How can intracranial recordings assist MEG source localization?
Halgren E Massachusetts General Hospital, Massachusetts Institute of Technology, Harvard Medical School, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA 02129, USA. halgren@nmr.mgh.harvard.edu MEG/EEG are the only non-invasive methods to instantaneously and directly measure the currents underlying cerebral information processing, but their ability to localize those currents is limited. Source localization from MEG is always uncertain, unless the signal is already known to be coming exclusively from a single focal source, or a few highly separated focal sources. Furthermore, since many cerebral currents produce little or no MEG signal, even accurate localization of the MEG sources may provide a very incomplete map of brain activation. Intracranial EEG (iEEG) can unambiguously localize sources, using steep voltage gradients, doubly-inverting gradients, traverses of the source structure from multiple directions, and/or spatial arrays of microelectrodes. These recordin
