After an amputation, some people can still perceive touch and pain sensations in their missing arm or leg. This is known as "phantom limb." Sometimes, these sensations can be triggered by nerve endings in the residual upper limb. Now, a man who had his right arm amputated below the elbow has been able to feel hot and cold in his missing hand via a modified prosthetic arm with thermal sensors. The prosthetic works by applying heat or cold to the skin on the upper arm in specific locations that trigger a thermal sensation in the phantom hand. Solaiman Shokur of the Swiss Federal Institute of Technology and his colleagues mapped spots in the Fabrizio Fidati’s upper arm to identify the locations that trigger sensations in different parts of his phantom hand. Then they adapted his existing prosthetic hand and socket with sensors and devices that can be made hot or cold, called thermodes. Tests showed that Fidati could identify bottles that were hot, cold or at ambient temperature with 100% accuracy by touching them with his modified prosthetic. When the thermal sensor in the prosthetic was turned off, his accuracy dropped to a third. The prosthetic also allowed Fidati to successfully distinguish, when blindfolded, glass, copper and plastic by touch with an accuracy just above two-thirds – the same as his uninjured left hand. Shokur cautions, however, that the study they did was not a clinical trial and they are left wondering how well the technology will work in the real world, where there are vast extremes of warm and cold weather.
