Learning and retrieval of spatio-temporal sequences in the hippocampal network with theta phase precession

Recently it is proposed that theta phase precession contributes to the encoding and memory of the temporal sequence of experience in the hippocampus. By using a hippocampal network model, the potential advantage of theta phase precession on encoding and storage of temporal sequence has been shown in our previous work. But the ability on memory and retrieval for spatio-temporal sequence remains to be elucidated in the sense of not only the temporal order but also the spatial content of experience. In this paper, we try to elucidate such an ability by using the model with theta phase precession. Both long-term potentiation (LTP) and depression (LTD), which is asymmetric with respect to the spike-timing of pre- and postsynaptic neurons, as a biologically plausible rule, are employed in this model. Two conditions are found to be crucial for the storage of spatio-temporal sequences. One is asymmetric synaptic connection, another is input-dependent spatial structure of synaptic connection distribution in the network. Computer experiments show that spatio-temporal sequence can be stored and retrieved in a considerable accuracy. These results suggest that the hippocampus is able to store spatio-temporal sequence which is necessary for the storage of episodic memory.