Twelve rats with amygdala damage (CBM) and 20 sham-operated controls were tested in several food-related situations. The CBM rats showed a longer latency to eat than controls in a novel environment due to more pronounced exploration. In the competition for food, CBM rats lost 85% of encounters with controls. Immediately after the contest, when allowed to eat singly, CBM rats displayed a higher persistence of alimentary responses to an emptied cup than did controls, presumably because they experienced more losses in the food competition. Both groups were equally able to overcome obstacles on the way to food, which suggests similar alimentary motivation. The only direct indication of a lowered responsiveness to hunger in CBM rats was 24-hr-fasting-induced hypophagia. The results of this study indicate the involvement of the cortico-basomedial amygdaloid region in the control of relations between alimentary and other motivations. The contribution of eventual changes of food motivation in the postoperative alteration of this balance is discussed.
Experiments were performed on dogs with bilateral electrolytic damage of dorso-medial amygdala. Before the operation dogs were trained in alimentary-social reward differentiation. It consisted in conditioning of instrumental responses of either right or left foreleg to two different tones respectively. Chlorpromazine was injected intramuscularly in 1.5 mg/kg dose during four consecutive days, beginning at third to fifth week after the operation. Amygdala damage produced significant deterioration of the instrumental performance both reinforced by food and by social-sensory rewards. Chlorpromazine produced further dramatic decrease of performance of both responses. It was concluded that chlorpromazine exerts a suppressing effect on motivated behavior reinforced by positive rewards in amygdala dogs. As the effect of chlorpromazine and medial amygdalar damage are summated it may be suggested that the deficit of medial amygdala neurons impairs similar neurochemical mechanisms, (probably dopaminergic and alpha-adrenergic transmission) as does chlorpromazine.
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