Goal-directed remapping of enthorhinal cortex neural coding

The medial enthorhinal cortex (MEC) is a core brain region involved in spatial navigation, and provides navigational information to the downstream hippocampus. Neurons in the MEC respond to an animal's location and heading direction in an environment, as well as boundaries and an animals' distance from objects. Other studies have demonstrated that MEC neurons respond to more than navigation, illustrating the flexibility of the region in adjusting response profiles in different contexts. However, it remains poorly understood under what conditions and at what time-scale changes in MEC coding occur, or to what extent these changes are indicative of behavior. In the spatial navigation context, this study sought to examine if MEC neurons reflect trial-wise changes in spatial representations, and how these changes relate to behavior. The experimental paradigm required subjects to navigate to a reward location based on a visual-cue while neurons were recorded from the rat MEC. Firing-rate spatial maps were then compared across Cue and Reward conditions for recorded neurons. Spatial remapping is defined by changes in firing-rate or translation of the spatial location in which a neuron is maximally active (measured by spatial correlation). Results of these analyses reveal Cue induced remapping that exceed what can be expected by trial-wise firing-rate fluctuations in the spatial maps. Furthermore, the extent of remapping on a given session strongly correlated with behavioral performance, the greater the remap the better the subject's performance was on the task. Reward-induced remapping was examined by comparing rewarded and unrewarded trials. We find that most neurons remap due to reward, and that remapping strength correlated with performance on the task. We thus demonstrate that trial-wise response profiles of MEC neurons change within the same environment in a behaviorally and context-dependent manner, computations previously thought to be generated within the hippocampus.