EEG–fMRI of idiopathic and secondarily generalized epilepsies

Abstract

We used simultaneous EEG and functional MRI (EEG-fMRI) to study generalized spike wave activity (GSW) in idiopathic and secondary generalized epilepsy (SGE). Recent studies have demonstrated thalamic and cortical fMRI signal changes in association with GSW in idiopathic generalized epilepsy (IGE). We report on a large cohort of patients that included both IGE and SGE, and give a functional interpretation of our findings. Forty six patients with GSW were studied with EEG-fMRI; 30 with IGE and 16 with SGE. GSWrelated BOLD signal changes were seen in 25 of 36 individual patients who had GSW during EEG-fMRI. This was seen in thalamus (60%) and symmetrically in frontal cortex (92%), parietal cortex (76%) and posterior cingulate cortex / precuneus (80%). Thalamic BOLD changes were predominantly positive and cortical changes predominantly negative.Group analysis showed a negative BOLD response in the cortex in the IGE group and to a lesser extent a positive response in thalamus. Thalamic activation was consistent with its known role in GSW, and its detection with EEG-fMRI may in part be related to the frequency and duration of GSW epochs recorded. The spatial distribution of the cortical fMRI response to GSW in both IGE and SGE involved areas of association cortex that are most active during conscious rest. Reduction of activity in these regions during GSW is consistent with the clinical manifestation of absence seizures. EEG-fMRI of GSWHamandi K 3

Imaging haemodynamic changes related to seizures: Comparison of EEG-based general linear model, independent component analysis of fMRI and intracranial EEG

“…BOLD decreases have previously been reported in the DMN related to IEDs in temporal lobe epilepsy and generalised epilepsy (Archer et al, 2003;Hamandi et al, 2006) and are thought to reflect suspension of the resting state related to epileptic activity. Cases #1, 2 and 5 had mesial neo-cortical seizures with rapid EEG propagation, and BOLD decreases in the thalamus or basal ganglia.…”

Network Analysis of the Default Mode Network Using Functional Connectivity MRI in Temporal Lobe Epilepsy

“…Such a secondary involvement of the DMN may also be causative for the clinical effects of other conditions affecting the temporal lobe/ limbic system such as schizophrenia 25 and Alzheimer's disease 22,26 . Prior studies have shown DMN involvement in TLE and other forms of epilepsy during seizures, during interictal epileptiform discharges, and in the interictal state 9,[28][29][30][31][32][33] . These studies indicate a potentially important role of the DMN in the interictal electrographic and the ictal behavioral characteristics of TLE.…”

Cluster analysis detection of functional MRI activity in temporal lobe epilepsy

“…In healthy subjects these regions are negatively activated using a task-rest paradigm and are functionally connected at rest and during some passive sensory processing (Greicius et al, 2003). Similarly, these regions have demonstrated primarily negative fMRI activation resulting from epileptic spiking in studies with simultaneous EEG/fMRI in generalized epilepsy (Archer et al, 2003;Salek-Haddadi et al, 2003;Aghakhani et al, 2004;Hamandi et al, 2006;Laufs et al, 2006). Kobayashi et al (Kobayashi et al, 2006b) and Salek-Haddadi et al (Salek-Haddadi et al, 2006) also found negative activation due to EEG spiking in default-mode regions in approximately 12% and 11.1% of focal epilepsy patients, respectively.…”

“…In this group of patients with temporal lobe epilepsy, we focused on temporal lobe activations and concordance with the epileptogenic region. Additionally, default-mode region activation is also reported, considering recent interest in this network (Archer et al, 2003;Salek-Haddadi et al, 2003;Aghakhani et al, 2004;Gotman et al, 2005;Hamandi et al, 2006;Kobayashi et al, 2006b;Laufs et al, 2006;Salek-Haddadi et al, 2006).…”