Critical Period Plasticity:
Neuronal circuits that process sensory information are shaped by patterns of cellular activity during early brain development called critical periods. The term ‘critical period’ (CP) refers to a specific developmental window during which target systems are sensitive to a specific environmental input. CPs are known to be present in several sensory systems in the brain, such as the barrel representation of whiskers in somatosensory cortex, tonotopic map refinement in auditory cortex and human language acquisition in the Bora’s area but the best-described case is the role of light on the development of the visual system.
Visual cortical circuits exhibit maximal plasticity during the CP and this plasticity is lost by adulthood. This loss of this extraordinary plasticity may reflect sequential locks placed on a molecular pathway as the visual cortex consolidates into a structurally elaborated circuitry. Recently, the critical period in mouse visual cortex has been linked to a specific molecular logic of gene regulation and we propose that epigenetics helps to fine-tune gene activity and their expression essential for defining plasticity. We hypothesize the interaction between environment and epigenetics results in the formation of CP plasticity. Epigenetics is a control system of molecular switches, consisting of histone modifications, microRNA, non-coding RNA and DNA methylation, that help fine-tune to the degree in which a gene is activated or repressed. While the role of epigenetic modifications in brain plasticity has only begun to be understood, the critical period is an ideal model for the study of experience-dependent epigenetic modifications in validating our core hypothesis of environmental-epigenetics interaction.
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