The Sleeping Rat Shows Signs of Orienting Response to Neutral Stimuli

Abstract

Cortical arousal, cardiac response, and body movement to auditory stimuli were studied during slow wave sleep (SWS) of the rat. Rats were exposed to sequences of 10 tone pulses of a frequency of 16 kHz, a sound pressure level of 60dB, and n duration of 2 s (Experiment I) or 10 s (Experiment II). Repeated stimulus presentations permitted the evaluation of short‐term habitation. Similar results were found in both experiments, i.e. habitation of the cortical arousal response and of the phasic cardiac deceleration to stimulus onset and offset. With repeated presentations, cardiac acceleration showed a less regular course than cardiac deceleration and cortical arousal. Subsequently presented tone pulses of 80dB did not result in a recovery of the habituated response. Cardiac deceleration and cortical arousal on the one hand, and cardiac acceleration and motor activity on the other hand, were strongly correlated. The results are compared with human studies.

Habituation of the rat’s respiratory response to auditory stimulation during sleeping and waking

“…There were no differences between the two groups in rate of habituation. Tbis is in accordance with the results of Johnen (1987), who found dear habituation ofthe sleeping rat's heart-rate response to auditory stimulation. It thus appears that the rat's habituation to auditory stimulation does not depend on its state of vigilance.…”

“…However, there are contradictory experimental findings, which raise the question of whether habituation can occur during sleep. Jung (1954) and Sokolov and Paramanova (1961) reported habituation in humans during sleep, and Johnen (1987) found habituation ofthe rat's heart-rate response during SWS.…”

Second-order conditioning during sleep

“…On the other hand, very little is known about the possibility that acquisition processes may take place during sleep. One kind of learning that seems to occur during sleep is habituation (Johnen, 1987;Rudolph, 1987;Yehuda et aI., 1979). There are also some reports that extinction can develop during sleep (Izquierdo, Wyrwicka, Sierra, & Segundo, 1965;Oniani & Lortkipanidze, 1985).…”