Functional MRI Activation Pattern in Runs of Focal and Generalized Spike Wave Discharges

Using fMRI correlated with simultaneous and continuous registration of electroencephalography (EEG/fMRI), we analyzed regional changes in blood oxygen level-dependent (BOLD) activity in association with spontaneous focal interictal spikes and generalized spike and waves in two epileptic patients. Patient 1 had newly diagnosed symptomatic focal seizures caused by an astrocytoma WHO Grade II in the right frontal lobe and the right thalamus. Patient 2 suffered from idiopathic generalized epilepsy with frequent absence seizures (GWSD). A 32-channel MR-compatible EEG was recorded continuously inside a 3 T MR scanner. Gradient EEG artefacts were subtracted, image pre-processing and statistical analyses were performed using SPM2. Finally, an event-related model was generated. In patient 1, only runs of spikes showed significant BOLD signal changes, there was no correlation between individual spikes and BOLD signal changes. Brain areas with highest significant (p<0.001 uncorrected) negative correlations were observed in regions adjacent to the brain tumor and in right frontal and temporo-parietal regions. On the left side less significant deactivation in the corresponding regions was observed. In patient 2, highly significant (p<0.001 uncorrected) negative correlations were observed bilaterally in frontal, temporo-parietal and retrosplenial areas. These frontal and parietal cortical areas have often been considered to be attention modulation areas. A functional hypothesis of this „deactivation“ pattern related to interictal epileptiform discharges (IED) is that runs of IED (but not isolated IED) are associated with a decreased attentional level. Therefore, we conclude that deactivation of frontal and temporo-parietal cortices are possibly an fMRI-signature of transient cognitive impairment during prolonged generalized and focal IED.