The human orbitofrontal cortex: linking reward to hedonic experience

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Abstract
The prefrontal cortex seems to be essential for the control and organization of behaviour. In particular, it has been linked to the relative cognitive sophistication that has been reached by higher primates, especially humans. However, the functions of one of its constituent regions, the orbitofrontal cortex, have remained enigmatic. In terms of neuroanatomical connectivity, the primate orbitofrontal cortex is uniquely placed to integrate sensory and autonomic information to modulate behaviour through both visceral and motor systems. Recent neuroimaging studies in humans have confirmed the role of the human orbitofrontal cortex as a nexus for sensory integration, modulation of visceral reactions, and participation in learning, prediction and decision making for emotional and reward-related behaviours. But these studies have also shown that the human orbitofrontal cortex is a highly heterogeneous brain region that encompasses many different functions. In particular, the human orbitofrontal cortex has been found to represent not only the reward value and expected reward value of foods and other reinforcers, but also their subjective pleasantness. This link to subjective hedonic processing could provide a basis for further exploration of the brain systems involved in the conscious experience of pleasure and reward, and, as such, offer a unique method for studying the hedonic quality of human experience. Based on the available evidence from neuroimaging and neuropsychology, a tentative new model of the functional neuroanatomy of the orbitofrontal cortex is offered with medial–lateral and posterior–anterior distinctions, in which the implicit reward value is assigned early on in the hierarchy for each type of reinforcer, with a further progression up the processing hierarchy (reflecting the effects of combinations of stimuli) towards areas that are connected to brain regions necessary for conscious hedonic processing. At present, little is known about the functional and structural development of the human orbitofrontal cortex in children and adolescents. However, further investigation of the link to hedonic processing could potentially lead to a better understanding of and novel treatments for disorders linked to anhedonia, such as depression, obesity and eating disorders.