Context-specific behavioral surprise is differentially correlated with activity in anterior and posterior brain systems

This experiment investigated whether behavioral surprise, an information-theoretic measure of the amount of memory and information integration associated with a response, is correlated with neural activity during decision making. A total of 30 participants (age 18-30) were scanned with functional MRI while completing 240 trials of a sequential decision-making task in which they selected an amount to wager from four possible values on each trial. Behavioral surprise was computed trial by trial using both context-free and context-specific formulations, and was used as a parametric modulator in functional MRI analyses. Whereas context-free surprise was not significantly correlated, two sets of clusters (P<0.005; cluster size>156 voxels) were differentially modulated by context-specific behavioral surprise. An anterior system comprised of the inferior frontal gyrus and anterior cingulate (each bilaterally), and left caudate, was positively modulated. A posterior system comprised of the posterior cingulate, parahippocampal gyrus and posterior hippocampus (each bilaterally), and left angular gyrus, was negatively modulated. These anticorrelated systems indicate that more surprising (resource demanding) actions recruit greater activity from the anterior system and less activity from the posterior system and less surprising actions (memory-guided) recruit greater activity from the posterior system and less activity from the anterior system. These results show that context-specific behavioral surprise is a unique neural signal and may be related to mechanisms for both cognitive control and memory-guided behavior, and support contemporary theories that the brain is a statistical observer of external and internal events.