Schizophrenia Bulletin Advance Access published online on October 3, 2008
Schizophrenia Bulletin, doi:10.1093/schbul/sbn119
Schizophrenia Patients Show Task Switching Deficits Consistent With N-Methyl-D-Aspartate System Dysfunction But Not Global Executive Deficits: Implications for Pathophysiology of Executive Dysfunction in Schizophrenia
2 Neuropsychology and Neuroscience Laboratory, Kessler Medical Rehabilitation Research and Education Center, 300 Executive Drive, Suite 10, West Orange, NJ 07052
3 Department of Psychology, The City College of the City University of New York, North Academic Complex, 138th Street and Convent Avenue, New York, NY 10031
4 The University of Medicine and Dentistry of New Jersey, New Jersey Medical School, New Jersey
5 Program in Cognitive Neuroscience and Schizophrenia, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY 10962
1 To whom correspondence should be addressed; tel: +973-530-3664, fax: +973-736-7880, e-mail: gwylie{at}kmrrec.org.
Schizophrenia is associated with cognitive processing deficits, including deficits in executive processing, that represent a core component of the disorder. In the Task Switching Test, subjects view ambiguous stimuli and must alternate between competing rules to generate correct responses. Subjects show worse performance (prolonged response time and/or increased error rates) on the first response after a switch than on subsequent responses ("switch costs"), as well as performing worse when stimuli are incongruent as opposed to congruent ("congruence costs"). Finally, subjects show worse performance in the dual vs single task condition ("mixing costs"). In monkeys, the N-methyl-D-aspartate (NMDA) antagonist ketamine has been shown to increase congruence but not switch costs. Here, subjects viewed colored letters and had to respond alternately based upon letter (X vs O) or color (red vs blue). Switch, congruence and mixing costs were calculated. Patients with schizophrenia (n = 16) and controls (n = 17) showed similar switch costs, consistent with prior literature. Patients nevertheless showed increased congruence and mixing costs. In addition, relative to controls, patients showed worse performance across conditions in the letter vs color tasks, suggesting deficits in form vs color processing. Overall, while confirming executive dysfunction in schizophrenia, this study indicates that not all aspects of executive control are impaired and that the task switching paradigm may be useful for evaluating neurochemical vs neuroanatomic hypotheses of schizophrenia.
Keywords: executive control / task switching / schizophrenia / N-methyl-D-aspartate