Negative BOLD Response to Interictal Epileptic Discharges in Focal Epilepsy

Abstract

In EEG-fMRI studies, BOLD responses related to interictal epileptic discharges (IEDs) are most often the expected positive response (activation) but sometimes a surprising negative response (deactivation). The significance of deactivation in the region of IED generation is uncertain. The aim of this study was to determine if BOLD deactivation was caused by specific IED characteristics. Among focal epilepsy patients who underwent 3T EEG-fMRI from 2006 to 2011, those with negative BOLD having a maximum t-value in the IED generating region were selected.As controls, subjects with maximum activation in the IED generating region were selected. We established the relationship between the type of response (activation/deactivation) and (1) presence of slow wave in the IEDs, (2) lobe of epileptic focus, (3) occurrence as isolated events or bursts, (4) spatial extent of the EEG discharge. Fifteen patients with deactivation and 15 with activation were included. The IEDs were accompanied by a slow wave in 87 % of patients whose primary BOLD was a deactivation and only in 33 % of patients with activation. In the deactivation group, the epileptic focus was more frequently in the posterior quadrant and involved larger cortical areas, whereas in the activation group it was more frequently temporal. IEDs were more frequently of long duration in the deactivation group. The main factor responsible for focal deactivations is the Correspondence to: Jean Gotman. Electronic supplementary material The online version of this article

A study of the electro-haemodynamic coupling using simultaneously acquired intracranial EEG and fMRI data in humans

“…the sharp wave width explains additional variance of the BOLD signal amplitude in voxels where a linear combination of the events onsets and widths is positively or negatively correlated with the BOLD signal amplitude. Both IED onsets - related BOLD signal increases and decreases have been reported (Benar et al, 2006, Gotman et al, 2006, Grouiller et al, 2010, Jacobs et al, 2014, Lemieux et al, 2008, Moeller et al, 2009, Pittau et al, 2013, Salek-Haddadi et al, 2006). However, the mechanisms underlying BOLD signal decreases are not completely understood: they may result from (1) neuronal activity decreases (Shmuel et al, 2006) and associated CBF decreases (Carmichael et al, 2008), or (2) neuronal activity increases that lead to tissue oxygen consumption increases that exceed the simultaneous CBF increases, resulting in local deoxyhaemoglobin concentration increases (Schridde et al, 2008).…”

Dysfunction of Neurovascular/Metabolic Coupling in Chronic Focal Epilepsy

“…The IED detection method is similar to those reported in human studies [17,18], as well as animal studies [19,20]. Subsequently, spikes and sharp-waves were separated into multiple sub-types using a series of feature extraction and classification methods described previously [19,20]. Each sub-type of IEDs was considered as a unique event.…”

“…Therefore, conclusions from such acute models should be carefully interpreted, and will require future validations, first in chronic preclinical models of epilepsy and later in epileptic patients. In addition, abnormal increases in the BOLD signal undershoots, in some cases causing an apparent negative BOLD response, have been reported in epileptogenic cortices [17][18][19][20]. This phenomenon has been associated with dysregulations in oxygen metabolisms within epileptogenic cortices.…”

Mapping (and modeling) physiological movements during EEG–fMRI recordings: The added value of the video acquired simultaneously

“…This technique has been largely applied in numerous studies to characterize the hemodynamic correlates of interictal epileptiform activity (IED) (Pittau et al, 2012;Thornton et al, 2011) as well as ictal discharges (Chaudhary et al, 2013(Chaudhary et al, , 2012b and it is employed in the pre-surgical evaluation of refractory focal epilepsy for the localization of the epileptogenic zone (EZ) (Pittau et al, 2013;Zhang et al, 2012). Despite this great success, the sensitivity of EEG-fMRI studies in epilepsy is still limited.…”