Philippa Hennessey : Sparse connectivity and theta-gated inhibition enable selective routing in the dentate gyrus
| When |
Nov 17, 2026
from 05:15 PM to 06:00 PM |
|---|---|
| Where | Bernstein Center Freiburg, Hansastr. 9a, 79104 Freiburg, Lecture Hall |
| Contact Name | Zahra Dandani |
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ABSTRACT
Theta oscillations are a hallmark of hippocampal activity during periods of exploration and are thought to organize memory formation and communication between hippocampal regions. Experimental observations reveal a striking asymmetry between entorhinal cortex layer II (EC2) and dentate gyrus (DG) activity across the theta cycle: while EC2 exhibits distinct activity regimes at different theta phases, granule cell population activity is confined to a narrow window of activation. Moreover, periods of strong EC2 population activity do not coincide with increased DG output, suggesting that entorhinal inputs are filtered according to theta phase rather than transmitted uniformly.
Here, we investigate whether theta-modulated inhibitory circuits can provide a mechanism for such phase-dependent routing. Using experimental recordings, spiking network simulations, and theoretical analysis, we show that rhythmic inhibitory input from the medial septum generates transient windows of granule cell excitability through its action on dentate gyrus interneuron populations. Within these windows, sparse high-frequency EC2 activity is preferentially transmitted, whereas dense low-frequency population activity arriving at other phases is suppressed.
Our theoretical work further demonstrates that sparse connectivity between EC and DG populations promotes robust granule cell phase locking across a broad range of input strengths. Together, these results identify theta-modulated inhibition as a circuit mechanism for phase- dependent filtering of entorhinal input and suggest a role for theta oscillations in regulating information flow through the dentate gyrus.