Separate value comparison and learning mechanisms in macaque medial and lateral orbitofrontal cortex

Abstract

Uncertainty about the function of orbitofrontal cortex (OFC) in guiding decision-making may be a result of its medial (mOFC) and lateral (lOFC) divisions having distinct functions. Here we test the hypothesis that the mOFC is more concerned with reward-guided decision making, in contrast with the lOFC's role in reward-guided learning. Macaques performed three-armed bandit tasks and the effects of selective mOFC lesions were contrasted against lOFC lesions. First, we present analyses that make it possible to measure reward-credit assignment-a crucial component of reward-value learning-independently of the decisions animals make. The mOFC lesions do not lead to impairments in reward-credit assignment that are seen after lOFC lesions. Second, we examined how the reward values of choice options were compared. We present three analyses, one of which examines reward-guided decision making independently of reward-value learning. Lesions of the mOFC, but not the lOFC, disrupted reward-guided decision making. Impairments after mOFC lesions were a function of the multiple option contexts in which decisions were made. Contrary to axiomatic assumptions of decision theory, the mOFC-lesioned animals' value comparisons were no longer independent of irrelevant alternatives.A lthough it is widely agreed that the orbitofrontal cortex (OFC) is important for value-guided behavior (1, 2), the precise nature of its contribution is unclear. On the one hand, neuroimaging experiments suggest its ventromedial aspect is part of the circuit for deciding between options on the basis of their value (3, 4). Moreover De Martino et al. (5) have reported that ventromedial frontal activity is correlated with the degree to which subjects' decisions are rational and uninfluenced by irrelevant features of the context in which they are made. In contrast, other accounts emphasize a role in learning and storage of option values (6).One potential reason for lack of consensus about the OFC may be that there is functional specialization within it, as suggested by the distinct anatomical connections of its ventromedial and lateral divisions (7) The aim of our study was, therefore, to assess evidence of functional specialization within the OFC for value learning and value-guided decision making. The effect of medial OFC (mOFC) lesions was compared with that of lateral OFC (lOFC) lesions in two groups of animals.The investigation of value-guided decision making was based on the premise that a lesion that disrupts part a circuit for deciding and discriminating between choice options of differing value should impair decision making as a function of the proximity of options' values. By analogy, lesions of visual feature-discrimination mechanisms disrupt discrimination as a function of the similarity of the visual features (8). In experiments reported below, macaques were trained to choose between three stimuli associated with differing probabilities of reward. The probabilities of reward, therefore, determined the options' values and the proximity of the best (...

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

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Morphometric Correlation of Impulsivity in Medial Prefrontal Cortex

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Anorexia Nervosa and Obesity are Associated with Opposite Brain Reward Response

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