A STABLE ENTORHINAL HEAD DIRECTION SIGNAL FOR STEERING GRID CELLS

Grid cells in the medial entorhinal cortex (MEC) are thought to provide the neural substrate for path integration, the process by which animals track their position relative to a starting point using self-motion cues.
Path integration requires correct tracking of direction, which is known to modulate the firing of MEC neurons, and is used by models to steer the grid cell circuit.
When navigating 1D environments, grid fields are thought to be sliced, predicting a fixed unidirectional signal.
Recent work by Hermansen et al. (2024) found evidence for straight slices during 1D navigation.
Yet, the (uni)directional signal that models of grid cells require to produce straight slices remains to be investigated.
To that end, we used Neuropixels 2.0 to record across all layers of the MEC of 7 mice while foraging in an open field (OF), then during a virtual reality location memory task (VR), and then back in the open field (A).
We find that around 40% of 8545 MEC neurons are modulated by head direction (HD) in any one OF session, half being so in both (B).
The HD tuning curves are stable, with similar shapes and mean firing rates across OFs (C), and highly correlated HD information and mean vector length (MVL; D-E).
We then trained HD decoders on the OF data such that we can predict the entorhinal HD signal during 1D head-fixed navigation (F-G).
We found a number of sessions where predicted HD in 1D is unimodal, indicative of straight slices (H).