失読症における音読と黙読の神経認知基盤の共有と相違：病変部位からの検討

Reading is a fundamental skill for communication, learning, and daily life. Alexia, an acquired reading disorder typically caused by left hemisphere stroke, impairs both oral and silent word reading. However, most research and clinical assessments focus on oral reading. Functional imaging studies in typical readers suggest partly shared and partly distinct neural bases of oral versus silent reading, but this has never been assessed in a lesion study. We examined oral word reading and silent word recognition, measured by a lexical decision task, in 85 chronic left hemisphere stroke survivors (46 males, 39 females), comparing efficiency scores combining speed and accuracy to those of 69 neurologically healthy adults (36 males, 33 females). The stroke group had greater deficits in oral reading than lexical decision. Performance on the two tasks was highly correlated suggesting shared substrates, albeit with considerable unexplained variance. Support vector regression-based lesion-symptom mapping localized lesions associated with deficits in the two tasks. Oral reading deficits were associated with lesions to the superior temporal and supramarginal gyri, and the rolandic operculum after controlling for lexical decision performance. Lexical decision deficits were linked to lesions in angular gyrus, even after controlling for oral reading performance. A novel conjunction analysis found that lesions of angular and middle temporal gyri, extending into ventral occipitotemporal cortex, affected performance on both tasks, suggesting shared neural substrates. These findings suggest that neurocognitive bases of silent reading and reading aloud are partly shared and partly distinct. Alexia assessments should include both silent and oral reading tasks.Significance Statement Silent reading is essential for daily life, but has received less attention than oral reading in research on acquired reading deficits, i.e., alexia. While functional imaging suggests partially distinct activation patterns for oral and silent reading, lesion-symptom mapping offers a critical method for identifying brain regions necessary for task performance. This is the first lesion mapping study to compare oral and silent reading within the same individuals. Using lexical decision as a proxy for silent reading, we found partly shared and partly distinct neural substrates for silent versus oral reading. These findings reveal overlapping but differentially weighted neural systems and underscore the need to assess silent reading alongside oral reading when assessing alexia.