"Our results show that visual experience differently activates intracellular signaling pathways that control gene expression in the visual cortex of juvenile and adult mice, and that this developmental downregulation could regulate the developmental reduction of plasticity occurring in the adult visual cortex," concluded Pizzorusso and colleagues. They also concluded that the closure of the critical period was associated with a decrease in the ability of visual experience to drive the histone modifications that are necessary for neural rewiring.
The researchers concluded that the mechanism they discovered "might be important for plasticity in the visual cortex during the critical period, and its downregulation could be involved in the closure of the critical period."
They wrote that "Thus, multiple molecular mechanisms acting at different levels—extracellularly, on the cell membrane, and intracellularly—might contribute to the developmental downregulation of plasticity occurring in coincidence with the closure of the critical period."