A SYNAPTIC BASIS FOR MEMORY STORAGE IN THE CEREBRAL-CORTEX

A cardinal feature of neurons in the cerebral cortex is stimulus selec tivity, and experience-dependent shifts in selectivity are a common co rrelate of memory formation. We have used a theoretical ''learning rul e,'' devised to account for experience-dependent shifts in neuronal se lectivity, to guide experiments on the elementary mechanisms of synapt ic plasticity in hippocampus and neocortex, These experiments reveal t hat many synapses in hippocampus and neocortex are bidirectionally mod ifiable, that the modifications persist long enough to contribute to l ong-term memory storage, and that key variables governing the sign of synaptic plasticity are the amount of NMDA receptor activation and the recent history of cortical activity.