Dynamic Statistical Parametric Neurotechnique Mapping: Combining fMRI and MEG for High-Resolution Imaging of Cortical Activity

of focal sources (Sherg and VonCramon, 1985; Schmidt Functional magnetic resonance imaging (fMRI) can et al., 1999). An additional constraint can be derived provide maps of brain activation with millimeter spatial from the assumption that the sources are temporally resolution but is limited in its temporal resolution to uncorrelated (Mosher et al., 1992). These assumptions the order of seconds. Here, we describe a technique are particularly appropriate when analyzing early senthat combines structural and functional MRI with magsory responses, where the activity might reasonably be netoencephalography (MEG) to obtain spatiotemporal expected to be relatively focal and constrained to a maps of human brain activity with millisecond tempofew primary sensory areas. On the other hand, such ral resolution. This new technique was used to obtain assumptions are less justified in higher-level cognitive dynamic statistical parametric maps of cortical activexperiments, which have been found by intracranial reity during semantic processing of visually presented cordings in humans to involve extensive networks of words. An initial wave of activity was found to spread more or less synchronously activated brain areas (Halrapidly from occipital visual cortex to temporal, parigren et al., 1994a, 1994b, 1995a, 1995b; Baudena et al., etal, and frontal areas within 185 ms, with a high de1995). Similarly, the interictal spikes characteristic of gree of temporal overlap between different areas. Reppartial epilepsy typically spread very rapidly to involve etition effects were observed in many of the same a network extended across multiple cortical and limbic areas following this initial wave of activation, providing regions (Chauvel et al., 1987). evidence for the involvement of feedback mechanisms An alternative approach to analyzing EEG/MEG sigin repetition priming. nals is to impose constraints based on anatomical and