fMRI-Based Effective Connectivity in Surgical Remediable Epilepsies: A Pilot Study

Area of Science:

• Neuroscience
• Medical Imaging
• Epilepsy Research

Background:

• Simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) aids in identifying the epileptogenic zone (EZ) in focal epilepsies.
• fMRI maps associated with Interictal Epileptiform Discharges (IED) often display widespread signal changes, complicating precise localization.
• Dynamic Causal Modeling (DCM) estimates effective connectivity from fMRI data, revealing causal interactions between brain regions.

Purpose of the Study:

• To evaluate the utility of DCM applied to fMRI data in localizing the EZ in focal epilepsy patients.
• To assess if DCM can resolve ambiguities in EZ localization arising from multiple IED-related fMRI signal changes.

Main Methods:

• DCM was applied to fMRI data from 10 focal epilepsy patients exhibiting multiple IED-related BOLD signal changes.
• A family of competing DCM models was constructed for each subject, with IEDs serving as the autonomous input at each node.
• DCM findings were compared against presurgical evaluations and validated through intracranial EEG or surgical outcomes.

Main Results:

• The effective connectivity focus identified by DCM was concordant with the presumed EZ in 7 out of 10 patients.
• DCM findings were validated in 4 of the 6 surgically treated patients.
• Discordant and invalidated DCM results were associated with poor surgical outcomes.

Conclusions:

• DCM applied to fMRI data shows preliminary evidence of applicability in investigating epileptic networks in focal epilepsy.
• DCM may be particularly useful for identifying the EZ in complex epilepsy cases with diffuse fMRI signal changes.
• Accurate EZ localization using DCM could potentially improve surgical outcomes in focal epilepsy.