科学美国人60秒:Body's Pain Perception Mapped for First Time

Pain is an immediate attention getter. And when we’re in pain, we think we know the exact location of the source of that pain, for example, your knee or your back. But our ability to pinpoint pain varies across the body, and in a specific pattern.
 
Scientists created stinglike discomfort on the surfaces of volunteers’ bodies using two lasers. They measured the minimum distance between the two pain points where the volunteer could still distinguish between the two stings. And they found that this capacity to discern different pain points, called spatial acuity, improves as we move towards the center of our bodies. For example, we’re better at detecting the two pain points on the shoulders than at the wrists.
 
The scientists also tested our acuity for touch, assuming it might be similar to pain. While we tend to have an equal ability to detect touch and pain, scientists found that our acuity for simple touch decreases towards the center of the body. So in this case it’s harder for us to detect non-painful touch at our shoulders than at our wrists. [Flavia Mancini et al, Whole-body mapping of spatial acuity for pain and touch, in Annals of Neurology]

The exception to this rule of thumb, if you will, is our fingers. The digits are sensitive to both pain and touch. But it’s not because fingers have more nerve fibers. The researchers think it might be a question of information processing. Because we use our fingers constantly, we’re more practiced at sensing them. Whether they’re playing the piano, or hammering a nail.
 
—Christie Nicholson