Intracranial EEG fMRI
Intracranial EEG fMRI combines the best temporal and spatial neuroimaging techniques to map brain activity comprehensively.
A sample of our fMRI results and the simultaneous EEG results collected from electrodes implanted within the skull.
Due to its excellent temporal resolution, EEG is commonly used in refractory epilepsy investigation to characterize and localize seizures and other epileptiform electrical activity in the brain to guide future resective surgery. EEG electrodes are often placed on the scalp during basic investigations, however, scalp electrodes are susceptible to artifacts created by hair, sweat, and muscle activity, making them insufficient for use during presurgical planning. It has therefore become increasingly common for presurgical investigation to use electrodes implanted into patients' brains to more precisely identify the seizure-generating brain tissue. The use of these intracranial electrodes greatly increases our ability to determine the location and extent of the seizure generating tissue over scalp electrodes. However, the imaging resolution of intracranial electrodes is limited to immediate tissue, providing less information for distant tissue.
Another method of imaging, functional MRI (fMRI), provides excellent spatial maps of activity across the whole brain at the cost of a decreased temporal resolution. The use of fMRI concurrent with intracranial EEG overcomes both these problems, allowing us to record from all locations within the brain, not just tissue immediately surrounding the electrodes while maintaining the temporally rich signal provided by intracranial EEG. Our lab is interested in using fMRI to record changes in the blood oxygen level-dependent (BOLD) response throughout the brain concurrent with epileptiform activity captured on intracranial EEG. We believe changes as the result of epileptic discharges may provide insight into regions of the brain responsible for creating seizures.
To date, we have studied the BOLD response to interictal epileptiform discharges and found concordance between tissue identified using intracranial EEG-fMRI and those involved in generating seizures. Consequently, intracranial EEG-fMRI may be useful in defining the surgical target in epilepsy surgery.
We are currently exploring the dynamic and static functional connectivity of regions associated with interictal spikes, in hopes that network dynamics may shed light on how epileptic activity alters the brain. We also are investigating how other forms of epileptiform activity, such as high-frequency oscillations, are reflected on fMRI.
Click here to view our most recent paper on intracranial EEG fMRI.