Yuk-Hoi Yiu: Distinct directional modulations of hippocampal theta scale spike timing in areas CA1 and CA3
| When |
Dec 14, 2021
from 05:15 PM to 05:45 PM |
|---|---|
| Where | Zoom Lecture! |
| Contact Name | Fiona Siegfried |
| Contact Phone | 0761 203 9549 |
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Abstract
Place cells in the cornu ammonis (CA) regions of the rodent hippocampus are able to encode the positional information by place-specific firing activities and are thought to be crucial for spatial navigation tasks. It was later revealed that place cells also exhibit firing rate selectivity for different heading directions of the animal, and furthermore, encode the space via spike timing with respect to the background theta (5-12Hz) oscillation. One can observe the temporal code in individual place cells, where the spike phases advance in each theta cycle as the rat runs across a place field, or in theta spike sequences from a series of place cells when they are traversed consecutively. While previous studies focused mainly on positional information in theta spike timing, it is still unexplored whether such theta temporal code is related to the firing rate modulation across different directions of travel.
To study the directional information in theta spike timing, we re-analyzed a previously published dataset that contains spike activity of rat hippocampal place cells in the CA1, CA2 and CA3 subregions when rats were free-foraging in a 2D environment. We found that the spike timing code is also directionally modulated. When a rat traverses a place field against its preferred firing rate direction, spikes occur at later phases during phase precession.
Furthermore, we discovered a subset of field pairs which maintain the same firing order in their theta spike correlations when the running direction is reversed, revealing the “intrinsic” theta sequences which are only played out in fixed directions and also associated with later spike phases. Both effects are more noticeable in CA3 than CA1. We thus hypothesize that the intrinsic sequences contribute to the directionality of phase precession and their effect becomes overt when the directionally modulated sensory-motor drive of hippocampal firing rates is minimal.