Seizure-like discharges recorded in human dysplastic neocortex maintained in vitro

Application of the convulsant drug 4-aminopyridine (50 to 100 microM) induced spontaneous seizure-like discharges (duration = 76.3 +/- 46.8 sec, mean +/- SD; interval of occurrence = 225.2 +/- 87.9 sec) in slices of neocortex obtained from patients with a diagnosis of focal neuronal migration disorders during neurosurgical procedures for relief of drug-resistant seizures. Similar epileptiform discharges could also be elicited in these slices by single-shock stimuli delivered in the underlying white matter or within the gray matter. By contrast, neocortical slices obtained from patients suffering from temporal lobe epilepsy (which is characterized by Ammon's horn sclerosis but relatively normal neocortex) did not generate any epileptiform activity during 4-aminopyridine application. Thus, our study is the first to provide experimental evidence for the intrinsic epileptogenicity that characterizes neuronal migration disorders.