Constraints and Degrees of Freedom of Representational Drift in the Hippocampal-Entorhinal Network

Hippocampal spatial codes change gradually over days, even in familiar environments, but whether their entorhinal inputs also drift has been unknown. Yaniv Ziv presents two longitudinal calcium-imaging studies asking which components of hippocampal and entorhinal codes drift and which stay fixed. In mice living continuously in a familiar home cage for weeks, CA1 representations of position, head direction and time all drifted, at different rates for different encoded variables, pointing to input-specific rather than purely cell-intrinsic mechanisms, and the drift cannot be explained by changes in behaviour. Imaging hundreds of entorhinal grid cells over weeks showed the population activity on a linear track shifting in phase while keeping its orientation, with grid orientation coupled to head-direction codes. Simultaneous MEC and CA1 recordings showed hippocampal maps staying spatially anchored despite drift in the phase of their grid inputs, challenging models in which hippocampal anchoring is inherited directly from entorhinal grid inputs. Part of the NITMB Seminar Series, which brings mathematicians and biologists together to foster discussion and collaboration between the two fields; talks are held in person at NITMB with the ability to join remotely via the Zoom webinar link on the event page.