Task Displays, Timing, and Design
Each trial began by the subject indicating his or her preference for either a song that the subject provided or an unrecognized alternative (by moving his or her picture beneath the preference). Songs choices (one on left, one on right) appeared above pictures of reviewers and the subject (aligned in the center) in white font. Pictures were black and white. Subjects pressed the left button to move their picture left or the right button to move it right. A scrambled picture of the subject was placed on the opposite side. Next, subjects learned the reviewer opinions. The picture of each reviewer was moved under his or her respective preference. A scrambled picture of each reviewer was placed on the opposite side. Finally, the songs flashed between white and green font and one song was chosen for the subject's token, which appeared at the bottom of the screen in green font. Review outcomes were independent of object outcomes. Subjects knew that the ten songs with the most tokens at the end of the task would be purchased for them. A 2 s intertrial display (not shown) was a fixation cross.
In the 2 × 3 design (top right), the independent variables were review outcome: R_S (reviewers chose the subject's preferred song), R_A (reviewers chose the alternative), and R_SPLIT (split; one reviewer chose the subject's preferred song; the other chose the alternative); and object outcome: S (subject gained a token for his or her preferred song) and A (subject gained a token for the alternative song). These variables formed a 2 × 3 design matrix of six conditions: R_SS, R_SA, R_AS, R_AA, R_SPLITS, and R_SPLITA. The example shown corresponds to the R_AS condition. See Supplemental Experimental Procedures for full task description.

Main Effects
(A) Object outcome [R_SS + R_AS] – [R_SA + R_AA]. Highlighted anatomy was more active when the participant received a token for his or her originally preferred song relative to receiving one for the alternative.
(B) Review outcome [R_SS + R_SA] – [R_AS + R_AA]. Highlighted anatomy was more active when both reviewers agreed with the subject's preference compared to when they both preferred the alternative. Green maps show activation of the same contrast at a slightly reduced cluster definition threshold (Z > 2.0, p < 0.05). See also Figure S2 and Table S2.
(C) Unanimous reviewer agreement [R_SA + R_SA] – [R_SPLIT]. Highlighted anatomy is more active when both reviewers agree with the subject than when one chooses the subject's song and the other chooses the alternative.
(D) Unanimous reviewer disagreement [R_AA + R_AS] – [R_SPLIT]. Highlighted anatomy is more active when both reviewers disagree with the subject compared to when one chooses the subject's song and the other chooses the alternative. Unless otherwise specified, all activations are whole-brain cluster-corrected Z statistic maps (Z > 2.3, p < 0.05), which were overlaid onto the standard MNI brain. Coordinates of brain sections are indicated in MNI space (mm).

Disagreement with Others and Social Influence
[[R_AS + R_AA] – [R_SS + R_SA]] × B_inf. In the contrast of disagreement relative to agreement, the highlighted anatomy's activation varied between subjects with B_inf. The more an individual was influenced by reviewer opinions, the more insula cortex and/or central opercular cortex (right peak 52, 8, 2; left peak −38, 14, 0), dorsal anterior cingulate cortex (peak 4, 16, 34), and lateral prefrontal cortex (right peak 36, 48, 22; left peak −44, 48, 4) and right temporoparietal junction (TPJ) (66, −30, 36) activity was produced when he or she disagreed with the reviewer. Activations are whole-brain cluster-corrected Z statistic maps (Z > 2.3, p < 0.05), which were overlaid onto the standard MNI brain at coordinates (mm) 4, 48, 0. Search depth of overlay in 3D image is 8 mm from the surface.

Social Influence on Value of Objects
[[R_SS – R_SA] – [R_AS – R_AA]] × B_inf. Subjects received their preferred song or the alternative after learning what reviewers preferred. The left panel shows the location of statistically significant reward activation due to social influence in the ventral striatum (400 voxels, Z_max = 3.44, right peak 10, 18, −8; left peak −6, 14, −8). The map results from the contrast of the interaction between review outcome and object outcome varying between subjects with B_inf. Activations are whole-brain cluster-corrected Z statistic maps (Z > 2.3, p < 0.05), which were overlaid onto the standard MNI brain at coordinates (mm): −8, 14, −8. The right panels plot the mean parameter estimates (PEs) for five high-influence (most positive B_inf), five low-influence (B_inf near 0), and five anti-influence subjects (most negative B_inf) within the active cluster in the left panel (ventral striatum). The right panel is for illustration of the interaction only. This plot's standard error bars (±1) should be interpreted knowing that only five participants are indicated in each panel. Statistical inference should be made from the left panel and Table S1.