Some Effects of Thiamine Deficiency and Reduced Caloric Intake on Avoidance Training and on Reactions to Conflict

Abstract

The present experiment was designed to test four predictions based upon results of our earlier study (Knöpfelmacber et al., 1956) in which we observed some effects of thiamine deficiency and reduced caloric intake on “behaviour under stress” and on learning. The first two predictions stated that thiamine deficiency of a degree not severe enough to produce polyneuritis (a) would not affect the efficiency of conditioning and (b) would not be associated with exaggerated reactions to conflict. The third prediction arose from our previous observations of the effects of “irrelevant drives” on learning and stated that animals on reduced caloric intakes would condition more rapidly as a group than would animals fed ad libitum. The fourth prediction was that reduced caloric intake would not be associated with increased susceptibility to stress. The experiment was identical in its design to our previous study. It required one experimental and two control groups, all matched by a littermate control technique. The experimental group was maintained on a thiamine-deficient diet throughout the entire experimental period. A caloric control group received adequate thiamine, but a food intake reduced to that of the vitamin-deficient animals. A general control group received adequate thiamine and an unrestricted food intake. Because of the effects of thiamine deficiency on caloric intake, food-hunger was never used as a form of motivation. Behaviour in three different situations was studied: in an instrumental conditioning situation involving jumping to a platform to avoid shock; in an avoidance-avoidance conflict situation; and in a second instrumental conditioning situation requiring lever-pressing to avoid shock. The results confirmed some of our predictions, but not others. In general, they indicated that thiamine deficiency of the level we induced did not affect the efficiency of conditioning. This conclusion conforms with the findings of our earlier experiment that the deficiency did not affect maze or discrimination learning, but it is contrary to the observations of certain other investigators. The evidence did suggest that thiamine deficiency was associated with exaggerated reactions during exposure of the animals to conflict, deficient animals tending to show greater response rigidity and “displacement activity.” The divergences in the behaviour of these animals and their paired caloric controls became more noticeable as the number of conflict trials increased. Our prediction that reduced caloric intake would be associated with more rapid conditioning was confirmed. We believe this result suggests that “irrelevant drives” were operating in a manner similar to that reported in our previous study. The overall results support our fourth prediction that reduced caloric intake would not affect reactions to conflict. However, an analysis of behaviour trends during the conflict trials suggests that reduced caloric intake may have affected reactions early during exposure to conflict and only became differentiated from the effects of thiamine deficiency as the duration of exposure increased.