Structural and effective brain connectivity in focal epilepsy.

Area of Science:

• Neuroscience
• Medical Imaging
• Computational Biology

Background:

• Epilepsy surgery traditionally targets localized epileptogenic zones.
• Viewing epilepsy as a network disease necessitates patient-specific network analysis.
• Developing network-based surgical strategies requires detailed insight into individual epileptic brain networks.

Purpose of the Study:

• To investigate the relationship between structural and effective brain connectivity in epilepsy surgery candidates.
• To assess the overlap between non-invasively measured structural connectivity and invasively measured effective connectivity.
• To evaluate the potential of combining these connectivity measures for improved understanding and surgical planning in epilepsy.

Main Methods:

• Diffusion-weighted imaging (DWI) and intracranial EEG with single pulse electrical stimulation (SPES) were used in 13 epilepsy surgery candidates.
• Structural connectivity was reconstructed using fiber tractography.
• Effective connectivity was derived from SPES cortico-cortical evoked responses.
• Inter-modal similarity was quantified using the Jaccard index, and network topologies were compared using centrality measures.

Main Results:

• A moderate overlap (median Jaccard index of 0.25) was found between structural and effective connectivity, significantly higher than chance.
• Structural connectivity degree positively correlated with effective connectivity degree in 9/13 patients and at the group level.
• Seizure onset zone and electrode contact area volume did not significantly predict the structural-effective connectivity correlation.

Conclusions:

• There is a moderate overlap between non-invasive structural and invasive effective connectivity in epileptic brain networks.
• These findings support the use of non-invasively acquired connectivity data alongside intracranial EEG for understanding the epileptic brain.
• Further research is needed to translate these network insights into effective, network-based surgical strategies for epilepsy.