Memory on a chip

The rat hippocampal neurons were cultured on a dish with 64 planer micro electrodes array. Neurons reorganized a functional network, and an external inputs form outer world elicited a reproducible, particular spatiotemporal pattern of evoked action potentials. The patterns were not completely uniform for repeptive stimulation but varied slightly. We previously reported that dissociated rat hippocampal neurons possessed hysterical function in its network dynamics. The spatio-temporal electrical activity of the living neuronal network evoked by paired stimulation is quite different from one evoked by a single stimulation, suggested that the network can “memorize” an existence of precedent stimulation. In this report, the feature of this type of network hysteresis was investigated and the hysteresis was kept for at least 1s and not kept for 10s. In addition, this hysteresis was remarkable only in aged cultures with matured complex network. Network hysteresis depends on internal state of the network, generated by the autonomous activity in self-organized networks.