Negative BOLD response to interictal discharges in epilepsy using intracranial EEG-fMRI

Area of Science:

• Neuroimaging
• Epileptology
• Functional MRI

Background:

• Combined electroencephalography and functional magnetic resonance imaging (EEG-fMRI) detects neural activity during interictal epileptiform discharges (IEDs).
• Positive BOLD responses are traditionally used for localizing epileptogenic zones, but negative BOLD responses are less understood.
• The relationship between BOLD responses, epileptogenic tissue, and the default mode network (DMN) requires further investigation.

Purpose of the Study:

• To investigate the spatial relationship between positive and negative BOLD responses to IEDs.
• To assess the association of BOLD responses with epileptogenic tissue and the DMN using intracranial EEG-fMRI.
• To determine the clinical utility of positive versus negative BOLD responses in epilepsy presurgical evaluation.

Main Methods:

• Intracranial EEG-fMRI was performed on 57 adult participants with drug-resistant focal epilepsy.
• BOLD response maps were analyzed to identify maximum positive and negative clusters.
• Linear mixed models assessed distances between BOLD clusters and seizure onset zones; DMN overlap was evaluated in a subset of participants.

Main Results:

• Positive BOLD clusters were significantly closer to IED-generating contacts and seizure onset zones compared to negative BOLD clusters.
• Negative BOLD clusters exhibited greater spatial overlap with the DMN (22.5%) than positive BOLD clusters (10.0%).

Conclusions:

• Positive BOLD responses offer superior localization of epileptogenic tissue in intracranial EEG-fMRI compared to negative responses.
• Negative BOLD clusters' overlap with the DMN suggests they may represent network deactivation during IEDs.
• Prioritizing positive BOLD responses is recommended for clinical decision-making in epilepsy presurgical evaluations.