Different brain circuits in static and dynamic social decision-making in real-time sibling interactions

Description: Manuscript Abstract: In traditional game theory tasks, social decision-making is centered on the prediction of the intentions (i.e., mentalizing) of strangers or manipulated responses. In contrast, real-life scenarios often involve familiar individuals in dynamic environments. Further research is needed to explore neural correlates of social decision-making with changes in the available information and environmental settings. The current study collected fMRI hyperscanning data (N = 100, 46 same-sex pairs were analyzed) to investigate sibling pairs engaging in an iterated Chicken Game task, including two decision-making phases. In the static phase, participants chose between turning (cooperate) and continuing (defect) in a fixed time window. Participants could estimate the probability of different events based on their priors (previous outcomes and representation of other’s intentions) and report their decision plan. The dynamic phase mirrored real-world interactions in which information is continuously changing in a virtual environment. Individuals had to simultaneously update their beliefs, monitor the actions of the other, and adjust their decisions. Our findings revealed substantial choice consistency between the two phases and evidence for shared neural correlates in mentalizing-related brain regions, including the prefrontal cortex, temporoparietal junction (TPJ), and precuneus. Specific neural correlates were associated with each phase; increased activation of areas associated with action planning and outcome evaluation were found in the static compared to the dynamic phase. Using the opposite contrast, dynamic decision-making showed higher activation in regions related to predicting and monitoring other´s actions, including the anterior cingulate cortex and insula. Cooperation (turn choice), compared to defection (continue choice), showed increased activation in mentalizing-related regions only in the static phase, while defection, relative to cooperation, exhibited higher activation in areas associated with conflict monitoring and risk processing in the dynamic phase. Men were less cooperative and had greater TPJ activation. Sibling competitive relationship did not predict competitive behavior but showed a tendency to predict brain activity during dynamic decision-making. Only individual brain activation results are included here, and no inter-brain analyses are reported. These neural correlates emphasize the significance of considering varying levels of information available and environmental settings when delving into the intricacies of mentalizing during social decision-making among familiar individuals. Task description: The Chicken Game simulates a risky situation where two participants drive cars towards each other; the one who swerves first loses and is labeled as the “chicken”. The Interactive Chicken Game task integrates decision-making in static and dynamic context, and feedback phases. During strategic decision-making in the static phase, participants had to answer the question "what is your plan?" by choosing between turning or continuing. This phase lasted for 4 seconds. After a brief fixation cross (0.5 s), the dynamic decision-making phase began with a car video (7 s). During this phase, participants adopted a first-person driver perspective on the video of their car driving toward the other participant's car, including the sound of an accelerating engine. They had to decide whether they wanted to turn and when. The decision period was divided into 5 one-second intervals to allow small windows that reflected a turn at the same interval. After five seconds, a "point of no return" was reached where participants could no longer press, and the car crash was imminent; simulating real-life scenarios where the risk of crashing escalates as the trial progresses. This phase not only increased immersion but also facilitated the exploration of decision-making within a more interactive framework. This was achieved by having different possible outcomes based on both the participant´s decisions and the timing of the decision. This design permitted the investigation of different degrees of cooperation beyond the binary “cooperate” or “defect” option in the static phase. During the car video phase, participants were exposed to different "feedback videos" depending on their decisions. If the participant (or both) chose to turn, the screen displayed the video of the participant’s car turning at different intervals (1-5 s). If the other participant opted to turn, the current participant saw the other car turning at different intervals (1-5 s). If neither participant turned, a car crash was shown (2 s). The game structure created the following outcomes: both turning (mutual cooperation), one turning (unilateral cooperation/defection), and both crashing (mutual defection). At the end of each trial, participants received points based on both participants’ decisions during the dynamic decision-making phase