Modulation of the default mode network is task-dependant in chronic schizophrenia patients.

The activity of brain regions of the so-called default mode network (DMN) attenuates during the performance of goal-directed tasks. These activity decreases (named task-induced deactivations; TID) are though to reflect the reallocation of cognitive resources from the DMN to areas implicated in the execution of the task. Recently, DMN activity suppression has been studied in schizophrenia patients. Although these works showed that TID are altered in schizophrenia, they also revealed inconsistent findings. We hypothesized that reallocation of resources is altered in schizophrenia patients and is context or task specific. We investigated TID using functional MRI in 26 schizophrenic patients and 13 control subjects while performing two different goal-directed tasks (the Hayling Sentence Completion Test and the N-Back task). Both whole brain and region of interest conjunction analyses were conducted to investigate brain areas commonly deactivated in the two tasks (task unspecific deactivations). Task-unspecific deactivations were not observed in the schizophrenia group, although these were strongly significant in the control group. Differences between patient and control participants were observed in different regions of the DMN depending whether the subjects performed the Hayling or the N-back task. These results suggest that reallocation of cognitive resources is altered in our patient sample. Moreover, TID were task-unspecific indicating that resources reallocation is context dependent in schizophrenia. DMN activity attenuates differently in schizophrenia patients depending on the cognitive processes involved in the task.