RESEARCH ARTICLE Experience-Related Structural Changes of Degenerated Occipital White Matter in Late- Blind Humans – A Diffusion Tensor Imaging Study

Late-blind humans can learn to understand speech at ultra-fast syllable rates (ca. 20 sylla-bles/s), a capability associated with hemodynamic activation of the central-visual system. Thus, the observed functional cross-modal recruitment of occipital cortex might facilitate ultra-fast speech processing in these individuals. To further elucidate the structural prereq-uisites of this skill, diffusion tensor imaging (DTI) was conducted in late-blind subjects differ-ing in their capability of understanding ultra-fast speech. Fractional anisotropy (FA) was determined as a quantitative measure of the directionality of water diffusion, indicating fiber tract characteristics that might be influenced by blindness as well as the acquired perceptu-al skills. Analysis of the diffusion images revealed reduced FA in late-blind individuals rela-tive to sighted controls at the level of the optic radiations at either side and the right-hemisphere dorsal thalamus (pulvinar). Moreover, late-blind subjects showed significant positive correlations between FA and the capacity of ultra-fast speech comprehension with-in right-hemisphere optic radiation and thalamus. Thus, experience-related structural alter-ations occurred in late-blind individuals within visual pathways that, presumably, are linked to higher order frontal language areas