Status & monetary downward comparisons activated brain regions associated with reward processing while upward comparisons yielded loss‐related activity, as if downward/upward comparisons resembled gains/losses

Upward and downward comparisons across monetary and status domains. Zachary A. Yaple  Rongjun Yu. Human Brain Mapping, July 23 2020. https://doi.org/10.1002/hbm.25148

Abstract: The ability to accurately infer one's place with respect to others is crucial for social interactions. Individuals tend to evaluate their own actions and outcomes by comparing themselves to others in either an upward or downward direction. We performed two fMRI meta‐analyses on monetary (n = 39; 1,231 participants) and status (n = 23; 572 participants) social comparisons to examine how domain and the direction of comparison can modulate neural correlates of social hierarchy. Overall, both status and monetary downward comparisons activated regions associated with reward processing (striatum) while upward comparisons yielded loss‐related activity. These findings provide partial support for the common currency hypothesis in that downward and upward comparisons from both monetary and status domains resemble gains and losses, respectively. Furthermore, status upward and monetary downward comparisons revealed concordant orbitofrontal cortical activity, an area associated with evaluating the value of goals and decisions implicated in both lesion and empirical fMRI studies investigating social hierarchy. These findings may offer new insight into how people relate to individuals with higher social status and how these social comparisons deviate across monetary and social status domains.

4 DISCUSSION

For this study we were determined to test the common currency hypothesis for social status and monetary comparisons by performing a series of fMRI meta‐analyses. Common‐currency hypothesis assumes that the brain uses a ‘common currency’ to rank outcomes and actions analogous to monetary gains and losses (Landreth & Bickle, 2008). According to this hypothesis, we expected to show a similar pattern of activity for monetary and social status. First we adopted social comparison theory to operationally define downward and upward comparisons. To test the common‐currency hypothesis for monetary and social status contexts, we expected both brain maps to yield regions associated with reward and losses. This assumption was based on a previous meta‐analysis (Luo et al., 2018) showing that downward comparisons recruit reward‐related striatum while upward comparisons yielded bilateral insula and anterior cingulate cortical activation, reflecting neural processes associated with losses. Due to the inclusion of monetary and status‐related contrasts in this prior report, we found it necessary to separately perform and contrast meta‐analyses of monetary and status upward and downward comparisons.

4.1 Common activity for downward and upward comparisons

First and foremost, meta‐analyses of downward comparisons in both domains demonstrated common patterns of activity, namely activity within the right striatum. The right striatum is associated with learning associations between rewarding stimuli and motor responses (Pizzagalli, 2014), habitual learning (Patterson & Knowlton, 2018) and with learning new stimulus–reward contingencies (Knutson & Cooper, 2005; Rogers et al., 2004). This result confirms the notion that downward comparisons in both monetary and status domains are compatible with the common currency hypothesis since the striatum is typically associated with the reception of reward (Delgado, 2007; Haber & Knutson, 2010).

The common currency hypothesis would also predict regions associated with losses during upward comparisons such as the ACC and insula (Luo et al., 2018). Indeed, our meta‐analyses of upward comparisons in both domains demonstrated common patterns of activity, namely activity within the dorsal ACC (dACC). For status and monetary upward comparisons, the dorsal ACC was concordant across studies. Among social comparisons, the ACC is often associated with psychosocial functioning such as social neglect (Lockwood, Apps, Roiser, & Viding, 2015; Lockwood & Wittmann, 2018; van der Molen, Dekkers, Westenberg, van der Veen, & van der Molen, 2017), monitoring of other people's decisions (Apps, Balsters, & Ramnani, 2012), and motivated social cognition (Hughes & Beer, 2012; Wittmann, Lockwood, & Rushworth, 2018). This may suggest that the ACC is a common active region associated with social interactions. The dorsal ACC also plays a key role in the processing of prediction errors and expectation violation (Kedia et al., 2014; van der Molen et al., 2017), which may corroborate the common currency hypothesis since individuals viewing others as beneficial may reflect a “worse than expected” prediction error (van der Molen et al., 2017; Yu & Zhang, 2014).

Such downward‐striatum and upward‐dACC activity patterns in social comparison across domains suggest that the basic reward and aversion brain systems are underlying this well‐known social phenomenon, regardless of the social settings. These findings highlight the pervasiveness of human tendency to compare with others and point out that such tendency is closed linked to the basic reward evaluation system. Our study may help explain why humans are prone to social comparison in all types of social areas, ranging from important social dimensions like attractiveness, wealth, and intelligence, to trivial things such as speech order and seating arrangement. It has been demonstrated that humans learn and evaluate values in a relative—context‐dependent—scale such that the context value sets the reference point to which an outcome should be compared (Palminteri, Khamassi, Joffily, & Coricelli, 2015). Hence, individuals may drive pleasure for winning $100 in the context of others winning only $10 or for publishing a paper in a mediocre journal in the context of colleagues having no publications. The reward evaluation system may convert all values to a common currency and scale it to a relative value so that even a small value can have huge impact on an individual's emotions. The computational mechanisms of common currency evaluation circuits may help explain how individuals respond to social comparison in different domains and with different magnitude of importance.

4.2 Unique activity for monetary and status comparisons

The contrast analyses revealed domain‐specific activity in social status and monetary comparisons. For example, downward comparisons in the monetary domain recruited greater activity within the orbital frontal gyrus/ventral ACC, right striatum as well as right precuneus and precentral gyrus, while status downward comparisons revealed no additional clusters, indicating additional processes for monetary compared to status comparisons. Upward monetary comparisons demonstrated larger clusters within the bilateral insula and dorsal anterior cingulate cortex compared to status comparisons. The insula may account for evaluations of social comparisons since the insula has been attributed to anticipating and evaluating the consequences of one's actions (Simmons et al., 2011; Späti et al., 2014), and self‐initiated actions in social exclusion trials (Wang et al., 2019). Additional activity in monetary domain for downward comparison may indicate that financial advantage is more salient than social status advantage. On the other hand, social status upward comparisons yielded activity within the orbitofrontal cortex/ventral ACC, as well as left superior occipital and posterior cingulate cortex. Such unique activity pattern for social upward comparison may speak to the strong motivational nature of lagging behind in social ladders. Being lower in social status is an important teaching signal for individuals as it is often linked to social defeat and other disadvantages when acquiring social resources. Lower social ranking in the animal kingdom may also be associated with social threat and being intimidated by higher ranking others. Interestingly, the orbital frontal cortex was the only region active in both upward and downward comparisons, greater in the monetary context when making downward comparisons, yet greater in the social status context when comparing others with higher status. The orbital frontal cortex is an area commonly known for evaluating value of goals and decisions (Elliott, Newman, Longe, & Deakin, 2003; Hare, O'Doherty, Camerer, Schultz, & Rangel, 2008; O'Doherty, Critchley, Deichmann, & Dolan, 2003), and which has been implicated in both lesion (Karafin et al., 2004; Mah et al., 2004) and empirical fMRI studies investigating social hierarchy (Kumaran et al., 2016). Recently a large meta‐analysis had shown that the medial orbital part of the medial prefrontal cortex (i.e., the ventral medial prefrontal cortex; BA 11) is specifically recruited for the processing of situations, while processing of self and others recruits mainly the anteromedial and dorsomedial sub‐regions of the prefrontal cortex, respectively (Lieberman, Straccia, Meyer, Du, & Tan, 2019). With regard to the current study, this may suggest that upward status and downward monetary comparisons involve situational processing since both yielded medial prefrontal cortical activity (labeled as orbitofrontal cortex in Tables 3, 4, 5, and 6). However, downward monetary comparisons appeared to yield a medial prefrontal cortex cluster slightly more anterior than the upward status comparison contrast, possibly indicating additional self‐referential processing.

Upward and downward social comparisons have been shown to reflect both positive and negative outcomes. For instance, evaluation of others in the upward direction may include admiration or envy toward superior peers (Hagerty, 2000; Suls, Martin, & Wheeler, 2002) whereas downward comparisons may lead to the encouragement of subordinates to strive for success rather than gloat over one's own gains (Gibbons, 1986; Wills, 1981). The finding that the OFC is activated by both upward and downward comparison may suggest that humans are actively engaged in the detection of “self‐other” differences. Monitoring whether others are different from us, regardless of being better or worse, may help mobilize resources to evaluate and resolve the social deviation. This finding indicates that social comparison is an important learning process that helps individuals to sense whether anything, in comparison with others, is out of order. Perhaps differential activation of the orbitofrontal cortex may relate to how one may be evaluating others since this region is the only region to be associated with both directions of the comparison and is functionally related to evaluation (Cloutier & Gyurovski, 2014; Elliott et al., 2003; Hare et al., 2008; O'Doherty et al., 2003). However, this notion has yet to be tested in an empirical setting. Moreover, we were unable to distinguish upward and downward comparisons that were either worse or better than expected. Few articles examined whether participants perform better or worse than someone lower in the social hierarchy (Zink et al., 2008), which may account for the functional differences in upward and downward comparisons. Potentially achieving a higher superior position could be a rewarding experience but also be associated with antagonistic retaliation (Fiske, 2010). The interaction between social status and relative performance and its relationship to the orbitofrontal cortex could be an exciting topic for future neuroimaging research.