Identification at Parallel Distributed Processing in the Plasticity of Neural Networks by Using on Optical Recording System

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1. We developed a 144-channels optical recording system, by which we succeeded in recording multi-units activities of hippocampal neurons. By using the method, the different LTP of CA1 neurons induced by the temporal pattern stimuli were identified.2. We find that the potentiation depend not only on the frequency of the stimulus, but on the degree of correlation between successive intervals, even when the average frequency of the stimulus set is held constant. This suggests that detailed temporal properties of the stimulus are important factors for inducing LTP, and hence could play a crucial role in learning and memory phenomenan.3. We proposed a mathematical model for the induction of LTP in the CA1 region of the hippocampus based on the physiological data obtained above. The model learning rule is essentially Hebbian in nature in the sense that the amount of the LTP induced increases with frequency of synaptic activation, but it also has a sensitivity on the correlation between inter-stimulus intervals of applied stimulus chain.4. Based on the physiological evidence, we proposed a hypothesis on how association and dissociation of event memories are made in the hippocampal-cortical memory system. It is postulated that association /dissociation of memory is carried out by indexing the representations of events (memory contents) with temporal codes.