From BetterHumans.com > News > Eureka Moments Brain-mapped -- Findings help provide a physiological basis for insight and intuition :

First, the researchers found that about 0.3 seconds before the subjects indicated solutions achieved through insight there was a sudden burst of high-frequency activity often associated with complex cognitive processing.

A second, unexpected EEG effect also was observed: About 1.5 seconds prior to insight solutions, an increase in lower frequency activity appeared over the right posterior cortex.