The effects of certain neural lesions upon sound-maintained escape behavior in the rat. Part I: anterior cingulate cortex. Part II: Septal nuclei and fornix components
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This study stems from equivocal reports concerning the behavioral effectiveness of noxious stimuli following lesions of the anterior cingulate cortex or the septal region. Evidence in the experimental literature indicated that removal of the anterior cingulate region or destruction of the anterior thalamus resulted in a reduced reaction to various noxious stimuli. Other work seemed to cast doubt on this conclusion. There is also equivocal evidence concerning the effect of lesions in the hippocampus (thus affecting its outflow), or in the septal region, upon behavior maintained by the use of noxious stimuli. Contrary results have been reported concerning the effect of such lesions upon avoidance responding maintained by shock. Also reported were the post-operative weakening of a CER and the loss of a sound-maintained escape response following septal region lesions in the rat. Other, non-aversive, behaviors were reportedly unaffected by such lesions. The two things in need of further clarification were the animal's reaction to a specific noxious stimulus and the analysis of the anatomical destruction supposedly changing this reaction. Therefore, conditioned escape responding maintained by the termination of intense sound was compared with ratings of the amount of destruction within a large number of individual structures. The subjects were albino rats. The experimental space contained a sound source for white noise, from which the animals could escape for 20" by depressing a lever. Responses during the silence were non-contingent. Daily sessions were 56' long at 105 db. Following pre-operative escape training the animals were subjected to surgery, allowed to recover physically, then returned to the .experimental sessions and run until they reached a response criterion. The number of days to the first criterion day was labelled the "response recovery time" (RRT). Histological examination allowed comparison of the extent of damage, to single structures or to combinations, with the RRT which accompanied the lesion. Nine animals sustained lesions varying from slight to complete destruction of the anterior cingulate cortex. These animals exhibited a distribution of RRT's from 0 to 19 days, but there was no apparent relation between the amount of anterior cingulate damage and the length of the RRT. Seven control animals, with non-cingulate lesions, exhibited RRT's from 0 to 14 days. For the septal region and fornix components there were 15 animals, with lesions ranging from bilateral obliteration to small or unilateral damage. The range of RRT's was 0 to 23 days, and careful examination of the extent of damage to various structures again revealed no relation to the length of the RRT. Five control animals with caudate nucleus lesions exhibited RRT's of 0 to 12 days, which were unrelated to the severity of caudate damage. Nine additional septal animals were subjected to behavior conditions approximating those of Tracy and Harrison (who had reported long losses of sound-maintained escape responding in rats with septal damage). These animals received daily 15' sessions at 117 db. Nevertheless, the range of RRT's (to relative criteria) was from 1 to 27 days and no consistent relation was found between the anatomical destruction and the length of the RRT. These results indicate that the loss of escape responding to white noise is not primarily related to lesions of the anterior cingulate cortex, the septal region or the fornix components. Furthermore, it was shown that very similar distributions of RRT's may accompany lesions elsewhere. The reduction in effectiveness of noxious stimulation, as measured by the RRT appears in quite an irregular manner and is probably not the result of a unitary factor such as damage to a single structure or area.
Thesis (Ph.D.)--Boston University
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