Thursday 26th October 2017
Ground Floor Seminar Room
25 Howland Street, London, W1T 4JG
Space and time in the entorhinal cortex
The medial entorhinal cortex is part of a neural system for mapping of self-location. One of the first components to be detected in this internal map was the grid cell. Grid cells fire electric impulses when animals are at particular locations that together tile the environment in a periodic hexagonal pattern. Today the entorhinal space circuit is known to embody a spectrum of functional cell types, including head direction cells, speed cells, and border cells - all intermingled among the grid cells. All of these cell types were discovered in simple featureless environments where the animal’s behaviour changes little over the course of the experiment. In this lecture, I will show that additional features of experience are expressed in entorhinal cells when the complexity of the environment is increased. First, I will show that in large environments, grid cells may develop sub-maps that anchor to different boundaries of the environment and then reorganize to establish spatial periodicity at the transition between the map fragments. I will further show that when spatial behavior is tested in environments with salient objects or landmarks, a new subset of medial entorhinal cells fires in a vector-like manner at distinct distances and directions from objects inserted in the recording enclosure, irrespective of where in the enclosure the object is located, and irrespective of the identity of the object. I will discuss possible roles of inhibitory networks in the entorhinal representation of space and show that different functional cell types may be regulated by distinct classes of GABAergic interneurons. Finally, I will show that temporal information is robustly encoded across a time scales from seconds to tens of minutes within the overall population state of entorhinal cortex, particularly in the lateral entorhinal cortex, during free behavior. When entering the hippocampus, time-stamped information from lateral entorhinal circuits may be efficiently stored into episodic memory.