The Journal of Neuroscience, June 1, 2001, 21(11):3955-3967
Recognition Memory Correlates of Hippocampal Theta Cells
Sherman P.
Wiebe and
Ursula V.
Stäubli
Center for Neural Science, New York University, New York, New York
10003
Investigations of hippocampal theta cell activity have typically
involved behavioral tasks with modest cognitive demands. Recordings in
rats locomoting through space or engaged in simple stimulus
discrimination or conditioning have revealed some place specificity and
S+/S
selectivity in addition to
the hippocampal EEG theta-related behavioral/motor
correlates. However, little data exist regarding theta cell
activity during performance of more cognitively demanding, hippocampal-dependent recognition memory tasks. Here, we examined the
cognitive firing correlates of theta cells in rats that were performing
an olfactory recognition memory task with distinct sample and test
phases. Discriminant analysis revealed odor and match/nonmatch memory
correlates in theta cell activity comparable in relative
magnitude to that of the principal cells. Odor-specific theta cell responses in the sample phase were restricted primarily to
CA1 and linked to task performance. In the test recognition phase,
match/nonmatch theta cells were found primarily in the CA3 and CA1
fields, most of which exhibited greater activity on correct nonmatch
trials in which recognition occurred than on error match trials in
which recognition failed. Odor selectivity of the match/nonmatch
signaling was greatest in the dentate gyrus (DG) and CA3 and least in
CA1. This inverted pattern of stimulus specificity in the sample versus
test phase was similar to that observed in principal cells but with a
greater contrast between the CA1 and DG/CA3 fields. Together, these
findings suggest that theta cells actively participate in hippocampal
recognition memory processing and play a specific role in shaping the
cognitive firing properties of the hippocampal principal cells.
Key words:
interneurons; theta cells; hippocampus; DNMS; odors; spatial; match/nonmatch discrimination; recognition memory; cognition; dynamic filtering; generalization; dentate gyrus; CA3; CA1; principal
cells
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