Multi-modal connectome analysis of the stereoelectroencephalography implantation effect: a case report.

Stereoelectroencephalography (SEEG) may induce seizure reduction in some patients, known as the implantation effect, but its network mechanism remains unclear. We investigated whether SEEG electrode insertion is associated with measurable brain network reorganisation using longitudinal multi-modal analysis. We studied a patient with drug-resistant right temporal lobe epilepsy who experienced seizure reduction after SEEG implantation and subsequently underwent anterior temporal lobectomy, achieving ILAE class 1a seizure freedom at 6-month follow-up. Structural connectivity from diffusion MRI, resting-state functional connectivity and intracranial EEG connectivity were analysed longitudinally. Connectome gradients were computed using diffusion map embedding, and resected tissue was examined histopathologically. Multi-modal analysis showed convergent connectivity changes after SEEG implantation: decreased hippocampus-amygdala connectivity, decreased fusiform gyrus-temporal pole connectivity and increased hippocampus-posterior cingulate connectivity. Diffusion MRI gradient analysis showed eccentricity reduction of 11.9% after SEEG and 17.6% after lobectomy, consistent with greater network integration. SEEG connectivity showed reduced limbic synchronisation between days 3 and 7 of monitoring. Histopathology demonstrated lymphocytic infiltration and reactive gliosis around electrode trajectories, consistent with chronic inflammation. SEEG implantation was associated with limbic disconnection, enhanced hippocampus-posterior cingulate connectivity and partial normalisation of connectome topology. The convergent findings suggest that electrode-induced micro-lesions may produce network-modifying effects that contribute to the implantation effect.