Sensitivity of prefrontal cortex to changes in target probability: A functional MRI study

Electrophysiological studies suggest sensitivity of the prefrontal cortex t o changes in the probability of an event. The purpose of this study was to determine if subregions of the prefrontal cortex respond differentially to changes in target probabilities using functional magnetic resonance imaging (fMRI). Ten right-handed adults were scanned using a gradient-echo, echo p lanar imaging sequence during performance of an oddball paradigm. Subjects were instructed to respond to any letter but "X". The frequency of targets (i.e., any letter but X) varied across trials. The results showed that dors al prefrontal regions were active during infrequent events and ventral pref rontal regions were active during frequent events. Further, we observed an inverse relation between the dorsal and ventral prefrontal regions such tha t when activity in dorsal prefrontal regions increased, activity in ventral prefrontal regions decreased, and vice versa. This finding may index compe ting cognitive processes or capacity limitations. Most importantly, these f indings taken as a whole suggest that any simple theory of prefrontal corte x function must take into account the sensitivity of this region to changes in target probability. Hum. Brain Mapping 13:26-33, 2001. (C) 2001 Wiley-L iss, Inc.