Psychophysiological correlates of patients with delusional misidentification syndromes and psychotic major depression.

Background: Psychotic major depression (PMD) and delusional misidentification syndromes (DMS) exhibit cognitive deficits. Since the P300 component of event-related potentials (ERPs) provides valuable information concerning cognition, we studied this component of ERPs in DMS and PMD patients. Methods: Nine patients with DMS, 15 patients with PMD, and 11 healthy controls, matched for age, sex and educational level, were tested using the auditory P300 component of ERPs. Results: Both patient groups showed significant reductions in P300 amplitude at the right frontal region, while DMS group showed significant attenuation of the P300 amplitude at the right parietal area. P300 latency was significantly prolonged in the central midline brain region in the DMS group. Limitations: The smallness of the sample size and the hypothetical post-hoc assignation of psychological function to regional activation. Conclusion: PMD and DMS patients may share similar psychophysiological alterations connected to the right frontal region, mediating automatic processes, while DMS are associated with dysfunction of effortful mechanisms and allocation of attentional resources involving the interhemispheric and right parietal circuitry.