Response of hippocampal synapses to natural stimulation patterns

We have studied the synaptic responses in hippocampal slices to stimulus pa tterns derived from in vivo recordings of place cell firing in a behaving r odent. We find that synaptic strength is strongly modulated during the pres entation of these natural stimulus trains, varying 2-fold or more because o f short-term plasticity. This modulation of synaptic strength is precise an d deterministic, because the pattern of synaptic response amplitudes is nea rly identical from one presentation of the train to the next. The mechanism of synaptic modulation is primarily a change in release probability rather than a change in the size of the elementary postsynaptic response. In addi tion, natural stimulus trains are effective in inducing long-term potentiat ion (LTP). We conclude that short-term synaptic plasticity-facilitation, au gmentation, and depression-plays a prominent role in normal synaptic functi on.