INFLUENCE OF MOTOR ACTIVITY ON CLICK-EVOKED RESPONSES IN THE AUDITORY PATHWAY OF WAKING CATS.

Click evoked responses were recorded from waking cats by means of electrodes chronically implanted along the auditory pathway. The animals were studied in three different situations: sitting still, during bodily movements, and during presentations of novel stimuli. The responses recorded from the round window cochlear nucleus, superior olive, inferior colliculus, medial geniculate body, and auditory cortex were of smaller amplitude during movements than responses recorded in the same animals while sitting still. They were attenuated during the initial moments following the presentation of a novel stimulus at a time when the animal was engaged in orienting movements. However, when animals were sitting still and merely staring at the novel stimulus, click evoked responses were of control amplitudes. A dual regulatory system consisting of both peripheral neuromuscular as well as of central mechanisms is active in modifying click evoked responses during movements. In animals with the tendons of the middle ear muscles sectioned bilaterally, responses recorded from subcortical stations along the auditory pathway did not decrease in amplitude during movements, whereas cortical evoked responses were still attenuated. Thus, modifications of evoked responses in subcortical stations along the auditory pathway are a passive reflection of middle ear muscle induced modifications of sound input. Changes in cortical evoked responses during movements depend, in addition, upon central mechanisms. These mechanisms do not appear to act on the cortex itself but, rather, on pathways connecting brainstem stations of the auditory pathway with auditory cortex. © 1964