Search for dynamic neuronal assemblies underlying memory processes for order information

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(1) For rats, we developed behavioral tasks to see memory for duration or order of presented tone stimuli and trained rats to perform both tasks. The rats acquired both tasks in three weeks. We recorded multi-neuronal activity. from their hippocampal formation during the performance of the tasks.(2) For mice, we developed a behavioral task to see memory for order of presented light stimuli and trained mice to perform the task. Some mice could not fully acquire the task in a long training period and we needed to change parameters of the task to more adequate ones.(3) We developed new techniques, i.e., electrode, head-amp, microdrive, and spike-sorting system, to record and analyze multi-neuronal activity in behaving animals.(4) The most remarkable one of the newly developed techniques is a new method to detect precise sub-millisecond interactions among neurons in freely behaving animals. That is an in vivo electrophysiological technique capable of real-time and automatic sorting of extracellular activity of closely neighboring single-neurons to detect their sub-millisecond interactions. The technique uses a combination of independent component analysis (ICA) and newly developed multi-electrodes, dozentrodes.(5) Up to 10 interacting single-neurons were simultaneously recorded with two dozentrodes implanted in the hippocampal CA1 and CA3 regions and the somatosensory cortex in.the rats.(6) The technique also could detect dendritic backpropagation of action potentials and electrically coupled cells via gap junctions. These results demonstrate that our method can be employed to investigate extremely precise neuronal interactions, as well as the functions of dendritic compartments that underlie learning and motor control in freely behaving animals.