Defining a cognitive function decrement in schizophrenia.

BACKGROUND: Although cognitive impairment is described as a core component of the characterization of schizophrenia, a sizable percentage of patients are classified as unimpaired by traditional definitions of impairment. The purpose of this study was to determine the percentage of patients with schizophrenia meeting criteria for a "cognitive function decrement" defined as a current level of cognitive function that falls below the level predicted by premorbid estimates. METHODS: Linear regression analyses were performed on a healthy control population to determine a predicted composite cognitive score based on maternal education, paternal education, and reading score as indicators of premorbid intellectual function. The percentages of patients with current cognitive function above and below predicted values were calculated. RESULTS: When the Wide Range Achievement Test-3 (WRAT-3) score and maternal education are both used to predict current cognitive performance, as expected, about half (42%) of control subjects fall below expectations. However, 98.1 % of patients fall below expectations. CONCLUSIONS: When cognitive function decrement is defined as a failure to reach the expected level of cognitive functioning, almost all patients with schizophrenia meet this definition.

The Brief Assessment of Cognition in Schizophrenia: reliability, sensitivity, and comparison with a standard neurocognitive battery.

Studies of neurocognitive function in patients with schizophrenia use widely variable assessment techniques. Clinical trials assessing the cognitive enhancing effect of new medications have used neurocognitive assessment batteries that differed in content, length and administration procedures. The Brief Assessment of Cognition in Schizophrenia (BACS) is a newly developed instrument that assesses the aspects of cognition found to be most impaired and most strongly correlated with outcome in patients with schizophrenia. The BACS requires less than 35 min to complete in patients with schizophrenia, yields a high completion rate in these patients, and has high reliability. The BACS was found to be as sensitive to cognitive impairment in patients with schizophrenia as a standard battery of tests that required over 2 h to administer. Compared to healthy controls matched for age and parental education, patients with schizophrenia performed 1.49 standard deviations lower on a composite score calculated from the BACS and 1.61 standard deviations lower on a composite score calculated from the standard battery. The BACS composite scores were highly correlated with the standard battery composite scores in patients (r=0.76) and healthy controls (r=0.90). These psychometric properties make the BACS a promising tool for assessing cognition repeatedly in patients with schizophrenia, especially in clinical trials of cognitive enhancement.

Source monitoring improvement in patients with schizophrenia receiving antipsychotic medications.

RATIONALE: The absence of a relationship between cognitive deficit treatment response and positive symptom treatment response is often assumed, and few data have shed light on this issue. Most of these data have been collected using standard neuropsychological measures, which are ill-designed to assess the types of neurocognitive disturbances associated with psychotic symptoms. This study investigates the effect of treatment on source monitoring performance and its relation to the reduction of certain psychotic symptoms associated with the inability to identify self-generated mental events, known as "autonoetic agnosia". OBJECTIVES: To determine whether risperidone, olanzapine, and haloperidol were differentially effective in reducing autonoetic agnosia and whether changes in this aspect of cognition were related to reduction of specific symptoms of psychosis. METHODS: From a cohort of 49 patients diagnosed with schizophrenia by DSM-IV criteria and randomly assigned to double-blind treatment with risperidone, olanzapine, or haloperidol, 16 patients were identified with symptoms believed to reflect autonoetic agnosia ("target symptoms") as assessed with the Schneiderian Symptom Rating Scale, and then evaluated during a baseline period, and then at 1, 2, and 3 weeks. Autonoetic agnosia was assessed as the ability of a patient to distinguish self-generated words from both experimenter-generated words and pictorially presented words. RESULTS: Analysis of patients from all treatment groups found a significant reduction in the number of "target" Schneiderian symptoms. Discrimination for items from the self-generated and heard sources significantly improved with treatment, as did the number of self-generated items that patients remembered as coming from the heard source ("self-hear errors"). The correlation between improvement in recognition of self-generated items and reduction in target Schneiderian symptoms after 2 weeks of treatment suggested a modest relationship between symptom improvement and changes in autonoetic agnosia. CONCLUSIONS: While the differences between medications were not statistically significant, antipsychotic medication in general was associated with improvements in symptoms and cognitive deficits that may underlie autonoetic agnosia. Improvement of autonoetic agnosia was a weak predictor of positive symptom improvement in a limited sample.