Spatio-temporal imaging of focal interictal epileptiform activity using EEG-triggered functional MRI

EEG-triggered, blood oxygen level-dependent functional MRI (BOLD-fMRI) was used in 24 patients with localization-related epilepsy and frequent interic tal epileptiform discharges (spikes) to identity those brain areas involved in generating the spikes, and to study the evolution of the BOLD signal ch ange over time. The location of the fMRI activation was compared with the s calp EEG spike focus and the structural MR abnormality. Twelve patients (50 %) had an fMRI activation concordant with the EEG focus and structural brai n abnormalities where present (n = 7). In 2 other patients, the fMRI activa tion was non-concordant with electroclinical findings. The remaining 10 pat ients (41.7%) showed no significant fMRI activation. These patients had sig nificantly lower mean spike amplitudes compared to those with positive fMRI results (p=0.03). The time course of the BOLD response was studied in 3 pa tients and this revealed a maximum signal change 1.5 to 7.5 sec after the s pike. In conclusion, EEG-triggered fMRI can directly identify the generator s of interictal epileptiform activity, with high spatial resolution, in sel ected patients with frequent spikes. The superior spatial resolution obtain able through EEG-triggered fMRI may provide an additional non-invasive tool in the presurgical evaluation of patients with intractable focal seizures.