The Neurology of our Bias

Bias,  is not merely a learned phenomenon but one that involves neurological patterns that are “tuned” by cultural experience. So why do our brains see the world as US versus THEM

At the most fundamental level of biology, people recognize the innate advantage of defining differences in species. But even within species, is there something in our neural circuits that leads us to find comfort in those like us and unease with those who may differ?

Brain imaging studies have found increased signaling in the amygdala when people make millisecond judgments of “trustworthiness” of faces. That’s too short a time to reflect conscious processes and likely reveal implicit fears.Implicit association tests can uncover the strength of unconscious associations. 

Scientists have shown that many people harbor an implicit preference for their in-group – iN one study, researchers tapped into negative black stereotypes by playing violent rap music for white participants who had no external biases. This kind of priming made it hard for the brain’s cortex to suppress amygdala activation and implicit bias. Usually these “executive control” regions can override the amygdala’s push toward prejudice when confronted with out-group members.

Whether or not such biases are learned or in some way hardwired, do they reflect conflicting activity of the amygdala versus the mesolimbic system? That is, how do our brains balance distrust and fear versus social reward when it comes to our perceptions of people not like


Research suggests that signaling within the amygdala underlies the degree to which people are reluctant to trust others, especially regarding in-group versus out-group preference. It’s reasonable to conclude that much of the human instinct to distrust “others” can be traced to this part of the brain that’s important for feelings of fear and anxiety.

As opposed to fear, distrust and anxiety, circuits of neurons in brain regions called the mesolimbic system are critical mediators of our sense of “reward.” These neurons control the release of the transmitter dopamine, which is associated with an enhanced sense of pleasure. The addictive nature of some drugs, as well as pathological gaming and gambling, are correlated with increased dopamine in mesolimbic circuits.

In addition to dopamine itself, neurochemicals such as oxytocin can significantly alter the sense of reward and pleasure, especially in relationship to social interactions, by modulating these mesolimbic circuits.
Reward from ‘sameness’

For example, in a seminal paper, neuroscientist Karl Deisseroth and his colleagues at Stanford combined genetics and behavioral tests with a cutting-edge approach called fiber photometry where light can turn on and off specific cells. Using this process, the researchers were able to both stimulate and measure activity in identified neurons in the reward pathways, with an exquisite degree of precision. And they were able to do this in mice as they behaved in social settings.

They showed that neural signaling in a specific group of these dopamine neurons within these mesolimbic reward loops are jazzed up when a mouse encounters a new mouse – one it’s never met before, but that is of its own genetic line. Is this dopamine reward reaction the mouse corollary of human in-group recognition?

What if the mouse were of a different genetic line with different external characteristics? What about with other small mammals such as voles who have dramatically different social relationships depending upon whether they are the type that lives in the prairie or in the mountains? Is there the same positive mesolimbic signaling when a prairie vole encounters a mountain vole, or does this “out-group” difference tip the balance toward the amygdala and expressing fear and distrust?

Scientists don’t know how these or even more subtle differences in animals might affect how their neural circuits promote social responses. But by studying them, researchers may better understand how human brain systems contribute to the implicit and unconscious bias people feel toward those in our own species who are nonetheless somewhat different.

Neural signaling is not destiny

Even if evolution has tilted the  balance toward our brains rewarding “like” and distrusting “difference,” this need not be destiny. Activity in our brains is malleable, allowing higher-order circuits in the cortex to modify the more primitive fear and reward systems to produce different behavioral outcomes.