Topographical characteristics of slow wave activities during the transition from wakefulness to sleep

Objectives: This study examined the topographical characteristics of slow wave(delta and theta) activities during the transition from wakefulness to sleep, using topographic mapping of EEG power and coherence. Methods: Sonography of nocturnal sleep was recorded on 10 male subjects. Each recording, from ‘lights-off’ to 5 min after the appearance of the first sleep spindles, was analyzed. Typical EEG patterns during the transition from wakefulness to sleep were classified into 9 stages (EEG stages). Results and conclusions: Topographic maps of coherence in delta-and theta-band activities demonstrated that the synchronous component at the anterior-central areas of the scalp appeared corresponding with increasing power. The populations of high coherence pairs among total pairs were computed for each band and each EEG stage to examine the regional differences of EEG. The populations of the delta-band activity increased clearly from EEG stage 6 in the anterior-central areas. The populations of the theta-band activity increased clearly from EEG stage 7 in the anterior-central areas. These results suggest that the dominant synchronous component of slow wave activities during the transition from wakefulness to sleep increased as a function of EEG stages in the anterior-central areas and increased clearly after the appearance of vertex sharp waves.