UNSPECIFIC LONG-TERM POTENTIATION CAN EVOKE FUNCTIONAL SEGREGATION INA MODEL OF AREA-17

IT has been shown recently in rat hippocampus that the synapse specifi city of Hebbian long-term potentiation breaks down at short distances (<100 mu m). Using a neural network model we show that this unspecific component of long-term potentiation can be responsible for the robust formation and maintainance of cortical organization during activity-d riven development. When the model is applied to the formation of orien tation and ocular dominance in visual cortex, addition of an unspecifi c component to standard Hebbian learning, in combination with a tenden cy of left-eye and right-eye driven synapses to initially group togeth er on the postsynaptic neuron, induces the simultaneous emergence and stabilization of ocular dominance and of segregated, oriented ON/OFF s ubfields. Since standard Hebbian learning cannot account for the simul taneous stabilization of both structures, unspecific LTP thus induces a qualitatively new behaviour. Since unspecific LTP only acts between synapses which are locally clustered in space? our results imply that details of the local grouping of synapses on the dendritic arbors of p ostsynaptic sells can considerably influence the formation of the cort ical functional organization at the systems level. (C) 1998 Lippincott Williams & Wilkins.