SOME FACTORS MODULATING NEURAL ACTIVITIES IN PERIPHERAL AUDITORY CENTERS

Some central and peripheral factors modulating sound-evoked neural activities, as measured by the frequency following response (FFR), were investigated in peripheral levels of the central auditory pathway in cat. It was shown that middle ear muscle activity modulates FFR, and that these modulations closely parallel those observed in the cochlear microphonic. In the absence of ear muscle activity (tenotomy, Flaxedil) we were unable to demonstrate any modulation of sound-evoked responses of the cochlea (microphonic) or of the central auditory relays (cochlear nucleas, trapezoid body, and medial accessory olivary nucleus). This suggests that, if central efferent influences act upon afferent activities at these levels of the auditory pathway, they exert their effects in forms not evident in the neural FFR. Some implications of these results are discussed. © 1969.