Us vs. Them: Understanding the Neurobiology of Stereotypes

Summary: Non-invasive brain stimulation helps researchers investigate the neural foundations of implicit bias.

Source: BIDMC.

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Research into how people perceive members of other social groups shows that many biases operate below conscious awareness. Known as implicit bias, this automatic tendency to distrust or stereotype those perceived as different likely evolved in our ancestral past, when small groups competed over limited resources. Today, these ingrained mental shortcuts can contribute to discrimination, unequal treatment, and social conflict.

In a review published in Trends in Cognitive Science, Alvaro Pascual-Leone, MD, PhD, and colleagues analyze how non-invasive brain stimulation (NIBS) can illuminate the neurobiology that supports implicit social cognition. The authors—who have pioneered the use of NIBS to probe brain function—argue that these techniques not only reveal which brain regions causally contribute to biases, but may also help evaluate interventions designed to reduce stereotyping and unfair behavior.

Non-invasive brain stimulation involves applying a weak electrical current or magnetic pulse to the scalp to modulate neural activity in targeted brain areas. Unlike correlative imaging methods, NIBS methods such as transcranial magnetic stimulation (TMS) and transcranial direct-current stimulation (tDCS) can transiently alter activity and thereby provide causal evidence that a particular region contributes to a given mental process. In experimental settings, researchers apply stimulation while participants perform tasks that probe social judgments, associations, or decision-making to test how modulating a region changes behavior.

“Non-invasive brain stimulation can directly affect brain activity and provide strong evidence linking specific regions to social behaviors such as implicit attitudes and stereotyping,” said Pascual-Leone, Chief of the Division of Cognitive Neurology and Director of the Berenson-Allen Center for Noninvasive Brain Stimulation at BIDMC. “Studying how modulation of these regions changes implicit responses gives us insight into why primitive group allegiances sometimes clash with modern values of fairness and equal opportunity.”

The review examines experiments in which participants completed a well-validated implicit bias assessment commonly referred to as the Implicit Association Test (IAT) while receiving NIBS. These studies manipulated activity in brain areas hypothesized to support stereotype representation and control. For example, stimulation of the anterior temporal lobe reduced the automatic association between the category “Arab” and the concept “terrorist.” Other experiments found that modulating regions involved in social categorization and value representation decreased implicit links such as “male–science” and “female–humanities.”

Maddalena Marini, the paper’s lead author and formerly a postdoctoral fellow in Harvard’s Department of Psychology, emphasizes the difficulty of changing social beliefs through behavioral training alone. “Social associations are deeply embedded in neural circuits, so durable change likely requires reshaping those underlying processes,” Marini said. “Behavioral approaches like empathy training have had limited, short-lived effects; NIBS can reveal neural targets and mechanisms that might improve the design and evaluation of interventions aimed at reducing prejudice.”

Co-authors include Maddalena Marini (Istituto Italiano di Tecnologia), Mahzarin R. Banaji (Department of Psychology, Harvard University), and Alvaro Pascual-Leone (Division of Cognitive Neurology, BIDMC).

Funding: The work was supported by the 2016–2017 Postdoctoral Fellow Award of the Harvard Mind, Brain, and Behavior Interfaculty Initiative (MBB) awarded to Maddalena Marini.

Source: Jacqueline Mitchell, BIDMC.
Publisher: NeuroscienceNews.com (organized coverage).
Image Source: Image in the public domain.
Original Research: “Studying Implicit Social Cognition with Noninvasive Brain Stimulation” by Maddalena Marini, Mahzarin R. Banaji, and Alvaro Pascual-Leone, Trends in Cognitive Sciences. DOI: 10.1016/j.tics.2018.07.014.

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Abstract (summary of key points)

Noninvasive brain-stimulation techniques provide a valuable method for probing the neural mechanisms of implicit attitudes and stereotypes because they allow researchers to test causal links between specific brain regions and observable social behaviors. Several converging findings point to distinct contributions of multiple cortical areas:

• The anterior temporal lobe appears critical for representing conceptual associations that link attributes (for example, “terrorist” versus “law-abiding”) with social groups (for example, Arab versus non-Arab).
• The inferior parietal lobe contributes to processing implicit attitudes that rely on perspective-taking and moral reasoning, functions tied to theory of mind.
• The medial prefrontal cortex plays a regulatory role: modulating this region can alter how implicit stereotypes are expressed by changing control and evaluative processes.
• Perceptual components of stereotyping—such as rapid assessment of physical characteristics—are mediated by extrastriate regions involved in body and face perception.

As globalization brings diverse sociocultural groups into closer contact, understanding the brain bases of intergroup behavior is increasingly urgent. NIBS methods such as TMS and tDCS offer a way to interfere with ongoing neural activity in targeted regions and distributed networks, yielding mechanistic insights into how we perceive, evaluate, and decide about others. These approaches represent a promising path toward a more complete neuroscience of social cognition and toward better-informed strategies for reducing bias.