Abstract
Late-blind humans can learn to understand speech at ultra-fast syllable rates (ca. 20 syllables/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 prerequisites of this skill, diffusion tensor imaging (DTI) was conducted in late-blind subjects differing 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 perceptual skills. Analysis of the diffusion images revealed reduced FA in late-blind individuals relative 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 within right-hemisphere optic radiation and thalamus. Thus, experience-related structural alterations occurred in late-blind individuals within visual pathways that, presumably, are linked to higher order frontal language areas.
Highlights
It is well established that early-blind individuals, i.e., people with congenital blindness or loss of sight soon after birth, show structural changes of the pathways and relay stations of the cerebral visual system [1,2,3,4,5]
Results were exposed at a threshold of p < 0.05, family-wise error (FWE) corrected. doi:10.1371/journal.pone.0122863.t002
The late-blind individuals of the present study showed more or less the same distributional pattern of white matter changes—in terms of Fractional anisotropy (FA) reduction—as the early-blind subjects of preceding investigations, including the optic radiations and thalamus/Pv
Summary
It is well established that early-blind individuals, i.e., people with congenital blindness or loss of sight soon after birth, show structural changes of the pathways and relay stations of the cerebral visual system [1,2,3,4,5]. Cross-Modal Reorganization in Late-Blind Humans and radiations both in early- and late-blind subjects Structural measures appear to predict pitch and melody discrimination abilities at least in early-blind subjects [14,15]. Such morphological changes likely reflect neural degenerative processes subsequent to loss of afferent input and/or the consequences of altered visual experience during sensitive periods of brain development [1]. Besides blindness-induced structural alterations, vision loss may give rise to cross-modal reorganization of the visual system
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