Hippocampal theta oscillations orchestrate faster beta-to-gamma oscillations facilitating
the segmentation of neural representations during navigation and episodic memory.
Supra-theta rhythms of hippocampal CA1 are coordinated by local interactions as well
as inputs from the entorhinal cortex (EC) and CA3 inputs. However, theta-nested gamma-band
activity in the medial septum (MS) suggests that the MS may control supra-theta CA1
oscillations. To address this, we performed multi-electrode recordings of MS and CA1
activity in rodents and found that MS neuron firing showed strong phase-coupling to
theta-nested supra-theta episodes and predicted changes in CA1 beta-to-gamma oscillations
on a cycle-by-cycle basis. Unique coupling patterns of anatomically defined MS cell
types suggested that indirect MS-to-CA1 pathways via the EC and CA3 mediate distinct
CA1 gamma-band oscillations. Optogenetic activation of MS parvalbumin-expressing neurons
elicited theta-nested beta-to-gamma oscillations in CA1. Thus, the MS orchestrates
hippocampal network activity at multiple temporal scales to mediate memory encoding
and retrieval.
