The neurocognitive literature on test performance in schizophrenia is reviewed quantitatively. The authors report 22 mean effect sizes from 204 studies to index schizophrenia versus control differences in global and selective verbal memory, nonverbal memory, bilateral and unilateral motor performance, visual and auditory attention, general intelligence, spatial ability, executive function, language, and interhemispheric tactile-transfer test performance. Moderate to large raw effect sizes (d > .60) were obtained for all 22 neurocognitive test variables, and none of the associated confidence intervals included zero. The results indicate that schizophrenia is characterized by a broadly based cognitive impairment, with varying degrees of deficit in all ability domains measured by standard clinical tests.

Neurocognitive Deficit in Schizophrenia: A Quantitative Review of the Evidence

Clinical and experimental research have provided anatomical, pharmacological, and behavioral evidence for a prominent prefrontal dysfunction in schizophrenia. Negative symptoms and behavioral disorganization in the disorder can be understood as a failure in the working memory functions of the prefrontal cortex by which information is updated on a moment-to-moment basis or retrieved from long-term stores, held in mind, and used to guide behavior by ideas, concepts, and stored knowledge. This article recounts efforts to dissect the cellular and circuit basis of working memory with the goal of extending the insights gained from the study of normal brain organization in animal models to an understanding of the clinical disorder; it includes recent neuropathological findings that indicate that neural dystrophy rather than cell loss predominates in schizophrenia. Evidence from a variety of studies is accumulating to indicate that dopamine has a major role in regulating the excitability of the cortical neurons upon which the working memory function of the prefrontal cortex depends. Interactions between monoamines and a compromised cortical circuitry may hold the key to the salience of frontal lobe symptoms in schizophrenia, in spite of widespread pathological changes. We outline several direct and indirect intercellular mechanisms for modulating working memory function in the prefrontal cortex based on the localization of dopamine receptors on the distal dendrites and spines of glutamatergic pyramidal cells and on gamma-aminobutyric acid (GABA) ergic interneurons in the prefrontal cortex. Understanding the interactions between the major cellular constituents of cortical circuits-pyramidal and nonpyramidal cells-is a necessary step in unraveling the receptor mechanisms, which could lead to an effective pharmacological treatment of negative and cognitive symptoms, as well as improved insight into the pathophysiological basis of the disorder.

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Nancy L. Talbot

Papers

Neuropsychological probes of fronto-limbic system dysfunction in schizophrenia. Olfactory identification and Wisconsin Card Sorting performance.