Theta rhythm: A Memory Clock

The hippocampal theta rhythm is a 4–12 Hz oscillation arising from coordinated activity of large neural populations, driven by pacemaker neurons in the medial septum and intrinsic hippocampal circuitry.

Hippocampal theta oscillations provide a shared temporal reference frame that allows distributed neural assemblies—coding for location, sensory cues, emotions, and social context—to bind into unified episodic memories.

Beyond encoding externally driven sequences (like walking through a colored corridor), hippocampal networks can internally generate ordered sequences of assemblies during imagination, planning, and memory recall, with theta oscillations playing a key organizing role.

Place cells in hippocampus do not just encode position via firing rate; they also shift their spike timing relative to theta phase—a phenomenon called phase precession—that enables compact representation of past, present, and future within each theta cycle.