Pointwise transinformation distinguishes a recurrent increase of synchronization in the rapid eye movement sleep electroencephalogram.

The analysis of electroencephalogram (EEG) coupling patterns is essential for understanding how interrelations between cortical sites change with the wake-sleep cycle. Waking and sleep EEGs of 12 normal sleepers were analyzed by pointwise transinformation (PTI). Stage-dependent differences of PTI were assessed, and a spectral analysis of synchronized events was performed. A pattern of recurrent EEG synchronization was distinguished in all rapid eye movement (REM) sleep phases. The mean coupling of EEG leads differed regionally, with high coupling levels of frontal and occipital derivations and lower midtemporal and central coupling levels. Mean coupling levels were comparable in stages R, W, and N1 but were lower than in N2 and N3. An REM-specific pattern of low EEG synchronization was identified for F7-F8 and T3-T4, with lowest coupling levels during tonic REM sleep. Also, maximal intervals of uncoupled EEG were longer during tonic REM sleep. Because of these results, a new descriptive entity is proposed: the recurrent increase of synchronization in the EEG (RISE). This seems to reflect the dynamic aspects of spatiotemporal EEG synchronization on small time scales. A possibly specific low coupling pattern of the temporal leads may distinguish REM sleep from other states with a "desynchronized" EEG and, to some extent, tonic from phasic REM sleep.