Variations of slow eye movements as an indicator of hypnagogic state

Abstract

The present study examined slow eye movements (SEMs) during early sleep in twenty female subjects, aiming at the detection of hypnagogic state. SEMs were recorded as slow deflections on a pair of horizontal EOGs with the opposite polarity-a phase method (Rechtschaffen & Kales, 1968). SEMs were prominent at the beginning of EEG stage 1, and they terminated when stage 2 lasted about 5 min and kept stable. No recovery of SEMs was seen during slow wave sleep. Analyses of a rising angle revealed that SEM wave form became slower with the progress of sleep. All epochs of the first SEM and 70% of maximum SEMs fell into stage W, preceding the first stage 1. Sleepiness, which subjects signaled by pressing a button switch, induced significant increases in SEMs, whether or not stage 1 developed. These data suggest that SEMs can give a useful criterion to define the temporal range of hypnagogic state.