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Kevin C Chan, Antoinette J. Charles, Ji Won Bang, Giles Hamilton-Fletcher, Carlos Parra, Matthew C. Murphy, Amy C. Nau; Structure and Metabolism in the Brains of the Congenitally Blind Using Magnetic Resonance Imaging and Spectroscopy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4746. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
While recent studies show that blind subjects can recruit the occipital cortex to interact with their visual environment indirectly via their remaining senses, the underlying neural mechanisms remain unclear. In this study, we used magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) to determine the plasticity in the brains of the blind.
Nine congenitally blind and 8 sighted subjects underwent anatomical MRI, diffusion tensor MRI (DTI) and MRS in a 3-Tesla Siemens scanner. The sizes of optic chiasm (OC) and superior colliculus (SC) were measured manually on anatomical MRI using ImageJ; The structural integrity of major white matter tracts was assessed using tract-based spatial statistics in DTI, and the metabolic contents in the occipital cortex were estimated using the Syngo software on the spectra in MRS using creatine (Cr) as an internal control.
In anatomical MRI, congenitally blind subjects had significantly smaller OC than sighted controls, whereas no apparent difference was observed in the SC of either hemisphere (Figure 1A, B). In DTI, congenitally blind subjects also showed significantly lower fractional anisotropy in the optic radiation when compared to sighted subjects (Figure 1C). In MRS, congenitally blind subjects exhibited significantly higher glutamate and glutamine complex (Glx) levels compared to sighted subjects in the occipital cortex (Figure 2).
The current findings suggest the involvements of structural and metabolic brain changes along the central visual pathway in congenital blindness compared to sighted subjects. The structural connections between the eye and the occipital cortex of the congenitally blind appeared compromised, whereas the occipital cortex in the congenitally blind appeared more excitatory due to the stronger glutamatergic function from higher glutamate and glutamine levels compared to sighted subjects.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Figure 1. (A) Illustrations of the OC and SC in anatomical MRI. (B) Group comparisons (mean±SD) of OC and SC sizes. Unpaired t-tests, *p<0.05; (C) Tract-based spatial statistics of significantly lower fractional anisotropy (red/orange) in the congenitally blind than sighted subjects.
Figure 2: (A) Illustrations of spectral quality and voxel localization in the occipital cortex in MRS; (B) Group comparisons (mean±SD) of metabolic ratios in MRS. Unpaired t-tests, *p<0.05.
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