Changes during pentetrazol induced epilepsy in rat recorded by simultaneous EEG/MRI at 7T

Simultaneously acquired EEG and BOLD (Blood Oxygenation level dependent contrast) MRI allowed to study on line the neurophysiological changes in rat brain during epileptic seizures. MRI and EEG data were acquired with a specially designed high quality MR RF-antenna with incorporated non-invasive carbon EEG electrodes. The problem of severe pollution of the EEG data due to MR gradient switching during simultaneous EEG/MRI acquisitions was solved by a specially designed automated effective filtering algorithm. We measured continuously EEG data, and T2-weighted coronal MRI sections of rat brain before and after the injection of pentetrazol (43mg/(kg body weight) PTZ; convulsive dose 97%), an epilepsy inductor. In this way, we could correlate the abnormalities in the EEG traces, with changes in the MRI BOLD signal intensities. Immediately after PTZ induction and before epileptic discharges were observed on the EEG traces, the cortex displayed an increase in BOLD signal intensity (increase in blood flow). Much later and correlated with epileptic discharges on the EEG traces, the ventromedial hypothalamic nuclei showed an increased BOLD signal while the BOLD signal intensity dropped in the entire brain, except for the hypothalamus. The decreased BOLD signal reflected general hypoxia and subsequent ischemia as a consequence of the sustained depolarization of neurons during the seizure.