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The structural disconnection model of reading-evidence from patients with alexia
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Poster B58 in Poster Session B, Friday, October 25, 10:00 - 11:30 am, Great Hall 4
Qingchun WANG1, Lu YU2, Fang WANG2, Yang LIU2, Xinjun WANG*2,3, Wai-Ting SIOK*1; 1The Hong Kong Polytechnic University, Hong Kong SAR, China, 2The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou University, Zhengzhou, China, 3The Third Affiliated Hospital of Zhengzhou University, Zhengzhou University, Zhengzhou, China
Alexia is an acquired reading disorder, which typically results from neurological diseases. The neuroanatomical characteristics of alexia indicate abnormalities in cortical and subcortical regions or interruption of structural connectivity in the reading system. Recently, the diffusion magnetic resonance imaging (MRI) technique with advanced algorithm has identified several major white matter tracts to support successful reading, including the arcuate fasciculus (AF), inferior longitudinal fasciculus (ILF) inferior frontal-occipital fasciculus (IFOF), and vertical occipital fasciculus (VOF). Yet, the modern understanding of the structural disconnection model of atypical reading has not been examined on brain damaged patients with pure alexia, owing to these cases are rare in clinical settings. Here, we present two cases with pure alexia resulting from hypoxic-ischemic brain damage. Both patients are right-handed, well-educated Mandarin speakers with no previous neurological or psychiatric disorders. Behavioral assessments and neuroimaging were used to examine the disconnection structural model of reading. Language abilities and related cognitive functions of the patients were measured by multiple behavioral tasks. To examine the neural mechanism underlying the atypical reading system, both patients underwent anatomical and diffusion MRI performed by a 3.0 T Philips Ingenia scanner. Ten healthy participants matched in gender, age, and education served as controls. Language related cognitive functions including visuospatial ability and memory were assessed with standardized neuropsychological batteries. Language evaluations included aphasia screening, reading ability tests (single word identification, words identification, phonological awareness, and orthographic awareness) and handwriting ability tests. Initial neuroimaging assessments including computed tomography (CT) and MRI exhibited a similar pathological pattern in both patients, which revealed bilateral structural abnormalities such as degeneration and atrophy of the cortical and subcortical regions. Using Voxel-Based Morphometry (VBM) and the Computational Anatomy Toolbox (CAT12), we observed anatomical brain features. Diffusion metrics reflecting white matter integrity were extracted for target fiber pathways (AF, ILF, VOF, IFOF). Patients received lower scores in visual perception, praxis and visuomotor construction compared to the normative ranges, but memory tasks suggested intact memory function. In reading tasks, patients scored significantly lower than controls in single character identification, word identification, and component search (p < 0.001, one-tailed). No significant differences were found in syllable deletion and tone judgment tasks. Handwriting performance was also significantly worse in patients compared to controls (p < 0.001, one-tailed). Gray matter atrophy was most obvious bilaterally in the middle occipital gyrus, superior occipital gyrus, inferior parietal lobule, fusiform gyrus, superior temporal gyrus, middle temporal gyrus, and inferior temporal gyrus. White matter atrophy was relatively less severe, involving tissues underneath the parahippocampal gyrus, middle occipital gyrus, fusiform gyrus and inferior temporal gyrus bilaterally. Patients exhibited significant lower FA values in all selected white matter tracts (p < 0.01) compared with controls. Our findings highlight the relationship between visual perception and reading based on the behavioral patterns of patients with pure alexia. Neuroimaging revealed interruptions in anatomical connections and cortical computations, underscoring the importance of white matter integrity and cortical structures in reading. This study provides valuable insights into the neural mechanisms underlying reading disorders.
Topic Areas: Disorders: Acquired,