Objectives: To investigate the brain topography of human sleep electroencephalography (EEG) along the antero-posterior axis during rapid eye movement sleep (REM) onset and REM offset, by means of a quantitative analysis of EEG changes. Methods: EEG power values were calculated across a 1.00-25.75 Hz frequency range during time intervals preceding and following REM onset of the first 4 sleep cycles of 10 normal subjects. Topographical changes were assessed through Fpz-A1, Fz-A1, Cz-A1, Pz-A1, Oz-A1 recordings during NREM-REM-NREM transitions. Results: The temporal dynamics of REM onset is characterized by a specific topographical pattern of EEG changes with a relatively higher EEG activity at posterior sites: Oz does not show any clear change within the alpha and beta frequencies, at variance with the marked reductions of the other sites, while it shows reductions of power in the delta/theta and sigma frequency ranges of smaller size as compared to the other sites. REM offset does not appear as a mirror-image of REM onset, since the pattern of regional differences characterizing the NREM sleep preceding REM onset is not fully reached. Conclusions: REM onset is characterized by a general change of EEG activity toward a relative occipital diffusion of power, specifically distinguished by a posterior dominance of middle and high frequencies. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.