In a series of depressed subjects receiving open-label treatment, we previously have shown that cordance detects changes in prefrontal activity (using a within-subjects design) as early as after three days of treatment in patients who will later show clinical response to antidepressant medication. Subjects who did not respond to antidepressant medication, as well as those receiving placebo, did not show these early changes in cordance (Leuchter et al 1997; Cook et al 1998; Cook et al., in submission). These data suggest that QEEG cordance may be a more specific indicator of antidepressant treatment effectiveness than traditional QEEG power measures, since antidepressant non-responders and placebo treated subjects showed no early change in this measure. It is important, however, to determine if the effects that we have observed in depressed subjects during treatment are specific for this population, or are seen in normal controls as well. First, examination of specificity in normal controls during treatment is a logical first step in the process of examining other groups, eventually including other patient groups. Second, examination of normal subjects will help us to determine whether the observed changes in brain function are a pharmacodynamic effect of antidepressant medication which could be seen in any individual, or an effect seen exclusively in depressed subjects early in the course of effective antidepressant treatment.