Proposal of Brain Plasticity Index Based on Navigated Transcranial Magnetic Stimulation: Metric of Functional Displacement for Language Function

Objective: To identify a brain plasticity index (BPI) that accounts for the cortical variation in language function on the basis of preoperative/postoperative navigated transcranial magnetic stimulation (nTMS) mapping. Methods: This was a prospective, monocentric study of preoperative/postoperative nTMS mapping. A Python-based open-source pipeline was created to objectively quantify BPI maps, calculated with 2-dimensional nearest-neighbor interpolation of nTMS points for the 2 hemispheres (right/left). BPI maps registered on the Montreal Neurological Institute neuro-anatomy-atlas. Tumoral segmentation was performed with the BraTS toolkit. Results: Between January 2024 and December 2024, 40 subjects were selected and 41 nTMS procedures (65.8% bilateral) were performed preoperatively/postoperatively. Data for language mapping on 40 patients were analyzed on the basis of the lesion volumes: average: 60.85 cm3 (standard deviation: 66.04 cm3). A subanalysis of 7 high-grade (HGG) and 7 low-grade gliomas (LGG) was then performed. Quantitative analyses: Estimation of BPI values specific for Language function: for patients with HGG, BPI was greater in the left hemisphere (46.07 powered by Editorial Manager and ProduXion Manager from Aries Systems Corporation, in mm). Conversely, for patients with LGG, a greater BPI was found in the right hemisphere (57.58 mm). However, an overall greater BPI value was obtained for HGG (46.70 mm) than for LGG (28.19 mm). Qualitative analyses showed linguistic pathway reshaping from temporoparietal areas to the inferior frontal gyrus. The relationship between BPI and Mini-Mental State Examination showed that for HGG, the greater the BPI, the more difficult cognitive recovery was (R = −0.80). Coherently, for LGG the trend was the same (R = −0.17). The variation in different linguistic components at the Aachen Aphasia test documented that linguistic performance had an average greater value for patients with HGG than LGG, with comparable final recovery (90.67% vs. 90%). Conclusions: Identifying a subject-specific BPI may noninvasively define functional reshaping of corticosubcortical circuits.