Regional voltage map of the hippocampus during seizures

The hallmark of brain tissue is its electrical activity. However, few techniques are available to directly monitor voltage changes in neural tissue, especially in whole brain preparation. A technique has been developed using a fluorescent voltage-sensitive dye and digital image analysis to produce a high spatial resolution map of the voltage changes induced by seizures in the hippocampus. Eight different anatomical regions within the septal hippocampus of the rat were analyzed. Seizures were produced in vivo by methods which use entirely different mechanisms and produce electrographically and behaviorally different types of seizures. Kainic acid produced depolarization during the seizure, whereas bicuculline produced hyperpolarization. The results provide experimental evidence that all seizures do not induce a depolarized state in the brain.