Inhibition Found to Be Essential for Brain Development Laboratory for Neuronal Circuit Development Dr. Takao K. Hensch, head of the Laboratory for Neuronal Circuit Development, announced for the first time that the factor controlling a critical period for development of the visual system was the inhibition of sensory signals. In the binocular region of visual cortex (the area that first receives input from both eyes), neuronal circuits are reorganized under the influence of visual experience only during a specific period following birth (the so-called critical period). Importantly, large-scale rewiring does not occur after the critical period. Using a mouse model whose inhibitory transmission was genetically reduced, it was possible to observe circuit reorganization even in adult animals once inhibition was pharmacologically restored. The normal maturation of inhibitory interactions within the brain may allow proper coding of sensory signals for plasticity to occur (cf. Fig.), but only once in life. This revelation has established that inhibition is essential for plasticity of neuronal circuits. The discovery is expected not only to provide new insight into basic brain mechanisms, but also to contribute toward making transplanted tissues function normally and understanding appropriate forms of stimulation for healthy brain development in infants. magnified scene by clicking image Inhibitory threshold for plasticity Fagiolini, M., Hensch, T. K. Inhibitory threshold for critical-period activation in primary visual cortex Nature, 404, pp183-186, 9, March (2000)