Brain maturation and epilepsy.

At full term, both glutamate and gamma-amino-butyric acid (GABA) are excitatory; cortical synapses are beginning to appear, there is little myelin in the cerebral hemispheres, and long tracts hardly start to develop. Neonatal myoclonic encephalopathy can result from premature activation of N-methyl-D-aspartate (NMDA) transmission. Benign neonatal seizures and migrating partial seizures in infancy could involve excessive or premature excitability of deep cortical layers. Benign rolandic epilepsy and continuous spike waves in slow sleep are consistent with an excess of both excitatory and inhibitory cortical synapses. West and Lennox-Gastaut syndromes express age-related diffuse cortical hyperexcitability, the pattern depending on the age of occurrence; synchronization of spikes is becoming possible with maturation of the myelin. Idiopathic generalized epilepsy is itself modulated by maturation that causes frontal hyperexcitability generating myoclonic-astatic seizures, between the ages of infantile and juvenile myoclonic epilepsies. Physiological delay of hippocampo-neocortical pathways maturation could account for the delayed occurrence of mesial temporal epilepsy following infantile damage, whereas premature maturation could contribute to fronto-temporal damage characteristic of fever-induced epileptic encephalopathy in school-age children, a dramatic school-age epileptic encephalopathy.