Interictal epileptiform discharge-related BOLD responses in the default mode network and subcortical regions

To examine the blood oxygen level-dependent (BOLD) responses in the default mode network (DMN) and subcortical regions in relation to epileptic events in scalp EEG and intracranial EEG (iEEG).

We retrospectively compared BOLD responses in the DMN and subcortical regions to interictal epileptiform discharge (IED) characteristics of the scalp and iEEG in consecutive patients with focal epilepsy. All voxels were used as the denominator to assess the positive and negative BOLD ratios in each region, and the percentage of voxels with significant activation or deactivation was assessed.

Seventy-one EEG-fMRI studies were included. The widespread IED group showed a higher negative BOLD ratio in the DMN than did the focal IED group. Spike and ripple spreads in iEEG positively correlated with a positive BOLD ratio in the DMN and subcortical regions and a negative BOLD ratio in the DMN. Fast ripple spread showed no correlation with the BOLD ratio in any region.

IEDs affect local regions, as well as distant neocortical (DMN) and subcortical regions, depending on their localization and characteristics.

Our findings showed both positive and negative IED-related BOLD responses in subcortical regions and new evidence of network dysfunction related to focal epileptic activity.