Differential activation of the human orbital, mid-ventrolateral, and mid-dorsolateral prefrontal cortex during the processing of visual stimuli.

There is considerable uncertainty about the precise functional contribution of the different parts of the prefrontal cortex to mnemonic processing. Changes in regional cerebral blood flow were measured with positron emission tomography in normal human subjects exposed to abstract visual designs under various conditions. It was demonstrated that the processing of stimuli that deviate from expectations involves selectively the orbitofrontal cortex, namely the part of the frontal cortex that is preferentially linked with the limbic system. By contrast, when the subject is making an explicit decision on the contents of memory (e.g., judgments of relative stimulus familiarity), the mid-ventrolateral prefrontal cortex is involved. The mid-dorsolateral prefrontal cortex is engaged when monitoring of information within working memory is required.