Neural structures for ingroup bias and its malleability.

805 

Abstract Submission 

Pyungwon Kang¹, Yurong Sun², JuYoung Kim³, Hackjin Kim³, Sunhae Sul⁴, Grit Hein⁵, Philippe Tobler⁶

¹University of Zurich, Zürich, Switzerland, Other, ²East China Normal university, Shanhai, China, ³Korea University, Seoul, Korea, Republic of, ⁴Pusan National University, Pusan, Pusan, ⁵University of Würzburg, Würzburg, Germany, ⁶University of Zurich, Zurich, Switzerland

Pyungwon Kang  
University of Zurich
Zürich, Switzerland, Other

Yurong Sun  
East China Normal university
Shanhai, China

JuYoung Kim  
Korea University
Seoul, Korea, Republic of

Hackjin Kim  
Korea University
Seoul, Korea, Republic of

Sunhae Sul  
Pusan National University
Pusan, Pusan

Grit Hein  
University of Würzburg
Würzburg, Germany

Philippe Tobler  
University of Zurich
Zurich, Switzerland

Ingroup bias is the tendency to favor ingroup members over outgroup members. It is pervasive in humans and contributes to inter-group conflict based on nationality or race (Bernhard, Fischbacher, & Fehr, 2006; Brewer, 1979, 1999). Although many neuroimaging studies investigated brain correlates of ingroup bias, most of them focused on differences in neural activity elicited by ingroup versus outgroup conditions (Han, 2018; Molenberg 2013). Thus, it remained largely unknown whether differences in neural structures underpin differences in ingroup bias. Here, we investigated the grey-matter volume of brain areas associated with implicit (implicit association test) and explicit (donation) measures of ingroup bias as well as their change over time.

We combined two studies, performed with two different types of outgroups in South Korea, and measured the bias of South Koreans against individuals from outside South Korea. More specifically, in both studies, participants (Study 1: n=70, 35 female, age: 25.75±3.86 years; Study 2: n=108, 52 female, age: 23.44±2.24 years) decided whether to incur a monetary cost to donate to charities benefitting the ingroup (Study 1 and 2: South-Koreans) or outgroup (Study 1: North Koreans; Study 2: Southeast Asians in South Korea) and performed an implicit association task (Greenwald et al. 1998) towards ingroup and outgroup members with positive and negative words. We examined whether the association between the volume of cortical and subcortical brain regions and behavior were specific for the type of ingroup bias measure and/or for the type of outgroup or whether a brain region commonly associated with multiple ingroup bias behavior.
In addition, to investigate structural commonalities related to the change of implicit and explicit biases in different types of behaviors as well as different intergroup settings, we measured the same types of behaviors (IAT and donation) before and after indirect exposure to outgroup-related information through a political event (Study 1 : inter Korea summit which occurred only for the second time within 70 years at the time of the first measurement) and to video-clips featuring interviews with outgroup members conducted in Korean (Study 2).

We found that the grey-matter volume of a cluster in the putamen (Z=3.76, small volume corrected p < 0.05) was positively correlated with greater donation to charities benefitting the ingroup. In contrast, the volume of clusters in ventromedial prefrontal cortex (Z =4.74, whole brain corrected p < 0.001) and inferior temporal lobe (Z = 3.86, whole brain corrected p < 0.001) correlated positively and primarily with stronger implicit bias (i.e. D score) favoring the ingroup, indicating that the grey-matter volume and ingroup bias relations are more task specific. In addition, grey-matter volume in a dorsal anterior cingulate cortex (dACC) cluster correlated with the change of the ingroup biases in both implicit and explicit biases in the two studies (IAT: Z= 3.93, whole brain corrected FWE p <0.05, donation : Z = 3.09, small volume corrected FWE p <0.05) indicating that the dACC may contribute to the change of ingroup bias in a broad sense. Age, total intracranial volume, and the experiment types were controlled in all analyses.

Both the strength of the ingroup bias and its malleability appear to be related to differences in neuroarchitecture, in-keeping with the notion that brain-based interventions can reduce the bias.

Social Cognition ¹

Social Neuroscience Other ²

Social Interactions

Other - ingroup bias