Avoidance, classical, and pseudoconditioning as a function of species-specific defense reactions in high- and low-avoider rat strains

Abstract

Rats of the Australian High Avoider (AHA) and Australian Low Avoider (ALA) strains and their reciprocal crosses were exposed to 50 trials of one of three shuttlebox procedures. The avoidance group received pairings of a tone and shock. If the animals shuttled during the tone, they avoided the shock. If they waited until the shock came on, they could then escape it. The classical group received pairings of the tone and a brief inescapable shock. If they shuttled during the tone, the tone ceased and they immediately received the shock. If they did not shuttle, they received the brief shock at the termination of the tone. The pseudoconditioning group received the tone and the shock explicitly unpaired. If they shuttled during either the tone or the shock, the stimulus was terminated. There was no acquisition of anticipatory responding under the pseudoconditioning procedure. All groups evidenced an increase in anticipatory responding over trials under the classical procedure. The ARAs acquired the response faster and reached a higher asymptote than did the ALAs. Performance of the two reciprocal crosses fell in between. A similar pattern was observed under the avoidance procedure, albeit at slightly higher response levels. Subsequent studies established that the AHAs acquired a one-way avoidance response quickly, but were impaired on a passive avoidance task, whereas the reverse was the case for the ALAs. The reciprocal crosses were proficient at both tasks. These results suggest that shuttlebox avoidance is largely accounted for by classical conditioning of the predominant defensive response. When that response is compatible with performance on the task, acquisition is rapid (ARAs), and when it is not, acquisition is slow (ALAs).