Journal of Neuroscience, Vol 15, 7323-7329, Copyright © 1995 by Society for Neuroscience
Hippocampal lesions disrupt decrements but not increments in conditioned stimulus processing
JS Han, M Gallagher and P Holland
Department of Psychology, University of North Carolina at Chapel Hill 27599, USA.
Studies recording hippocampal neural activity show widespread registration
of events during associative learning. Recent computational models of
hippocampal function have stressed its role in attentional processes
specified by well-developed modern theories of associative learning. These
modeling efforts are largely aimed at accounting for the behavioral
outcomes of damage to the hippocampal system in terms of underlying changes
in information processing. Two experiments examined the effects of
neurotoxic lesions of the hippocampus on changes in attentional processing
of a conditioned stimulus (CS) in appetitive Pavlovian conditioning in
rats. In Experiment 1, hippocampal lesions eliminated the reduction in
associability of a CS usually produced by preexposure to that cue (latent
inhibition). In Experiment 2, hippocampal lesions interfered with the loss
in associability of a CS normally produced when that CS consistently
predicts another event. In contrast, in Experiment 2, hippocampal lesions
did not prevent the enhancement of CS associability when a previously
consistent predictive relation between two events was made inconsistent.
This research supports previous claims that the hippocampus is involved in
regulating the processing of CSs in Pavlovian conditioning, and provides
new evidence for a hippocampal role in decremental, but not incremental,
changes in attention.