Anna-Lena Stroh¹, Daniel Haenelt², Luke J. Edwards², Fakhereh Movahedian Attar², Kerrin J. Pine², Trampel Robert², Marcin Szwed¹, Nikolaus Weiskopf^2,3,4; ¹Institute of Psychology, Jagiellonian University, ul. Ingardena 6, 30-060 Kraków, Poland, ²Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1a, 04103 Leipzig, Germany, ³Wellcome Centre for Human Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3AR, UK, ⁴Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth System Sciences, Leipzig University, Linnéstraße 5, 04103 Leipzig, Germany

The study of congenitally blind individuals can provide unique insights into how sensory experience shapes the structural organization of the brain. Studies with enucleated macaques have revealed remarkable alterations in the early visual cortex (EVC), including the emergence of new cytoarchitectonic areas. Studying such microscopic alterations in humans has been challenging due to limitations in conventional imaging methods. Thus, human research has primarily relied on coarse measurements, such as cortical thickness. To fully grasp the influence of sensory experience on the structure of the EVC, we need to go beyond conventional imaging methods that lack information about the underlying myelo- and cytoarchitecture. Here, we investigated differences in the myelo- and cytoarchitecture between congenitally blind and sighted individuals in different cortical layers of the EVC and the superficial white matter (SWM). To this end, we used ultra-high spatial resolution multiple parameter mapping (MPM) and diffusion-weighted imaging (DWI) to obtain quantifiable parameters, such as the longitudinal relaxation rate (R1), effective transverse relaxation rate (R2*), proton density (PD), and Magnetization Transfer Saturation (MTsat), as well as axial diffusivity (AD), mean diffusivity (MD), radial diffusivity (RD), apparent fiber density (neurite density index; NDI) and fiber dispersion (orientation dispersion index; ODI). In the gray matter of congenitally blind individuals, we observed reduced R2*, MTsat, and NDI, along with increased AD, MD, and RD. In the SWM, congenitally blind individuals exhibited reduced R2* and NDI, along with increased AD, MD, RD, and ODI. Our findings suggest that a lack of visual input during development results in reduced iron and myelin content in the EVC. Previous studies have suggested that myelination stabilizes neuronal circuits and regulates plasticity during development. Thus, our findings underscore the crucial role of sensory experience in the maturation and stabilization of cortical circuits.