Brain-Inspired Memory Model

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We obtained following results using a hippocampal network model based on the physiological knowledge.1.Stochastic resonance took place in the present hippocampal model. The membrane potential fluctuations in CA1 pyramidal cells caused by complex spatiotemporal activity of the CA3 network works as a subthreshold noise, and a periodic perforant path signal to the CA1 network may be regarded as a subthreshold signal.2.Memory patterns stored as spatial patterns of augmented Shaffer collateral synapses were recalled as activity patterns of the CA 1 network taking advantage of the stochastic resonance.3.LTP was induced in Schaffer collateral synapses by the chaotic response of the CA3 network to a periodic stimulation; the CA3 network caused a delta rhythm spontaneously and Schaffer collateral synapses were modified depending on the Ca^<2+> concentration inside the CA1 pyramidal cells.4.Bimodal distribution of recurrent synaptic conductances was achieved in the CA3 network by STDP. The avera … More ge synaptic weight and the frequency of the rhythmic activity were not altered after the convergence of the distribution even if the spatial distribution of synaptic weights was changed by learning, because LTP and LTD were induced simultaneously in recurrent connections.5.When theta burst stimuli were fed into local sites in the CA3 network, radial propagation of neuronal activity was produced from the stimulus sites due to asymmetric augmentation of the recurrent connections. This radial propagation is regarded as a short-term memory because the propagation is repeated for about 30 s after the termination of stimuli ; the radial patterns of synaptic weight are modified with time by the spontaneous activity of the CA3 network through STDP.6.Neurons in the CA1 network learned temporal sequence of signals fed into the hippocampal model using the radial propagation of neuronal activity in the CA3 network when Schaffer collateral synapses were subject to a STDP rule, besides recurrent synapses in the CA3 network. Less