Both amputees gave free report statements implying ownership of the rubber limb. During the synchronous conditions Subject S-2 was often observed pushing her residual limb towards the prosthesis as though she was attempting to make them align. She did not score highly on question 4 with her intact side above. The just noticeable difference for Subject S-2 was These values were not significantly different from each other. The just noticeable difference for Subject S-1 was No values for Subject S-1 were significantly different from each other.
A—C Use of the vibratory units to generate the Rubber Hand Illusion; D—F use of the touch interface to generate the Rubber Hand Illusion while vibratory input for the temporal order judgement task was applied to the shoulders.
Mind-Controlled Artificial Arm Begins the First Human Testing
A Diagrams of projected sensation elicited by the vibratory input applied to the reinnervated skin. B The point of subjective simultaneity. C The just noticeable difference. D Diagrams of projected sensation elicited by the G10 tactor pushing into the reinnervated skin. E The point of subjective simultaneity. F The just noticeable difference. In the second experimental configuration the conditions of the Rubber Hand Illusion were generated by pressing the reinnervated skin of the residual limb with the robotic touch interface at the same time that the vibratory stimuli for the temporal order judgement task were applied to each shoulder Figs 2 C and 5 D.
We found that the point of subjective simultaneity and just noticeable difference values were not significantly different between conditions Fig. The residual limb skin temperature was measured during three conditions of the Rubber Hand Illusion presented with the robotic touch interface Fig.
There was also a small average absolute change in temperature during the synchronous condition for her mid residual limb; 0.
This temperature fluctuation was associated with a strong agreement with ownership statement 1 on a questionnaire questionnaires were administered at the termination of all temperature and temporal order judgement tasks, Supplementary Fig. We also saw no condition specific modulation of temperature for Subject S-1 during this experiment Supplementary Fig. Colours correspond to individual temperature traces in Supplementary Fig.
The results of this study provide evidence that a robotic touch interface, linking a prosthetic arm to the previously amputated cutaneous sensory nerves of a missing limb, can be used to elicit a shift in perception towards incorporation of the artificial limb into the self-image of two targeted reinnervation amputees.
Taken collectively, these results suggest that providing physiologically and anatomically appropriate direct sensory feedback for a prosthetic limb creates a vivid sense of ownership of the device. In the questionnaire experiments we hypothesized that, when stimulated in the synchronous condition versus the control conditions, the subjects would agree more strongly with the three embodiment-related statements than the other five control statements.
We found that both amputees agreed more strongly with statements 1—3, which reflected ownership of the limb and scored significantly higher in the synchronous condition than in the temporally asynchronous, visual only, and fixation conditions Fig. In contrast, Subject S-2 showed less distinction between the ownership and control statements although her responses indicated a stronger reaction than Subject S-1 to the synchronous condition. Subject S-2 agreed with control questions mentioning movement or transformation.
Self reports also suggested a perceptual shift towards ownership of the prosthetic limb. The responses indicated that the illusion was not completely abolished by the spatially mismatched condition. The vividness of the Rubber Hand Illusion appears to relate to the magnitude of the agreement with the ownership statements Botvinick and Cohen, ; Ehrsson et al.
We hypothesized that if the robotic touch interface created a vivid sense of embodiment then we should see similar magnitudes of questionnaire responses between the amputated and intact limbs.
The artificial hand that can 'feel' - enosesimaxes.ml
The robotic touch interface appeared to provide strong sense of embodiment because the magnitude of the agreement with ownership statements was similar for both amputees between both sides Fig. However, their approach probably activates sensory pathways not directly connected to the afferent channels of the missing limb, which may be reflected in lower response magnitudes Ehrsson et al.
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We also found that presentation of the Rubber Hand Illusion did not appear to alter perception of the illusion administered to the amputated side Supplementary Fig. Shifts in the output measurements of the temporal order judgement task reflect modulations of central tactile processing mechanisms related to incorporation of a rubber hand into the self-image of able bodied individuals Moseley et al.
In the first configuration of the experiment we compared input from both fingertips intact and projected sensation by using similar testing points for application of the vibratory input Fig. We hypothesized that when performing the temporal order judgement task under the synchronous condition, the point of subjective simultaneity would show a greater shift than in comparison with the fixation and spatially mismatched conditions.
Subject S-1 did not respond robustly to this experiment. However, for Subject S-2 the synchronous condition triggered the strongest shift of the point of subjective simultaneity Fig. The point of subjective simultaneity is a reflection of the relative weighting given to processing input from each limb Moseley et al. This suggests that for Subject S-2 observing the correct tactile input to the prosthesis modulated the weighting of central temporal processing relative to tactile input from each limb.
In the second configuration of the experiment we generated the conditions of the Rubber Hand Illusion by pressing the reinnervated skin with the robotic touch interface while applying the vibratory stimuli for the psychophysical task to each shoulder. We hypothesized that when performing the temporal order judgement task under the synchronous condition, the point of subjective simultaneity would show a greater shift than in comparison with the fixation and temporally asynchronous conditions.
Neither amputee appeared to respond robustly to this experiment, probably because they had to simultaneously attend to two different tasks Fig. When his perception of the prosthesis shifted towards embodiment under the synchronous condition, his performance on the task improved markedly as opposed to operating at near chance with either incongruous or non-existent input Fig.
We calculated the just noticeable difference, a measure of the time difference between stimulus onsets that is needed for the subject to determine which one came first Schicke and Roder, , for both configurations of the temporal order judgement task. This measure indicates how well the subject performed; the smaller the difference the better the performance. We hypothesized that when performing the temporal order judgement task under the synchronous condition the just noticeable difference would show a greater decrease than in comparison with the control conditions.
While there was overlap of the CI across the two configurations of the tests for both amputees, in all but one instance the just noticeable difference was lower for the synchronous conditions than for the asynchronous and mismatched conditions. It appears that presenting the amputees with synchronous visual and tactile input helped them process tactile information more effectively than incongruous presentation.
Skin temperature regulation reflects Rubber Hand Illusion mediated limb ownership and disownership in able-bodied subjects. When individuals take ownership of the rubber hand the temperature of the disowned real hand drops Moseley et al. We hypothesized that if the robotic touch interface provided a vivid sense of embodiment then we should observe a measurable change in the physiological skin temperature of the residual limb during the synchronous condition versus the fixation and temporal asynchrony conditions.
We found that during the synchronous condition of the illusion Subject S-2 showed a modulation of temperature of her residual limb Fig. This result suggests that the ownership illusion generated by the robotic touch interface was vivid enough to elicit a physiological change in temperature regulation. Subject S-1 did not show a similar physiological temperature response to the Rubber Hand Illusion in these experiments Supplementary Fig.
When Subject S-2 experienced the illusion we saw a net increase in temperature for her proximal residual limb Supplementary Fig. It is possible that the observed temperature differential was associated with amputation related peripheral nerve damage and complex regional pain syndrome Uematsu, ; Bruehl et al. However, it is conceivable that the changes in temperature regulation of the residual limb when the amputee received synchronous visual and tactile feedback may reflect a restoration of the limb within her self-image Moseley et al. Here we found evidence of systematic changes in the testing results of both amputees related to the synchronous condition, however, both amputees responded somewhat differently to testing.
The differences in responses may reflect physiological variations in post-reinnervation sensation characteristics. For instance, in other studies with targeted reinnervation amputees we have observed variations in interpretation of sensation projected to the missing limb, tactile acuity, vibratory frequency discrimination and pressure discrimination Kuiken et al.
We chose to use the Rubber Hand Illusion because we could uncouple the motor control of the limb from the test of sensory functionality. For example, a lag in command and control speeds during typical functional testing would likely mask any observable changes in sensory outcomes relying on the speed of the user. In addition, there is not currently an appropriately sensorized multifunctional prosthetic hand that could be used to conduct functional tests. The questionnaires and temporal order judgement tasks have been used by others to examine the Rubber Hand Illusion Botvinick and Cohen, ; Ehrsson et al.
The Rubber Hand Illusion is a robust phenomenon Armel and Ramachandran, and appears to be sensitive to the relative strength of the tactile input Ehrsson et al. The Rubber Hand Illusion has also provided a new understanding of how multisensory integration contributes to body-ownership Makin et al.
While we were able to readily generate the Rubber Hand Illusion with these two amputees, future studies will be required in more individuals to determine if the use of a robotic touch interface can routinely be used to establish a sense of embodiment for a prosthetic limb. Here we have described how using a neural-machine-interface that provides a physiologically appropriate artificial sense of cutaneous touch appears to elicit a shift in perception towards incorporation of a prosthetic limb into the self-image of two targeted reinnervation amputees.
Long-term use of a physiologically relevant cutaneous touch interface of this type may help to augment mechanisms of prosthetic motor control and function Dhillon and Horch, ; Wang et al. The results presented here also suggest that this approach may help amputees regain more intact self-images Van Dorsten, ; Murray, ; Rybarczyk and Behel, seeing prosthetic devices less as tools that they simply wear and more as parts of their own bodies.
Conflict of interest: J. Supplementary material is available at Brain online. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents.
Materials and methods. Supplementary material. Robotic touch shifts perception of embodiment to a prosthesis in targeted reinnervation amputees Paul D. Oxford Academic. Google Scholar.
Capturing Touch for Prosthetic Limbs Through Artificial Skin
Keehoon Kim. James Edward Colgate. While myoelectric prosthetic devices have been used for decades in the upper extremities, only recently have motorized knee and ankle components proven durable and effective enough for use in the lower extremity amputee. The control schemes developed to capitalize on these prosthetic advances must take into account the biomechanical differences between upper and lower extremity function. Already a valuable adjunct for the myoelectric control of upper extremity prostheses, targeted muscle reinnervation in the transfemoral amputee offers the potential to further enhance lower extremity prosthesis control and may simultaneously address post-amputation neuroma pain.
Current strategies for lower extremity prosthesis control are discussed, along with a review of the transfemoral TMR technique and early clinical experience. This correlates to roughly 1 in Americans, with the number of amputees in the United States projected to double by [ 1 , 2 ]. Between and , the US military interventions in Iraq and Afghanistan produced 1, major limb amputations [ 4 ]. While the relative number of amputations due to these conflicts is small, the dramatic nature of these high-level, multiple limb combat injuries has brought amputee care to the forefront of the American consciousness.
The increased public awareness of the challenges faced by amputees has been matched by a renewed scientific interest in a field of surgery that is as old as war itself. Targeted muscle reinnervation TMR is one of the notable recent advances in amputee care. A true multidisciplinary endeavor, TMR combines peripheral nerve surgery with electromyography-based prosthetic control algorithms and advanced prosthetics to provide intuitive and coordinated control of multi-jointed prosthetic devices. Developed for use in the upper extremity amputee, TMR reroutes the distally transected brachial nerves and coapts them to small recipient nerves innervating residual limb muscles that have been left otherwise nonfunctional due to the amputation.
Once reinnervated by the donor nerves, the muscles act as biologic amplifiers, creating an electromyographic EMG representation of the lost limb that can be captured by surface electrodes and used for prosthesis control [ 5 , 6 , 7 ]. The retained neural information provides a rich source of data, which when combined with pattern recognition algorithms, has been demonstrated to provide functional benefits during reaching or grasping tasks [ 8 , 9 , 10 ].
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First performed in as an experimental procedure for a patient with bilateral shoulder disarticulations, TMR has now become an established part of upper extremity amputee care [ 15 ]. Lower extremity amputations are not only more common, but are often more proximal than those that occur in the upper extremity [ 2 , 16 ]. However, the infrequent use of lower extremity myoelectric devices precluded early adaptation of the TMR technique for use in the lower extremity.
Continued advances in motorized knees and ankles now justify more thorough evaluation of the possible benefits of TMR for the lower extremity amputee. Analogous to the concept behind TMR in the upper extremity, the goal of the transfemoral TMR procedure is to use nerve transfers between distally transected nerves and functionally redundant muscles in the residual limb to increase the number of independently innervated muscles from which to harvest EMG data. Early experience with this technique is promising. Using conventional prostheses and rehabilitative care practices, individuals with lower extremity amputations commonly develop asymmetrical gait characteristics [ 17 , 18 ] that increase the metabolic energy costs of transport [ 19 ].
These abnormal gait patterns are frequently associated with chronic leg and back pain, and increased incidences of degenerative joint disorders such as osteoarthritis are well-documented [ 20 , 21 , 22 , 23 , 24 ]. These behaviors are typically more severe and more prevalent as the level of leg amputation increases [ 19 , 20 ]. This trend is to be expected, as higher levels of amputation result in greater functional loss, thus placing increased demand on the prosthetic replacement. Therefore, improved prostheses design and control methods are of particular value to the transfemoral amputee.
Nearly all commercially available prosthetic knees and ankles are mechanically passive e. In fact, as opposed to delivering increased energy, passive devices dissipate energy from step to step. This is particularly problematic during the demanding tasks of daily living, such as ambulating up stairs or an incline, or rising from a seated position.
This constraint also limits some low-demand activities, such as repositioning the prosthesis during non-weight-bearing tasks. Simple tasks like dressing or transitioning into or out of a vehicle can be difficult and require compensatory movements of the sound limbs.
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The development of mechanically active i. However, the current control systems for these devices are lacking, particularly in transfemoral prostheses. Incorporating the use of neural information into the control of powered knee and ankle prostheses allows user intent to be paired with function. Specifically, neural information can enable direct control of non-weight-bearing i. In addition, it can provide more seamless without stopping , automatic without manual adjustments , and natural without compensation transitions between modes of ambulation.
As demonstrated in upper extremity amputees, TMR provides a means by which to deliver neural information for the control of joints distal to the level of amputation [ 6 , 7 , 33 ]. The characteristics of measured EMG signals vary with specific tasks. For example, during sustained contractions like those used during grasping, the EMG signals are typically stationary i. Techniques for upper-limb prostheses control and exploit these signal characteristics [ 33 , 34 , 35 , 36 ]. Similar EMG characteristics can be observed in sustained contractions of lower-limb muscles during non-weight-bearing tasks.
Thus, it would follow that the pattern recognition approaches used to govern non-weight-bearing tasks of lower-limb amputees should be very similar to those used to control upper-limb functions. These approaches have been applied to transfemoral prostheses control, and high classification accuracies have been shown in offline analyses, particularly for seated knee flexion and extension movements [ 37 , 38 ]. In addition, advanced filtering methods and other pattern recognition algorithms that record from smaller sets of muscle sites have shown promise when used for knee control in offline analyses or in virtual environments [ 39 , 40 ].
Comparison of the seated non-weight-bearing control performance of a knee disarticulation amputee with TMR to transfemoral amputees without TMR. A pattern recognition algorithm was used to interpret surface electromyography signals acquired from natively innervated and reinnervated muscles of the residual limb. Two and four knee and ankle degrees-of-freedom tasks, respectively, were tested to examine the influence of varied task complexities. In contrast to the EMG patterns exhibited during non-weight-bearing functions, lower limb EMG recordings during overground ambulation show greater variability in time i.
These differences necessitate alternative pattern recognition-based approaches for lower limb prosthesis control. Alternative algorithms have been developed to select EMG data from discrete portions of the gait cycle to predict various modes of ambulation e. These approaches merge EMG data with data from mechanical sensors e. This fusion of signal modalities EMG and mechanical has shown better performance than using mechanical sensor data alone [ 44 ]. A more advanced approach to lower extremity prosthesis control incorporates time-history information how EMG and mechanical signals vary in time collected over the course of the gait cycle to allow ambulation mode switching decisions to occur at specific gait cycle events i.
This control scheme has been tested on multiple transfemoral amputees without TMR. These studies found that combining time-history information with a fusion of mechanical and EMG data offers the lowest error rate when predicting ambulation mode [ 45 , 46 ]. This advanced pattern recognition approach was evaluated across various ambulation modes in the same knee-disarticulation-level TMR patient previously mentioned. While the error rate for ambulation mode prediction was low using mechanical data and EMG data captured exclusively from natively innervated muscles 2. The additional neural information provided by TMR may provide additional benefits.
Recent research has used EMG from the residual limb gastrocnemius muscle of transtibial amputees to modify the plantar-flexion mechanics of a powered ankle prosthesis during the terminal stance phase of walking [ 47 ]. This would be impossible in transfemoral amputees without TMR.
Despite being developed primarily for prosthesis function, TMR has been demonstrated to have a beneficial effect on residual limb neuroma pain. These painful neuromas often limit prosthesis use, thus further reducing the functional capacity of the amputee.
Early clinical observations of improved residual limb pain following TMR were confirmed by a retrospective review of 28 consecutive upper extremity TMR cases performed at our institution, in conjunction with the San Antonio Military Medical Center. In addition to these clinical reviews, a novel rabbit neuroma model demonstrated significant improvement in fascicle number and size following neuroma excision and subsequent TMR [ 12 ].
Similarly, a rat hind-limb model showed improved nerve histology after TMR was performed with both mixed and pure sensory nerves. By providing both a distal target and a vascularized scaffold upon which to guide sprouting nerve axons, TMR offers the potential to restore continuity to the peripheral nervous system despite amputation of the native distal nerve segments.
Motivated by these retrospective outcomes and supportive preclinical findings, seven cases of lower extremity TMR have been performed at our institution for the primary purpose of improving persistent post-amputation neuroma pain. Standardized patient-reported pain outcomes were collected prior to these procedures. However, while our early experience has been uniformly positive, the duration of follow-up is still too short to allow for meaningful interpretation of the pain outcomes data. Beyond this small subset of patients, a large multi-institutional randomized clinical trial of TMR versus standard neuroma excision and muscle implantation is now underway.
Motor point locations represented as a percentage of thigh length within the anterior, medial, and posterior compartments of the thigh. Reproduced with permission from: Agnew et al. Targeted reinnervation in the transfemoral amputee: A preliminary study of surgical technique. Reprinted from Agnew et al. Cadaveric dissection of the posterior thigh. Transfemoral amputee with sciatic neuroma requiring operative treatment.
The patient expressed interest in pursuing improved myoelectric prosthetic control. Recipient motor nerve branches to the biceps femoris and semitendinosus have been identified yellow backgrounds. High-density electromyography imaging experiment from a patient who received TMR at our institution. The evolution in motorized knee and ankle components of lower extremity prostheses has introduced a need for more advanced approaches to prosthesis control.
Some of the myoelectric control schemes useful in the upper extremity can be applied to the lower extremity, but must be merged with mechanical and timing-based control methods if seamless and natural ambulation is to be achieved. TMR in the transfemoral amputee offers the potential to further enhance prosthesis control by providing an EMG representation of the amputated lower leg muscles within the residual limb. While the early results are promising, critical assessment of outcomes will be needed in order to obtain a deeper understanding of the true benefits offered by this technique.
Skip to main content Skip to sections. Advertisement Hide. Download PDF. Current Surgery Reports May , Cite as. A recent report combined the use of similar pattern recognition algorithms with recording EMGs from nine residual limb muscle sites in several transfemoral amputees who had not undergone TMR. The ankle outcomes are especially notable, considering that the lower leg muscles responsible for ankle control had been amputated, and were thus not available for recording.
This procedure is known as targeted muscle reinnervation and it constituted a breakthrough in prosthetics. Thus, the solution has been to associate some nerves related with hand and arm movements rerouted to muscles in their chest. These thoracic muscles act as amplifiers of the signal, allowing a correct identification of the desired movements by the sensors.
The motor-neuron behavior was identified by deconvolution of the electrical activity of muscles reinnervated by nerves of a missing limb in patients with amputation at the shoulder or humeral level. The combination of surgical procedures, decoding and mapping into effective commands constitutes an interface with the output layers of the spinal cord circuitry that allows for the intuitive control of multiple degrees of freedom.
T he authors have proven the possibility of decoding the behavior of virtually all the pools of motor neurons that physiologically innervated the muscles responsible for the movement of a missing limb and that are surgically reinnervated to other muscle tissues 4. This decoding was demonstrated in those six patients with different amputation levels and procedures. At this early stage of the work, the participants controlled a virtual arm on a screen rather than a real prosthetic, a necessary future study. They were able to move the virtual prosthetic with greater freedom than has been achieved with muscle-controlled prosthetics.
The approach is the ultimate exploitation of the targeted muscle reinnervation concept that allows spinal interfacing using muscles as natural amplifiers of nerve activity. A full clinical translation of this new concept requires online implementation of the proposed algorithms and testing the long-term adaptation of the user.
People who use prosthetic limbs capable of movement may abandon them if they are too difficult to control or do not offer a useful range of movement 3. Prostheses controlled by nerve signals could be presumably the best option. How Stuff Works Science. Front Syst Neurosci 9: New Scientist.
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