How accurately can you locate pain? When laser pulses were fired at the back of the hands of volunteers, most could tell that the pinprick sensations were at separate locations on their skin only if they were a centimetre or more apart. When the experiment was repeated on their fingertips, the distance was halved. The result is surprising because, as these highly magnified images show, there are more pain receptors, stained red, in the epidermis [surface tissue above the dotted line] in the back of the hand (left) than in a fingertip (right) which should therefore be less sensitive. The researchers think that our ability to locate pain may be aided by a connection yet to be discovered, between pain sensors and touch sensors, which are especially abundant in the deeper tissue of fingertips.
Written by Mick Warwicker