Smoking improves divided attention in schizophrenia

Background: Smoking is highly prevalent in schizophrenia and there is evidence for beneficial effects on neurocognition. Smoking is therefore hypothesized a self-medication in schizophrenia. Although much effort is devoted to characterize those cognitive domains that potentially benefit from smoking, divided attention has not yet been analyzed. Methods: We investigated divided attention in a sample of 48 schizophrenic patients and 48 controls (24 current smokers and non-smokers each) carefully matched for age, sex, education, verbal IQ and smoking status with general linear models that included 'Diagnostic group' and 'Smoking status' as factors. Results: 'Diagnostic group' significantly contributed to mean reaction time, valid reactions, and errors of omission. 'Smoking status' was significantly associated with valid reactions and errors of omission. Most importantly within the scope of this study, significant interactional effects were found for valid reactions and errors of omission: performance substantially increased in smoking schizophrenia patients, but not in controls. Conclusions: Results suggest a clear-cut positive effect of smoking on divided attention in schizophrenia patients. This study provides first evidence that the complex domain of divided attention is improved by smoking, which has as yet been shown mainly for sustained and selective attention. The proposed self-medication hypothesis of smoking in schizophrenia is thus further substantiated.