But what is really going on in the brain when the light bulb goes off?
For one thing, a striking increase in neural activity in a specific area of the right hemisphere, according to a recent study by a team of cognitive neuroscientists including Mark Jung-Beeman and Edward Bowden of Northwestern University and John Kounios of Drexel University. Their results will appear online April 13 in this month's edition of PLoS Biology, an open-access scientific journal published by the Public Library of Science.
"For thousands of years people have said that insight feels different from more straightforward problem solving," said Jung-Beeman, an associate professor of psychology. "We believe this is the first research showing that distinct computational and neural mechanisms lead to these breakthrough moments."
Princeton University Stuart Professor of Psychology Philip Johnson-Laird, who was not involved in the work, described the study as "one of the most original studies of insight that I have ever seen."
Using two different brain imaging techniques, the team found an increase in neural activity in part of the brain's right temporal lobe when people solved problems with insight that was not present when problems were solved without insight. This demonstrates that insight relies on at least one distinct brain mechanism, and the nature of that area also points to a specific cognitive process that makes insight special.
According to legend, after stepping into his bath Archimedes shouted "Eureka!" ("I have found it") when an insight allowed him to determine whether or not his king's crown was pure gold, a problem that had previously stumped him.
"As supposedly happened to Archimedes, prior to solving problems with insight people often reach an impasse and are not able to make any progress," said Edward Bowden, a senior research associate at Northwestern. "They need to reinterpret the problem and integrate information in a new way. Sometimes the mind does this unconsciously, and then the solution suddenly appears in consciousness. To the solver, the solution seems to have come out of thin air, yet is obviously correct."
In two experiments, Jung-Beeman and his colleagues gave study participants a series of word problems to solve. Each problem presented three words, such as fence, card and master, and asked participants to think of one word that would form a compound word or phrase for each of the words. (The answer? Post.) In addition to solving the problem, each person reported whether or not the solution felt like an insight. (The problems were designed to evoke a distinct "Aha!" moment about half the time they are solved.) Brain activity was assessed while participants tackled, and sometimes solved, these problems.
In the first experiment, functional magnetic resonance imaging (fMRI) revealed increased activity in a small part of the right temporal lobe (the anterior superior temporal gyrus) during insight solutions and little activity during non-insight solutions. No insight effect was observed anywhere within the temporal lobe of the left hemisphere. Prior evidence suggests that the right temporal area, which is associated with insight, may be important for drawing distantly related information together when comprehending complex language.
"Archimedes' sudden observation that water displacement could be used to calculate density resulted from his connecting known concepts in new ways," said Jung-Beeman. "This is the nature of many insights, the recognition of new connections across existing knowledge."
In the second experiment, an electroencephalogram (EEG) tracked brainwave activity during insight and non-insight solutions. About one-third of a second before the subjects indicated solutions achieved through insight, there was a sudden burst of high-frequency (gamma band) activity, relative to solutions achieved without insight. This neural activity, often associated with complex cognitive processing, was observed at scalp electrodes over the same right temporal area observed with fMRI, replicating the effect with new participants and a different measure of brain activity.
A second, unexpected EEG effect also was observed: About 1.5 seconds prior to insight solutions, an increase in lower frequency (alpha band) activity appeared over the right posterior cortex. This effect disappeared precisely when the high-frequency activity began over the right temporal lobe. The researchers interpreted the posterior effect as evidence of "gating," or attenuation, of visual input, and suggested that this occurs to allow initially weak solution-related activity to gain strength, then burst into consciousness as an insight.
"This is like closing your eyes so you can concentrate when you are trying to solve a difficult problem," said Kounios, professor of psychology at Drexel. "But in this case, your brain is blocking out just the visual inputs to your right hemisphere."
Success in solving insight problems is associated with creative thinking. "If there is one human trait that would seem impervious to scientific study, it is intuition or insight -- that seemingly nonrational 'Aha!' that accompanies sudden recognition or solution," said Howard Gardner, Hobbs Professor of Education and Cognition at the Harvard Graduate School of Education, who was not involved in the study. "In showing that distinctive cortical activity characterizes self reports of insight, while being absent on solutions bereft of insight, Jung-Beeman and his colleagues have helped to demystify the creative process."
In addition to Jung-Beeman, Bowden and Kounios, other authors on the PLoS Biology paper are Jason Haberman, Stella Arambel-Liu and Paul J. Reber, from Northwestern University; Jennifer L. Frymiare, from Drexel University; and Richard Greenblatt, from Source Signal Imaging, Inc.
The research was supported by the National Institute of Deafness and Other Communication Disorders.