Triggering factors for seizures ‐‐ Introduction Volume 16, issue 1, Janvier-Février-Mars 2004

Clinique d‘épilepsie, Hôpital neurologique et Hôpital du Sacré‐Cœur, Montréal, Canada

Seizure triggers have been described for centuries and may be divided into specific and nonspecific factors. Nonspecific factors such as sleep deprivation and fever are important in most if not all patients with epilepsy but despite this, their mechanisms of action are not well understood. Less well known yet more extensively studied, external and relatively specific seizure triggers are less common but are of great interest. All seizures triggered or spontaneous require neuronal hyperexcitability and cortical hypersynchrony: seizure triggers are those that can increase either regional cortical synchrony or the recruitment of several cortical regions by activating neuronal networks which may extend over several regions and even over both hemispheres. Several models in animals either spontaneously or artificially hypersensitive to certain sensory modalities depend on these characteristics to make up the cortical mass needed to produce seizures. The idea of an epileptogenic network was developed in the photosensitive baboon: the hypersensitive region is activated by a specific stimulus but the development and progression of a seizure depend on activation of a progressively more complex network. In humans, the study of reflex seizures, especially those triggered by pattern, reading, and by nonverbal cognitive tasks, confirms the essential role of a critical mass of cortex, and emphasizes the participation of functional networks in seizure genesis. They also show that while specific seizure‐triggering components may be identified in complex stimuli encountered in daily life, other characteristics can be identified which make seizures or EEG paroxysmal activity less likely. Recently functional imaging has been added to the study of seizure triggers: these methods permit new approaches whose limits are still unknown. The analysis of seizure triggers and of the mechanisms of triggered seizures remains of capital importance in understanding both epilepsy and brain function in the broadest sense.