| Description |
In the developing brain, predetermined patterning shapes early neuronal circuits while a later period of heightened experience-dependent synaptic plasticity refines them. In the visual cortex, there is a brief developmental window known as the ocular dominance critical period when neuronal circuits are sensitive to binocular experience. If one eye has disrupted vision during the critical period, the input from that eye weakens and cannot recover later in life. It is unclear both why experience can drive such plasticity during the critical period but not in adulthood, and what aspects of binocular development require this heightened experience-dependent plasticity. Experience drives activity-dependent gene expression, and one of the first transcribed is Arc, a gene required for many types of neuronal plasticity. Indeed, mice lacking Arc do not have an ocular dominance critical period. Arc seems well-positioned to link experience to plasticity, and we, therefore, hypothesized that Arc protein expression gates binocular developmental plasticity in the visual cortex. We first assessed whether Arc expression changes from development to adulthood. We found that visual experience drives Arc expression during the critical period but not in adult animals. We reasoned that lack of Arc could explain why critical period plasticity is absent in the adult. Using electrophysiology, we measured critical period plasticity following unilateral eye closure in mice overexpressing Arc. We found that these adult mice displayed critical period plasticity similar to juvenile animals. iv Indeed, acute viral overexpression of Arc was sufficient to reopen the critical period. However, it was still unclear if Arc mediated normal experience-dependent binocular development. To examine the development of binocular neurons, we utilized two-photon calcium imaging. We found that few neurons were binocular before the critical period and that early visual experience was required for binocular neurons to emerge and mature. Surprisingly, in the absence of Arc, more binocular neurons emerged. In the adult brain, acutely eliminating Arc expression still led to the appearance of more binocular neurons. Thus, visual experience serves to promote the development of binocular neurons while the experience-dependent transcription of Arc limits their number, potentially to conserve the capacity of the brain for later experience-dependent change |
