Changing economic and social reward based decision making with activation of the orbitofrontal cortex by transcranial direct current stimulation

Abstract

Decision making based on reward has attracted the attention of researchers, and considerable progress has been made in understanding its neural basis. In the present study, reward processing were divided into two different types of reward, economic and social decision making. There is only few research to compare encoding two different reward and investigate the behaviors in identical condition. Understanding how people behave in conflict situation between economic and social decision making is important. Orbitofrontal cortex (OFC) is one of brain regions to encode reward value in reward processing. Several human neuroimaging studied are shown that activity in the OFC correlates with behavioral measures of reward magnitude for the monetary and social reward modalities. In this study, we designed an experiment paradigm aiming to investigate changing reward based decision making after modulation over the OFC by transcranial direct current stimulation (tDCS). We used incentive delay task to quantify to monetary and social reward sensitivity, and investigated conflict situation between monetary and social reward in trust game. Also to identify stimulating to the OFC enough, we conducted Stroop Color word task. From the result in baseline study, there is no difference in reward and punishment sensitivity in each of monetary and social stimuli. In conflict situation between monetary and social reward, people who are more concerning other people returned more money. People who are more sociable in conflict situation may have higher social reward sensitivity. There was no significant change in reward sensitivity. Active tDCS applied over the OFC did not influence with overall return rate. Participants are divided into two types (showing increased return rate and decreased return rate) because the OFC is related to both monetary and social reward processing. People who are changed to be social after tDCS to the right OFC are more sensitive to social reward and punishment. It indicated that the right OFC is significantly associated with social reward based decision making. Our experimental results showed that participants receiving anodal tDCS over the OFC have higher monetary sensitivity when they care money more than social reward in limited resource condition. It suggested that the right OFC is significantly associate brain region with social reward based decision making, and both right and left OFC is related to monetary reward based decision making. Our results support the notion that the OFC plays an important role in reward processing.