Changes in rem dream content during the night: implications for a hypothesis about changes in cerebral dominance across rem periods.

REM dream content was scored for categories suggesting the predominant influence of the left hemisphere, e.g., good ego functioning, verbalization, or the right hemisphere, e.g., music, spatial salience, bizarreness. Data from 5 samples of college men showed consistent evidence of an increase in the prominence of left-, but not right-, related categories from earlier to later REM periods. These data suggest there is an increase in left hemisphere control/dominance across the REM periods during the night. Two sets of predictions based on this hypothesis (using more direct estimates of the hypothesized change) yielded supportive evidence. First, as predicted, there was a positive relation between change in percentage of right eye movement (R%) and (a) temporal position of the REM period and (b) change in left-related categories; greater R% was associated with later REM periods and with more prominent left- (but not right-) hemisphere categories. Second, as predicted, there was a positive relation between the diminution of the ratio of left to right EEG amplitudes (L/R) and (a) temporal position of the REM period and (b) prominence of verbal activity. As expected, this relation was attenuated for those subjects showing a preference for left-handedness. Two possible explanations for the inferred increase in left-hemispheric influence during the night are suggested.