Orbitofrontal Cortex

The importance of the frontal lobes in social and emotional behavior was demonstrated in the mid-1800s by the famous case of Phineas Gage. Gage, a railroad construction foreman, was injured in an accident in which a metal tamping rod shot under his cheekbone and through his brain, exiting through the top of his head. Whereas Gage had been a diligent, reliable, polite, and socially adept person before his accident, he subsequently became uncaring, profane, and socially inappropriate in his conduct. Extensive study of modern-day patients with similar anatomical profiles (i.e., bilateral damage to the ventromedial frontal lobes), has shed more light on this fascinating historical case. These patients show a severely impaired ability to function in society, even with normal IQ, language, perception, and memory. The work of Antonio Damasio and others has illuminated the importance of ventromedial frontal cortices (VMF; we use ventromedial frontal cortex and orbitofrontal cortex interchangeably here) in linking stimuli with their emotional and social significance. This function bears some resemblance to that of the amygdala outlined previously but with two important differences. First, it is clear that the ventromedial frontal cortices play an equally important role in processing stimuli with either rewarding or aversive contingencies, whereas the amygdala's role, at least in humans, is clearest for aversive contingencies. Second, reward-related representations in VMF cortex are less stimulus driven than in the amygdala and thus can play a role in more flexible computations regarding punishing or rewarding contingencies.

Antonio Damasio and colleagues tested VMF-lesioned patients on several types of tasks involving the relation of body states of emotion to behavioral responses. When patients with bilateral VMF damage were shown slides of emotionally significant stimuli such as mutilation or nudity, they did not show a change in skin conductance (indicative of autonomic activation). Control groups showed larger skin conductance responses to emotionally significant stimuli, compared to neutral stimuli, suggesting that VMF patients are defective in their ability to trigger somatic responses to stimuli with emotional meaning. In a gambling task in which subjects must develop hunches about certain decks of cards in order to win money, VMF-lesioned patients made poor card choices and also acquired neither subjective feeling regarding their choices nor any anticipatory autonomic changes before making these poor choices. All these findings support the idea that the VMF cortices are a critical component of the neural systems by which we acquire, represent, and retrieve the values of our actions, and they emphasize the close link between emotion and other aspects of cognitive function, such as reasoning and decision making. Damasio presented a specific neuroanatomical theory of how emotions play a critical role in reasoning and decision making—the somatic marker hypothesis. According to this hypothesis, our deliberation of choices and planning of the future depend critically on how we feel about the different possibilities with which we are faced. The construction of some of the components of an emotional state and the feeling that this engenders serve to tag response options with value and serve to bias behavior toward those choices associated with positive emotions. This set of processes may operate either under considerable volitional guidance, and as such may be accessible to conscious awareness, or it may play out in a more automatic and covert fashion.

Both the amygdala and the orbitofrontal cortex function as components of a neural system that can trigger emotional responses. The structure of such a physiological emotional response may also participate in attempts to reconstruct what it would feel like to be in a certain dispositional (emotional or social) state and hence to simulate the internal state of another person. In the case of the amygdala, the evidence thus far points toward such a role specifically in regard to states associated with threat and danger; in the case of the orbitofrontal cortex, this role may be somewhat more general.

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