Journal of Neuroscience, Vol 15, 1162-1171, Copyright © 1995 by Society for Neuroscience
Variants of olfactory memory and their dependencies on the hippocampal formation
U Staubli, TT Le and G Lynch
Center for Neural Science, New York University, New York 10003.
Olfactory memory in control rats and in animals with entorhinal cortex
lesions was tested in four paradigms: (1) a known correct odor was present
in a group of familiar but nonrewarded odors, (2) six known correct odors
were simultaneously present in a maze, (3) correct responses required the
learning of associations between odors and objects, and (4) six odors, each
associated with a choice between two objects, were presented
simultaneously. Control rats had no difficulty with the first problem and
avoided repeating selections in the second; this latter behavior resembles
that reported for spatial mazes but, in the present experiments, was not
dependent upon memory for the configuration of pertinent cues. Control
animals varied considerably in their acquisition of odor-object
associations with only a subgroup learning every set of pairings. These
latter animals also performed well in the fourth task and, as indicated by
post hoc analyses, developed complex strategies in dealing with the problem
of serial odor- object pairs. Lesioned animals had no difficulty in
selecting correct odors learned prior to surgery (problem one) but repeated
their choices in problem two. This latter result suggests that hippocampus
contributes to the transient memory of prior choices for odors as it does
for prior choices in spatial mazes. Entorhinal rats were able to form
odor-object associations (problem three), and a subgroup of the animals
periodically succeeded in doing a long series of such choices (problem
four), though with less frequency than controls. These results indicate
that rats use both long-term memory and transient memory in dealing with
olfactory problems and suggest that the second of these is dependent upon a
hippocampal process that encodes a type of information other than the
relationship between cues.
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