Relative reward preference in primate orbitofrontal cortex

The orbital part of prefrontal cortex appears to be crucially involved in the motivational control of goal-directed behaviour1,2. Patients with lesions of orbitofrontal cortex show impairments in making decisions about the expected outcome of actions3. Monkeys with orbitofrontal lesions respond abnormally to changes in reward expectations4,5 and show altered reward preferences6. As rewards constitute basic goals of behaviour7, we investigated here how neurons in the orbitofrontal cortex of monkeys process information about liquid and food rewards in a typical frontal task, spatial delayed responding8. The activity of orbitofrontal neurons increases in response to reward-predicting signals, during the expectation of rewards, and after the receipt of rewards. Neurons discriminate between different rewards, mainly irrespective of the spatial and visual features of reward-predicting stimuli and behavioural reactions. Most reward discriminations reflect the animals' relative preference among the available rewards, as expressed by their choice behaviour, rather than physical reward properties. Thus, neurons in the orbitofrontal cortex appear to process the motivational value of rewarding outcomes of voluntary action.