The electroclinical patterns of generalized reflex seizures (GRS) triggered by sensory or cognitive stimuli are reviewed in a report from Montreal Neurological Hospital, Canada; and Universita degli Studi di Messina, Italy. Four major patterns of GRS having a focal cortical trigger are identified: 1) photosensitive seizures are subserved by the occipital cortex; 2) tactile or noise-induced seizures, by the sensorimotor cortex; 3) cognitive-induced (mental arithmetic, block design) by the non-dominant parietal lobe; and 4) reading, talking, and writing-induced epilepsies, by dominant frontotemporal lobes. Clinically, the seizures induced by these stimuli are idiopathic generalized epilepsies, especially juvenile myoclonic epilepsy, and the cortical mechanisms are complex, ultimately involving cortico-reticular or cortico-cortical pathways. 
COMMENT. The authors hypothesize that patients with cortical triggers of GRS present regions of cortical hyperexcitability overlapping with the areas activated during sensory stimulation and cognitive or planned motor (praxis) activities. When these hyperexcitable areas are activated sufficiently, epileptic activity is produced that involves cortico-reticular or cortico-cortical pathways, resulting in a generalized reflex seizure. Genetic or acquired lesions may be responsible for the neuronal hyperexcitability.
Pattern sensitive epilepsy, discussed in Ped Neur Briefs February 2005, has a higher incidence of focal symptomatic seizures than the generalized idiopathic reflex epilepsies. The EEG in pattern-sensitive epilepsies shows focal epileptiform discharges, whereas photosensitive epilepsies are usually accompanied by generalized polyspike-wave and spike-wave complexes.