<i>Background:</i> Executive functions, which are neuroanatomically associated with the frontal lobe, are known to be impaired in schizophrenia. It is, however, still unclear whether the underlying functional disturbance is due to a hyper- or a hypoactivation of the dorsolateral prefrontal cortex (DLPFC) or neither. <i>Methods:</i> To address this question, we examined the brain activation of 21 schizophrenic patients on atypical antipsychotic medication and 21 healthy control subjects during a mental maze task by means of fMRI. <i>Results:</i> We found no significant overall difference in cerebral activation between the groups, but differences in the change in DLPFC activation from the first to the second half of the experiment. In the maze compared to the control task, there was a decrease in activation in the DLPFC in the patients and an almost significant increase in the controls. The change in activation in the patient group correlated with a change in subjective sleepiness, while the increase in activation in the controls could be attributed to learning processes. <i>Conclusion:</i> We hypothesized that differential temporal influences on brain activation could lead to either hyper- or hypoactivation of the DLPFC in schizophrenia.