Auditory brain stem responses in the cat. I. Intracranial and extracranial recordings.

A spatial and temporal analysis of auditory evoked potentials within the brain stem were performed in cats to determine the areas of the brain stem having large amplitude voltage fields, corresponding in latency to each of the components of the scalp-recorded auditory brain stem response (ABR). On the basis of this criterion, the first few components (occurring within 2 msec post-stimulus) were attributed to activity in a single structure, the eighth nerve. In contrast, each of the other components was correlated with large amplitude fields in at least two sites within the brain stem auditory pathways. The findings demonstrate a complex spatial and temporal distribution of electrical events within the auditory brain stem pathways, which preclude any simple one-to-one relationship between a given anatomical site and a particular component of the ABR. The possibility that the determination of the generators might be influenced by filtering of the evoked potentials was also examined. High-pass filtering of the evoked potentials resulted in a modification of the defined generators for only one of the components studied (P4). Filtering had little effect on the components of the scalp-recorded ABR

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

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. © 1980

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

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. © 1980

Auditory brain stem responses in the cat. I. Intracranial and extracranial recordings.

A spatial and temporal analysis of auditory evoked potentials within the brain stem were performed in cats to determine the areas of the brain stem having large amplitude voltage fields, corresponding in latency to each of the components of the scalp-recorded auditory brain stem response (ABR). On the basis of this criterion, the first few components (occurring within 2 msec post-stimulus) were attributed to activity in a single structure, the eighth nerve. In contrast, each of the other components was correlated with large amplitude fields in at least two sites within the brain stem auditory pathways. The findings demonstrate a complex spatial and temporal distribution of electrical events within the auditory brain stem pathways, which preclude any simple one-to-one relationship between a given anatomical site and a particular component of the ABR. The possibility that the determination of the generators might be influenced by filtering of the evoked potentials was also examined. High-pass filtering of the evoked potentials resulted in a modification of the defined generators for only one of the components studied (P4). Filtering had little effect on the components of the scalp-recorded ABR