Temporal isolation of neural processes underlying face preference decisions

Abstract

Decisions about whether we like someone are often made so rapidly from first impressions that it is difficult to examine the engagement of neural structures at specific points in time. Here, we used a temporally extended decision-making paradigm to examine brain activation with functional MRI (fMRI) at sequential stages of the decision-making process. Activity in reward-related brain structures-the nucleus accumbens (NAC) and orbitofrontal cortex (OFC)-was found to occur at temporally dissociable phases while subjects decided which of two unfamiliar faces they preferred. Increases in activation in the OFC occurred late in the trial, consistent with a role for this area in computing the decision of which face to choose. Signal increases in the NAC occurred early in the trial, consistent with a role for this area in initial preference formation. Moreover, early signal increases in the NAC also occurred while subjects performed a control task (judging face roundness) when these data were analyzed on the basis of which of those faces were subsequently chosen as preferred in a later task. The findings support a model in which rapid, automatic engagement of the NAC conveys a preference signal to the OFC, which in turn is used to guide choice.

Fig. 1.

Schematic diagram of a typical decision trial in the experiment. For each trial, two faces were briefly presented (50 ms) and repeated with one face alternating with the other until a subject makes a decision within 30 s by pressing a key. A blank screen with a cross-hair was inserted between each face presentation with a randomly varying interval between 1 and 3 s.

Fig. 2.

Regions showing greater response to chosen (C) vs. unchosen (U) faces in the preference-first group at different time points while deciding which face was preferred. (A) A statistical contrast map at the early repetition of faces (C_E–U_E) showing right NAC (arrow; x = 15, y = 3, z = −12; Z = 3.50, P < 0.001, uncorrected). (B and C) Statistical contrast maps of C–U for the late repetition of two cycle trials (C_L–U_L) shows left mOFC (x = −15, y = 27, z = −15; Z = 3.78, P < 0.001, uncorrected) (B) and left OP/INS (x = −39, y = 0, z = 15; Z = 3.94, P < 0.001, uncorrected) (C). (D) Temporal change of β coefficients in the max voxels of all three clusters, indicating a significant interaction of region × time [F (2, 26) = 6.27, P < 0.006]. Error bars indicate standard errors.

Fig. 3.

Brain responses to implicit face preferences. (A) Overall order of tasks in the two subject groups. The labels “Explicit” and “Implicit” refer to the kind of preference judgments in each task. While subjects performed an explicit roundness decision, we contrasted faces based on subjects' choices to those same faces in the preference decision task performed either earlier or later to examine neural activities related to implicit preference (shown in B and C). (B) NAC activity (arrows; x = 12, y = 3, z = −15; Z = 3.59, P < 0.001) in early cycles during roundness judgments correlating with subsequent preference judgments in the roundness-first group. (C) Implicit preference during the roundness task from the preference-first group showed a significant correlation with the activity in mOFC (x = 0, y = 39, z = −27; Z = 3.06, P = 0.001) at early cycles. (D) NAC showing greater responses to preferred vs. nonpreferred faces during early cycles for first, but not second, decisions on the same faces, regardless of the decision task that was explicitly performed.