Congenital blindness reduces myelination in human visual cortex

Sensory experience is critical for cortical maturation, but the cellular consequences of its absence remain poorly understood in humans. Using in vivo sub-millimeter 3 T and 7 T MRI and ultra-high-gradient diffusion MRI, we investigated the effects of congenital blindness on the human early visual cortex. Blind individuals showed reduced R₂^* and MT_sat-markers of iron and myelin-along with increased diffusivity, orientation dispersion, and reduced neurite density in the gray and superficial white matter. Cortical thickness was increased in blind individuals and associated with lower myelin and iron, questioning the long-standing assumption that increased thickness primarily reflects disrupted pruning. Our results provide no direct evidence for disrupted pruning. However, they suggest reduced myelination and oligodendrogenesis as key effects of congenital blindness and highlight the critical role of sensory input in shaping and stabilizing cortical circuits.