Schizophrenic subjects show deficient inhibition but intact task switching on saccadic tasks.
BACKGROUND
Schizophrenic patients have executive function deficits, presumably on the basis of prefrontal cortex dysfunction. Although they consistently show impaired inhibition, the evidence of a task switching deficit is less consistent and is often based on performance of neuropsychological tests that require several cognitive processes (e.g., the Wisconsin Card Sort Test [WCST]). We investigated inhibition and task switching using saccadic tasks to determine whether schizophrenic patients have selective impairments of these executive functions.


METHODS
Sixteen normal and 21 schizophrenic subjects performed blocks of randomly mixed prosaccade and antisaccade trials. This gave rise to four trial types: prosaccades and antisaccades that were either repeated or switched. Response accuracy and latency were measured. Schizophrenic subjects also performed the WCST.


RESULTS
Schizophrenic subjects showed abnormal antisaccade and WCST performance. In contrast, task switching was normal and unrelated to either antisaccade or WCST performance.


CONCLUSIONS
The finding of intact task switching performance that is unrelated to other measures of executive function demonstrates selective rather than general impairments of executive functions in schizophrenia. The findings also suggest that abnormal WCST performance is unlikely to be a consequence of deficient task switching. We hypothesize that inhibition and task switching are mediated by distinct neural networks, only one of which is dysfunctional in schizophrenia.
Manoach
Dara S
DS
Department of Neurology, Human Vision and Eye Movement Laboratory, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
Lindgren
Kristen A
KA
Cherkasova
Mariya V
MV
Goff
Donald C
DC
Halpern
Elkan F
EF
Intriligator
James
J
Barton
Jason J S
JJ
D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use; D003072:Cognition Disorders / Q000175:diagnosis / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000503:physiopathology*; D009433:Neural Inhibition / Q000502:physiology*; D009483:Neuropsychological Tests; D011897:Random Allocation; D012438:Saccades / Q000502:physiology*; D012559:Schizophrenia / Q000150:complications / Q000188:drug therapy / Q000503:physiopathology*; D013647:Task Performance and Analysis
D014150:Antipsychotic Agents