Neural ensemble interactions underlying memory consolidation

Abstract

Episodic memory formation and spatial navigation are core functions of the hippocampus. Embedded in a path integration based navigational system, the hippocampus generates orthogonal codes for different environments. To separate events within the same spatial map, the magnitude of individual place cell firing is modulated by external sensory information. The rate differences are also expressed to separate different running directions within an environment. Previous work suggested that the maps can be perturbed by external cues, but that the rate perturbations are not associatively stored. The present result shows that the rate code is reinstated offline and thus likely associatively stored, which fits well with the theory that describes the hippocampus as generating an index code for episodic memories to assist in retrieval of distributed information stored in the cortex. Lastly, this thesis addresses the methodological challenges of current electrophysiological techniques in detecting excitatory local connectivity on the example of the prefrontal cortex.