Abstract
Auditory brain stem potentials were recorded between the skull (vertex) and a non-cephalic reference in guinea pig before and after making discrete lesions of the auditory pathway in the pons and midbrain. Lesions of the superior olivary complex were accompanied by attenuation of P3 and N3 to contralateral input. Lesions of the lateral lemniscus were accompanied by attenuation of N3 to contralateral input. Lesions of the lateral portion of the pons adjacent to the lateral superior olivary nucleus were accompanied by attenuation of P4 to ipsilateral input. Lesions of the inferior colliculus were without effect on the ABR. These data are interpreted as supporting the hypothesis that each component of the ABR arises from a focal region of the brain stem auditory pathway.
Highlights
MethodsSubjects Twenty-six adult guinea pigs weighing between0.7 and 1.1 kg were subjected to lesions of the pans and midbrain.Stimulus generation, auditory brain stem responses (ABRs) recording and data analyses were the same as in the first two studies (Wada and Starr 1983a, b).Surgery The animals were deeply anesthetized with sodium pentobarbital
The effects of lesions of the region of the superior olivary complex, the lateral lemniscus and inferior colliculus on the amplitude and latency of the auditory brain stem responses (ABRs) are summarized in Tables I and II
P3 is attenuated with lesions in the region of the medial superior olivary nucleus contralateral to the ear stimulated; N3 is lost with lesions in the ventral region of the lateral lemniscus contralateral to the ear stimulated; 1)4 is attenuated with lesions in the lateral portions of the pons involving the tegmentum adjacent to the lateral superior olivary nucleus ipsilateral to the ear stimulated; N4 is attenuated with lesions in any of the 3 aforementioned areas
Summary
Subjects Twenty-six adult guinea pigs weighing between0.7 and 1.1 kg were subjected to lesions of the pans and midbrain.Stimulus generation, ABR recording and data analyses were the same as in the first two studies (Wada and Starr 1983a, b).Surgery The animals were deeply anesthetized with sodium pentobarbital. 0.7 and 1.1 kg were subjected to lesions of the pans and midbrain. Following a tracheotomy and fixation of a small screw at a point 3 mm posterior to the bregma to serve as the 'active' electrode for recording the ABR, 3 different surgical approaches were employed to make the brain stem lesions. A ventral approach was similar to that described in the first two papers and was used to lesion the superior olivary complex. A lateral approach through the bulla and temporal bone was used to expose the lateral aspect of the brain stem for unilateral lesions of the superior olivary complex or lateral lemniscus
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