UC San Diego

The hippocampus (HPC) is a brain region known for playing a role in learning and memory. Theta oscillations (7-9 Hz) are found in the HPC and are believed to be linked to the sequential firing pattern of HPC place cells through phase precession. Studies have demonstrated that accelerated theta oscillation frequencies resulted in spatial working memory deficits, but the role that HPC theta oscillations play in memory encoding and retrieval is still unclear. Our study utilized an optogenetic technique that targeted GABAergic PV cells in the mouse MSA, the pacemakers for HPC theta oscillation. We entrained the HPC theta oscillation frequency to both below and above the endogenous range. We then performed electrophysiological recordings from cells in the HPC CA1 layer while mice were completing a spatial alternation task with variable delays. We saw memory impairments in trials with lower frequencies (4 Hz) and long delays (10-s). Follow-up analyses can reveal how the relative timing between cells has changed.