Associative vs topographical accounts of the immediate shock-freezing deficit in rats: Implications for the response selection rules governing species-specific defensive reactions

Rats were placed in a novel chamber and were given a single shock, either immediately upon placement in the chamber or after a 2-m delay. During a postshock observation period, delayed shock animals froze while immediate shock rats did not (Experiments 1–5). Additionally, delayed shock animals showed an elevation in defecation, relative to unshocked controls, while immediate shock animals did not (Experiment 1). Freezing and elevated defecation were first found with a 9-s delay between placement and shock, and both responses increased linearly with increasing delays up to at least 81 s (Experiment 2). Immediate shock rats did not show escape-related behaviors when potential escape routes were available (Experiments 3–4). A 2-m preexposure to the chamber, that was separated in time from shock, did not alleviate the immediate shock deficit (Experiments 4–5). The immediate shock deficit was also apparent in a test given 24 h after shock receipt (Experiment 6). If immediate shock rats were later given delayed shock they began to freeze but showed no carryover effects of their prior shock experience (Experiment 6). It was concluded that the immediate shock deficit reflects a deficit in association formation between contextual stimuli and shock rather than a difference in defensive behavioral topography. It also appears that freezing is the dominant conditional response to shock-associated stimuli even though freezing is not unconditionally elicited by the shock itself.