Denis Alevi: Memory transformations in a mechanistic model of systems memory consolidation

BCCN Berlin and TU Berlin

 

Abstract

Systems memory consolidation describes the process of transferring and transforming initially hippocampus-dependent declarative memories into stable representations in the neocortex. Experimental evidence indicates that neural replay during sleep is linked to this process. While multiple phenomenological theories of systems memory consolidation have been proposed over the last decades, a consensus has not been found and most importantly, a mechanistic theory on the level of neurons and synapses is missing.

Recently it has been suggested that systems memory consolidation could arise from Hebbian synaptic plasticity in networks with parallel synaptic pathways. It has been shown in computational models that this circuit mechanism – which is widely encountered throughout the brain – can account for the transfer of memories from the hippocampus to  neocortex.

In this thesis, the functional consequences of the proposed mechanism are investigated with respect to their memory transforming properties. By implementing the proposed circuit in artificial neural networks, it is shown that it can account for the forgetting of episodic detail and the extraction of semantic memories from episodic experiences. Hereby, neural replay enhances the speed of consolidation and can in certain situations be necessary for the extraction of semantic memories. The results suggest that this is specifically the case for the extraction of semantic memories from an initial fast learning hippocampal system. Further, the simulation results suggest the existence of spatial gradients of episodic and semantic memories when implementing full consolidation from hippocampus to neocortex. This leads to the hypothesis that episodic memories quickly loose episodic detail with distance from the hippocampus while semantic memory content gradually increases. Consequences of the proposed mechanism for the trace transformation theory of systems consolidation are discussed and explanations for contradicting experimental observations are suggested.

Organized by

Henning Sprekeler / Robert Martin

Location

BCCN Berlin, lecture hall, Philippstr. 13 Haus 6, 10115 Berlin