The stimulus dependent induction of long-term potentiation in the hippocampal CA1 area identified by the optical imaging method

Long-term potentiation (LTP) in the CA1 area of hippocampus is highly sensitive to the higher order statistical characteristics of the stimulus (correlation between successive pairs of inter-stimulus intervals) (Tsukada, 1990, 1992; Aihara, 1991, 1992). The temporal-pattern sensitivity in LTP was identified in a slice preparation by using the optical imaging method. In this experiment, the authors found that the spatial pattern of LTP in the CA1 area differed depending on the temporal pattern of the stimulus; positively correlated sequences were much more effective (large area) in producing LTP, while negatively correlated sequences were ineffective (small area). The spatial pattern of LTP, was closely related to the position where the repetitive firing of population spikes was evoked during the period of temporal-pattern stimuli. These results suggest that there is a transformation from the temporal pattern into the spatial pattern in the coding process of the hippocampal learning system.