Positive occipital sharp transients in the human sleep EEG.

The characteristics of positive occipital sharp transients (POSTs) in the human sleep EEG were studied, and their characteristics were compared with those of lambda waves appearing in the occipital EEG during the waking state. The following findings were obtained: 1) POSTs were observed in 57% of 189 subjects examined during sleep. The incidence of the subjects showing POSTs was highest in the group of subjects aged 21-30 years. 2) The incidence of the subjects showing POSTs tended to be high among the subjects with a high alpha wave index. 3) The wave form and topography of POSTs had striking similarities to those of lambda waves. 4) The frequency of POSTs was highest during the initial 30 minutes' period of NREM sleep after the sleep onset in both nocturnal and diurnal sleep. 5) The frequency and amplitude of POSTs were not modified by changing the background illumination in the recording room. 6) No significant relation was found between the frequency of POSTs and dream experience during NREM sleep.