EEG asymmetry during sleep.

The ratio of integrated EEG amplitude from left and right temporal areas was analyzed during sleep in normal subjects for two consecutive nights. The results showed that the differences between the subjects were similar in both nights and were much larger than the differences between the stages of sleep. No significant variation was found between stages, although stage 1 tended to show greater relative right activation in night 1. Also, the relative right activation was greater in wakefulness in night 2 as compared to night 1. The classification of the correlation coefficients between stages corresponded to the physiological transitions between stages, suggesting that the small source of variance due to sleep stage contains relevant information.