[Synchronized neural rhythms in rat hippocampal CA1 region and orbitofrontal cortex are involved in learning and...

To investigate the neural mechanisms of rhythmic activity in the hippocampal CA1 region and orbitofrontal cortex (OFC) during a spatial goal-directed task.

Four long-Evans rats were trained to perform a spatial goal-directed task in a land-based water maze (Cheese-board maze). The task was divided into 5 periods: Pre-test, Pre-sleep, Learning, Post-sleep, and Post-test. During the Learning phase, the task was split into two goal navigation and two reward acquisition processes with a total of 8 learning stages. Local field potentials (LFP) from the CA1 and the OFC were recorded, and power spectral density analysis was performed on Theta (6-12 Hz), Beta (15-30 Hz), Low gamma (30-60 Hz), and High gamma (60-90 Hz) bands. Coherence, phase-locking value (PLV), and phase-amplitude cross coupling (PAC) were used to assess the interactions between the CA1 and the OFC during learning and memory.

During the task training, the rats showed consistent rhythms of OFC neural activity across the task states (P>0.05) while exhibiting significant changes in Beta and High gamma rhythms in the CA1 region (P<0.05). Coherence and PLV between the CA1 and the OFC were higher during goal navigation, especially in the stable learning phase (Stage 8 vs Stage 1, P<0.01). The rats showed stronger cross-frequency coupling between CA1-Theta and OFC-Low gamma in the Post-test phase than in the Pre-test phase (P<0.05).

Learning and memory consolidation in goal-directed tasks involve synchronized activity between the CA1 region and the OFC, and cross-frequency coupling plays a key role in maintaining short-term memory of reward locations in rats.