Model-free decision making is prioritized when learning to avoid harming others

Model-free and model-based choices when avoiding harming oneself and others. (A) Logistic regression coefficients predicting first-level stay/switch choices (mean ± SEM). Participants exhibited a main effect of staying after no pain, which indicated model-free behavior [t(35) = 4.618, P < 0.001, CI for beta estimate: 0.17, 0.42, Cohen’s d = 0.77] and a outcome × transition interaction, which indicated model-based behavior [t(35) = −3.173, P = 0.003, CI for beta estimate: −0.23, −0.05, d = −0.53]. Intriguingly there was also an outcome × recipient interaction [t(35) = −2.31, P = 0.027, CI of beta estimates −0.12, −0.008, d = −0.39] showing that participants were more model-free, and thus more likely to switch after pain and stay after no pain, independent of transition type, when making choices for another person. (B). The probability of repeating a choice at the first level (“stay”) is plotted as a function of the transition and outcome on the previous trial. This shows that the outcome × recipient interaction in A is mostly driven by fewer stay trials after pain, regardless of transition (two rightmost blue vs. orange bars). Thus, the more pronounced model free behavior for others is mostly driven by a lower probability of staying after pain outcomes rather than a higher probability of staying after no pain outcomes). (C) ω estimates from the best-fitting model showed that the ω parameter was significantly lower for other (0.45) than self (0.55), consistent with the regression analyses that showed people were more model-free when avoiding harm to others compared to self (P < 0.02). Asterisks indicate significant difference at P < 0.05.

(A and B) Ventral striatum (VS) encodes prediction errors (PE) of pain avoidance for self and other. Ventral striatum (right x = 10, y = 12, z = −4, k = 236, z = 5.84; left x = −16, y = 6, z = −10, k = 458, z = 5.77, P < 0.05 FWE whole brain-corrected after initial thresholding at P < 0.001) tracked model-free prediction errors for both self and other bilaterally, with no significant differences between conditions.

Thalamus/caudate signal distinguishes model-free prediction errors for avoiding harm to other vs. self. (A) Thalamus cluster from the contrast other prediction error > self prediction error (x = 16, y = −18, z = 0, k = 84, P = 0.033, Z = 3.50 FWE-SVC from an independent anatomical mask of the thalamus and x = 12 y = −2 z = 4, Z = 4.08, k = 125, P = 0.005 FWE-SVC after initial thresholding at P < 0.001 for a functional ROI derived from Neurosynth to the term “pain” and x = 10 y = −4 z = 4, Z = 3.83, k = 54, and P = 0.002 FWE-SVC for an 8-mm sphere from a meta-analysis of observed pain (68) overlaid on an anatomical scan to show the extent of activation. (B) For illustration, parameter estimates extracted from the thalamus cluster are shown separately for self and other prediction error (PE). See SI Appendix, Fig. S1 for a meta-analysis of neuroimaging studies with the term “pain” that highlights overlapping activation in the thalamus.