The influence of thyroidectomy and thyroxin injection on the maze behavior of adult rats.

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Abstract
The animals (all [female][female]) were trained to a criterion of 3 out of 4 errorless trials on a simple maze, the animals running to milk at the correct one of 5 culs-de-sac. After the initial learning, thyroidectomy was performed on one group of animals (8 animals), and 3 weeks later the animals relearned the original habit. A control group (10 animals) relearned the maze 3 weeks after the last criterion trial of original learning, and 2 groups relearned the problem under conditions of increased metabolic rate induced by administration (subcut.) of synthetic d-l thyroxin. The thyroxin was administered daily from the 10th day before retraining began, and retraining began for all animals 3 weeks after initial learning. One group (8 animals) maintained an av. metabolic rate of about +9.5%; the other (7 animals) of about +87% (characterized as "toxic"). Although there seems a significant difference in the number of entries into certain of the incorrect culs-de-sac, total errors and total trials seem insignificantly different for the several groups on the relearning period. Although the +87% group had larger mean values for trials and errors to relearn to criterion, it seemed also to be considerably more variable (animal-to-animal) so that the differences were statistically insignificant. It is concluded that "thyroidectomy in white rats resulted in an apparent decrease in variability of maze behavior .... while mild hyperthyroidism resulted in an apparent increase in variability.....".

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