Discrimination learning and habit reversal as affected by thyroid hormone.

Abstract

Immature albino rats were subjected to a regime of either thyroxine injns. or a thiouracil diet to determine the effects of the consequent hyperthyroid and hypothyroid states upon learning of a brightness discrimination and its reversal after 1, 7, and 14 days. The hyperthyroid, control, and hypothyroid groups, containing 20 animals each, were trained in a single-unit water T-maze. In original learning the analysis of variance for both trial and error scores of the 3 groups fell just short of significance at the 5% level of confidence. There was a marked tendency for both exptl. groups to be inferior to the control group. With respect to habit reversal, the treatment and delay conditions had significant effects upon the trial scores. Treatment and delay interacted significantly. Analysis of the interaction suggests 3 trends in the mean trial scores: (1) a positive relationship between metabolic activity and ability to reverse the habit after 7 days'' delay; (2) a negative relationship between metabolic activity and ability to reverse the habit after a 14 day delay; (3) a negative relationship between delay and habit reversal ability in the Hyper-groups.