The role of affect and reasoning in a patient with a delusion of misidentification

Introduction. This study investigated a patient with a delusion of misidentification (DM) resembling a Capgras delusion. Instead of the typical Capgras delusion-the false belief that someone has been replaced by an almost identical impostor-patient MF misidentified his wife as his former business partner. Method. Detailed investigation of MF's face processing, affective response and affect perception, and ability to evaluate, and reject, implausible ideas was undertaken. Results. MF's visual processing of identity, gender, and age of familiar and unknown faces was intact but he was unable to identify the facial expressions of anger, disgust, and fear, or to match faces across expressions. MF also showed a reduced affective responsiveness to his environment, and impaired reasoning ability. Conclusions. We propose that MF's delusion of misidentification resulted from a combination of affective deficits, including impairment of both affective response and affect perception, in addition to an inability to evaluate, and reject, implausible ideas. These deficits, in combination with specific life events at the time of onset of the delusion, may have contributed to the form and content of the delusion. In addition, the results raise the possibility that the processing of face identity and facial expression are not as independent as previously proposed in models of face processing.