Spontaneous eyelid movements during human sleep: a possible ponto-geniculo-occipital analogue?

The aim of the present study was to investigate whether eye lid movements (ELMs) were temporally related to the activity of other skeletal musculature and to proposed analogues of ponto-geniculo-occipital (PGO) waves during human sleep. Electroencephalogram (EEG), laryngeal-masseter electromyogram (EMG), electrooculgram (EOG), peri-orbital integrated potentials (PIPs), middle ear muscle activity (MEMA), ankle flexion (AF) and respiration (RESP) were monitored with ELMs during one night's sleep. Results showed that ELMs always occurred during full arousal and movement time. The ELMs that occurred during sleep were most prominent during rapid eye movement (REM) sleep, occurred at higher frequency just before REM, and were observed synchronously with other PGO analogues, supporting the notion that ELMs may be an indicator of PGO activity in humans. Of the ELMs observed during sleep, 16% showed changes in EOG, PIP, MEMA, AF and RESP simultaneously, suggesting generalized muscle activation. This coactivation of muscle activity suggested that the relationship between the muscular measures and PGO activity might be an indirect one, possibly mediated by alerting mechanisms, previously shown to be related to PGO waves in animals. Such an interpretation is consistent with the use of ELM as a widely accepted measure of the eye-blink startle response in awake human subjects.