Possible role of cooperative action of NMDA receptor and GABA function in developmental plasticity.

The maturation of cortical circuits is strongly influenced by sensory experience during a restricted critical period. The developmental alteration in the subunit composition of NMDA receptors (NMDARs) has been suggested to be involved in regulating the timing of such plasticity. However, this hypothesis does not explain the evidence that enhancing GABA inhibition triggers a critical period in the visual cortex. Here, to investigate how the NMDAR and GABA functions influence synaptic organization, we examine an spike-timing-dependent plasticity (STDP) model that incorporates the dynamic modulation of LTP, associated with the activity- and subunit-dependent desensitization of NMDARs, as well as the background inhibition by GABA. We show that the competitive interaction between correlated input groups, required for experience-dependent synaptic modifications, may emerge when both the NMDAR subunit expression and GABA inhibition reach a sufficiently mature state. This may suggest that the cooperative action of these two developmental mechanisms can contribute to embedding the spatiotemporal structure of input spikes in synaptic patterns and providing the trigger for experience-dependent cortical plasticity.