Activity of the auditory system related to cortical arousal

Abstract

To determine whether or not the central auditory pathway shows variations in its activity which parallel changes in arcusal, multiple unit activity was recorded from the medial geniculate body, inferior colliculus, superior olivary complex, and cochlear nucleus in cats and was compared with simultaneously recorded electrocorticogram (ECoG) fluctations. Animals were paralyzed to assure auditory activity unconfounded by middle ear muscle contractions and movement-induced noise; extraneous outside noises were also carefully controlled. Under those conditions the medial geniculate body shows activity, both spontaneous and scund-elicited, which increases, usually linearly, as the amplitude of the cortical ECoG decreases. Lower auditory nuclei also vary their discharge, but in a more variable and unpredictable manner. The most common response observed among these lower nuclei was an increase in discharge during ECoG desynchronization, but with no change during the wide range of moderate- to high-amplitude ECoG. Present anatomical knowledge suggests the cortex as the most likely source of the geniculate effect. The mechanism responsible for modifying the activity of the lower auditory nuclei is not known, but the “descending auditory system” and efferents from the reticular formation are likely candidates.