BioRxiv Weekend Review: Dealing with Complexity in Patterns of individual variation in visual pathway structure and function in the sighted and blind

When discussing complex systems like brains and other societies, it is easy to oversimplify: I call this Occam's lobotomy.

-- I. J. Good

Our BioRxiv preprint review this weekend is of an article which confirms the complexity of brain structure and its tendency to variation among different persons. The article shows that individual differences rule the type and location of brain adaptations that occur to visual loss, though the directions of that adaptation seem to stay the same for a given visual system variant. Perhaps those adaptations occur differently in different blind individuals because of preexisting individual differences in the affected visual systems. The authors may have found reason to take Good's warning to heart.



Patterns of individual variation in visual pathway structure and function in the sighted and blind

AUTHORS: Karl Aguirre, Ritobrato Datta, Noah Benson, Sashank Prasad, Samuel G Jacobson, Artur V Cideciyan, Holly Bridge, Kate Watkins, Omar H Butt, Alexsandra S Dain, Lauren Brandes, Efstathios Gennatas



Many structural and functional brain alterations accompany blindness. In normally sighted people, there is correlated individual variation in some visual pathway structures. Here we examined if the changes in brain anatomy produced by blindness alter this pattern of variation. We derived eight measures of central visual pathway anatomy from an MPRAGE image of the brain from 59 sighted and 53 blind people. These measures showed highly significant differences in mean size between the sighted and blind cohorts. When we examined the measurements across individuals within each group, we found three clusters of correlated variation, with V1 surface area and pericalcarine volume linked, and independent of the thickness of V1 cortex. These two clusters were in turn relatively independent of the volumes of the optic chiasm and lateral geniculate nucleus. This same pattern of variation in visual pathway anatomy was found in the sighted and the blind. Anatomical changes within these clusters were graded by the duration of blindness, with those subjects with a post-natal onset of blindness having alterations in brain anatomy that were intermediate to those seen in the sighted and congenitally blind. Many of the blind and sighted subjects also contributed BOLD fMRI measures of cross-modal responses within visual cortex, and a diffusion tensor imaging measure of fractional anisotropy within the optic radiations and the splenium of the corpus callosum. We again found group differences between the blind and sighted in these measures. The previously identified clusters of anatomical variation were also found to be differentially related to these additional measures: across subjects, V1 cortical thickness was related to cross-modal activation, and the volume of the optic chiasm and lateral geniculate was related to fractional anisotropy in the visual pathway. Our findings show that several of the structural and functional effects of blindness may be reduced to a smaller set of dimensions. It also seems that the changes in the brain that accompany blindness are on a continuum with normal variation found in the sighted.

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