Photosensitivity in Epilepsy Syndromes: Age Differences?

The presence of paroxysmal abnormalities of brain electrical activity provoked by intermittent photic stimulation, is an age-dependent EEG pattern usually first seen in childhood and adolescence. Indirect evidence suggests that this maps onto the time-course of the maturation of excitatory and inhibitory brain systems. Recent studies have confirmed the role of abnormal gating mechanisms in the abnormal susceptibility of the posterior cortex to visual stimuli in young patients with photosensitive epilepsy. Similarly, the later maturation of the parvocellular systems which has been associated with the photoparoxysmal EEG response might account for the low prevalence of photosensitivity in the very young patients. From the clinical perspective, while photosensitivity has a preferential onset in pediatric age, it tends to persist in adulthood, with two-thirds of the patients continuing to show the EEG trait even though 85% of them will no longer experience overt clinical seizures. The data presented in this chapter give an account of the role of maturational progression in the manifestations of photosensitivity at mesoscopic level and their integration with genetic data might provide a clearer account of the variability in genotype/phenotype association seen in photosensitive patients.