Article Figures & Data
Figures
- Figure 1.
Experimental design. A, One round of the two-player RTG. P1 is the payoff of the participant, who always plays as investor; P2 is the payoff of his counterpart, who plays as trustee. Before each round both players are endowed with €1. The participant moves first and chooses either to “keep” or “share.” If he keeps, both players maintain their initial endowments. If he shares the participant's endowment is multiplied by 3 and passed to the counterpart. The trustee then decides whether to share in turn (by returning €2), or to keep (by returning nothing). RTGs consisted of several consecutive rounds with the same counterpart. Participants played with many different counterparts and were told that their counterparts had already made their choices. B, Experimental conditions. Two conditions were adopted: (1) the “type” of counterpart and (2) the presence versus absence of “reputational priors.” Types: counterparts could be either “cooperative” or “individualistic” in their (simulated) behavior in RTGs; the former shared and the latter kept in 80% of RTG rounds. Reputational priors: participants were told that cues indicated whether the current counterpart had obtained a high or low score in a social orientation task (triangles indicated low scores, circles indicated high scores). Such priors reliably differentiated between the two counterpart types. C, Time line of the first RTG round. Presentation: face of the counterpart (with a prior or no-prior) was displayed for 3.5 s, and only presented for the first round of an RTG. Fixation: Fixation cross was presented during a jittered ISI. Choice: participants made their choice by pressing “Keep” or “Share.” Delay: ISI corresponding to the (simulated) decision of the counterpart. Outcome: outcome of the game and the payoffs of each player.
- Figure 2.
Behavioral results. A, Average percentage of decision to trust across conditions. Mean ± SE of participants' decision to trust (share) are broken down for trustee's type (Cooperative/Individualistic) and prior condition (Prior/No Prior); ***p < 0.001. Priors enabled participants to match (on average) their choices with the counterpart's level of trustworthiness. B, Learning dynamics across RTG rounds. Average percentage of the decision to trust for each round when playing with a “cooperative” versus “individualistic” counterpart, and when priors were present versus absent. When participants know nothing of their counterparts they tend to randomize between trusting and not trusting during initial rounds and adjust their choices to their counterparts' type in succeeding rounds. On the other hand, when priors are present, participants tend to rely on them already from early rounds. Shaded areas above and below the curves are SEs. C, Average payoffs in the Prior and No-Prior conditions. Average payoffs ± SE (in €) in Prior/No Prior conditions. When priors are available, participants significantly earn more when they adjust their choices to counterparts' types; **p < 0.01. D, Choices following unexpected behavior of cooperative and individualistic counterparts. Average (±SE) of percentage of “keep” choices in prior versus no-prior condition at time t, following rounds in which participants shared and a cooperative counterpart violated their trust by deciding to keep (at t − 1). Decisions to Keep at time t (i.e., retaliation) were less frequent when priors were available. E, Percentage of “share” choices (at t) following rounds in which participants had kept and an individualistic counterpart has shared (at t − 1).
- Figure 3.
mPFC encodes reputational priors when a new counterpart is first presented. A, Random effect analysis. When contrasting (Prior) > (No Prior) conditions at time of counterpart presentation, activity in the mPFC survived FWE correction, p < 0.05. B, Functional ROI analysis in mPFC. Functional ROI analyses further revealed percentage signal changes in the mPFC cortex MNI (0, 62, 31). The figure shows an increased activity when priors were present, regardless of their type, and decreased activity when there were no priors.
- Figure 4.
Brain regions parametrically correlated with the estimated “optimistic” and “pessimistic” decision value from the Prior model. A, Random effect fMRI analysis. To look for neural correlates of value signals (Qt) at time of choice, we entered the trial-by-trial estimates of the values of the two stimuli (Share and Keep) into a regression analysis against the fMRI data. We found enhanced activation in mPFC and dLPFC, surviving FWE correction, p < 0.05. B, Functional ROI analysis in mPFC. Percentage signal change by condition in the mPFC area represented in A. A similar pattern of activity was found in the dLPFC (not reported). These regions encoded prior valence (positive and negative) that guided decision to trust at time of choice. Error bars indicate SE.
- Figure 5.
Brain regions parametrically correlated with the estimated prediction error of the best-fitting RL model. A, Random effect fMRI analysis: Activity of the caudate showed significant correlation to the estimated prediction error signal in the no-prior condition (p < 0.05 FWE corrected). Such activities were not observed in this brain area in the prior condition. Peak coordinates are given in MNI space. Color bars indicate T values. B, Parameter estimates were extracted from the left caudate (−12, 20, 8) for the direct comparison between prior and no-prior conditions. Caudate activity correlates with prediction error in the no-prior condition only.
- Figure 6.
Functional connectivity between the caudate nucleus and vLPFC correlates with the choice to retaliate after violation of trust in the prior condition. A, PPI analysis. With a caudate seed, bilateral vLPFC shows stronger connectivity with this region in the prior compared with the no-prior conditions. B, vLPFC prevents retaliation to violation of trust in the prior condition. vLPFC anticorrelates with retaliation rate in the prior condition after participants experimented violation of trust from a cooperative counterpart. Spearman r = −0.6, p < 0.009. C, Reputational priors magnify striatal response to violation of trust. The caudate shows a stronger deactivation to violation of trust from a cooperative counterpart in the prior condition compared with the no-prior condition. D, Striatal responses to violation of trust and learning rates. The correlation between caudate and learning rates is significant only in the no-prior condition, thus striatal responses to violation of trust in the prior condition are not reflected in learning.
Tables
Learning model comparison Classical model-free TD learning model Prior+ and Prior− expectations RL learning model BIC 7619 6460 Log likelihood (random model = −4442) −3809 −3230 Pseudo r2 0.14 0.273 Bayesian information criterion value (BIC), Log likelihood, and the pseudo r2 suggest that the Prior+ and Prior− expectations TD learning model fits the observed behavior better the other TD learning models.
Parameter estimate for best behavioral model, depicted as mean ± SE Mean SE Learning rate Prior condition αP 0.3373 ± 0.0456 Estimates for Cooperative counterparts 0.327 ± 0.0424 Estimates for Individualistic counterparts 0.3475 ± 0.0398 Learning rate No Prior condition αNP 0.5075 ± 0.0689 Estimates for Cooperative counterparts 0.4686 ± 0.0701 Estimates for Individualistic counterparts 0.539 ± 0.0599 Estimates learning rates for Invest trials (participants shared) 0.3845 ± 0.0459 Estimates learning rates for Non-Invest trials (participants kept) 0.4603 ± 0.0476 Softmax inv. Temp Betha β 4.7769 ± 0.3149 Initial value Cooperative Prior condition, QP+(0) 1.3814 ± 0.1031 Initial value Individualistic Prior condition, QP−(0) 0.9838 ± 0.1055 Initial value No Prior condition QNP(0) 1.0641 ± 0.126 Analysis/Location BA Side Cluster size T p value FWE cor. MNI coordinates (mm) X Y Z Prior > No Prior (GLM 1) mPFC 10 95 8.26 6.8 × 10−06 0 62 31 VTA — 14 3.177 0.0032 unc. 0 −1 −5 No Prior > Prior (GLM 1) Anterior insula 44 Left 106 3.912 0.0009 unc. −36 −4 15 Anterior insula 44 Right 55 3.450 0.0017 unc. 38 3 10 Parametric regression of Choice (GLM 2) mPFC 10 — 87 6.562 2.7 × 10−06 −2 64 10 Lateral PFC 46 Left 122 5.987 7.8 × 10−05 −38 38 32 Lateral PFC 46 Right 109 6.342 2.1 × 10−06 30 38 34 Superior parietal lobule 48 Left 43 5.01 6.7 × 10−04 −38 6 24 Parametric regression at Outcome for the No Prior condition (GLM 2) Caudate nucleus — Left 77 7.091 8.9 × 10−06 −14 20 2 Caudate nucleus — Right 56 8.298 7.9 × 10−06 12 16 8 Violation of rust in the Prior condition (GLM 3, Cons > Incons) Caudate nucleus — Left 82 6.78 2.8 × 10−06 −10 18 11 Caudate nucleus — Right 56 6.34 2.4 × 10−06 12 21 5 Note: BA, Brodmann area; mPFC, medial prefrontal cortex; VTA, ventral tegmental area.
