Schizophrenia has been associated with deficits in functional brain lateralization and some authors even argue that the reduction of asymmetry produces the psychosis. However, there is one major and often overlooked confound: Schizophrenic patients are extreme cigarette smokers. This association is very interesting, because a team from the Bochum Biopsychology Department could recently show that smoking can reduce auditory language asymmetry. Thus, the altered laterality pattern in schizophrenia could, at least in part, result from secondary artifacts due to smoking rather than being a pure cause of the disease itself. To test this hypothesis, the present study examined auditory language lateralization in 67 schizophrenia patients and in 72 healthy controls. Again it was found that smoking reduces language lateralization. Most importantly, no further effect of schizophrenia on language asymmetry was found. This opens the tantalizing possibility that at least some of the asymmetry alterations in schizophrenia are not a primary consequence of the disease but a secondary effect of increased smoking habits.

Hahn, C., Neuhaus, A. H., Pogun, S., Dettling, M., Kotz, S. A., Hahn, E., Brüne, M., Güntürkün, O. (2011). Smoking reduces language lateralization: A dichotic listening study with control participants and schizophrenia patients. Brain Cogn., 76, 300-309.