Dissociable roles of ventromedial prefrontal cortex (vmPFC) and rostral anterior cingulate cortex (rACC) in value representation and optimistic bias.

Optimistic bias (OB) is seen when individuals underestimate their probability of experiencing negative life events and overestimate their probability of experiencing positive life events. A reduced OB has been linked with increased depression symptoms. However, given the relevance of this information to mood and anxiety disorders, little is currently known regarding the neurobiology of OB. In the current study, we examine the neural basis of OB in healthy individuals (n=33) during probability estimation of future positive and negative events occurring to themselves relative to other, comparable individuals. In line with previous work, subjects showed significant OB; they considered themselves significantly more likely to experience future positive and significantly less likely to experience future negative events relative to comparable others. Positive, relative to negative events, un-modulated by subjects' probability estimates, were associated with significantly greater activity within the ventromedial prefrontal cortex (vmPFC) and posterior cingulate cortex (PCC). Moreover, responses within both regions to positive events negatively related to the healthy subjects' self reports of depression symptoms. However, there was no significant modulation of activity in either region by the subject's OB, objectified as the level to which they thought the event was more likely [positive events] or less likely [negative events] to occur to them relative to comparable others. In contrast, activity within the rostral anterior cingulate cortex (rACC) was positively modulated by OB for positive events and activity within the anterior insula and dorsomedial prefrontal cortex (dmPFC) was negatively modulated by OB for negative events. However, there was no significant relationship between responsiveness within these regions and self reports of depression symptoms. The data are discussed with reference to current models of vmPFC, rACC and anterior insula functioning.