Topographic mapping of EEG spectral power and coherence in delta activity during the transition from wakefulness to sleep.

The present study examined the topographic characteristics in delta band activity during the transition from wakefulness to sleep, using topographic mapping of electroencephalogram (EEG) power and coherence corresponding to nine EEG stages. The dominant topographic components of delta band activity increased clearly from the vertex sharp-wave stage EEG stage 6) in the anterior-central area. Principal component maps revealed the scalp distribution of EEG. Delta activity in the sleep onset period were composed of two covariant components. One is a diffuse component widely distributed on the scalp and the other is a local component at the temporo-occipital area.