Ventromedial prefrontal cortex mediates guessing

Guessing is an important component of everyday cognition. The present study examined the neural substrates of guessing using a simple card-playing tas k in conjunction with functional magnetic resonance imaging (fMRI). Subject s were scanned under four conditions. In two, they were shown images of the back of a playing card and had to guess either the colour or the suit of t he card. In the other two they ware shown the face of a card and had to rep ort either the colour or the suit. Guessing compared to reporting was assoc iated with significant activations in lateral prefrontal cortex (right more than left), right orbitofrontal cortex, anterior cingulate, bilateral infe rior parietal cortex and right thalamus. Increasing the guessing demands by manipulating the number of alternative outcomes was associated with activa tion of the left lateral acid medial orbitofrontal cortex. These data sugge st that while simple two choice guessing depends on an extensive neural sys tem including regions of the right lateral prefrontal cortex, activation of orbitofrontal cortex increases as the probabilistic contingencies become m ore complex. Guessing thus involves not only systems implicated in working memory processes but also depends upon orbitofrontal cortex. This region is not typically activated in working memory tasks and its activation may ref lect additional requirements of dealing with uncertainty. (C) 1999 Elsevier Science Ltd. All rights reserved.