Sentence-level language processing speed in diffuse glioma: lesion location and contralesional structural variability

• Glioma in the left superior temporal gyrus slows sentence processing speed. • Right frontal cortical complexity relates to preserved sentence processing speed. • Lesion burden and cortical complexity show additive effects on processing speed. • The right-hemisphere structural capacity reflects neural reserve in glioma patients. Diffuse gliomas frequently lead to cognitive deficits, including slowed language processing speed at both the lexical and sentence level. Although sentence-level slowing appears to exert the critical influence on linguistic function in this population, the mechanisms underlying this slowing remain even less well characterized. The present study investigated how lesion location and inter-individual differences in brain structure relate to sentence-level language processing speed in patients with diffuse glioma. We assessed sentence-level language processing speed in 28 patients with left hemispheric glioma and compared their performance with that of 20 healthy participants. All participants performed a picture–sentence matching task comprising two sentence structures: an active sentence condition with subject–object–verb word order and a one-argument condition with subject–verb word order. Region of interest-based lesion–symptom mapping was used to identify lesion sites associated with slowed sentence-level processing speed, while surface-based morphometry was applied to assess cortical thickness and fractal dimension across the entire brain. Slowed sentence-level processing was associated with glioma involving the left superior temporal gyrus, indicating disruption of core language-related regions. In contrast, greater cortical complexity in the contralesional right superior frontal gyrus was associated with faster sentence-level processing speed. Multiple regression analyses further revealed that tumor volume in the left superior temporal gyrus and cortical complexity in the right superior frontal gyrus independently contributed to sentence-level processing speed. Together, these findings highlight how tumor-related damage and inter-individual differences in brain structure jointly shape language performance in diffuse glioma, consistent with a neural reserve framework.