EU researchers get a feel for the real limb
EU-funded scientists in Sweden have succeeded in making upper-limb amputees experience a prosthetic hand as their own by 'tricking' their brains. The results represent a major breakthrough in neuroprosthetics, bringing research one step closer to developing an 'intelligent', touch-sensitive prosthetic hand. The study is published in the journal Brain. The research was supported by the SmartHand ('Smart bio-adaptive hand prosthesis') project, which received EUR 1.8 million from the EU's Sixth Framework Programme (FP6), with additional funding coming from the European Research Council. SmartHand researchers aim to incorporate advances in nanobioscience, cognitive neuroscience and information technologies to develop an intelligent prosthetic hand with all the basic features of a real one. In addition to experiencing phantom pains, people who live with an amputation often suffer from severe depression, distorted self-image and social anxiety. According to SmartHand's mission, creating a functional artificial hand that feels like part of the person's body would go a long way towards improving quality of life by restoring the patient's positive self image and perception of social acceptance. The researchers studied 18 people with an amputation somewhere between the wrist and elbow who used their prosthesis regularly. The subjects were interviewed about 'phantom pain' and other sensations of their missing limb, and were asked if they felt that their fingers or another part of the hand were being touched when they touched different parts of the stump. After this evaluation, they were subjected to the so-called 'rubber hand illusion'. The rubber hand illusion entailed touching the stump of the amputated arm out of the subject's sight while at the same time touching the rubber hand in full view. This experiment forces the brain to interpret conflicting visual, touch, and position information; the result is an altered perception. The subjects, to varying degrees, experienced an illusion that the touch was coming from the prosthetic hand rather than from the stump. The scientists were pleasantly surprised because when this experiment is carried out in 'normal' subjects, it has to be very exact or the illusion fails. 'In normal individuals it is critical to stimulate exactly the same locations on the rubber hand and the real hand for an illusion to be produced,' they write. 'So how could the illusion possibly work in upper-limb amputees, who do not even have a hand to stimulate?' The findings raise fundamental questions about the way the brain distinguishes between parts of one's body and objects in the external world. The success of the illusion was confirmed by the subjects' descriptions of their experience, their tendency to point to the hand when asked to localise the point of stimulation, and physiological-response tests, for example whether they started to sweat when the rubber hand was pricked with a needle. Several of the subjects experienced the rubber hand as their own. Interestingly, the researchers observed that the shorter the time period since amputation, the greater the illusion. The findings open up new opportunities to create prosthetic hands that can be felt by their wearers as being part of their own bodies. 'We'll now be looking into the possibilities of developing a prosthetic hand that can register touch and stimulate the stump to which it is attached,' said Dr Henrik Ehrsson of Sweden's Karolinska Institute. 'If this makes it possible to make a prosthetic sensitive by cheating the brain, it can prove an important step towards better and more practical prosthetic hands than those available today.'
Countries
Sweden