Changes in reliability of synaptic function as a mechanism for plasticity.

Synaptic transmission in the hippocampus is rather unreliable, with many presynaptic action potentials failing to release neurotransmitter. How is this unreliability affected by the alterations in synaptic strength seen in long-term potentiation (LTP) and long-term depression (LTD)? We find that LTP increases synaptic reliability, and LTD decreases it, both without a change in the size of those postsynaptic currents that do occur. Thus LTD is a functional inverse of LTP.