Acting together: A study reveals the neural dynamics of shared action.

Anyone who has ever danced a tango or mixed a cocktail with a friend knows that acting together isn't the same as simply moving side by side. Yet, despite this difference being an integral part of everyday experience and crucial to understanding the evolution and development of human sociality, cognitive neuroscience has long overlooked it.

A new study—coordinated by Corrado Sinigaglia, head of the Cognition in Action Lab (PHILAB) at the University of Milan, and Marta Bortoletto, a cognitive neuroscience researcher at the IMT School for Advanced Studies in Lucca, in collaboration with Sapienza University of Rome and the Centro San Giovanni di Dio Fatebenefratelli Institute in Brescia—has investigated for the first time the neural dynamics that distinguish acting together from acting in parallel.

The research, published in Social Cognitive and Affective Neuroscience, shows that the neural processes underlying shared action are profoundly different from those regulating simply acting "side by side": sharing a collective goal initially entails a cognitive cost, but this is offset by a facilitation in the final phase of the action, likely due to the greater predictability of the partner's movements.
"These discoveries shed new light on the mechanisms underlying human sociality and open up exciting prospects for understanding and treating disorders characterized by social difficulties, such as autism and schizophrenia," explained Corrado Sinigaglia, corresponding author of the study.

Methodology of the study

By simultaneously recording the brain activity of pairs of participants via electroencephalography (dual EEG) during a video game, the researchers were able to compare two conditions: in the first, the participants jointly transported an object toward a shared goal (joint action), while in the second, each pursued an individual but parallel goal (parallel action). The tasks were equally difficult, but the results revealed surprising differences.
Behavioral variability between partners decreased when participants acted together. Neural variability, however, revealed a distinctive pattern shift in ERPs (electrophysiological responses) during action preparation: in the initial phase, amplitude was greater during the joint action, but in the final phase—the actual motor preparation—the opposite occurred. Even more importantly, the reduced amplitude of late ERPs correlated with lower variability in the partner's behavior, indicating that different cognitive processes operate in the different phases of action preparation.