Spectral features of EEG alpha activity in human REM sleep: Two variants with different functional roles?

Evidence suggests that an important contribution of spectral power in the a lpha range is characteristic of human REM sleep. This contribution is, in p art, due to the appearance of well-defined bursts of alpha activity not ass ociated with arousals during both tonic and phasic REM fragments. The prese nt study aims at determining if the REM-alpha bursts constitute a different alpha variant from the REM background alpha activity. Since previous findi ngs showed a selective suppression of background alpha activity over occipi tal regions during phasic REM fragments and, on the other hand, the density of alpha bursts seem to be independent of the presence or absence of rapid eye movements, one expects to find the same spectral power contribution of alpha bursts in tonic and phasic REM fragments. The results indicated that REM-alpha bursts showed a similar power contribu tion and topographic distribution (maximum energy over occipital regions) b oth in tonic and phasic REM fragments. This suggests that two variants of a lpha activity with different functional roles are present during the human REM sleep: i) background alpha activity, modulated over occipital regions b y the presence of rapid eye movements, which may be an electrophysiological correlate of the visual dream contents; and ii) REM-alpha bursts, independ ent of the presence of rapid eye movements, which could be facilitating the connection between the dreaming brain and the external world, working as a micro-arousal in this brain state.