I know that the Wisconsin Card Sorting Task is used to diagnose various mental disfunctions such as schizophrenia and drug addiction. However, has it been specified what brain regions or structures are being evaluated and how?
As predicted by the acquired brain injury literature, early PET studies have shown the task involves significant activation of the dorsolateral prefrontal cortex. However, more recent fMRI studies have shown that the ventrolateral prefrontal cortex together with the caudate nucleus may be the regions most important for the set-shifting process required in the WCST. These regions are also associated with working memory functions.
Furthermore, according to Andrew Amos preservative errors are due to frontal lobe dysfunction, while random errors are due to basal ganglia dysfunction.
At a glance, this does seem to make sense since the dorsolateral prefrontal cortex has been associated previously with working memory and the caudate nucleus (as part of the basal ganglia) is known to be associated with switching between rewarding tasks.
More recently a series of lesion studies have been conducted with an analogous task with monkeys providing further insights into brain areas, with a summary of the most important summaries here.