Neuroimaging Evidence of Structural and Functional Brain Plasticity After Sight Onset Late in Childhood
(RSNA 2018, Mon Nov 26 2018 3:00PM – 3:10PM ROOM Z21)
Direct data from human subjects on the validity of the “critical period” of brain development and the permanent detrimental impact of sensory deprivation during this period is lacking. We present evidence for neural plasticity in congenitally blind children following sight restoration.
METHOD AND MATERIALS
Pre- and post-treatment scans of 15 participants (8 to 24 years) who had been treated for bilateral congenital blindness were done on a 3.0T MRI (750w, GE Healthcare) using a 32 channel brain coil. A high-resolution T1-weighted fast spoiled gradient echo anatomical scan was acquired for each participant. To measure blood oxygen level dependent (BOLD) contrast, 35 slices parallel to the AC/PC were acquired using standard T2 weighted gradient-echo echoplanar imaging. A diffusion-weighted scan (40 direction + 5 b0; 74.4 ms TE; 13.7s TR; 2×0.86×0.86 mm3; FOV: 256 x 256 x 72; b = 1000 nm/s2) was performed for diffusion tensor tractography.
Using functional connectivity analyses, we find marked changes in the functional organization of the visual cortex. There is a significant enhancement of cortical decorrelation as a function of time following sight onset. The fusiform facial area (FFA) and occipital facial area (OFA) develop rapidly. Structural imaging demonstrates increase in both volume and thickness of grey matter compared to controls, especially in the fusiform. Analysis of the optic tract in the same participants revealed no change in mean diffusivity (MD) and fractional anisotropy (FA) during the post-treatment period, while the FA of the optic radiation decreased steeply over 2 years.
Contrary to our expectation of limited neural plasticity late in the developmental timeline, we find strong evidence of brain malleability using both functional and structural imaging. Our findings help explain the behaviourally observed gains in visual proficiency congenitally blind individuals exhibit as a function of time after sight restoring surgery.
Our study presents evidence for brain plasticity and hence opens up treatment avenues for conditions such as late-diagnosed congenital blindness.