The role of the hippocampus in the performance of a continuous nonmatching task
Tóm tắt
Rats with hippocampal aspiration lesions (HIPP), cortical control lesions (CORT), or sham operations (SHAM) were trained on a continuous nonmatching task, using a bright or a dim wall light as the stimulus. Trials with the bright light were intermixed with trials with the dim light. On trials when the stimulus had changed, leverpressing was reinforced (nonmatch trials). When a stimulus was repeated, leverpressing was not reinforced (match trials). The intertriai intervals were varied and between-trial interference was introduced in order to compare the differential effects of these manipulations across lesion groups. Performance was assessed using signal detection theory. HIPP rats showed a significantly greater tendency to respond (bias) than did SHAM animals, with CORT animals showing an intermediate level of response output. However, there were no consistent differences between lesion groups in their ability to discriminate nonmatch from match trials (sensitivity). These findings contrast with deficits in performance reported following lesions of the fornix-fimbria and hippocampus on a similar matching-to-sample task. It is suggested that differences in response requirement between the tasks may induce rats to adopt different response strategies, which may in part explain the discrepant results. A methodological note of caution is also sounded concerning the utility of computed measures of performance on operant alternation tasks. In addition to derived measures, such as sensitivity and bias, computationally simpler indices of performance should be examined: if derived measures alone are used, spurious significant differences may arise that are not born out by more detailed analyses of response and latency data.
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