the user experience and resulting functionality. ...
Objective. Transcutaneous Electrical Nerve Stimulation (TENS) has been recently introduced in neurorehabilitation and neuroprosthetics as a promising, non-invasive sensory feedback restoration alternative to implantable neurostimulation. Yet, the adopted stimulation paradigms are typically based on single-parameter modulations (e.g., pulse amplitude PA, pulse-width PW or pulse frequency PF). They elicit artificial sensations characterized by a low intensity resolution (e.g., few perceived levels), low naturalness and intuitiveness, hindering the acceptance of this technology. To address these issues, we designed novel multiparametric stimulation paradigms, featuring the simultaneous modulation of multiple parameters, and implemented them in real-time tests of performance when exploited as artificial sensory inputs.
Approach. We initially investigated the contribution of PW and PF variations to the perceived sensation magnitude through discrimination tests. Then, we designed three multiparametric stimulation paradigms comparing them with a standard PW linear modulation in terms of evoked sensation naturalness and intensity. The most performant paradigms were then implemented in real-time in a Virtual Reality - TENS platform to assess their ability to provide intuitive somatosensory feedback in a functional task.
Main results. Our study highlighted a strong negative correlation between perceived naturalness and intensity: less intense sensations are usually deemed as more like natural touch. In addition, we observed that PF and PW changes have a different weight on the perceived sensation intensity. As a result, we adapted the Activation Charge Rate (ACR) equation, proposed for implantable neurostimulation to predict the perceived intensity while co-modulating the PF and charge per pulse, to TENS (ACRT). ACRT allowed to design different multiparametric TENS paradigms with the same absolute perceived intensity. Although not reported as more natural, the multiparametric paradigm, based on sinusoidal PF modulation, resulted being more intuitive and subconsciously integrated than the standard linear one. This allowed subjects to achieve a faster and more accurate functional performance.
Significance. Our findings suggest that TENS-based, multiparametric neurostimulation, despite not consciously perceived naturally, can provide integrated and more intuitive somatosensory information, as functionally proved. This could be exploited to design novel encoding strategies able to improve the performance of non-invasive sensory feedback technologies.
... Evidence to support the preservation, but suppression, of the canonical topographic cortical map following a limb amputation stems from studies where the nervous system was stimulated and sensory percepts were evoked (64). Sensory percepts have been evoked in the missing limbs of people with amputations using electrical stimulation of the peripheral nerves, (73)(74)(75)(76)(77), spinal cord (27,78,79), and thalamus (69), as well as magnetic stimulation of the contralateral primary motor cortex (80,81). Collectively, it is likely that a loss of somatosensory input from an amputation results in a suppression of somatosensory pathways corresponding to the affected limb, and that stimulation, including tSCS, 'reawakens' or unmasks the sensorimotor nervous system. ...
Objective
Phantom limb pain (PLP) is debilitating and affects over 70% of people with lower-limb amputation. Other neuropathic pain conditions correspond with increased spinal excitability, which can be measured using reflexes and F-waves. Spinal cord neuromodulation can be used to reduce neuropathic pain in a variety of conditions and may affect spinal excitability, but has not been extensively used for treating phantom limb pain. Here, we propose using a non-invasive neuromodulation method, transcutaneous spinal cord stimulation (tSCS), to reduce PLP and modulate spinal excitability after transtibial amputation.
Approach
We recruited three participants, two males (5- and 9-years post-amputation, traumatic and alcohol-induced neuropathy) and one female (3 months post-amputation, diabetic neuropathy) for this 5-day study. We measured pain using the McGill Pain Questionnaire, visual analog scale, and pain pressure threshold test. We measured spinal reflex and motoneuron excitability using posterior root-muscle (PRM) reflexes and F-waves, respectively. We delivered tSCS for 30 minutes/day for 5 days.
Main Results
After 5 days of tSCS, pain scores decreased by clinically-meaningful amounts for all participants from 34.0±7.0 to 18.3±6.8. Two participants had increased pain pressure thresholds across the residual limb (Day 1: 5.4±1.6 lbf; Day 5: 11.4±1.0 lbf). F-waves had normal latencies but small amplitudes. PRM reflexes had high thresholds (59.5±6.1 µC) and low amplitudes, suggesting that in PLP, the spinal cord is hypoexcitable. After 5 days of tSCS, reflex thresholds decreased significantly (38.6±12.2 µC; p<0.001).
Significance
Overall, limb amputation and PLP may be associated with reduced spinal excitability and tSCS can increase spinal excitability and reduce PLP.
... D'Anna et al., investigated the effect of TENS on induced sensations in four amputees. They observed that even if most of the sensations were of paresthesia, the stimulation improved subjects' control of a prosthetic hand [27]. Pan et al., used a high-density electrode grid to induce haptic sensation on the lower limb of five trans-radial amputee subjects, showing the possibility of eliciting sensation in different regions of the foot [28]. ...
Transcutaneous Electrical Nerve Stimulation (TENS) is a promising technique for eliciting referred tactile sensations in patients with limb amputation. Although several studies show the validity of this technique, its application in daily life and away from laboratories is limited by the need for more portable instrumentation that guarantees the necessary voltage and current requirements for proper sensory stimulation. This study proposes a low-cost, wearable high-voltage compliant current stimulator with four independent channels based on Components-Off-The-Shelf (COTS). This microcontroller-based system implements a voltage-current converter controllable through a digital-to-analog converter that delivers up to 25 mA to load up to 3.6 kΩ. The high-voltage compliance enables the system to adapt to variations in electrode-skin impedance, allowing it to stimulate loads over 10 kΩ with currents of 5 mA. The system was realized on a four-layer PCB (115.9 mm × 61 mm, 52 g). The functionality of the device was tested on resistive loads and on an equivalent skin-like RC circuit. Moreover, the possibility of implementing an amplitude modulation was demonstrated.
