Neurons in the temporal cortex signal object familiarityby modulating their spiking activity as the object isrepeatedly experienced. However, the neural mechanismsunderlying this ‘‘repetition effect’’ and its functionalsignificance remain unknown. We investigatedthis process in a goal-directed object recognitiontask in which rats were required to recognize familiarand novel objects. Single-unit spiking activity andlocal field potential were recorded from the hippocampusand perirhinal cortex (PER) as rats performedthe task. Repetition effects were detectedin both the hippocampus and PER. However,phase-locking to the theta rhythm was strengthenedwith object repetitions in the hippocampus but not inthe PER, whereas stronger phase-locking wasobserved with gamma rhythm in the PER but not inthe hippocampus. Our findings suggest that therepetition effect occurs in sync with different rhythmicoscillations across different regions and may underlieneural ‘‘pruning’’ of noise that facilitates objectrecognition.
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