Phantom-Mobility-Based Prosthesis Control in Transhumeral Amputees Without Surgical Reinnervation: A Preliminary Study

Transhumeral amputees face substantial difficulties in efficiently controlling their prosthetic limb, leading to a high rate of rejection of these devices. Actual myoelectric control approaches make their use slow, sequential and unnatural, especially for these patients with a high level of amputation who need a prosthesis with numerous active degrees of freedom (powered elbow, wrist, and hand). While surgical muscle-reinnervation is becoming a generic solution for amputees to increase their control capabilities over a prosthesis, research is still being conducted on the possibility of using the surface myoelectric patterns specifically associated to voluntary Phantom Limb Mobilization (PLM), appearing naturally in most upper-limb amputees without requiring specific surgery. The objective of this study was to evaluate the possibility for transhumeral amputees to use a PLM-based control approach to perform more realistic functional grasping tasks. Two transhumeral amputated participants were asked to repetitively grasp one out of three different objects with an unworn eight-active-DoF prosthetic arm and release it in a dedicated drawer. The prosthesis control was based on phantom limb mobilization and myoelectric pattern recognition techniques, using only two repetitions of each PLM to train the classification architecture. The results show that the task could be successfully achieved with rather optimal strategies and joint trajectories, even if the completion time was increased in comparison with the performances obtained by a control group using a simple GUI control, and the control strategies required numerous corrections. While numerous limitations related to robustness of pattern recognition techniques and to the perturbations generated by actual wearing of the prosthesis remain to be solved, these preliminary results encourage further exploration and deeper understanding of the phenomenon of natural residual myoelectric activity related to PLM, since it could possibly be a viable option in some transhumeral amputees to extend their control abilities of functional upper limb prosthetics with multiple active joints without undergoing muscular reinnervation surgery

Phantom Sensations Influenced by Global and Local Modifications of the Prosthetic Socket as a Potential Solution for Natural Somatosensory Feedback During Walking: A Preliminary Study of a Single Case

Following lower limb amputation, amputees are trained to walk with a prosthesis. The loss of a lower limb deprives them of essential somatosensory information, which is one of the causes of the difficulties of walking with a prosthesis. We here explored whether a solution to this lack of somatosensory feedback could come from natural sensations of the phantom limb, present in most amputees, instead of from substitutive technologies. Indeed, it is known that phantom sensations can be modulated by (i) global mechanical characteristics of the prosthesis socket, and (ii) locally applying a stimulus on an area of the residual limb. The purpose of this pilot study was to verify the feasibility of influencing phantom sensations via such socket modifications in a participant with transfemoral amputation. Four prosthetic interface conditions were studied: a rigid and a semi-rigid socket, each one with and without a focal pressure increase on a specific area of the residual limb. The results show that phantom sensations during walking were different according to the 4 interface conditions. The participant had more vivid phantom sensations in his foot and calf of which some varied as a function of the gait phases. Preliminary gait analysis with wearable sensors shows that these modifications were accompanied by changes in some gait spatiotemporal parameters. This preliminary study of single case demonstrates that phantom sensations can be modulated by the prosthetic interface and can provide natural somatosensory information dynamically varying with gait phases. Although this needs to be confirmed for a larger population of lower limb amputees, it already encourages non-painful phantom sensations to be considered early during the rehabilitation of lower limb amputees

Effects of short-term adaptation of saccadic gaze amplitude on hand-pointing movements

International audienceWe investigated whether and how adaptive changes in saccadic amplitudes (short-term saccadic adaptation) modify hand movements when subjects are involved in a pointing task to visual targets without vision of the hand. An experiment consisted of the pre-adaptation test of hand pointing (placing the finger tip on a LED position), a period of adaptation, and a post-adaptation test of hand pointing. In a basic task (transfer paradigm A), the pre-and post-adaptation trials were performed without accompanying eye and head movements: in the double-step gaze adaptation task, subjects had to fixate a single, suddenly displaced visual target by moving eyes and head in a natural way. Two experimental sessions were run with the visual target jumping during the saccades, either backwards (from 30 to 20°, gaze sac-cade shortening) or onwards (30 to 40°, gaze saccade lengthening). Following gaze-shortening adaptation (level of adaptation 79±10%, mean and s.d.), we found a statistically significant shift (t-test, error level P<0.05) in the final hand-movement points, possibly due to adaptation transfer, representing 15.2% of the respective gaze adaptation. After gaze-lengthening adaptation (level of adaptation 92±17%), a non-significant shift occurred in the opposite direction to that expected from adaptation transfer. The applied computations were also performed on some data of an earlier transfer paradigm (B, three target displacements at a time) with gain shortening. They revealed a significant transfer relative to the amount of adaptation of 18.5±17.5% (P<0.05). In the coupling paradigm (C), we studied the influence of gaze saccade adaptation of hand-pointing movements with concomitant orienting gaze shifts. The adaptation levels achieved were 59±20% (shortening) and 61±27% (lengthening). Shifts in the final fingertip positions were congruent with internal coupling between gaze and hand, representing 53% of the respective gaze-amplitude changes in the shortening session and 6% in the lengthening session. With an adaptation transfer of less than 20% (paradigm A and B), we concluded that saccadic adaptation does not " automatically " produce a functionally meaningful change in the skeleto-motor system controlling hand-pointing movements. In tasks with concomitant gaze saccades (coupling paradigm C), the modification of hand pointing by the adapted gaze comes out more clearly, but only in the shortening session

Specialization of left auditory cortex for speech perception in Man depends on temporal coding

International audienceSpeech perception requires cortical mechanisms capable of analysing and encoding successive spectral (frequency) changes in the acoustic signal. To study temporal speech processing in the human auditory cortex, we recorded intracerebral evoked potentials to syllables in right and left human auditory cortices including Heschl's gyrus (HG), planum temporale (PT) and the posterior part of superior temporal gyrus (area 22). Natural voiced (/ba/, /da/, /ga/) and voiceless (/pa/, /ta/, /ka/) syllables, spoken by a native French speaker, were used to study the processing of a specific temporally based acoustico-phonetic feature, the voice onset time (VOT). This acoustic feature is present in nearly all languages, and it is the VOT that provides the basis for the perceptual distinction between voiced and voiceless consonants. The present results show a lateralized processing of acoustic elements of syllables. First, processing of voiced and voiceless syllables is distinct in the left, but not in the right HG and PT. Second, only the evoked potentials in the left HG, and to a lesser extent in PT, reflect a sequential processing of the different components of the syllables. Third, we show that this acoustic temporal processing is not limited to speech sounds but applies also to non-verbal sounds mimicking the temporal structure of the syllable. Fourth, there was no difference between responses to voiced and voiceless syllables in either left or right areas 22. Our data suggest that a single mechanism in the auditory cortex, involved in general (not only speech-specific) temporal processing, may underlie the further processing of verbal (and non-verbal) stimuli. This coding, bilaterally localized in auditory cortex in animals, takes place specifically in the left HG in man. A defect of this mechanism could account for hearing discrimination impairments associated with language disorders

Classification of Phantom Finger, Hand, Wrist and Elbow Voluntary Gestures in Transhumeral Amputees with sEMG

International audienceDecoding finger and hand movements from sEMG electrodes placed on the forearm of transradial amputees has been commonly studied by many research groups. A few recent studies have shown an interesting phenomenon: simple correlations between distal phantom finger, hand and wrist voluntary movements and muscle activity in the residual upper arm in transhumeral amputees, i.e., of muscle groups that, prior to amputation, had no physical effect on the concerned hand and wrist joints. In this study, we are going further into the exploration of this phenomenon by setting up an evaluation study of phantom finger, hand, wrist and elbow (if present) movement classification based on the analysis of surface electromyographic (sEMG) signals measured by multiple electrodes placed on the residual upper arm of five transhumeral amputees with a controllable phantom limb who did not undergo any reinnervation surgery. We showed that with a state-of-the-art classification architecture, it is possible to correctly classify phantom limb activity (up to 14 movements) with a rather important average success (over 80% if considering basic sets of six hand, wrist and elbow movements) and to use this pattern recognition output to give online control of a device (here a graphical interface) to these transhumeral amputees. Beyond changing the way the phantom limb condition is apprehended by both patients and clinicians, such results could pave the road towards a new control approach for transhumeral amputated patients with a voluntary controllable phantom limb. This could ease and extend their control abilities of functional upper limb prosthetics with multiple active joints without undergoing muscular reinnervation surgery

Corticomuscular coherence (CMC) obtained for right hand muscles for 5 subjects in the bimanual and unimanual conditions.

<p><b>A.</b> Grand average time-frequency plots of the z-score CMC between right hand FDI and electrodes C3 and FCz in the bimanual condition (left side) and in the unimanual condition (right side). The color scale indicates the z-score CMC values, thresholded between 0 and 2 for clarity. The vertical axis represents the frequency scale ranging from 10 to 60 Hz. The horizontal axis represents the time scale ranging from 1.5 to 13.5 s (0 s, off-scale, corresponds to the beginning of the ascending ramp). The vertical dotted lines indicate the time windows over which we averaged to obtain the topographies. <b>B.</b> Grand average z-score CMC topographies averaged over the frequency band 20–30 Hz and over 2 s of the periods of interest SF1.5 and SF0.5 for right hand FDI obtained for the bimanual condition (left side) and the unimanual condition (right side). The color scale indicates the z-score CMC values, thresholded between 0 and 1 for clarity. <i>M1_R</i>: right primary motor cortex. <i>M1_L</i>: left primary motor cortex. <i>SMA</i>: supplementary motor area. Similar results were found for right AbPB (not shown).</p

A visuomotor force tracking task imposing bimanual cooperation.

<p>The left hand held the custom device at one extremity while the right hand concurrently performed the visuomotor force tracking task by producing low forces at the other extremity of the same device. <b>B.</b> EMG was simultaneously recorded on two muscles of right and left hands, the First Dorsal Interosseus (FDI) and the Abductor Pollicis Brevis (AbPB). <b>C.</b> The target force profile for the right hand was continuously presented in a 10 s window, moving from right to left on the computer screen. The right hand force production was represented by the position of a cursor moving vertically, upwards with increasing force, 1 N corresponding to 3 cm on the screen. The horizontal position of the cursor was fixed in the middle of the computer screen. The subjects were instructed to match the vertical position of the cursor with the target force. No feedback was given concerning left hand force production. <b>D.</b> The custom device was mounted with two strain gauges to detect the grip forces produced by the right and left hands. <b>E.</b> Time course of one trial, all trials had the same force profile and duration. Each trial was was divided into 4 characteristic periods: an ascending ramp of 4.5 s with a force level linearly increasing from 0 to 1.5 N, a static force period of 3 s with a force level fixed at 1.5 N (<b>SF1.5</b>), a descending ramp of 3 s with a force level linearly decreasing from 1.5 to 0.5 N, and a static force period of 3 s with a force level fixed at 0.5 N (<b>SF0.5</b>). The present study focussed on the time periods SF1.5 and SF0.5 (gray-shaded areas).</p

Behavioral and electrophysiological results for a typical subject in the bimanual condition.

<p><b>A.</b> Time-dependent plots of the force production and between-trial variability at each time point for left (in blue) and right (in red) hands. The vertical dotted lines indicate the time windows over which we averaged to obtain the topographies. <b>B.</b> Time-frequency plots of the z-score CMC between left hand FDI and electrodes C4 and FCz (left side), and between right hand FDI and electrodes C3 and FCz (right side). The color scale indicates the z-score CMC value, thresholded between 0 and 3 for clarity. The vertical axis represents the frequency scale ranging from 10 to 50 Hz. The horizontal axis represents the time scale ranging from 1.5 to 13.5 s (0 s, off-scale, corresponds to the beginning of the ascending ramp). <b>C.</b> Z-score CMC topographies averaged over the frequency band 20–30 Hz for left hand, over the frequency band 16–26 Hz for right hand, and over 2 s of the periods of interest SF1.5 and SF0.5, respectively. For the left hand, an additional topography averaged over 2 to 4 s after the beginning of the trials is shown. The color scale indicates the z-score CMC values, thresholded between 0 and 2 for clarity. <i>M1_R</i>: right primary motor cortex. <i>M1_L</i>: left primary motor cortex. <i>SMA</i>: supplementary motor area.</p

Corticomuscular coherence (CMC) obtained for left and right hand muscles in the bimanual condition.

<p><b>A.</b> Grand average time-frequency plots of the z-score CMC between left hand AbPB <i>and</i> electrodes C4 and FCz (left side) and between right hand AbPB <i>and</i> electrodes C3 and FCz (right side). The color scale indicates the z-score CMC values, thresholded between 0 and 2 for clarity. The vertical axis represents the frequency scale ranging from 10 to 60 Hz. The horizontal axis represents the time scale ranging from 1.5 to 13.5 s (0 s, off-scale, corresponds to the beginning of the ascending ramp). The vertical dotted lines indicate the time windows over which we averaged to obtain the topographies. <b>B.</b> Grand average z-score CMC topographies for AbPB and FDI of left hand (left side) and right hand (right side), averaged over the frequency band 20–30 Hz and over 2 s of the periods of interest SF1.5 and SF0.5, respectively. The color scale indicates the z-score CMC values, thresholded between 0 and 1 for clarity. <i>M1_R</i>: right primary motor cortex. <i>M1_L</i>: left primary motor cortex. <i>SMA</i>: supplementary motor area. The time-frequency plots for FDI were similar to those for AbPB (not shown).</p