The brain's temporal dynamics from a collective decision to individual action

Abstract

Social animals constantly make decisions together. What determines if individuals will subsequently adjust their behavior to align with collective choices? Here, using functional magnetic resonance imaging in humans, we characterize a novel temporal model of brain response from the time a collective decision is made to the time an individual action is required. We reveal that whether a behavioral modification will occur is determined not necessarily by the brain's response to the initial social influence, but by how that response (specifically in the orbitofrontal cortex; OFC) is mirrored at a later time when the individual selects their own action. This result suggests that the OFC may reconstitute an initial state of collective influence when individual action is subsequently needed. Importantly, these dynamics vary across individuals as a function of trait conformity and mediate the relationship between this personality characteristic and behavioral adjustment toward the group.

Keywords: OFC; collective behavior; decision-making; fMRI; orbitofrontal cortex; social influence.

Figure 1.

Experimental design. A, Participants came to the lab in groups of five and spent ∼30 min together filling forms and learning about the task. Then one participant completed the task inside the MRI scanner while the other four completed it in separate computer booths. The experiment consisted of four sessions. B, In Session 1 (rating session) subjects were presented with 120 items and asked how much they would like to receive the item at the end of the study. These ratings were used to pair stimuli in the decision-making task. C, Participants then completed a collective decision-making task in which 60 pairs of items were presented and each subject voted for their preferred item. The “majority vote” was then revealed with an asterisk (*). Subsequently, subjects rated all items again (D) and had the opportunity to make individual choices between all pairs of items (E).

Figure 2.

Collective decisions induce behavioral change. For high conformers (subjects scoring high on the trait conformity questionnaire), the likelihood of choice reversals following a collective decision that was inconsistent with their own vote was greater than when it was consistent and greater than for low conformers. Choice reversals were trials in which subjects selected an item during Session 4 (individual decision-making task) that was different from the item they voted for during Session 2 (collective decision-making task). The two-way (high/low conformers × consistent/inconsistent collective choices) interaction was significant. *p < 0.05, two-tailed t test; error bars indicate SEM.

Figure 3.

OFC response to a collective decision predicts subsequent response when making an individual choice. A, Enhanced BOLD response was observed in the right OFC when subjects learnt that the collective decision was inconsistent with their own vote, relative to when it was consistent (p < 0.05 FWE, anatomical SVC; displayed at p < 0.005, uncorrected). B, BOLD signal was extracted from this region for each specific trial and added as a parametric modulator predicting BOLD signal when an individual decision was to be made regarding the same pair at a later time. Parameter estimates were then averaged over the anatomically defined subregions of the right OFC as defined by the AAL atlas. For illustration purposes, the red frames in the trial design in A and B denotes the time of the trial when BOLD response was analyzed. C, A significant interaction emerged in the right superior OFC. Past OFC response to collective decision positively predicted subsequent OFC signal when making an individual selection between a pair of items for which subjects' initial vote was inconsistent with the collective decision in high conformers, a trend for a negative correlation emerged for low conformers, and no correlation emerged when the initial vote was consistent with group outcome. D, Across participants, the relationship between past and subsequent OFC response predicted behavioral change (i.e., choice reversals). Specifically, the greater the positive correlation between these signals on inconsistent trials, the more likely an individual was to reverse their choices to align with collective decisions that were initially inconsistent with their own. *p < 0.05, two-tailed t test; error bars indicate SEM.

Figure 4.

Mediation model: OFC temporal dynamics mediate the relationship between trait conformity and behavior. Values represent unstandardized coefficients for each effect of interest, with corresponding t statistics and p values or bootstrapping confidence interval (for indirect effect) to assess significance. Across subjects, the indirect effect of trait conformity on choice reversals, mediated by the strength of intertemporal coupling in the right OFC (red path) was significant.