Exploring the role of ventromedial prefrontal cortex in human social learning: a lesion study

Converging evidence suggests a critical role for the ventromedial prefrontal cortex (vmPFC) in social cognition, but its specific contribution to various aspects of social cognition, including the acquisition and updating of complex social information, is not well understood or documented via a systematic experimental approach. The primary aim of this dissertation is to determine whether the vmPFC is necessary for the integration of complex social information in order to form normal moral and social judgments about people. In the first of two studies presented here, I examined the roles of the vmPFC and the hippocampus in updating one's moral judgment of others. I hypothesized that both the vmPFC and the hippocampus are critical--but in different ways--for updating character judgments in light of new social and moral information. To test this hypothesis, I used a novel moral "updating" task and compared the performances of patients with bilateral vmPFC damage to patients with bilateral hippocampal damage (HC), and brain-damaged comparison (BDC) patients. The results suggest that the vmPFC may attribute emotional salience to moral information, whereas the hippocampus may provide necessary contextual information from which to make appropriate character judgments. In the second study, I specifically examined whether the vmPFC is necessary for the integration of simple versus complex, and social versus nonsocial information in order to form normal judgments about people. I hypothesized that patients with circumscribed damage to the vmPFC would be impaired in integrating complex social information. To test this prediction, I employed a novel decision making task and compared the performances of vmPFC patients with BDC patients, and a group of normal, healthy individuals. I also explored which anatomical sectors within the vmPFC system are responsible for normal social information integration. Going against my predictions, most participants were better at making the best choice when more information was available. On the whole, all groups were more accurate in choosing the best nonsocial choice versus the social choice, and this is attributed to the fact that the nonsocial trials were much easier for the participants. Overall, vmPFC patients were inferior to the other groups in choosing the best option for both the social and nonsocial conditions, which suggests that vmPFC patients may have a general impairment in integrating information. The subjective ratings data revealed that the vmPFC patients: perceived the choices to be more difficult overall, had difficulty discriminating between the best and worse options, did not provide the same subjective influence weights as the comparison groups, and endorsed social choices being overall more difficult than nonsocial choices. The neuroanatomical data revealed that unilateral left vmPFC damage may have contributed the most to impairment in making the correct choice for the social condition, and overall, left hemisphere vmPFC lesion volume correlated negatively with percentage correct on my experimental task.