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04-03-2012 | Physical rehabilitation | Article

‘Phantom limb’ sensation projected into artificial hand may aid prostheses development


Free abstract

MedWire News: Transcutaneous electrical nerve stimulation (TENS) of the forearm can project a "phantom limb" sensation into an artificial hand in able-bodied volunteers, show study findings.

The researchers say that these results may help scientists to develop more advanced prosthetic limbs that can be "perceptually integrated" into the pre-existing body schema of the wearer. They believe that such integration may improve manual control of prostheses for amputees.

Previous research has demonstrated that TENS can generate "somatic sensations" such as touch in an amputee's phantom limb, and can change existing phantom limb sensations.

"However, the effects of TENS on the perceptual embodiment of an artificial limb are not known," explain Matthew Mulvey (Leeds Metropolitan University, UK) and colleagues in Neuromodulation: Technology at the Neural Interface.

To investigate further, Mulvey and team recruited 30 able-bodied men and women to assess whether such sensations can be generated in non-amputees.

The researchers positioned TENS electrodes over the superficial radial nerve on the lateral side of the right forearm (1 cm proximal to the wrist) of each participant. For some, but not all experimental conditions a strong but non-painful pulse (120 Hz, 80 µs) was then generated inducing a feeling of numbness or paresthesia in the right wrist and hand of the participants.

The participants were then asked to place their right hands inside an open-ended canvas box out of their own field of view. A prosthetic hand was placed next to the box within view of the volunteer.

For the experiment, the participants were put through four scenarios to see if a "sense of embodiment" with the artificial hand could be generated. The first of which was a vision-only condition; the second a vision and TENS scenario; the third a vision and stroking scenario, in which the prosthetic hand and out-of-sight real hand were simultaneously stroked with brushes; and the fourth a vision, TENS, and stroking scenario.

Perceptual embodiment was scored on an 11-point scale with 0 corresponding to no embodiment and 11 a very strong sense of embodiment. Mean scores were 2.7, 3.5, 7.2, and 8.1, in scenarios one to four, respectively, with TENS contributing significantly to the participants' sense of embodiment of the artificial limb over vision alone.

Mulvey et al explain that "this study has shown for the first time that TENS paresthesias can be projected into a prosthetic limb to produce perceptual embodiment of a prosthetic hand in humans with intact limbs."

They add: "Our follow-up studies are investigating whether projecting TENS paresthesias into the prosthetic limb(s) of amputees will facilitate perceptual embodiment and aid functionality. This may prove to be a simple and inexpensive technique to facilitate ambulation and prosthesis success."

By Helen Albert

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