EFFECTS OF CENTRAL DEPRESSANTS ON THE CORTICAL AUDITORY RESPONSES EVOKED BY REPETITIVE CLICK STIMULI IN THE CAT

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The effects of central depressants on the evoked potential and ensued rhythmic after-discharges in the auditory cortex by a series of single click stimuli in cats were previously reported (1). In contrast to a progressive depression of the evoked potential by urethane and ethyl alcohol, the intravenous infusion of pentobarbital sodium, chloralose and chlorpromazine produced considerable increase in amplitude of the evoked potential followed by progressive decrease. The rhythmic after-discharges became to respond regularly and uniformly to the stimulation in small doses of the central depressants, and the duration of the discharges was prolonged with increase in the dose.
It is well-known that the acoustic impulses ascend to the middle ectosylvian gyrus of cerebral cortex via the specific sensory nerves and several relay nuclei. The cortical rhythmic discharges caused by afferent stimulation have been investigated by many workers (2-8). The augmenting response in the sensori-motor cortex is evoked by repetitive stimulation of the specific relay nuclei of thalamus and is related to the specific sensory pathway. Such cortical potential changes are evoked by repetitive stimulation of the diffuse thalamic projection nuclei: the recruiting response. Rhythmic cortical activity is also recorded during spontaneous sleep or barbiturate narcosis.
The response in the auditory cortex to repetitive acoustic stimuli was investigated by Goldstein et al. (9), Schwarz et al. (10, 11) and Kikuchi (12, 13). Kawamura and Yamamoto (14) observed the spindle discharges in the auditory cortex, which were induced by click stimulation or electrical stimulation of the medial geniculate body. However, there are few studies on the rhythmic after-discharges in the auditory cortex, and less is known of the influence of central depressants on the cortical responses evoked by repetitive click stimuli.
Therefore, the authors have designed to analyze the changes in the cortical activity caused by repetitive click stimuli. The study reported here shows that the effects of the central depressants on the cortical auditory responses evoked by repetitive click stimuli are considerably different from the effects on the responses by single click stimulus.