Rhythmic Pruning of Perceptual Noise for Object Representation in the Hippocampus and Perirhinal Cortex in Rats

Neurons in the temporal cortex signal object familiarity by modulating their spiking activity as the object is repeatedly experienced. However, the neural mechanisms underlying this "repetition effect" and its functional significance remain unknown. We investigated this process in a goal-directed object recognition task in which rats were required to recognize familiar and novel objects. Single-unit spiking activity and local field potential were recorded from the hippocampus and perirhinal cortex (PER) as rats performed the task. Repetition effects were detected in both the hippocampus and PER. However, phase-locking to the theta rhythm was strengthened with object repetitions in the hippocampus but not in the PER, whereas stronger phase-locking was observed with gamma rhythm in the PER but not in the hippocampus. Our findings suggest that the repetition effect occurs in sync with different rhythmic oscillations across different regions and may underlie neural "pruning" of noise that facilitates object recognition.