Some Effects of Thiamine Deficiency and Reduced Caloric Intake on “Behaviour under Stress” and on Learning

Abstract

The main purpose of the investigation was to determine the effects of thiamine deficiency in rats on behaviour under stress and on learning. Since thiamine deficiency reduces food intake, it was necessary to have two control groups. The first received adequate thiamine, but a food intake reduced to that of the vitamin-deficient animals; the second received adequate thiamine and an unrestricted food intake. It was thus possible to study the effects both of thiamine deficiency and of reduced caloric intake on the behaviour variables measured. The experimental group was maintained on a thiamine-deficient diet throughout the entire experimental period. Because of the effects of thiamine deficiency on caloric intake, food-hunger was never used as a form of motivation. Behaviour in four different situations was studied: in Hall's open-field test, in two discrimination situations both involving exposure to insoluble and soluble problems, and in a water maze. Contrary to the findings of several previous studies, there were no significant effects of thiamine deficiency on behaviour prior to the onset of polyneuritis with its debilitating effects on motor co-ordination. There was also no evidence of impairment in any of the behaviour studied which could be attributed to restrictions in caloric intake. This was the case even though the restrictions continued for a period of somewhat more than twelve months. Although these restrictions did not lead to impairment they were associated with certain changes in performance. Animals whose feeding was restricted were more active and, during the soluble phase of one discrimination situation, showed more vicarious trial and error and learned more readily than animals fed ad libitum on the same diet. It is suggested that these differences may be interpreted in terms of the effects of what previous investigators have referred to as “irrelevant drives”.