P 134 Photic driving response in epileptic and non-epileptic patients

Abstract

Objective To determine the prevalence of photic driving - a physiologic response to photic stimulation in the occipital cortex – at different frequencies and in different populations and to evaluate the role of the individual alpha-frequency on the reaction to photic driving. Methods We retrospectively searched our medical database for patients who have had an EEG with photic stimulation in the year 2016 and retrieved 20 EEGs of patients who finally turned out to have non-epileptic events (syncopies, migraine, non-epileptic seizures) (age 38.2 ± 12.1, 10 female) and 20 patients with focal epilepsy on a monotherapy with valproate, lamotrigine or levetiracetam (33.2 ± 12.5, 12 female) excluding those with occipital lesions or mental retardation. In all individuals photic stimulation was applied at 3, 6, 9, 12, 15, 20 and 30 Hz for 20 s (XLTEK XLPS-1F®) each with stimulation-free intervals of 10 s. Each 18 s of the stimulation sequence as well as 9 s of the interstimulus intervals were analyzed. The peak amplitude at each stimulation frequency as well as at first and second harmonic frequencies ±0.1 Hz were calculated in a fast Fourier transformation in the frequency domain. Similarly, the mean alpha-frequency and its amplitude of each subject were calculated as an average of the calculated alpha-frequency of each interstimulation interval. Results No significant differences were found between the amplitude of the photic driving response to the photic stimulation between the control group and the group with focal epilepsy at any basic stimulation frequency ( Fig. 1 ) as well as for its harmonics. Additionally, the alpha frequencies did neither differ between the groups nor did they change in the course of the photic stimulation. We also could not establish a relationship between the individual alpha-frequency and the individual propensity to react to a photic stimulation in the alpha-frequency-range (9 and 12 Hz in our laboratory) ( Fig. 2) . Conclusion The fundamental response to photic driving is not significantly influenced by focal epilepsy as well as a range of common antiepileptic drugs and may thus demonstrate a conservative response of the brain. While the photic driving response is maximal at the alpha-frequency range the individual alpha-frequency apparently does not significantly influence this response and thus both may be triggered by different generators.