Varying expressions of alerting mechanisms in wakefulness and across sleep states.

Alerting stimuli, such as intense tones, presented to cats in wakefulness (W) elicit the orienting response (OR) and/or the acoustic startle reflex (ASR) in conjunction with elicited ponto-geniculo-occipital waves (PGOE) from the lateral geniculate body (LGB) and elicited waves from the thalamic central lateral nucleus (CLE). Alerting stimuli presented during rapid eye movement sleep (REM) and non-rapid eye movement sleep (NREM) also elicit PGOE. We presented tones in W, REM and NREM to determine whether CLE could be obtained in sleep and to examine the patterns of responsiveness of PGOE and CLE across behavioral states. Also, we recorded ASR and OR and compared the response patterns of behavioral and central correlates of alerting. The subjects were 7 cats; all exhibited spontaneously occurring waves in LGB and CL. All cats exhibited PGOE and 5 cats exhibited CLE in W, REM and NREM. PGOE and CLE showed less evidence of habituation than did ASR and OR. The pattern of responsiveness of CLE across behavioral states was different from that found for PGOE, and spontaneous CL waves were much rarer than the LGB waves. ASR was elicited in 5 cats during W trials, and in 3 cats during REM trials. OR habituated rapidly in W and did not occur in REM and NREM. The data indicate that central mechanisms of alerting function in sleep states as well as in W and suggest that CLE and PGOE reflect activity in mechanisms underlying cortical desynchronization and visual processes which may act in concert during alerting.