Use of MRI to guide electrophysiology procedures

The susceptibility of cerebral cortex to epileptiform activity was studied in cats undergoing barbiturate withdrawal. Epileptiform afterdischarges were initiated in neuronally isolated cortex by electrical stimulation, and the threshold and duration of the afterdischarges were measured. In some animals, afterdischarges were prolonged during barbiturate withdrawal. In other animals who were judged to be equally dependent on barbiturates by their increased sensitivity to pentylenetetrazol, the duration and threshold of afterdischarges were in the normal range. The changes in the responsiveness of cortex to electrical stimulation during barbiturate withdrawal were small and unreliable in comparison to changes produced by chronic neuronal isolation of cortex. It was concluded that the principal change responsible for the increased susceptibility to seizures during barbiturate withdrawal occurred in subcortical structures. In control animals, the duration of afterdischarges in isolated cortex depended on the amplitude of the electrical shocks used to elicit the afterdischarge. The bearing of this observation on theories regarding the mechanism of electrically induced paroxysmal activity is discussed.