THE HUMAN LATERAL ORBITOFRONTAL CORTEX AND REPRESENTATIONS OF MOTIVATIONAL CONTEXT FOR ACTION: BASIC FINDINGS AND RELEVANCE FOR PSYCHOPATHOLOGY

The human orbitofrontal cortex (OFC) is known to play a critical role in goal-directed behavior. However, it is still unknown whether the OFC contribution to guiding behavior is through top-down control of inappropriate responses or through providing a motivational context by representing potential outcomes. This dilemma stems from the fact that research to date has not been able to clearly distinguish the effects of changes in motivational states from associated adjustments in cognitive control. In order to answer this question, two functional magnetic resonance imaging (fMRI) studies, simultaneously and independently manipulated demands for inhibitory control and monetary incentives for correct performance. Across experiments, demands for control only engaged the OFC when they also increased the likelihood of a negative outcome, in the form of increased error rates. In contrast to these effects of control, expected outcomes modulated the OFC activity irrespective of whether the demands for control were high or low. Moreover, the lateral areas of the OFC were maximally engaged during expectation of negative outcomes. Thus, we provided convergent evidence that the OFC is specifically involved in establishing the motivational context of behavior through representation of possible outcomes. Furthermore, the nature of outcome representations in these two experiments have potential implications for existing theories of decision making, by providing evidence that the OFCiiirepresentations of potential outcomes are influenced the whole range of possible alternative outcomes. In a third fMRI experiment, the framework laid out by the first two studies was applied in the analysis of data investigating the neural substrates of obsessive-compulsive disorder (OCD). Compared to control subjects, the OFC of patients showed increased activity in response to stimuli associated with relatively increased potential for negative outcomes, despite the fact that those stimuli were not directly relevant to obsessive-compulsive symptomatology. These findings suggest that the OFC hyperactivity in OCD may reflect an underlying neural dysfunction, and are consistent with the phenomenology of this disease, in which excessive concerns for potential negative outcomes of actions are a prominent feature of symptomatology