The amplitude of elicited PGO waves: a correlate of orienting.

Ponto-geniculo-occipital (PGO) waves spontaneously occur in the pons, lateral geniculate body (LGB), and occipital cortex during rapid eye movement sleep (REM), and PGO-like waves (PGOE) may be elicited in LGB during sleep and waking. Because REM has been hypothesized to be a state of continual "orienting" or "hyper-alertness," we tested whether the amplitudes of PGOE in "alerting" situations (the abrupt onset of a loud sound or presentation of a novel stimulus within a series of stimuli) that evoke orienting responses (OR) would be greater than those following stimuli without OR. We also compared PGOE accompanying OR to PGOE during REM and NREM when OR are absent. The amplitudes of PGOE in W were greatest when OR were observed, and the amplitudes of PGOE accompanying OR were not significantly different from PGOE amplitudes in REM. Likewise, the amplitudes of PGOE during REM were not significantly different from those of the highest amplitude spontaneous PGO waves. We propose that the presence of PGOE signals registration of stimuli and that stimuli of sufficient significance to induce behavioral OR in waking also elicit PGOE of significantly greater amplitudes in all behavioral states. These findings support the hypothesis that the presence of high-amplitude PGO waves in REM indicates that the brain is in a state of more-or-less continual orienting.