The transition from a fixed ratio to a fixed interval schedule of reinforcement in hypo and hyperthyroid rats

Abstract

The modification of behavior caused by hypo and hyperthyroidism were studied when the schedule of reinforcement was changed from a fixed ratio to a fixed interval. The conditions of hypo and hyperthyroidism were obtained with a chronic administration of methimazole and of 1-thyroxine. The level of the modifications of thyroid activity was determined by evaluation of the basal metabolic rate and of the plasma levels of T 4. Hyperthyroidism caused no modification of the rat behaviour. A difficulty in adapting to the new experimental situation (learning) was found in hypothyroidism. This effect is evident in high hypothyroidism. In low hypothyroidism a depression of the rat behaviour may interfere with the modification of the learning process.