(A) Schematic of social transfer of analgesia protocol and timeline. (B) Mechanical sensitivity at 0, 4, 24, 48, 72 h and 1 week post 1 h social interaction in CFA-Con/CFA-CON pairs and CFA-Mor/CFA-Analg-BY pairs. (C) Time (%) on the warm (40° C) floor in the thermal place test (TPT) prior to and 1 h and 1 week (wk) post CFA injection. (D) Time (%) on the warm (40° C) floor in the TPT immediately after the second 1 h social transfer of analgesia, 1 week post CFA injection. (E) Schematic of YFP and NpHR injection and optogenetic stimulation in ACC or NAc. Light stimulation (~10–15 mW, 8 s on/2 s off) periods represented by yellow-green boxes. (F) First light off session measuring mechanical sensitivity following light stimulation of ACC in YFP- and NpHR-expressing CFA-Con and CFA-Analg-BY mice during social transfer of analgesia. (G) Time (%) on the warm (40° C) floor in the TPT following light stimulation of ACC in YFP- and NpHR-expressing CFA-Con, CFA-Mor, and CFA-Analg-BY mice during the second social transfer of analgesia test. (H) First light off session measuring mechanical sensitivity following light stimulation of ACC→NAc projections in YFP- and NpHR-expressing CFA-Con and CFA-Analg-By mice during social transfer of analgesia. (I) Time (%) on the warm (40°C) floor in the TPT following ACC→NAc light stimulation in YFP- and NpHR-expressing CFA-Con, CFA-Mor, and CFA-Analg-BY mice during the second social transfer of analgesia test. Data are means ± s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, **** P < 0.0001. Two-way repeated measures (B) or one-way (C,D,F–I) ANOVA with Holm-Sidak post hoc tests comparing between groups. Not all significant post hoc analyses are displayed. All statistical measure details are presented in Table S1E.