Origin of the dual rate- and phase codes of space in the hippocampus and medial entorhinal cortex

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Space is neuronally represented in the hippocampal formation both in the firing rate of place-selective neurons and the spike timing with respect to the local field potential oscillation. A multitude of theoretical models exist, which provide possible mechanistic explanations of both codes in several parts of the hippocampal formation. In this project we analyse data from the laboratory of our collaborator, from animals with either hippocampal or medial entorhinal lesions. Since these two brain areas are connected in a loop, the lesioned animals provide an ideal model system to study the computations occurring in the individual brain areas alone. Preliminary results indicate that the medial entorhinal cortex is particularly important for the timing relations in the hippocampus, whereas, in contrast to current believe, it hardly affects the rate code. Analyzing recordings of medial entorhinal cortex neurons in hippocampus-lesioned animals allow us to refine current theoretical models of grid field formation. Particularly the reduction of place-specific firing asks for a new modeling approach. In this project we will develop a new spike-based model of entorhinal grid cells that will be cross-checked by data from hippocampus-lesioned animals.