Segregated Encoding of Reward–Identity and Stimulus–Reward Associations in Human Orbitofrontal Cortex

Abstract

A dominant focus in studies of learning and decision-making is the neural coding of scalar reward value. This emphasis ignores the fact that choices are strongly shaped by a rich representation of potential rewards. Here, using fMRI adaptation, we demonstrate that responses in the human orbitofrontal cortex (OFC) encode a representation of the specific type of food reward predicted by a visual cue. By controlling for value across rewards and by linking each reward with two distinct stimuli, we could test for representations of reward-identity that were independent of associative information. Our results show reward-identity representations in a medial-caudal region of OFC, independent of the associated predictive stimulus. This contrasts with a more rostro-lateral OFC region encoding rewardidentity representations tied to the predicate stimulus. This demonstration of adaptation in OFC to reward specific representations opens an avenue for investigation of more complex decision mechanisms that are not immediately accessible in standard analyses, which focus on correlates of average activity.

Connectivity reveals relationship of brain areas for reward-guided learning and decision making in human and monkey frontal cortex

“…Such a correspondence is consistent with this region being concerned with the mediation of behavioral change as a result of a general role in learning stimulus-reward associations (55,60,62). However, we were unable to match the more anterior human lOFC region linked to ambiguity (Fig.…”

“…For example, positive outcomes might lead to behavioral changes in learning situations. Consistent with this idea, some recent studies have suggested that the same lOFC region previously highlighted as responsive to punishers (33,56) has a more general role in credit assignment and the linking of stimuli to reward outcomes (55,60) (Fig. 5A).…”

“…1). The coupling did, however, correspond to the human region identified by Klein-Flügge et al (60) as coding reward identity. This pattern of results is broadly consistent with the scheme suggested by Rudebeck and Murray (78), in which value-based decisions and reward identity-based decisions are mediated by medial and central orbital regions, respectively.…”

“…This part of the human brain is not the same as the more medial vmPFC regions that have been the focus of investigations of value encoding in the human brain (Fig. 2), but it is similar to a region in which activity has been related to the identity of reward outcomes (60). In this central OFC region, unlike in the lOFC, activity is related to the identities of rewards rather than the association between rewards and predictive cues.…”

“…This pattern of results is broadly consistent with the scheme suggested by Rudebeck and Murray (78), in which value-based decisions and reward identity-based decisions are mediated by medial and central orbital regions, respectively. As discussed below, however, an even more lateral OFC region can be distinguished that is concerned with establishing stimulusreward associations and credit assignment (54,55,60).…”