Networks involved in seizure initiation. A reading epilepsy case studied with EEG-fMRI and MEG.

OBJECTIVE: To define the ictal cortical/subcortical network of reading-induced seizures. METHODS: We analyzed ictal magnetoencephalography (MEG) and EEG-correlated fMRI (EEG-fMRI) data in a unique patient with reading epilepsy (RE) affected by frequent perioral reflex myocloni triggered by reading silently. RESULTS: Ictal MEG corroborated EEG localization and revealed activity extending precentrally into Brodmann area (BA) 6. fMRI blood oxygen level-dependent (BOLD) signal changes in the left deep piriform cortex (PFC) and left BA6 preceded seizures and occurred before BOLD changes were observed in thalamus and right inferior frontal gyrus (BA44). Dynamic causal modeling provided evidence of a causal link between hemodynamic changes in the left PFC and reading-evoked seizures. CONCLUSION: Our findings support the important role of deep cortical and subcortical structures, in particular the frontal PFC, as key regions in initiating and modulating seizure activity. In our patient with RE, BA6 appeared to be the area linking cognitive activation and seizure activity.

EEG-fMRI of idiopathic and secondarily generalized epilepsies.

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. GSW-related 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 in individual cases with EEG-fMRI may in part be related to the number 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.

The MR detection of neuronal depolarization during 3-Hz spike-and-wave complexes in generalized epilepsy.

Previously, an analysis of activations observed in a patient with idiopathic generalized epilepsy using electroencephalogram-correlated functional magnetic resonance imaging (MRI) during runs of 3-Hz generalized spike-wave discharge (GSWD) was presented by Salek-Haddadi. Time-locked, bilateral, thalamic blood oxygenation level-dependent increases were reported to be accompanied by widespread, symmetric, cortical deactivation with a frontal maximum. In light of recent investigations into MRI detection of the magnetic field perturbations caused by neuronal current loops during depolarization, we revisited the analysis of the data of Salek-Haddadi as a preliminary search for a neuroelectric signal. We modeled the MRI response as the sum of a fast signal and a slower signal and demonstrated significant MRI activity at a time scale of the order of 30 ms associated with GSWDs. Further work is necessary before firm conclusions may be drawn about the nature of this signal.

Combined functional MRI and tractography to demonstrate the connectivity of the human primary motor cortex in vivo.

In this study, we combined advanced MR techniques to explore primary motor cortex (M1) connectivity in the human brain. We matched functional and anatomical information using motor functional MRI (fMRI) and white matter tractography inferred from diffusion tensor imaging (DTI). We performed coregistered DTI and motor task fMRI in 8 right-handed healthy subjects and in 1 right-handed patient presenting with a left precentral tumour. We used the fast-marching tractography (FMT) algorithm to define 3D connectivity maps within the whole brain, from seed points selected in the white matter adjacent to the location of the maximum of fMRI activation. Connectivity maps were then anatomically normalised and analysed using statistical parametric mapping software (SPM99) allowing group comparisons (left versus right hemisphere in control subjects and patient versus control subjects). The results demonstrated, in all control subjects, strong connections from M1 to the pyramidal tracts, premotor areas, parietal cortices, thalamus, and cerebellum. M1 connectivity was asymmetric, being more extensive in the dominant hemisphere. The patient had differences in M1 connectivity from the control group. Thus, fMRI-correlated DTI-FMT is a promising tool to study the structural basis of functional networks in the human brain in vivo.

Functional magnetic resonance imaging of human absence seizures.

We studied a patient with idiopathic generalized epilepsy and frequent absences, using electroencephalogram-correlated functional magnetic resonance imaging. Four prolonged runs of generalized spike-wave discharge occurred during a 35-minute experiment. Time-locked activation was observed bilaterally within the thalami in conjunction with widespread but symmetrical cortical deactivation with a frontal maximum. We demonstrate the reciprocal participation of focal thalamic and widespread cortical networks during human absence seizures and suggest reductions in cortical blood flow, in response to synchronized electroencephalogram activity.