The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

by V.S. Ramachandran

How does this explain Mikhey’s laughter? I didn’t know this at that time, but many years later I saw another patient named Dorothy with a similar “laughter from pain” syndrome. A CT (computed tomography) scan revealed that one of the pain pathways in her brain was damaged. Even though we think of pain as a single sensation, there are in fact several layers to it. The sensation of pain is initially processed in a small structure called the insula (“island”), which is folded deep beneath the temporal lobe on each side of the brain (see Figure Int.2, in the Introduction). From the insula the pain information is then relayed to the anterior cingulate in the frontal lobes. It is here you feel the actual unpleasantness—the agony and the awfulness of the pain—along with an expectation of danger. If this pathway is cut, as it was in Dorothy and presumably in Mikhey, the insula continues to provide the basic sensation of pain but it doesn’t lead to the expected awfulness and agony: The anterior cingulate doesn’t get the message. It says, in effect, “all’s okay.” So here we have the two key ingredients for laughter: A palpable and imminent indication that alarm is warranted (from the insula) followed by a “no big whoop” follow-up (from the silence of the anterior cingulate). So the patient laughs uncontrollably. And the same holds for tickling.