Smoking Status, Cognition, and Neurobiology in Schizophrenia

Cognitive impairments are considered a core feature of schizophrenia. Nicotine has been suggested to have an effect on cognition in individuals with schizophrenia and in the general population. Since smoking status is seldom controlled for in cognitive research studies understanding the contribution of nicotine dependence is a potentially important issue for data interpretation. Thus, the current study examined whether smoking status has a differential association with cognition and regional cortical thickness in 71 patients and 63 nonpsychiatric control participants. Cognition was measured with the MATRICS Consensus Cognitive Battery (MCCB) and social cognition was measured with the Faux Pas and Reading the Mind in the Eye tasks. The Vocabulary and Matrix Reasoning subtests of the Wechsler Abbreviated Scale of Intelligence (WASI) and Wide Range Achievement Test (WRAT-4) were used to assess general intelligence (IQ) and premorbid functioning, respectively. Cortical thickness was measured with a high-resolution 3-Tesla MR whole body scanner. Results revealed that patients (relative to controls) and smokers (as compared to nonsmokers) showed impairments on all cognitive measures (e.g., attention, processing speed, working memory, social cognition, etc.). Neuroimaging results indicated widespread cortical thinning among patients as compared to controls. However, patient smokers and control nonsmokers had similar cortical thickness patterns in the left parahippocampal gyrus and bilateral medial orbitofrontal gyri. The findings suggest that smoking status should be taken into consideration in cognitive research given that smoking status may confound overall results.