Effect of state of arousal on click-evoked responses in cats.

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Abstract
The click-evoked response in several portions of the central auditory system and in the cerebellar vermis was studied during the sleep-waking cycle in freely moving cats. The acoustic control procedures used (earphones, sectioning of middle ear muscles in some cats, and elimination of data confounded by masking noise and animal movement) resulted in a constant input to the auditory system. During the sleep-waking cycle, click-evoked responses from cochlear nucleus, superior olive, and inferior colliculus were stable, while responses from medial geniculate, auditory cortex, and cerebellar vermis were labile. The presence or absence of the middle ear muscles did not affect the results in this experiment. However, cats with uncut muscles were not studied during REM [rapid eye movement] sleep. At click rates over 6/sec, during states of drowsiness and slow-wave sleep, augmenting responses appeared at medial geniculate and auditory cortex. Augmenting responses were blocked by alerting stimuli.