Coding mechanisms in hippocampal networks for learning and memory

Abstract

The following coding mechanisms in the CA3-CA1 hippocampal networks were examined. Firstly, the way in which the information of the spatio-temporal sequence of the hippocampal CA1 pyramidal cells was clarified by using the patch-clamp recording method. The input-output relations were analyzed by applying "spatial clustering index" and its "self- similarity" (Cantor-like coding) measure of the sequences. The membrane potentials were hierarchically clustered in a self-similar manner to the input sequences. The property was found to be present at one and two time steps retrograde in the sequences. The experimental results closely matched theoretical results of Cantor coding, reported by Tsuda and Kuroda (2001). Secondly, in the consolidation process, the spatiotemporal learning rule (STLR) composed of the spatial coincidence and its time history plays an important role in mapping the Cantor-like property onto synaptic weight space. The coexistence of STLR and Cantor-like coding in single pyramidal neuron of the hippocampal CA1 area is discussed from the viewpoint of coding mechanisms of reinforcement learning. © 2009 Springer Berlin Heidelberg.