ACTIVATION OF DIFFERENT ANTERIOR CINGULATE FOCI IN ASSOCIATION WITH HYPOTHESIS-TESTING AND RESPONSE SELECTION

Much everyday behavior is implicitly guided by hypotheses about the wo rld which are monitored and updated in the light of changing circumsta nces. The process of translating these hypotheses into behavior typica lly involves implementing choices, often based on incompletely specifi ed information. The present study aimed at modeling these processes to determine the neural substrates of hypothesis testing and, in particu lar, how these are modulated by the requirement to make choices. We us ed positron emission tomography to study six right-handed volunteers p erforming an insoluble hypothesis testing task in which subjects attem pted to identify a rule determining which of two black and white check erboard stimuli was correct. This task was compared with a control tas k matched for perceptuomotor requirements, but involving no hypothesis testing. Both tasks were performed with or without a requirement to m ake a choice. Structures activated in association with hypothesis test ing included the cerebellum, left anterior cingulate, right precuneus, right thalamus, and left inferior frontal gyrus. The requirement to c hoose a response was associated with activation of the left anterior c ingulate and right lateral orbitofrontal cortex. A significant modulat ion of activation associated with hypothesis testing was observed in t he anterior cingulate region that was also activated by making a choic e. These findings are discussed in terms of the neural substrates of c omplex ''executive'' tasks. We argue that the precise cognitive parame ters of such tasks, and specifically the requirement to implement deci sions in actual behavior, are critical in determining the associated n eural response. (C) 1998 Academic Press.