Long-term Potentiation and Neural Coding of Learning, Memory in Rat Hippocampus

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(1) Interaction between place cell activity in rat hippocampal CA1 and low (1Hz) or high (100Hz) frequency electrical stimulation of the Scaffer collaterals was studied. High frequency stimelation impaired both random wandering and spatial navigation tasks, motivated by intracranial self-stimulation as a reward. However, low frequency stimulation did not impair its behaviors. The place cell activity was suppressed by high frequency stimulation and, as a result, the place field disappeared just after the stimulation. Within an hour, the nueronal activity and performance of task were recovered to the control level. However, the place fields recovered were different from the control. Low frequency stimulation on the same electrode also modified place field. These suggest that the place dependency in the CA1 neuron may be implemented through the Schaffer collateral of CA3, and that high or frequency information related to the LTP or LTD might be correlated to the place processing.(2) Lamella hypothesis in rat hippocampus was tested by correlation analysis of two neuronal activities. The two neuronal activities of rat hippocampal CA1 area were simultaneously recorded in an awake and anesthezed state. The normalized cross-correlation values in awake state were smaller than ones of anesthesia state. The complex-spike activity of CA1 pyramidal layr was correlated along septo-temporal axis over 1.1mm apart and showed almost uniform cross-correlation values of 0.02-0.1 in both awake and anesthesia state. These suggest that the neuron in hippocampal CA1 area may connect each other with weak distributed manners.