Along-the-tract analysis of white matter integrity in congenital cataract reversal individuals
Poster No:
2068
Submission Type:
Abstract Submission
Authors:
Jordan Hassett1, Cordula Hölig1, Sunitha Lingareddy2, Ramesh Kekunnaya3, Brigitte Röder1
Institutions:
1University of Hamburg, Hamburg, Germany, 2LUCID Medical Diagnostics, Hyderabad, India, 3L V Prasad Eye Institute, Hyderabad, India
First Author:
Co-Author(s):
Introduction:
Individuals born with dense bilateral cataracts, for whom sight was restored later in life, provide a unique opportunity to explore the impact of early visual experience on the development of the human brain. Diffusion MRI can be used to compute metrics that approximate white matter microstructure: Fractional anisotropy (FA) measures the fraction of diffusion that is directional, while mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD), measure the magnitude of diffusion directionally averaged, perpendicular, and parallel to fiber tracts, respectively. Impaired white matter integrity has been associated with increased MD and RD, and decreased FA and AD. We assessed white matter integrity in a sample of 20 congenital cataract reversal individuals (CC) using along-the-tract analysis of major visual white matter tracts. We additionally assessed three control groups: 8 permanently congenitally blind individuals (CB), 11 individuals with reversed later-onset cataracts (developmental cataract reversal individuals (DC)), and 24 age- and sex-matched typically sighted controls (SC). All participants were recruited at the L V Prasad Eye Institute (LVPEI) in Hyderabad, India. Given the importance of visual experience in supposed 'sensitive periods' of early development, we expected tensor metrics to reflect a persisting impairment in white matter integrity in CC individuals compared to SC. However, considering the observed functional recovery in CC individuals, though limited, we hypothesized that sight restoration can lead to white matter plasticity in visual tracts and thus structural recovery. We expected this to be exemplified by differences between CC and CB individuals.
Methods:
Diffusion MRIs were acquired on a 1.5T GE Signa scanner (55 slices, 2.5mm slice thickness). Using MRTrix (https://www.mrtrix.org/), images were processed and tensor metrics (FA, MD, RD & AD) were calculated. Nine visual tracts and seven non-visual control tracts (listed in figure 1 caption) were segmented with TractSeg (Wasserthal, Neher & Maier-Hein, 2018). Each tract was sampled at 98 points (100 – 2 end segments) along the length of the tract, and mean FA, MD, RD & AD were extracted at each point. Group means were compared for each segment using independent two sample t-tests. Multiple comparisons correction was performed by calculating a cluster size threshold. A maximum-cluster-size distribution was generated using 10,000 permutations to calculate the maximal number of consecutive segments within a tract that demonstrated significant (p < 0.05) group differences. Observed clusters exceeding the threshold set at the 99.9th percentile of this distribution were considered significant, resulting in a type 1 error rate of 0.001.
Results:
Tensor metrics exhibited significant group differences for visual tracts while, as expected, hardly any differences were observed in non-visual tracts (Figure 1). CB individuals showed decreased FA and increased MD and RD compared to matched SC individuals. CC individuals also demonstrated higher MD and RD values than matched SC individuals, but these were less spatially extensive than those observed in CB individuals, and only a few segments had reductions in FA (supported by a direct comparison of CC to CB individuals showing increased FA, and decreased MD and RD for the CC group). DC individuals exhibited decreases in FA and increases in MD, RD and AD compared to SC individuals as well, but diffusivity differences were primarily in early-visual tracts (optic radiation and splenium).
Conclusions:
Our results replicate findings in congenitally blind individuals, showing impaired white matter microstructure in visual tracts (Anurova et al., 2019). Despite some remaining white matter impairments, after cataract removal surgery these were largely reduced in extent. Thus, the present results suggest impressive white matter plasticity following sight restoration.
Learning and Memory:
Neural Plasticity and Recovery of Function
Modeling and Analysis Methods:
Diffusion MRI Modeling and Analysis 2
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
White Matter Anatomy, Fiber Pathways and Connectivity
Perception, Attention and Motor Behavior:
Perception: Visual 1
Keywords:
Plasticity
Tractography
Vision
White Matter
WHITE MATTER IMAGING - DTI, HARDI, DSI, ETC
Other - Tractometry; Visual Deprivation; Sight Restoration
1|2Indicates the priority used for review
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2. Wasserthal J. (2018). TractSeg – Fast and accurate white matter tract segmentation. NeuroImage, 183, 239-253. https://doi.org/10.1016/j.neuroimage.2018.07.070