Where does ‘us versus them’ bias in the brain come from?
Modern genetics has established that all humans are equal. But human history is replete with people from one cultural or social group treating those from others as if they are less than human. The basis of this deep-seated tendency continues to be the foc
“AAnimal Farm ll animals are equal, but some are more equal than others” — this line from George Orwell’s 1945 classic perfectly describes how bias operates in human societies.
In a study published in May last year, psychologists explored how people subconsciously evaluate dierent racial groups. They screened responses from more than 60,000 participants belonging to four groups: ‘white’, ‘blacks’, ‘Hispanics’, and ‘Asians’ (67% of them lived in the U.S.).
Using a psychological test called an implicit association test (IAT), scientists found stark dierences between participants’ explicit statements and their implicit beliefs. While everyone said they believed in the equality of all races, they also harboured implicit biases in favour of socially advantaged groups. This bias was also universal, irrespective of the racial identity of the participants.
The IAT is built on the premise that if two things — words, concepts, events, etc. — have co-occurred in our experience over and over again, we put those two things together very quickly. The test includes a series of quick-re rounds to sort words related to concepts (e.g. “thin”, “fat”, “white”, “black”, etc.) and assessments (“good” or “bad”) into categories. A participant’s score is based on the time taken to sort words when concepts and assessments are combined. For example, if test subjects combine “white” with “good” faster than they do “white” with “bad”, the test suggests they have an implicit bias favouring white people.
That all humans are equal is a scientic fact established by modern genetics. However, the history of humankind is replete with people from one cultural or social group treating those from others as if they are less than human — a phenomenon called pseudo-speciation. The basis of this deep-seated tendency in people continues to be the focus of intense research eorts in psychology and neuroscience.
Many recent studies have found that our brains process information about in-groups (i.e. “us”) and out-groups (“them”) dierently. In particular, a study published on March 18, 2024, in Frontiers
in Psychology reported that, bizarrely, the criteria our brains use to categorise others as “us” or “them” shift constantly. Researchers asked half of a group of young, white participants to describe how they — as white people — diered from black individuals. They asked the other half to describe how they diered from old persons. In this way, the researchers drew the participants’ attention to specic aspects of their own social identity (“white” or “young”) and to perceived dierences from the respective outgroups.
Assessing the participant responses with IAT, the researchers found that directing participants’ attention to dierent facets of their in-group identity was sucient to change their intergroup bias. That is, the participants’ preferences changed depending on whether their brains used age or race to classify others.
Neuroimaging studies have corroborated such ndings from psychology research, and have claried that information-processing in the brain is dierent depending on whether it pertains to “us” or to “them”.
Brain regions that activate in response to the direct experience of pain as well as empathy for the pain of others include parts of the anterior cingulate cortex and insula. The rst report showing this selective processing was published more than a decade ago. Participants were shown images of others in distress (e.g. people aected by natural disasters) and non-painful situations (e.g. people out on a picnic). Images of their brains showed lower activation in these brain regions when those in distress belonged to racial groups dierent from the participants.
Since then, several other studies have substantiated these endings. Depending on the context, this differential processing could be harmless, lead to subtle forms of in-group favouritism or, in extreme cases, to intergroup violence.
Bias doesn’t exist at birth. It is a learned response built on cultural associations together with the brain’s biology. Yet preferential bias towards in-group members doesn’t mean an individual will be hostile towards out-group members. Factors that lead to hostility include the notion of associating an out-group with a threat. Uncertain circumstances — such as those we witnessed during the pandemic — can also heighten mistrust towards the outgroup.
Neuroimaging studies that have explored the basis of intergroup threats have highlighted the role of a specic brain region called the amygdala. An almond-shaped region situated deep in the brain, the amygdala is central to detecting threats and fear-based learning. Imaging studies have shown the amygdala activates to a greater degree when the source of threat is from an out-group member.
In one 2020 study, psychologists imaged the brains of white, non-Muslim participants as they watched short videos of Muslim males with stereotypical appearances threatening their in-group and found this activated the amygdala more, as expected. This study was unique because it also included videos of reconciliatory statements — and watching them activated a very different neural circuit, involving different parts of the cortex, which are higher brain regions that control impulses and regulate emotions. The amygdala being activated by something perceived as a threat is an automatic part of information processing in the brain. But cortical activation implies more of a cognitive effort.
We need more research to better understand neural processing, particularly the extent to which these results are generalisable. A better understanding of the human brain in the context of intergroup threats can also shed light on ways to improve reconciliation.
Whenever you hear social and/or cultural narratives presented as a “fact of life” — that, say, “they are bad people” — and end yourself getting sucked into it, remember that somewhere behind this statement is a misappropriated bit of brain biology. Being aware of our own biology can make us more informed, especially when faced with narratives that arouse rather than inform.
(Dr. Reeteka Sud is a neuroscientist by training and a senior scientist at the Center for Brain and Mind, Department of Psychiatry, NIMHANS, Bengaluru.)
Psychologists explored how people subconsciously evaluate di erent racial groups in a study involving more than 60,000 participants