「ひらめいた！」の0.3秒前、脳の右側で速い脳波が急に強まっていた

Sometimes an answer suddenly comes into your head. We call this an "aha moment." Scientists studied this with word puzzles. They found that about 0.3 seconds before the answer came, fast brain waves appeared on the right side of the brain.

Just before that, the brain seemed to close its eyes for a moment and stop looking outside. Answers from an aha moment were often correct.

Most of us have experienced an "aha moment," when the answer to a problem suddenly appears in our mind. Researchers studied this by giving people word puzzles in which they had to find one word that connects three others. After each puzzle, participants said whether the answer came through sudden insight or step-by-step analysis.

When people solved a puzzle with insight, a burst of very fast gamma waves appeared over the right temporal lobe, an area near the right ear, about 0.3 seconds before the answer. About a second earlier, slow alpha waves increased at the back of the head, as if the brain were briefly shutting out what the eyes could see. Later research found that insight answers were correct more often than analytic ones.

The sudden "aha" experience may feel magical, but researchers have managed to catch it in brain recordings. In a 2004 study, participants solved compound remote associate problems, in which a single word must be found that links three others, and reported after each solution whether it had come through insight or analysis.

Insight solutions were accompanied by stronger activity in the right anterior superior temporal gyrus and, roughly 0.3 seconds before the answer reached awareness, by a sudden burst of high-frequency gamma waves there. This region is thought to support loose connections between distantly related meanings. About a second earlier, alpha waves increased over the right back of the head, which the researchers likened to a "brain blink" that temporarily blocks visual input.

Subsequent work found that insight answers were more often correct than analytic ones, and that a positive mood was linked to more insight. An aha feeling can also accompany wrong answers, though, so insights should be checked. There are methodological limits too: the solution type was classified by participants' own reports, and the brain-imaging and EEG experiments each involved fewer than 20 people. Claims that insight is purely a right-brain function oversimplify these findings.