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 (e.g. faces), abnormal reasoning, or a combination of both. The study investigated these hypotheses 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 normal controls were from local residential homes. PATIENTS Three subjects with late-onset schizophrenia, two currently deluded and one in remission. Both deluded subjects had persecutory beliefs. One had a delusion of misidentification. INTERVENTIONS All subjects were administered standardized neuropsychological tests of facial processing and tests 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 matching of unfamiliar faces in deluded subjects, particularly in the subject with delusional misidentification. Increasing the emotional content of logical reasoning problems had a significant effect on the deluded subjects' reasoning but not that of the normal controls. CONCLUSION The 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.