A behavioural analysis of some ventral auditory pathways in the medulla of the rat
Abelson, Robert Miles
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Rats were trained on three schedules of reinforcement, a sound aversive schedule, a light aversive schedule and a sound and light discrimination schedule. On the aversive schedules a press response terminated the aversive stimulus. On the discrimination schedule a response in the presence of either stimulus produced food. An auditory threshold was measured on this schedule. Following training the animals received electrolytic lesions in the ventral auditory system of the medulla. Following this they were tested on the behavioral schedules. The brain of each animal was then removed and impregnated with protargol for microscopic examination. Six rats received unilateral lesions, seven received bilateral lesions and six received sham operations. The results were as follows. Of the six animals who received unilateral lesions, one showed a substantial loss of the sound aversive behavior. Of the seven who received bilateral lesions five suffered a loss of the aversive behavior. Of these five, two had a substantial increase in the discriminative threshold. The behavior of the animals who received sham operations was essentially unaffected. There was a consistent relation between extensive damage to the large fiber pathway, the superior olivary pathway and the small fiber pathway and loss of the auditory aversive behavior. Destruction of the superior olivary pathway was not sufficient to produce a loss of the aversive behavior. The suggestion in the literature that the large fiber pathway is responsible for the maintenance of the aversive behavior was confirmed. Destruction of the superior olivary pathway either alone or in combination with destruction of the large fiber pathway did not materially change the auditory discriminative threshold. Destruction of all ventral acoustic pathways caused a loss of both aversive and discriminative auditory behaviors. Dorsal auditory pathways did not by themselves support either behavior. It has not been possible to determine if destruction of the small fiber pathway by itself can cause a loss of discriminative behavior. It was not possible to determine if return of the release response was due to the lesion or due to the loss of the press response.
Thesis (Ph.D.)--Boston University.