Temporal-pattern dependent spatial-distribution of LTP and LTD in hippocampal CA1 area

The spatial distribution of LTP and LTD induced by a temporal-pattern stimuli to Schaffer-commissural-collateral was investigated in the CA1 area of guinea-pig hippocampal slices using the optical-imaging method. (1)It was found that the spatial distribution of LTP depends on the number of stimuli and the amplitude of LTP depends on the frequency of stimuli, from the experiments using Periodic Stimuli with a range of frequencies (1Hz-10Hz) and number. (2)The spatial distribution and amplitude of LTP is highly sensitive to the statistical correlation between successive inter-stimulus intervals, even when their average frequency is held constant, from experiments by using nonperiodic stimuli (Markovian Stimuli). (3)When a temporal-modulated stimulus that sets (packets) consisted of a few pulses of high-frequency are separated by successive pulses of low frequency (five or ten long intervals) were applied, LTP and LTD were simultaneously observed in specific areas in CA1. The area of LTD corresponds to the localized area of pyramidal cell output layer of CA1, which differs from the area (stratum-radiatum) of that induced by low frequency stimulation (1Hz). The resultant LTP/LTD is closely related to the network structure of the CA1 area. The coding mechanism is discussed in the terms of the relation between the stimulus pattern and the network structure.