Electrically-evoked Referred Sensations Induce Embodiment of Rubber Limb

Introduction: Electrical stimulation is increasingly relevant in a variety of medical treatments. In this study, the quality of referred sensations evoked using surface electrical stimulation was evaluated using the rubber hand and foot illusions. Methods: The rubber hand and foot illusions were attempted under 4 conditions: (1) multi-location tapping; (2) one-location tapping; (3) electrical stimulation of sensation referred to the hand or foot; (4) asynchronous control. The strength of each illusion was quantified using a questionnaire and proprioceptive drift, where a stronger response suggested embodiment of the rubber limb. Results: 45 able-bodied individuals and two individuals with amputations participated in this study. Overall, the illusion evoked by nerve stimulation was not as strong as illusions evoked by physically tapping but stronger than the control illusion. Conclusion: This study has found that the rubber hand and foot illusion can be performed without touching the distal limb of the participant. Electrical stimulation that produced referred sensation in the distal extremity was realistic enough to partially incorporate the rubber limb into a person’s body image

Surface Stimulation as a Potential Treatment for Phantom Limb Pain

Phantom Limb Pain, a pain or discomfort in the missing limb, is experienced by the majority of amputees. We hypothesize that by eliciting a non-painful sensation in the missing limb, phantom limb pain may be reduced or eliminated. The overall goal of this project is to develop a therapy that consists of an electrically activated tapping sensation in the missing hand or foot combined with a robot tapping on the prosthesis. The goal of this project was to compare the electrically activated sensation with actual touch. The median or ulnar nerve was stimulated with the goal of creating a realistic tapping sensation in the subject’s hand and the common peroneal nerve was stimulated with the goal of eliciting sensation in the foot. The rubber hand and foot illusions were then used to quantify the authenticity of the stimulated sensation. A variety of rubber hand/foot illusion conditions were performed on each subject: three traditional trials where a human investigator tapped on both the real hand and the rubber hand and one artificial trial where surface electrical stimulation evoked a tapping sensation in the real limb while the robot tapped on the rubber limb. The results of the traditional and artificial methods were compared to determine if a significant difference was present. Data collected included: questionnaire results, proprioceptive drift, and temperature changes of the arm/leg. A total of twenty five rubber hand illusion trials were completed. Results demonstrate that both physical touch and artificial sensations were able to evoke a more realistic illusion than the control condition. However, sensations evoked by electrical stimulation were not as realistic as those produced by physical touch. The rubber foot illusion trials are still ongoing, but preliminary analysis shows that results are trending towards a positive illusion for both traditional and artificial conditions

Surface Stimulation as a Potential Treatment for Phantom Limb Pain

Phantom limb pain, a pain or discomfort in the missing limb, is experienced by a majority of amputees. Our work is based on the hypothesis that by eliciting a “real” sensation in the phantom limb, via surface electrical stimulation, pain may be decreased or even eliminated. Previously, we have shown that a variety of sensations can be obtained from stimulation on the surface of the skin. The goal of this study was to quantify the authenticity of the stimulated sensations using the rubber hand illusion. The median and ulnar nerves were stimulated with the goal of creating a realistic tapping sensation in the subject’s hand. The rubber hand illusion was then used to quantify the authenticity of the stimulated sensation. A total of five rubber hand illusion trials were performed on each subject: three traditional trials done by a human investigator tapping on both the real hand and the rubber hand, and two artificial trials using surface electrical stimulation to evoke a tapping sensation in the real hand while the robot tapped on the rubber hand. Data collected included: questionnaire results, proprioceptive drift, and temperature changes of the arm. The results of these measures were compared to determine if a significant difference was present between the traditional and artificial methods. The trials are still ongoing, but current analysis shows that the traditional method produced a more realistic illusion than the artificial method; however the artificial method produced a better illusion than the control. These results demonstrate the potential for using this combination of surface electrical stimulation and simultaneous visual feedback as a future therapy for phantom limb pain

Natural Sensations Evoked in Distal Extremities Using Surface Electrical Stimulation

Background: Electrical stimulation is increasingly relevant in a variety of medical treatments. In this study, surface electrical stimulation was evaluated as a method to non-invasively target a neural function, specifically natural sensation in the distal limbs. Method: Electrodes were placed over the median and ulnar nerves at the elbow and the common peroneal and lateral sural cutaneous nerves at the knee. Strength-duration curves for sensation were compared between nerves. The location, modality, and intensity of each sensation were also analyzed. In an effort to evoke natural sensations, several patterned waveforms were evaluated. Results: Distal sensation was obtained in all but one of the 48 nerves tested in able-bodied subjects and in the two nerves from subjects with an amputation. Increasing the pulse amplitude of the stimulus caused an increase in the area and magnitude of the sensation in a majority of subjects. A low frequency waveform evoked a tapping or tapping-like sensation in 29 out of the 31 able-bodied subjects and a sensation that could be considered natural in two subjects with an amputation. This waveform performed better than other patterned waveforms that had proven effective during implanted extra-neural stimulation. Conclusion: Surface electrical stimulation has the potential to be a powerful, non-invasive tool for activation of the nervous system. These results suggest that a tapping sensation in the distal extremity can be evoked in most able-bodied individuals and that targeting the nerve trunk from the surface is a valid method to evoke sensation in the phantom limb of individuals with an amputation for short term applications