Elsevier

Biological Psychiatry

Volume 64, Issue 9, 1 November 2008, Pages 823-827
Biological Psychiatry

Brief Report
General and Specific Cognitive Deficits in Schizophrenia: Goliath Defeats David?

https://doi.org/10.1016/j.biopsych.2008.04.005Get rights and content

Background

Our earlier work suggested that the cognitive performance impairment in individuals with schizophrenia relative to healthy control subjects was generalized, cutting across narrower cognitive ability dimensions. Current analyses sought to extend these findings.

Methods

Seventeen neuropsychological variables, available for 148 schizophrenia subjects and 157 control subjects, were subjected to structural equation modeling. Analyses incorporated a hierarchical model, grouping the variables into six familiar cognitive domains and linking these to a higher-order, general cognitive ability factor. We added diagnosis to the model as a grouping factor and estimated loadings from diagnosis to the general cognitive factor and, separately, to the domain factors.

Results

The fit of the final model was good (e.g., Non-Normed Fit Index [NNFI] = .988). Approximately 63.6% of the diagnosis-related variance in cognitive performance was mediated through the general factor, with smaller direct effects on verbal memory (13.8%) and processing speed (9.1%).

Conclusions

The schizophrenia cognitive deficit is largely generalized across performance domains, with small, direct effects of diagnostic group confined to selected domains. This generalized deficit sometimes has been seen as a function of the psychometric limitations of traditional cognitive test batteries. Alternatively, it may be a fundamental manifestation of schizophrenia, with similarly general neurobiological underpinnings.

Section snippets

Participants

Patients and control subjects were assessed and followed by the Schizophrenia Research Center at the University of Pennsylvania. Data for the present analyses were collected from January 1993 to May 1998, as described previously (6). Patients had DSM-III-R diagnoses of schizophrenia established by clinical examination and structured clinical interview but were free of other psychiatric conditions. Control subjects were free of psychiatric disorders in themselves and their first-degree

Sample Characteristics

Patients were significantly older than control subjects, more likely to be male, and less likely to be Caucasian. Patients also had fewer years of education, although parental education was statistically equivalent between groups (Table 2). To reduce the impact of demographic differences, all analyses covaried age, sex, race/ethnicity, and mother's/father's education.

The schizophrenia deficit was significant for every neuropsychological variable (all ps < .01). Wechsler Adult Intelligence Scale

Discussion

Results indicate that the deficit in schizophrenia neuropsychological performance relative to healthy control subjects is largely mediated through a common ability factor. Using a hierarchical model of cognitive structure, large samples of patients and control subjects, and a comprehensive neuropsychological battery, this factor accounted for 63% of the diagnosis-related variance in overall cognitive performance, consistent with our earlier report (5). Analyses revealed direct diagnosis effects

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