A CRITICAL WINDOW FOR COOPERATION AND COMPETITION AMONG DEVELOPING RETINOTECTAL SYNAPSES

In the developing frog visual system, topographic refinement of the re tinotectal projection depends on electrical activity. In vivo whole-ce ll recording from developing Xenopus tectal neurons shows that converg ent retinotectal synapses undergo activity-dependent cooperation and c ompetition following correlated pre- and postsynaptic spiking within a narrow time window. Synaptic inputs activated repetitively within 20 ms before spiking of the tectal neuron become potentiated, whereas sub threshold inputs activated within 20 ms after spiking become depressed . Thus both the initial synaptic strength and the temporal order of ac tivation are critical for heterosynaptic interactions among convergent synaptic inputs during activity-dependent refinement of developing ne ural networks.