Brain activation during intermittent photic stimulation: A [O-15]-water PET study on photosensitive epilepsy

Purpose: Intermittent photic stimulation (IPS) is an activation procedure u sed during electroencephalogram (EEG) recording to elicit paroxysmal discha rges in individuals with photosensitivity. Specific responses on EEG record ing may be provoked by LPS at different frequencies of flickering in normal individuals and in patients with photosensitive epilepsy. Methods: Changes in regional cerebral blood flow (rCBF) were studied during IFS in two groups of subjects by using [O-15]-water positron emission tomo graphy (PET): a control group consisting of eight healthy adults with photi c driving response during IFS on EEG recording (mean age, 25 +/- 10.5 years ) without history of neurologic or psychiatric abnormalities and a patient group consisting of four adults (mean age, 33 +/- 7.5 years) with history o f photosensitive epilepsy. [O-15]water PET scanning with concomitant EEG mo nitoring was performed during baseline and IFS at 4-, 14-, and 30-Hz freque ncies. Results: The control group showed photic driving response at 14-Hz IFS freq uency. The patient group showed photoparoxysmal response at 14 and 30 Hz, b ut not at 4 Hz. Changes in rCBF were determined by means of statistical par ametric mapping. Increases in rCBF in occipital cortex (Brodmann's areas 17 , 18, and 19) were observed in both groups. In addition, during photic driv ing responses, the control group showed rCBF increases in the insula and in the thalamus, on the right side. The patient group showed a significant rC BF increase in the hypothalamic region inferior to the left caudate nucleus during photoparoxysmal response. This activation was not found in the cont rol group. Increased rCBF also was observed in the patient group in the hea d of the left caudate nucleus, in the left hippocampus, and in left insula during IFS without photoparoxysmal response. No activations in these region s were observed during photoparoxysmal response. Conclusions: These data may indicate involvement of the hypothalamus in pho tosensitive epilepsy and may suggest a modulatory function of the caudate n ucleus, which might be associated with an inhibition of epileptic discharge s during IFS in patients with photosensitive epilepsy.