Generation, elimination and weight fluctuations of synapses in the cerebral cortex

Abstract

Most currently available neuronal network models define learning as changes in the strength of synaptic connectivity (i.e. weight plasticity), with synaptic weights assumed to remain constant in the absence of such learning. However, our recent study on excitatory neuronal networks in the cerebral cortex has revealed that, in addition to activity-dependent plasticity, these networks exhibit intrinsic fluctuations in synaptic weight and widespread spontaneous synapse formation and pruning, with a timecourse on the order of days. Our results indicate a coupling between weight plasticity and spine generation/elimination, and suggest that these mechanisms have complimentary but distinct functions in memory formation and maintenance. Three principles of plasticity in spine synapses are presented here to facilitate construction of a new network model for the cerebral cortex.