Structure-function coupling increases during interictal spikes in temporal lobe epilepsy: A graph signal processing study

Objective: Structure-function coupling remains largely unknown in brain disorders. We studied this coupling during interictal epileptic discharges (IEDs), using graph signal processing in temporal lobe epilepsy (TLE). Methods: We decomposed IEDs of 17 patients on spatial maps, i.e. network harmonics, extracted from a structural connectome. Harmonics were split in smooth maps (long-range interactions reflecting integration) and coarse maps (short-range interactions reflecting segregation) and were used to reconstruct the part of the signal coupled (Xc) and decoupled (Xd) from the structure, respectively. We analysed how Xc and Xd embed the IED energy over time, at global and regional level. Results: For Xc, the energy was smaller than for Xd before the IED onset (p <.001), but became larger around the first IED peak (p <.05, cluster 2, C2). Locally, the ipsilateral mesial regions were significantly coupled to the structure over the whole epoch. The ipsilateral hippocampus increased its coupling during C2 (p <.01). Conclusions: At whole-brain level, segregation gives way to integrative processes during the IED. Locally, brain regions commonly involved in the TLE epileptogenic network increase their reliance on long-range couplings during IED (C2). Significance: In TLE, integration mechanisms prevail during the IED and are localized in the ipsilateral mesial temporal regions. (c) 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study investigated the structure-function coupling during interictal epileptic discharges (IEDs) in temporal lobe epilepsy (TLE) using graph signal processing. The results showed that integrative mechanisms prevail during the IED at the whole-brain level, with increased reliance on long-range couplings in the mesial temporal regions. This study is significant for understanding the structure-function relationship in brain disorders.