Martin, Randall B.
M.A. (Master of Arts)
Department of Psychology
The purpose of this study v/as to investigate the effect of elevated levels of the hormone thyroxin upon the acquisition of fear in rats. More specifically, if thyroxin increases the speed of a response made to escape from fear, does it exert its effect on the acquisition of fear, the instrumental response made to escape from fear or upon both of these variables. An escape-from-fear paradigm, described by McAllister and McAllister (1968, 1971, 1972) and Daly (1968) was used. In this procedure a number of cue-shock pairings were administered in one session and in subsequent sessions rats were allowed to escape the aversive cues by jumping a hurdle into an adjacent compartment in the apparatus. Thirty light-shock pairings were given to four groups of 1 5 rats following oral administration of drug or placebo: two groups received two 75 microgram doses of L-thyroxin, the other two groups were given two doses of placebo. When 25 hurdle-jump trials were given 48 hours later, two groups were under the original and two groups were under the opposite drug conditions. Two days later all groups were given 25 hurdle-jump trials under placebo. The two groups given thyroxin before fear acquisition jumped faster on the last block of five trials on both days of escape training than the two groups given the placebo. The resulting divergence in performance caused a significant interaction with trial blocks on both days. Thyroxin given before escape training exerted a significant effect on performance on Day 2. Since both fear acquisition and escape training were facilitated it was proposed that thyroxin may have exerted two effects: an increase in the experience of fear via increased physical or emotional excitability and motor facilitation.
Hillstrom, Elizabeth L., "The effect of thyroxine on acquired fear" (1974). Graduate Research Theses & Dissertations. 5575.
v, 52 pages
Northern Illinois University
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