Two QEEG measures will be calculated for each subject. The first of these is cordance, which will be calculated using an algorithm that has been detailed elsewhere (Leuchter et al., 1999). Cordance is based upon a normalization of absolute and relative power values across all electrode sites and all frequency bands for a given recording. Cordance values have a stronger association with cerebral perfusion in brain tissue underlying each electrode site than do standard QEEG power measures. The second QEEG measure to be examined is QEEG coherence (Leuchter et al., 1992; 1994b), a measure of the shared functional activity between brain regions. Coherence values range between 0 - 1 and are analogous to a correlation coefficient, with values near 1 signifying highly coordinated cerebral activity. Coherence reflects not only cortical activity, but also the function of deep gray matter structures that coordinate cortical activity as well as white-matter tracts connecting brain regions.