###### Abstract  
This hyperscanning study explores the central (hemodynamic) and peripheral (autonomic) markers of persuasion within a shared decision-making process. Decision-making was examined through a task where two decision-makers assumed the role of Persuader (P-der) and Persuaded (P-ded), with the P-der aiming to increase group decision orientation in the P-ded. Data were collected from 14 dyads using functional near-infrared spectroscopy to measure prefrontal cortex (PFC) hemodynamic activity and collection and recording of autonomic indices including heart rate (HR) and HR variability (HRV). The analysis focused on two phases: Phase 1, where the P-der presented the scenario and enacted their persuasive strategy, and Phase 2, characterized by the P-ded's response. The results revealed significant effects on the dissimilarity indices at the dyadic level. Compared with Phase 1, Phase 2 included higher oxygenated hemoglobin dissimilarity in the PFC, indicating greater inter-dyadic divergence during the P-ded's response. HR dissimilarity increased when the P-ded spoke, suggesting disrupted synergy, while HRV dissimilarity was higher when the P-der spoke, potentially reflecting differences in stress regulation. These findings suggest that neurophysiological coherence varies based on persuasion phases within shared decision-making, with P-ded introducing greater dissonance in dyads synergy. Compared with single-subject approaches, dyadic analyses offer a more accurate understanding of the interpersonal nature of persuasion dynamics during decision-making. decision-making; persuasion; fNIRS; autonomic indices; hyperscanning; dyadic interaction; dissimilarity index +
Footnote †: journal: Applied sciences  
0000-0002-4000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-00000-000 For instance, hyperscanning enables the simultaneous monitoring of brain activity in two individuals engaged in a shared task, capturing the implicit mechanisms of interaction between them [2]: this approach offers valuable insights into the intricate dynamics of persuasion [3; 4; 5]. The majority of studies have traditionally focused on examining the neural activity of P-ders and P-deds separately, analyzing intra-brain processes while overlooking the dynamic two-way interactions between them; this approach provides only a partial understanding. In contrast, a brain-to-brain perspective offers a valuable method for investigating functional connectivity between individuals during social interactions [4; 6; 7]. This perspective can shed light on cognitive, emotional, and behavioral similarities or differences between P-ders and P-deds during communication exchanges when a shared decision must be taken [8]. Indeed, by conducting coherence analysis on dyads rather than focusing solely on individual subjects, it becomes possible to observe the interpersonal dynamics at play. This approach reveals how strategies differ depending on whether the P-der or the P-ded is speaking, independent of their assigned roles. Hyperscanning, in particular, highlights the synergy between strategies, not as isolated elements (i.e., not just the P-der and the P-ded alone) but as a cohesive interplay. Previous hyperscanning research on the persuasion process highlighted that interpersonal coupling between P-der and P-ded could be read as a crucial component of effective persuasion, beyond the brain activity observed in each individual alone [9; 10]. Shared neural responses are often seen as indicative of successful communication and proximity and synergy within a social group [10; 11; 12; 13]. In a recent hyperscanning study with functional near-infrared spectroscopy (fNIRS), [PERSON] and colleagues [10] demonstrated that neural coupling of oxyhemoglobin was a key predictor of persuasion outcomes (i.e., the P-ded's compliance).