Inferior colliculus unitary activity in wakefulness, sleep and under barbiturates.

The spontaneous unitary activity and the response to contralateral tone-burst were analyzed in the inferior colliculus (IC) of guinea pigs during the sleep-waking cycle and under the effects of pentobarbital anesthesia. Minor changes were observed in both spontaneous and evoked activity between wakefulness (W) and slow wave sleep (SWS). On the other hand, a consistent increase in the mean spontaneous firing rate and a significant decrement in the signal-to-noise ratio (S/N ratio) was observed during paradoxical sleep (PS). Pentobarbital anesthesia reduced the spontaneous and evoked firing rate, the duration of the excitatory response and increased the duration of the post-excitatory suppression. We conclude, that the processing of auditory information in the IC change markedly during PS. Because the IC is a compulsory station for almost all the ascending auditory pathways, the observed decrease in the S/N ratio may deeply affect the auditory perception during this behavioral state. Finally, the alteration of the neuronal activity induced by pentobarbital differs not only with the activity observed during W, but also with the activity observed during both SWS and PS.