A COGNITIVE NEUROPSYCHOLOGICAL APPROACH TO THE STUDY OF DELUSIONS IN LATE-ONSET SCHIZOPHRENIA

Objective. Hypotheses to explain delusion formation include distorted perceptual processing of meaningful stimuli leg faces), abnormal reaso ning, or a combination of both. The study investigated these hypothese s using standardized neuropsychological tests. Design. A three-patient case-study, compared with a small group (n = 8) of age-matched normal control subjects. Setting. Hospital in-and outpatients. Age-matched n ormal controls were from local residential homes. Patients. Three subj ects with late-onset schizophrenia, two currently deluded and one in r emission. Both deluded subjects had persecutory beliefs. One had a del usion of misidentification. Interventions. All subjects were administe red standardized neuropsychological tests of facial processing and tes ts of verbal reasoning. Main outcome measures. The test scores of the three patients were compared with published normal values and the age- matched control data, Results. The tests demonstrated impaired matchin g of unfamiliar faces in deluded subjects, particularly in the subject with delusional misidentification. Increasing the emotional content o f logical reasoning problems had a significant effect on the deluded s ubjects' reasoning but not that of the normal controls. Conclusion. Th e findings suggest impaired visual processing plus abnormal reasoning in deluded subjects. However, these impairments are relatively subtle given the severity of psychiatric disorder in the patients studied. (C ) 1997 John Wiley & Sons, Ltd.