Medial prefrontal activity during shifting under novel situations.

Neuropsychological studies of the Wisconsin Card Sorting Test (WCST), where the WCST was administered to patients without prior knowledge of the test, have revealed that the performance is impaired by lesions to the dorsolateral and medial prefrontal cortex. The aim of this functional magnetic resonance imaging (fMRI) study is to explore the brain activity related to shifting under novel situations by adopting a modified WCST. The order of the WCST dimensions was determined based on the subjects' own choice, whereby subjects were more likely to shift without prior attempt of shifting in a similar situation. The brain activity in the initial shifts under novel situations was contrasted with the brain activity in the subsequent shifts under less novel situations. The contrast revealed significant brain activity both in the dorsolateral and medial prefrontal regions. Moreover, the brain activity in the dorsolateral prefrontal region was significantly lower at the very first of the initial shifts, where inhibition of proactive interference was needed to a lesser degree, while the medial prefrontal region showed a constant activation level across the initial shifts. These results demonstrate the involvement of the medial prefrontal region in the shifting in the WCST, and suggest the differential roles of the dorsolateral and medial prefrontal regions during shifting under novel situations.