EEG-linked functional magnetic-resonance imaging in epilepsy and cognitiveneurophysiology

The ability to trigger functional magnetic resonance imaging (fMRI) acquisi tions related to the occurrence of LEG-based physiologic transients has cha nged the field of fMRI into a more dynamically based technique. By knowing the temporal relationship between focal increases in neuronal firing rates and the provoked focal increase in blood flow, investigators are able to ma ximize the fMR-linked images that show where the activity originates. Our m astery of recording EEG inside the bore of a MR scanner has also allowed us to develop cognitive paradigms that record not only the fMR BOLD images, b ut also the evoked potentials (EPs). The EPs can subsequently be subjected to localization paradigms that can be compared to the localization seen on the BOLD images. These two techniques will most probably be complimentary. BOLD responses are dependent on a focal increase in metabolic demand while the EPs may or may not be related to energy demand increases. Additionally, recording EPs require that the source or sources of that potential come fr om an area that is able to generate far-field potentials. These potentials are related to the laminar organization of the neuronal population generati ng that potential. As best we know the BOLD response does not depend on any inherent laminar neuronal organization. Therefore, by merging these two re cording methods, it is likely that we will gain a more detailed understandi ng of not only the areas involved in certain physiologic events, e,g, focal epilepsy or cognitive processing, but also on the sequencing of the activa tion of the various participating regions.