Psychiatric research has had a longstanding interest in developing reliable biomarkers, clinically useful biological features that are associated with psychopathology. A valid biomarker could lead to improved diagnosis, prognosis, and treatment as well as provide clues to the nature of underlying pathophysiology (W. G. Iacono, 1985). Although biomarkers such as neurochemical metabolites or measures of inflammatory response have obvious face value, for the vast majority of disorders, there is no consensus regarding which molecules are likely to make the best marker targets. Absent a solid theoretical foundation from which a vast array of possible biochemical markers can be reduced to a few plausible candidates, identifying valid biomarkers remains a daunting empirical task. Part of the appeal of psychophysiological measures derives from their tapping central nervous system function broadly; if the integrity of any element of a brain system is compromised, an electrophysiological measure associated with that system may be affected. However, this advantage may be offset by the measure's spatial coarseness and inability to identify the exact locus of dysfunction or precise mechanism involved.
