Activation of specific cortical territories by sensory stimuli or of less restricted areas of the brain by cognitive stimuli is known to induce apparently generalized seizures in predisposed patients; this is clinically and electroencephalographically distinct from reflex triggering of partial seizures. Photosensitive patients may have seizures when exposed to environmental stimuli producing appropriate flickering light or geometric patterns. Some children with benign myoclonic epilepsy in infancy have seizures triggered by unexpected touch or noise. Seizures induced by thinking have been reported in response to non-verbal higher mental activity such as mental arithmetic. Praxis-induced seizures are triggered by similar mental activities accompanied by the use of the hands. Language-induced seizures are usually triggered by verbal higher mental activity. Functional imaging and other methods have contributed to understanding how these seizures arise. Patients with these generalized reflex seizures appear to have regions of cortical hyperexcitability overlapping or coinciding with areas physiologically activated during specific sensory stimulations and cognitive or motor activities. When these areas receive appropriate afferent volleys and a critical mass of cortex is activated, an epileptic activity is produced that ultimately involves cortico-reticular or cortico-cortical pathways resulting in a generalized or bilateral epileptic event.

NCSE of frontal origin is a heterogeneous syndrome. Some cases are best described as simple partial NCSE, others as complex partial SE, and there are forms that overlap with absence SE. Emergency EEG and neuropsychological assessment are diagnostic, and SPECT may be useful. Many patients may not respond to IV BZ.

JME is clinically and genetically heterogeneous and should be considered separately from other IGE syndromes. Proposed mechanisms, such as those involving microdysgenesis or altered neuronal inhibition, may be related to different genetic abnormalities in different patients. Major genes account for relatively few cases, and most cases appear to involve multifactorial or complex inheritance.

MELAS is a mitochondrial encephalomyopathy characterized clinically by recurrent stroke‐like episodes, seizures, sensorineural deafness, dementia, hypertrophic cardiomyopathy, and short stature. The majority of patients are heteroplasmic for a mutation (A3243G) in the tRNAleu(UUR) gene in mitochondrial DNA (mtDNA). In cells cultured in vitro, the mutation produces a severe mitochondrial translation defect only when the proportion of mutant mtDNAs exceeds 95% of total mtDNAs. However, most patients are symptomatic well below this threshold, a paradox that remains unexplained. We studied the relationship between the level of heteroplasmy for the mutant mtDNA and the clinical and biochemical abnormalities in a large pedigree that included 8 individuals carrying the A3243G mutation, 4 of whom were asymptomatic. Unexpectedly, we found that brain lactate, a sensitive indicator of oxidative phosphorylation dysfunction, was linearly related to the proportion of mutant mtDNAs in all individuals carrying the mutation, whether they were symptomatic or not. There was no evidence for threshold expression of the metabolic defect. These results suggest that marked tissue‐specific differences may exist in the pathogenic expression of the A3243G mutation and explain why a neurological phenotype can be observed at relatively low levels of heteroplasmy. Ann Neurol 2000;47:179–185.

Summary: Benign occipital epilepsy of childhood is an idiopathic partial epilepsy syndrome with elementary visual symptomatology, frequently associated with other ictal phenomena. Seizures are usually followed by postictal headache and are often associated with interictal occipital rhythmic paroxysmal EEG activity that appears only after eye closure. In some children the ictal visual symptoms or the interictal EEG abnormalities may not be demonstrated. The clinical and/or EEG manifestations of other forms of idiopathic partial or generalized epilepsy may be found in association. Occipital spikes in non‐epileptic children with defective vision, occipital slow spike‐and‐wave found in some patients with the Lennox‐Gastaut syndrome, focal epilepsy due to occipital lesions, seizures originating in the temporal lobe secondary to an occipital abnormality, and complicated or basilar migraine must be considered in the differential diagnosis. Early‐onset benign occipital epilepsy or seizure susceptibility syndrome deserves to be considered separately. It has been defined by Panayiotopoulos as consisting of brief, infrequent attacks or prolonged status epilepticus and characterized by ictal deviation of the eyes and/or head and vomiting, occurring in children usually between the ages of 3 and 7 years. Advances in molecular genetics will help decide whether these two disorders are indeed distinct. Benign occipital and benign rolandic epilepsy are commonly associated with migraine. The selective involvement of the occipital lobe in migraine has not been fully explained. The association between benign occipital epilepsy and migraine is likely related to this underlying mechanism as well. The “fixation off‘ phenomenon or blocking of occipital epileptic discharges by eye opening is not specific to benign occipital epilepsy of childhood and may be found in symptomatic epilepsies as well. Migraine and epilepsy are distinct disorders, both as far as their pathophysiologic mechanisms and clinical symptomatology are concerned. There is however an overlap in some patients and a causal relationship may exist in some, leading to clinically distinct migraine epilepsy syndromes. Here too, clarification of the molecular basis of migraine and of epilepsy will throw light on the nature of the relationship between the two conditions.