Epileptic Discharges Affect the Default Mode Network – fMRI and Intracerebral EEG Evidence

Abstract

Functional neuroimaging studies of epilepsy patients often show, at the time of epileptic activity, deactivation in default mode network (DMN) regions, which is hypothesized to reflect altered consciousness. We aimed to study the metabolic and electrophysiological correlates of these changes in the DMN regions. We studied six epilepsy patients that underwent scalp EEG-fMRI and later stereotaxic intracerebral EEG (SEEG) sampling regions of DMN (posterior cingulate cortex, Pre-cuneus, inferior parietal lobule, medial prefrontal cortex and dorsolateral frontal cortex) as well as non-DMN regions. SEEG recordings were subject to frequency analyses comparing sections with interictal epileptic discharges (IED) to IED-free baselines in the IED-generating region, DMN and non-DMN regions. EEG-fMRI and SEEG were obtained at rest. During IEDs, EEG-fMRI demonstrated deactivation in various DMN nodes in 5 of 6 patients, most frequently the pre-cuneus and inferior parietal lobule, and less frequently the other DMN nodes. SEEG analyses demonstrated decrease in gamma power (50–150 Hz), and increase in the power of lower frequencies (<30 Hz) at times of IEDs, in at least one DMN node in all patients. These changes were not apparent in the non-DMN regions. We demonstrate that, at the time of IEDs, DMN regions decrease their metabolic demand and undergo an EEG change consisting of decreased gamma and increased lower frequencies. These findings, specific to DMN regions, confirm in a pathological condition a direct relationship between DMN BOLD activity and EEG activity. They indicate that epileptic activity affects the DMN, and therefore may momentarily reduce the consciousness level and cognitive reserve.

The relation between cortisol and functional connectivity in people with and without stress‐sensitive epilepsy

“…A comparable relationship was absent in non-stress-sensitive subjects might be the change in functional connectivity that facilitates IED. [38][39][40][41] Furthermore, a relationship between changes in EEG network topology and the IED frequency was found. 41 Whether IEDs in turn affect functional connectivity is under debate.…”

Abnormal Baseline Brain Activity in Patients with Pulsatile Tinnitus: A Resting-State fMRI Study

“…The direct relationship between the sLORETA analysis results and the BOLD signal remains unclear. Direct relationship between fMRI signal and EEG activity was reported in a study [64]. There is also some resting-state studies reporting that EEG is not directly linked to the changes in neural activity as measured by BOLD fMRI [65, 66].…”

Slow Activity in Focal Epilepsy During Sleep and Wakefulness

“…43 Invasive studies are concordant with this line and show that the epileptic focus modulates brain activity in remote areas of both hemispheres. 44 The interpretation of the quite diffuse difference during the last sleep cycle might be slightly different ( Figure 2B). This cycle is less stable, and unrecognized intrusions of brief arousal or transitions to REM sleep are common.…”