Different Contributions of the Human Amygdala and Ventromedial Prefrontal Cortex to Decision-Making

TLDR

The somatic marker hypothesis posits that emotion guides decision‑making, and lesions of the ventromedial prefrontal cortex impair the use of somatic signals for advantageous choices. This study investigates whether amygdala damage similarly disrupts decision‑making and whether the amygdala and VMF play distinct roles. Patients with bilateral amygdala or VMF lesions performed a gambling task while skin‑conductance responses were recorded to index somatic state activation. Both groups were impaired on the gambling task and lacked anticipatory SCRs, but VMF patients could still generate reward‑related SCRs and acquire conditioned responses, whereas amygdala patients could not.

Abstract

The somatic marker hypothesis proposes that decision-making is a process that depends on emotion. Studies have shown that damage of the ventromedial prefrontal (VMF) cortex precludes the ability to use somatic (emotional) signals that are necessary for guiding decisions in the advantageous direction. However, given the role of the amygdala in emotional processing, we asked whether amygdala damage also would interfere with decision-making. Furthermore, we asked whether there might be a difference between the roles that the amygdala and VMF cortex play in decision-making. To address these two questions, we studied a group of patients with bilateral amygdala, but not VMF, damage and a group of patients with bilateral VMF, but not amygdala, damage. We used the “gambling task” to measure decision-making performance and electrodermal activity (skin conductance responses, SCR) as an index of somatic state activation. All patients, those with amygdala damage as well as those with VMF damage, were (1) impaired on the gambling task and (2) unable to develop anticipatory SCRs while they pondered risky choices. However, VMF patients were able to generate SCRs when they received a reward or a punishment (play money), whereas amygdala patients failed to do so. In a Pavlovian conditioning experiment the VMF patients acquired a conditioned SCR to visual stimuli paired with an aversive loud sound, whereas amygdala patients failed to do so. The results suggest that amygdala damage is associated with impairment in decision-making and that the roles played by the amygdala and VMF in decision-making are different.