Structural Reorganization Of The Human Brain Cortex After Visual Deprivation Based On Magnetic Resonance Imaging

【Purpose】Early studies have shown that the visual cortex of blind subjects experiences structural reoganization after long term visual deprivation.It is still unkonwn if the visual-related areas outside the occipital cortex also had similar reoganization by visual deprivation;furthermore,it is interested to know the impact of onset of visual deprivation on the structural reorganization of these areas.In present study,we aimed to investigate the influence of visual deprivation with different onset age on the changes in the brain cortical thickness,surface area and cortical volume.We also introduced both linear and nonlinear association model to investigate the relationship between cortical thickness and onset age of visual deprivation,which would provide the neural mechanisms underlying the structural reorganization of these areas.【Subjects and Methods】One hundred and fourty five adult subjects were enrolled in this study,including 18 cases of congenitally blind(without any visual experience),30 cases of early blind(onset age from 1 to12 years old),47 cases of late blind(onset age higher than 12 years old),and 50 cases of normal controls matched for age and sex.Three dimensional T1 weighted imaging of all subjects was collected.Cortical surface was constructed using the standard pipeline of Free Surfer software,and three indexes including the cortical thickness,surface area and cortical volume were calculated based on the gray/white matter surface and pial surface.A general linear model was introduced to compare the inter-group differences in the cortical metrices among the groups.Then brain regions with significant inter-group differences in any cortical metrics were extracted as regions of interest.Paired-wise comparsions of the inter-group differences in cortical metrices of these brain regions were further analyzed.Finally,linear and exponential curve fitting were introduced to investigate the potential associations between the cortical thickness of blind subjects and onset age of visual deprivation.【Results】(1)Compared with the healthy controls,the congenitally blind subjects showed significantly increased cortical thickness in the bilateral primary visual cortex,lingual gyrus and cuneus,and decreased cortical thickness in the bilateral temporal pole and entorhinal cortex.The early blind subjects did not show any statistical changes in the occipital cortex.The late blind subjects demonstrated decreased cortical thickness in the bilateral inferior occipital cortex,lingual gyrus,fusiform gyrus and left cuneus.Both the early and late blind did not show any thickness changes in the temporal pole and entorhinal cortex.(2)Compared with the healthy controls,the congenitally blind subjects demonstrated significantly decreased surface area in the medial occipital cortex,including the primary visual cortex,cuneus,lingual gyrus,and fusiform gyrus,in which the primary visual cortex demonstrated severer surface atrophy than other visual areas,and the late blind showed more extended changes than the congenitally and early blind.(3)Compared with the healthy controls,the blind subjects showed decreased cortical volume in the occipital cortex,and the late blind showed more extended changes than the remaining blind subjects.(4)In the occipital cortex,region of interest-based analyses showed that the congenitally blind subjects had thicker cortical thickness,decreased surface area than the healthy controls.The congenitally blind had higher cortical volume than the remaing blind subjects,while showed no significant differences compared to the healthy controls.The early and late blind showed decreased cortical volume than the healthy controls.(5)In the temporal pole and entorhinal cortex,region of interest-based analysis demonstrated that the cortical thickness of the congenitally blind were significantly thinner than the remaining blind subjects and healthy controls.Besides,the cortical surface did not show any differences among the four groups.The congenitally blind subjects showed significantly decreased cortical volume in the left temporal pole than the late blind and healthy controls.(6)Curve fitting results showed that the exponential model was more robust than the linear model in fitting the association between the cortical thickness and onset age of visual deprivation in both the occipital cortex and temporal pole/entorhinal cortex,indicating that a sensitive period of visual inputs maybe exist during the reorganization of the thickness of these areas.Specifically,in the occipital cortex,the cortical thickness was exponentially decreased along with the onset age of visual depivation,and the cortical thickness reaches stable status that similar with normal subjects at about 1 to 2 years old.In the temporal pole/entorhinal cortex,the cortical thickness was exponentially increased following the onset age of visual deprivation,and the cortical thickness reaches stable at about 2-5 years old.【Summary】After visual deprivation,the cortical structural reorganzation of the brain not only occurs in the occipital cortex,but also in the distal ventral visual stream,such as the temporal pole and entorhinal cortex.The surface area of the occipital cortex is generally atrophied in all blind subjects,indicating axonal degeneration secondary to the impairment of the previsual pathway in the blind.Only the congenitally blind subjects showed increased cortical thickness in the occipital cortex,reflecting a mixure of axonal degeneration,cortical development and experience-dependent plasticity.The thinning in the temporal pole and entorhinal cortex in CB may be mainly driven by the mechanism of experience-dependent plasticity.