Visual callosal topography in the absence of retinal input

Abstract

Using probabilistic diffusion tractography, we examined the retinotopic organization of splenial callosal connections within early blind, anophthalmic, and control subjects. Early blind subjects experienced prenatal retinal “waves” of spontaneous activity similar to those of sighted subjects, and only lack postnatal visual experience. In anophthalmia, the eye is either absent or arrested at an early prenatal stage, depriving these subjects of both pre- and postnatal visual input. Therefore, comparing these two groups provides a way of separating the influence of pre- and postnatal retinal input on the organization of visual connections across hemispheres. We found that retinotopic mapping within the splenium was not measurably disrupted in early blind or anophthalmic subjects compared to visually normal controls. No significant differences in splenial volume were observed across groups. No significant differences in diffusivity were found between early blind subjects and sighted controls, through some differences in diffusivity were noted between anophthalmic subjects and controls. These results suggest that neither prenatal retinal activity nor postnatal visual experience play a role in the large-scale topographic organization of visual callosal connections within the splenium.

Strain differences of the effect of enucleation and anophthalmia on the size and growth of sensory cortices in mice

“…Although there are several studies on the structural consequences of early loss of sight on the visual brain in humans (Breitenseher et al, 1998;Buchel et al, 1998;Jiang et al, 2009;Noppeney et al, 2005;Pan et al, 2007;Park et al, 2007Park et al, , 2009Ptito et al, 2008), very few offer a direct comparison of early blind with anophthalmic subjects (Bock et al, 2013). This study provides evidence for altered callosal connections in anophthalmic compared to early blind subjects suggesting that the absence of prenatal retinal input can affect the corpus callosum (Bock et al, 2013). This also seems to be the case in anophthalmic ZRDCT mice b r a i n r e s e a r c h 1 5 8 8 ( 2 0 1 4 ) 1 1 3 -1 2 6 (Laramée et al, 2013;Olavarria and van Sluyters, 1984;Rhoades et al, 1984) and in anophthalmic rats (Laing et al, 2012).…”

“…The incidence of anophthalmia in the general population has been estimated at 1.8 in 100,000 (Shaw et al, 2005). Little is known about the neurobiological consequences of anophthalmia in humans (Bock et al, 2013;Bridge et al, 2009;Watkins et al, 2012). A reduced optic tract and lateral geniculate nucleus, no size reduction of the optic radiation and only a slight reduction of the gray matter volume in a small area of the primary visual cortex were reported in a sample of anophthalmic humans (Bridge et al, 2009).…”

Morphometric Changes of the Corpus Callosum in Congenital Blindness

“…The latter region contains small-to-medium sized fibers that mainly connect prefrontal cortical areas [27]. However, two other studies [2], [28] failed to find volumetric changes in the anterior and posterior part of the corpus callosum area in a small and heterogeneous group of early blind and anophthalmic individuals. The discrepancies between these studies may be due to differences in the type of patients, onset of blindness (late versus early versus since birth), sample size and the methodology used to compute brain volumetry.…”

Impact of Early and Late Visual Deprivation on the Structure of the Corpus Callosum: A Study Combining Thickness Profile with Surface Tensor-Based Morphometry

“…The corpus callosum (CC) is a particularly interesting subcortical structure to study in blind individuals (Leporé et al 2010; Bock et al 2013). The CC is the largest fiber bundle in the brain and establishes connections between the hemispheres, and predominantly, but not solely, between the cortical areas (Caleo et al 2013).…”

“…However, Bridge et al (2009) did not find any structural differences within the splenium of anophthalmic subjects. Moreover, a recent study demonstrated that the large-scale topographic organization of visual callosal connections within the splenium (dorsal/ventral and eccentricity mapping) remains unaffected in early blind individuals (Bock et al 2013). This last study therefore suggests that the gross retinotopic organization of visual fibers within the splenium develops and is maintained independently from any pre- or postnatal retinal input, and that changes as a result of blindness in this pathway may occur as white matter connections innervate cortex, rather than within the tracts themselves.…”