Auditory brain stem responses in the cat. II. Effects of lesions

Abstract

Abstract Discrete lesions of the brain stem auditory pathway in cats were found to have complex effects on the auditory brain stem response (ABR). These effects ranged from an amplitude change on only a single component of the ABR to latency and amplitude changes for that component plus some or all of the subsequent components. Lesions of certain portions of the classical primary auditory pathway (i.e., the dorsal cochlear nucleus, the dorsal acoustic stria, the lateral superior olivary nucleus, the posterior portion of the lateral lemniscus and the inferior colliculus) were not associated with changes in the ABR prior to component P5. Except for midline lesions, the effects of a brain stem lesion on the ABR were quite different for ipsilateral and contralateral stimulation. The predominant effect of brain stem lesions on the ABR was an attenuation of the amplitudes of the components and only an occasional increase in their latency. Opposite effects, i.e., increases in amplitude or decreases in latency, were rare. The acute effects of brain stem lesions on the ABR could be transient and not persist in chronic recordings. The components of the ABR were primarily affected by the following lesions. Component P0.8 was attenuated by a lesion of the eighth nerve. N1.0, P1.2 and N1.5 were unaffected by lesions of the cochlear nucleus but were affected by lesions of the eighth nerve, suggesting that the eighth nerve was the generator of these components. Except for one lesion of the trapezoid body component P1.7 was only affected by lesions of the cochlear nucleus or eighth nerve, suggesting its origin in one or both of these structures. N2.0 was affected by lesions of the ventral cochlear nucleus, the region of the superior olivary complex and the trapezoid body. P3 was affected by lesions in the region of the superior olivary complex and the trapezoid body. N3 and N4 were affected primarily by lesions of the lateral lemniscus, but also by lesions of the superior olivary complex and trapezoid body. The results suggest that except for the first few components (P0.8, N1.0, P1.2 and N1.5) each of the components has substantial contributions from more than one auditory brain stem structure. Component P0.8 was determined to have substantial contributions from both cochlear microphonic and neural activity.