Photosensitive epilepsy studied by functional magnetic resonance imaging and magnetic resonance spectroscopy

Purpose: To study metabolic and hemodynamic correlates of photic stimulatio n-triggered discharges. Methods: Simultaneous EEG, functional MRI (fMRI) and magnetic resonance spe ctroscopy (MRS) were performed in nine patients with photosensitive epileps y and in 12 normal subjects. Results: Prominent visual cortex activation was seen in all normal subjects and patients, and no fMRI-registered hemodynamic abnormalities were correl ated with the brief photoparoxysmal spike-wave activity evoked in the photo sensitive patients. However, irrespective of the presence of a spike-wave r esponse to the photic stimulation, the photosensitive patients showed four findings not seen in the normal subjects: (a) slightly, but significantly, elevated lactate levels in the occipital cortex in the resting state; (b) a n increased area of visual cortical activation with photic stimulation; (c) simultaneous with the occipital cortex stimulus-induced increased fMRI sig nal, there were noncontiguous areas of signal attenuation most prominent in perirolandic regions; and (d) a marked decrement (undershoot) of fMRI sign al intensity immediately after the photic stimulation in the occipital cort ex and in the region of the posterior cingulate gyrus, Conclusions: These findings suggest abnormal interictal metabolism and incr eased vascular reactivity in the photosensitive patients.