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J Exp Psychol Anim Behav Process. 2001 Oct;27(4):394-406.

An immediate-shock freezing deficit with discrete cues: a possible role for unconditioned stimulus processing mechanisms.

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Department of Biology, 3740 Hamilton Walk, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.


Five experiments with C57BL/6 mice (Mus musculus) investigated whether failures in shock processing might contribute to deficits in freezing that occur after an animal receives a shock immediately on exposure to a conditioning context. Experiment 1 found that more contextual freezing resulted from delayed shocks than from immediate shocks across 4 shock intensities. Experiment 2 extended the immediate-shock freezing deficit to discrete stimuli. Experiment 3 found that preexposure to the to-be-conditioned cue did not facilitate immediate cued conditioning. Experiment 4 found that context preexposure enhanced context-evoked fear after an immediate shock. Experiment 5 found that context preexposure also enhanced immediate cued conditioning. These findings are problematic for current theories of the immediate-shock freezing deficit that focus exclusively on processing of the conditioned stimulus, and they suggest that failures in shock processing may contribute to the deficit.

[Indexed for MEDLINE]

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