The Role of the Hippocampus in Instrumental Conditioning
Laura H.
Corbit and
Bernard W.
Balleine
Department of Psychology, University of California, Los Angeles,
Los Angeles, California 90095
Considerable evidence suggests that, in instrumental conditioning,
rats can encode both the specific action-outcome associations to which
they are exposed and the degree to which an action is causal in
producing its associated outcome. Three experiments assessed the
involvement of the hippocampus in encoding these aspects of
instrumental learning. In each study, rats with electrolytic lesions of
the dorsal hippocampus and sham-lesioned controls were trained while
hungry to press two levers, each of which delivered a unique food
outcome. Experiments 1A and 1B used an outcome devaluation procedure to
assess the effects of the lesion on encoding the action-outcome
relationship. After training, one of the two outcomes was devalued
using a specific satiety procedure, after which performance on the two
levers was assessed in a choice extinction test. The lesion had no
detectable effect on either the acquisition of instrumental performance
or on the rats' sensitivity to outcome devaluation; lesion and sham
groups both reduced responding on the lever associated with the
devalued outcome compared with the other lever. In experiment 2, the sensitivity of hippocampal rats to the causal efficacy of their
actions was assessed by selectively degrading the contingency between
one of the actions and its associated outcome. Whereas sham rats
selectively reduced performance on the lever for which the
action-outcome contingency had been degraded, hippocampal rats did
not. These results suggest that, in instrumental conditioning, lesions
of the dorsal hippocampus selectively impair the ability of rats to
represent the causal relationship between an action and its consequences.
Key words:
hippocampus; instrumental conditioning; outcome
devaluation; reward; contingency; rat
Copyright © 2000 Society for Neuroscience 0270-6474/00/20114233-07$05.00/0
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