The possible influence of fatigue on the reaction time of thyroidectomized sheep.

Abstract

The time required by a sheep to escape from a simple maze which it has previously learned has been taken as a measure of its reaction to environmental change. It was found that a thyroid-ectomized sheep exhibits a greater reaction time than does its normal twin when it runs a simple maze in which the position of the cul de sac is reversed at every trial and four successive trials per day are given. 1 These preliminary results were obtained with a maze sixty feet in length. The greater time required by the cretin sheep was largely due to frequent pauses but also to its sluggish progression through the maze. It was suspected that muscular fatigue might be a factor of importance in accounting for the difference in reaction time between the normal and cretin sheep. In order to eliminate this possibility by reducing locomotion to a minimum a system of three gates was constructed whereby the same maze could be shortened until the distance from the starting box to feeding compartment was reduced to six feet.

The twin sheep, above referred to, were caused to learn the same alternation problem in this short maze that they had previously learned in the long maze. In this case, also, the cretin required a greater time than its normal twin to escape from the labyrinth. The difference between the normal and thyroidectomized animals was largely due to pauses made by the cretin in choosing which way to turn after leaving the starting box. The experiments with the short maze have, thus far, verified the hypothesis previously advanced, viz.: that the greater time required by the cretin to escape from the maze is due to the lethargic functioning of the neural mechanism involved in avoiding the cul de sac when its position is changed at every trial. The expenses of this investigation were in part defrayed by a grant from the Heckscher Research Foundation.