2010-10-25 at 14:00
UMR 7102 - Neurobiology of Adaptive Processes, University Pierre and Marie Curie, Paris -- VI, Building B, 5th floor, Room 501 (How to come)
Does dendritic processing shape spatial representation in the hippocampus?
Animals are able to update their knowledge about their current position solely by integrating the speed and the direction of their movement, which is known as path integration. Recent discoveries suggest that grid cells in the medial entorhinal cortex might perform some of the essential underlying computations of path integration. However, a major concern over path integration is that as the measurement of speed and direction is inaccurate, the representation of the position will become increasingly unreliable. We set up the model of a mobile agent equipped with the entorhinal representation of idiothetic (grid cell) and allothetic (visual cells) information and simulated its place learning in a virtual environment and we study how allothetic and idiothetic inputs contribute to develop spatial represenatations within the hippocampus. Due to competitive learning, a robust hippocampal place code emerges rapidly in the model. At the same time, the hippocampo-entorhinal feed-back connections are modified via Hebbian learning in order to allow hippocampal place cells to influence the attractor dynamics in the entorhinal cortex. We show that the continuous feed-back from the integrated hippocampal place representation is able to stabilize the grid cell code and account for experience-dependent rescaling of entorhinal grids. However, this simple model is not able to generate multiple, independent place fields characteristic for hippocampal granule cells or to reproduce the independent spatial maps after global remapping. We argue that active dendritic processing or interactions between multiple hippocampal subfields are required to explain these more complex phenomena.