Functional connectivity of epileptogenic focus: detection and relationship with default mode network

Functional connectivity (FC) analysis with slow brain oscillation as measured by functional MRI has been shown to be useful in elucidating human brain's neural network activity. We examined if epileptogenic focus for the subjects with medically intractable lesion-related epilepsy could be detected by FC analysis. Cortical hub region map was created by calculating each cortical voxel's mean FC (correlation coefficient between the two voxels) to all other cortical voxels. Relatively high cortical hub regions were found around the lesions for all the subjects, which corresponded to the presumptive epileptogenic foci. These hubs had FC with the subcortical regions such as the basal ganglia and the thalamus. For 6 subjects with secondary generalized seizure, the hubs around the lesions had high FC with the ventral part of the posterior cingulate cortex (vPCC). The results suggest the usefulness of cortical hub map for the detection of epileptogenic focus and the networks involved in the propagation of seizure signals from the focus. Further, the FC between the presumptive focus and vPCC suggests that abnormal signal from the focus interferes the normal function of the default mode network even in inter-ictal state.