Effect of chlorpromazine on the interaction between phasic and tonic electrocortical arousal mechanisms.

The effect of chlorpromazine on the rate of habituation of phasic arousal responses has been studied in cats carrying permanently implanted cortical recording electrodes. In the sleeping animal repeated presentation of an auditory stimulus (1 sec duration, 3000 Hz) at intensities which only produced a localised, phasic electrocortical change in the auditory cortex, resulted in the rapid habituation of this latter response. Once habituation had occurred the intensity of the stimulus was increased until a similar change in electrocortical activity once again appeared in the auditory cortex. The habituation procedure was then repeated. In this way it was possible to habituate the animal gradually to successively higher intensities of auditory stimulation without ever inducing behavioural arousal or tonic, generalised changes in electrocortical activity. Indeed, it was possible to reach a level of stimulation which previously would have induced overt behavioural effects and tonic arousal. It may be concluded that alterations in the activity of the mechanisms responsible for phasic electrocortical responses leads to changes in the responsiveness of the animal even during sleep. Following chlorpromazine phasic electrocortical responses were still elicited but their rate of habituation was significantly increased. Thus the overall effect of chlorpromazine was a marked shortening in the time taken to "train" the animal while still asleep, not to respond behaviourally or with tonic electrocortical changes to a particular auditory stimulus.