The effects of tones on PGO waves in slow wave sleep and paradoxical sleep

Abstract

Ponto-geniculo-occipital (PGO) waves are macropotential waveforms occurring spontaneously during paradoxical sleep (PS) in the pons, the lateral geniculate body (LGB), and the occipital cortex of the cat. In our earlier work (6, 20) tones elicited waves in the LGB and the occipital cortex during both slow wave sleep (SWS) and PS that resembled PGO waves in form and amplitude. Using a limited and variable number of trials, we observed that these elicited waveforms, which we term elicited PGO waves (PGO E), seemed to decline rapidly in amplitude and probability during SWS but not during PS. The present two experiments served as a more rigorous test of the hypothesis that the rate of habituation of PGO E would be more rapid in SWS. In a first experiment seven cats were studied in up to four sessions in PS and four in SWS; each session consisted of 32 1000-Hz, 90-dB SPL tones lasting 90 ms. We found that (i) the number of PGO E was significantly greater in PS; (ii) the mean amplitude of the waves was greater in PS; (iii) the probability of eliciting a wave tended to decline faster in SWS, but some decline also occurred in PS; and (iv) on the first trial, PGO E were more easily produced in SWS. Results of a second experiment with five cats suggested that the decline in the probability of PGO E in PS was not accounted for by differences in the ease of eliciting them at different times into a PS episode. The role of the dorsal raphe nucleus (DRN) in modulating state-dependent differences in PGO E is discussed.