"Generating a grid cell: role of recurrent networks within the medical entorhinal cortex" will be presented by Ipshita Zutshi, Postdoctoral Fellow, New York University.

Pizza will be served.

Abstract:

The medial entorhinal cortex (mEC) is a brain region critical for spatial navigation - demonstrated by the presence of specialized cells within the mEC, such as head direction (HD) and grid cells. These location-selective cells are tuned to different aspects of space, for example, grid cells turn on only in selective locations to generate a pattern organized as a hexagon, and HD cells only turn on when the head of an animal is oriented at a preferred angle. It is currently unclear how these neurons located within the mEC generate their tuning properties - several computational models predict that recurrent connections within the mEC are essential for maintaining the hexagonal pattern of grid cells, but HD tuning in the mEC is likely directly inherited from upstream thalamic areas. We addressed whether functional firing is dependent on local mEC circuits by optogenetically activating locally projecting mEC cells and subsequently examining how various functional cell types responded to the perturbation. HD cells were unresponsive to the stimulation, while all other cell types including grid cells were strongly excited and inhibited. Notably, during periods of network inhibition, the accuracy of specifically grid firing also decreased. However, this error constantly self-corrected within a matter of milliseconds, as soon as the firing rates of the local network returned to baseline. These results suggest HD cells are embedded in a separate mEC sub-network from grid cells and receive their tuning properties directly from inputs to the mEC. On the contrary, grid tuning appears to not only be dependent on local processing but is also constantly updated by inputs to the mEC. Together, these results help refine several long-standing theories that model how functional firing might arise within the mEC, while providing the first experimental evidence that recurrent networks within the mEC play a role in grid cell firing.