The effect of stimulation of the fornix and caudate on the behavior of the cat
Barry, John Joseph, Jr.
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This experiment stemmed from the contradiction existing between the recent findings of Olds and Delgado et al concerning the effect of stimulating the fornix. The original design was later broadened to include the caudate when additional data was published by Heath et al. This evidence also conflicted with some earlier findings of Olds regarding this structure. The main problem was to determine whether stimulation of the caudate and fornix was noxious to the animal. In order to objectively appraise the effects of stimulation, it was necessary to provide some criterion of behavior as a base. For this reason the operant conditioning technique of Skinner was chosen, and grey noise was the noxious stimulus. The animals were conditioned to terminate the noise by pressing a lever. The intensity of the noise was plotted against the rate of responding of the animal (the escape function). Each animal then had 4 electrodes implanted, two in each hemisphere. The targets for the electrodes were the fornix and the caudate. After a short recovery period, the animals were again tested on the noxious stimulus. The results of this test period were used as the base to appraise the effects of stimulation. The stimulation sessions were conducted in the following manner: a) With the noise stimulus constant at 15v. the stimulation was gradually increased in intensity. Each time the animal pressed the lever, both noise and stimulation were terminated. b) With the noise gradually reduced to zero, the stimulation was gradually increased in intensity, as in the previous contingency. Depression of the lever terminated both stimulation and noise, as before. c) With the noise at 0, stimulation was given for each bar press (Olds effect). d) Finally, with the noise at 0, stimulation was administered at specified intervals over a wider range of intensities. During this test, the motor effects of the stimulation were noted. In the first two contingencies rate-intensity functions were plotted for each electrode in each animal. In the third contingency the number of responses were recorded against intensity. In the last behavior, stimulation effects were observed and noted in protocol form. After securing data in this manner, each animal was sacrificed, and the brains sectioned and mounted. The position of each electrode in each animal was then determined. It was found that stimulation of the fornix and caudate was not any more noxious to the animal than the original imput stimulus. The motor effect of fornix stimulation could not be clearly determined since it was impossible to control for current spread at high intensities.
Thesis (Ph.D.)--Boston University