Not explained by Descartes’ theory was the simple fact that rubbing an injured elbow makes
it feel better. In 1965, psychologist Ronald Melzack (b. 1929) and anatomist Patrick Wall
(1925–2001) proposed a new theory to account for the pain relief provided by counter-stimulation.
Their “gate control theory” asserts that pain and non-pain
sensations run on separate tracks that intersect where they
meet the spinal cord. Melzack and Wall conceive of these
intersections metaphorically as gates through which only
one type of sensation can pass at a time. In the absence
of other stimuli, pain signals from an injured elbow pass
easily through the gate, up the spinal cord, and to the
brain. If you begin to rub an injured elbow, however, both
sensation of pain and the non-pain sensation race from the
elbow to the spinal gate. The tracks that carry non-pain
sensation are faster than those that carry pain, so the
non-pain sensation gets to the spinal gate first, blocking the path to the brain. On the other hand,
recent evidence suggests that chronic pain may sensitize the gates to opening, so that pain is felt
more frequently and intensely, a phenomenon referred to as central sensitization.