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Abstract:
One proposed role of the hippocampal memory system is to
encode the spatio-temporal context of events (e.g., Nadel, 1978).
In support of this view, it has been shown in non-human animals
that contextually-mediated fear conditioning is hippocampal
dependent (e.g. Phillips & LeDoux, 1992). In the present study,
we tested amnesic patients and controls on a model of contextual
conditioning based on a fear reinstatement paradigm. Subjects
learned to relate a visual conditioned stimulus (CS) with a mild
electric shock uncondition-ed stimulus (US). Previous research has
shown that the learned association between the conditioning context
and the US can serve to facilitate reinstatement of an extinguished
conditioned response (Bouton, 1984). In our study, after extinction
subjects were placed back into the learning context and were given
several presentations of the US alone (contextual reinstatement
phase). Following reinstatement, the recovery of the conditioned
response to the CS was tested. Both amnesics and control subjects
were able to acquire and extinguish the CS-US association. However,
only control subjects showed evidence for contextual reinstatement
of the conditioned fear response. The results are similar to those
observed in rats with fornix lesions (Wilson et al., 1995) and
provide further evidence for a role of the human hippocampus in the
formation of complex, contextual representations.
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