Brain activation in complex partial seizures during switching from a the goal-directed task to a resting state: Comparison of fMRI maps to the default mode network

The default mode network (DMN) has been previously identified as a set of brain regions activated during internally directed cognition. The objective of this study was to investigate patterns of brain activation during switching between a goal-directed task and a rest period obtained from clinical functional magnetic resonance imaging (fMRI) paradigms in complex partial seizures (CPS) and age-matched controls. As part of pre-surgical evaluation with fMRI, a visually presented block-design language task was performed by eight subjects (4 CPS, 4 age-matched controls). Single subject fMRI maps were calculated and transferred into Talairach space for an atlas-based analysis. For the rest state, total volumes of activation, brain regions with largest volume of activation and regions commonly activated in the CPS and the control group were identified. A voxel-by-voxel comparison was conducted to reveal inter-group statistically significant differences. Average volume of activation in the CPS group was significantly higher (32,080 mm3) than in the control group (7,915 mm3, p-value < 0.03). In both groups, most of the common activation volume (81% in the CPS group and 98 % in the control group) was located in cognitive regions of the frontal lobe and temporal lobes as well as anterior cingulate cortex, precuneus and cuneus. The remaining 19% in the CPS group included regions in the precentral gyrus, the superior and medial occipital gyrus, the parahippocampal gyrus, the inferior parietal lobule and the angular gyrus. The voxel-byvoxel comparison showed larger areas of activation mostly in the frontal and temporal lobes in the CPS group (as well as in the cuneus and precuneus), while regions with larger activation in the control group were found mostly in the parietal lobe. Our findings implicate that switching from goal-directed behavior to the default mode in CPS patients is impaired. Information contained in clinical fMRI block-design image data can be used to quantify this impairment.