Choosing the lesser of two evils, the better of two goods: specifying the roles of ventromedial prefrontal cortex and dorsal anterior cingulate in object choice

Abstract

The ventromedial prefrontal cortex (vmPFC) and dorsal anterior cingulate cortices (ACd) are considered important for reward-based decision making. However, work distinguishing their individual functional contributions has only begun. One aspect of decision making that has received little attention is that making the right choice often translates to making the better choice. Thus, response choice often occurs in situations where both options are desirable (e.g., choosing between mousse au chocolat or crème caramel cheesecake from a menu) or, alternatively, in situations where both options are undesirable. Moreover, response choice is easier when the reinforcements associated with the objects are far apart, rather than close together, in value. We used functional magnetic resonance imaging to delineate the functional roles of the vmPFC and ACd by investigating these two aspects of decision making: (1) decision form (i.e., choosing between two objects to gain the greater reward or the lesser punishment), and (2) between-object reinforcement distance (i.e., the difference in reinforcements associated with the two objects). Blood oxygen level-dependent (BOLD) responses within the ACd and vmPFC were both related to decision form but differentially. Whereas ACd showed greater responses when deciding between objects to gain the lesser punishment, vmPFC showed greater responses when deciding between objects to gain the greater reward. Moreover, vmPFC was sensitive to reinforcement expectations associated with both the chosen and the forgone choice. In contrast, BOLD responses within ACd, but not vmPFC, related to between-object reinforcement distance, increasing as the distance between the reinforcements of the two objects decreased. These data are interpreted with reference to models of ACd and vmPFC functioning.

Figure 1.

RTs and error rates to decision form and between-object reinforcement distance. a, RTs and error rates were significantly affected by decision form. Subjects were significantly slower and made significantly more errors when they responded to PunPun relative to RewPun and RewRew trials. b, In addition, RTs and error rates were significantly affected by between-object reinforcement distance. Subjects were significantly slower and made significantly more errors when they responded to close relative to medium trials, and to medium relative to far trials. Error bars indicate SE.

Figure 2.

Decision form and ACd/vmPFC responses. a–c, Sample stimuli and results of (ringed) responses for PunPun (a), RewPun (b), and RewRew (c) trials. d, The BOLD response within the ACd (3, 16, 46) was significantly greater to PunPun relative to RewPun and RewRew trials. e, The BOLD response within the vmPFC (0, 51, 0) was significantly greater to RewRew relative to RewPun and PunPun trials. Error bars indicate SE.

Figure 3.

Between-object reinforcement distance and ACd/vmPFC responses. a–c, Sample stimuli and results of (ringed) responses for close (a), medium (b), or far (c) between-object reinforcement distance. d, The BOLD responses within the ACd (1, 12, 24) increased as between-object reinforcement distance decreased. e, In contrast, the vmPFC (0, 51, 0) did not show any differential activation for close, medium, or far trials. Error bars indicate SE.

Figure 4.

vmPFC (0, 51, 0) response to total available reinforcement. a, b, The BOLD response within vmPFC increased as a function of increased total available reinforcement value (a) and value of option chosen (b). Error bars indicate SE.

Figure 5.

Overlay analysis for ACd. a, b, The BOLD response within the three identified ACd areas differentiated for type of decision form (a) and between-object reinforcement distance (b). Error bars indicate SE.