SOME EMPIRICAL-DATA CONCERNING TIME OF DAY EFFECTS ON CONDITIONED FREEZING IN AN AVERSIVE CONTEXT-CONDITIONING PROCEDURE

The primary purpose of this article is to present some empirical data concerning three different potential time of day effects on conditione d freezing in a commonly-used aversive context-conditioning procedure with an unsignalled electric footshock as the unconditioned stimulus. In Experiment 1, rats were repeatedly placed In a conditioning box in which they received a shock. For one group of rats, these sessions con sistently occurred in the morning, for another group in the afternoon. In Experiments 2 and 3, rats received two training sessions per day. One group was consistently shocked in a training box on morning sessio ns but not on afternoon or evening sessions, whereas another group rec eived the reverse treatment. The pattern of freezing observed during r epeated non-shock morning and afternoon/evening test sessions reflecte d an effect of time of shock delivery on the acquisition of a context- shock association in Experiments 1 and 2, and a time of testing, or no n-specific performance, effect in experiments 1 and 3. In none of the experiments was there an effect that would reflect differential retrie val of a context-shock association by time cues. These results were di scussed in the light of data from previous experiments. (C) 1998 Elsev ier Science B.V.