The photic driving EEG response and photoreactive cerebral blood flow in the posterior cerebral artery in controls and in patients with epilepsy

Objectives: Instantaneous changes in blood flow velocities during visual stimulation can be assessed by transcranial Doppler sonography (TCD).

Methods: We investigated the possible relationship between the characteristics of photic driving in the EEG elicited by repetitive intermittent photic stimulation and the photoreactive flow changes in the posterior and middle cerebral artery (PCA, MCA) of 25 normal controls and 25 patients with focal epilepsy. Cerebral blood flow velocities (CBFV) of the right PCA (P2 segment) and the left middle cerebral artery (MCA) were measured using a 2 Hz transcranial Doppler device. Simultaneously, scalp EEGs were recorded.

Results: During photic stimulation the mean CBFV increase was 20.4±9.5% in the PCA of the controls (n=132 stimulations) and 16.0±10.8% in epileptic patients (n=150 stimulations, P<0.01). During those stimulation series with a good EEG driving response (n=203), the mean increase of CBFV in the PCA was 19.7±10.0%, as opposed to 14.4±10.5% during the stimulations with a poor EEG response (n=79, P<0.01). A good photic driving response was associated with a higher increase of CBFV in the PCA than a poor one. The increase in CBFV of the PCA in normal controls was higher than in patients with focal epilepsy.

Conclusions: This may indicate that epileptic patients have a reduced coupling between neuronal activation and blood flow.