Orbitofrontal cortex output pathways: cingulate cortex, basal ganglia, and dopamine

The medial orbitofrontal cortex projects reward-related information to the pregenual cingulate cortex, and the lateral orbitofrontal cortex projects punishment and non-reward information to the supracallosal anterior cingulate cortex. These projections provide the reward outcome information needed for action-outcome goal value dependent instrumental learning by the cingulate cortex. The orbitofrontal cortex also projects reward-related information to the striatum for stimulus-response habit learning. Via the striatal route, and further in part via the habenula, the orbitofrontal cortex provides information about rewards and non-rewards that reached the brainstem dopamine neurons, some of which respond to positive reward prediction error, and the serotonin (5HT) neurons. The orbitofrontal cortex is therefore perhaps the key brain region involved in reward processing in the brain. The orbitofrontal cortex also has projections that can influence autonomic function, in part via the insula.

Synthesis: the Roles of the Orbitofrontal Cortex

A synthesis is provided of how the functions of the orbitofrontal cortex fit into the organization of the primate including human brain, in terms of its roles as the key brain area involved in processing rewards and punishers, and in learning about them. These roles make it the crucial brain system for emotion. Possible future directions in the development of our understanding of the orbitofrontal cortex in health and disease, including depression, are highlighted.

Orbitofrontal cortex: anatomy and connections

The anatomical connections of the orbitofrontal cortex are described. The orbitofrontal cortex receives from the end of every sensory hierarchy information about what taste, smell, touch, visual stimulus including objects and faces, and what auditory stimuli including vocalization, is present. There are major outputs of the orbitofrontal cortex to the cingulate cortex, striatum, inferior frontal gyrus, and indirectly including via the habenula to the dopamine and serotonin neurons in the brainstem.

Orbitofrontal cortex computations in a systems-level perspective

This chapter describes some of the computational approaches that are useful to understand the functions of the orbitofrontal cortex. Section 9.1 describes the operation of pattern association networks which may be used in the orbitofrontal cortex to associate the sight of a stimulus with its taste. Section 9.2 describes the operation of autoassociation or attractor networks which may be used in the orbitofrontal cortex to maintain a rule online by continuing neuronal firing. Section 9.3 describes the operation of the integrate-and-fire attractor network used to model probabilistic decision-making. Section 9.4 describes a neurophysiological and computational model for stimulus-reinforcer association learning and reversal in the orbitofrontal cortex. Section 9.5 describes a theory and model of how non-reward neurons are produced in the orbitofrontal cortex.

The rodent orbitofrontal cortex

The rodent appears to have only agranular orbitofrontal, and not most of the parts present in primates including humans. In addition, many of the pathways involved in reward processing, including the taste pathways, are differently organized in rodents, with less emphasis on processing to the object level before the orbitofrontal cortex, and then reward value representations especially in the orbitofrontal cortex. For these reasons, a separate chapter is devoted to the rodent orbitofrontal cortex.

Orbitofrontal cortex damage effects in humans and other primates

Impairments in the rapid reversal learning of stimulus-reward associations, when expected rewards are not obtained or punishers are obtained, are produced by damage to the orbitofrontal cortex; and contribute to the major changes in emotion, personality, and impulsiveness that can be produced by damage to the orbitofrontal cortex. Impairments in the processing of rewards are found, with alterations in food choice and eating, and in the identification of face and voice expressions, which are important for social behavior.

Introduction to the orbitofrontal cortex

The orbitofrontal cortex has for long been implicated in emotion, though it is only relatively recently that there has been a firm scientific foundation for understanding how it functions, which is the central theme of this book. The different parts of the orbitofrontal cortex are described. Because of the major developments in the evolution of the orbitofrontal cortex in primates including humans, most of the book focusses on the functioning of the orbitofrontal cortex in primates including humans. However, the rodent orbitofrontal cortex is described in Chapter 8.

The orbitofrontal cortex, depression, and other mental disorders

An approach to depression is described, in which there is over-sensitivity of the lateral orbitofrontal cortex non-reward attractor system, and under-sensitivity of the medial orbitofrontal cortex reward system. Many functional connectivities involving the lateral orbitofrontal cortex are increased in depression, and many functional connectivities involving the medial orbitofrontal cortex are decreased in depression. Involvement of the orbitofrontal cortex in bipolar disorder, autism, attention-deficit hyperactivity disorder, and compulsivity including obsessive-compulsive disorder, is also described.

The orbitofrontal cortex and emotion

Emotions can be defined as states elicited by instrumental reinforcers, that is, by rewards and punishers. Because of its roles in processing rewards and punishers, the orbitofrontal cortex is therefore the key brain region in emotion. Cognition can have a top-down biasing effect on the emotion-related systems in the orbitofrontal cortex. In addition to the emotional route to behavior, there is also a rational route to behavior involving reasoning, which involves systems outside the orbitofrontal cortex. Individual differences in sensitivity to rewards and punishers also provide a foundation for understanding many aspects of personality. The functions of the orbitofrontal cortex in emotion are compared with those of the amygdala, which it is argued becomes overshadowed by the orbitofrontal cortex in humans. Indeed, a current topic of interest is that the orbitofrontal cortex appears to be involved much more in subjective aspects of emotion in humans than the amygdala.

Orbitofrontal cortex processing: neurophysiology and neuroimaging

The functioning of the orbitofrontal cortex is described. It is shown that it receives information about what stimulus is present from the sensory pathways, and represents this in terms of its reward value. There are reward outcome neurons (responding to taste and pleasant and unpleasant touch); expected value neurons (responding to visual stimuli according to the expected reward that they predict); and non-reward 'error' neurons that respond when an expected reward is less than expected. There are also neurons that respond to face identity and face expression, and to vocalization. The medial orbitofrontal cortex represents rewards and its activations are related to the pleasantness of stimuli. The lateral orbitofrontal cortex represents punishers and not receiving expected rewards (non-reward). Economic reward value is represented. An anterior region, the ventromedial prefrontal cortex, is implicated in decision-making between rewards of different value. The orbitofrontal cortex represents the reward and punishment value of stimuli, and not actions. Outputs of the orbitofrontal cortex to the cingulate cortex are involved in learning what actions to take to obtain rewards; and to the striatum for stimulus-response, habit, learning.