The effects of the hormones of peripheral endocrine glands on the processes of behavior, learning, and memory.

The effects of systemic administration of thyroid, adrenal cortex, and sex hormones on learning ability, memory trace retention, and behavior were compared in male rats. These studies showed that thyroid, corticosteroid, and sex hormones had no effect on passive learning. Excess quantities of sex hormones disrupted active learning and subsequent reproduction of received information; an excess of thyroid hormone improved the acquisition and retention of the active avoidance habit. Increases in the levels of adrenal cortex hormones worsened active learning and the retention of memory traces, and also increased the level of behavioral activity.