Neuroeconomics processes underlying decision-making in joint vs individual actions: a behavioral and EEG study on non-human primates

A hallmark of the successful evolution of our species could reside in the ability to optimize collective behavior in order to achieve goals otherwise unattainable by acting alone. Inter-individual motor coordination can be considered as a key feature of sharing actions with others. As much as advantageous though, acting together can also be costly since it requires special cognitive and motor skills. We know that non-human primates are able to coordinate their actions in a dyadic context by dynamically adapting their motor behavior in a way that favors inter-individual synchronization. However, this type of behavioral adaptation has been proved to entail a cost, which is evident in a reduction of successful monkeys’ performance when sharing actions for a common goal. In the recent years, the existence of internal models of the own and the other’s action has been hypothesized by several authors, but how these models are formed and coded at the neural level is still object of study. The currently most accredited hypothesis is that acting with others requires the ability to integrate one’s own and others’ action representations in a dyadic motor plan. In order to better understand the behavioral and neural underpinnings of sharing actions, we conducted three experiments. In the first part of this work (Experiment 1) we investigated whether, how and under which task conditions monkeys can improve their performance in a joint action task. To address these questions, we have investigated the influence of a pre-instructing “social cue” providing anticipatory information about action context (individual or joint). Our findings suggest that pre-instructing the action context increase the chances of dyadic success by establishing an optimal “kinematic setting” that ultimately facilitates inter-individual motor coordination. Moreover, we speculate that such joint performance improvement can be ascribe to a successful resort to a “we-representation”, possible only when the joint action is pre-cued. In the second part of this thesis (Experiment 2) we aimed at investigating monkeys’ ability to estimate the cost of acting together and to use this information to decide between acting alone or jointly with a partner. To this aim we trained two monkeys to choose between two possible goals, each associated to different action types (solo or together) and payoffs. Our findings suggest that their economic choice was not merely dictated by the reward offered but also by the action cost, whereby motor inter-individual coordination was evaluated as more demanding than individual action. In the third and final part (Experiment 3) we conducted dual neural recordings using electroencephalography (EEG) while the monkeys were working on the same task adopted in Experiment 2. Preliminary results demonstrate that monkeys’ response evoked by the two offers was modulated by the action type chosen or expected to be chosen by the partner. This provides, for the first time, evidence of the feasibility of studying neural correlates underlying value-based decision making in non-human primates by mean of EEG methods.