Censorship Hurts Our Brains—Literally

Neuroscience confirms the importance of free speech to individual citizens—and to democracy itself.

The assassination of Charlie Kirk on the campus of Utah Valley University is a human tragedy first: Two young children lost their father; a wife lost her husband. But it is also a cultural tragedy, revealing corrosion at the heart of our civic life. Violence against speech is the final symptom of a disease that begins much earlier—in our failure to teach the value of hearing other voices early on, in schools.

Charlie Kirk, founder of Turning Point USA, was remembered during a prayer vigil following his assassination. (REUTERS)

Our brains are built to form habits. The basal ganglia—deep learning circuits that automate whatever we repeat—don’t absorb only tennis serves or piano scales. They also wire in patterns of thought. If the only messages we hear are one-sided, the brain’s habit circuits carve them into grooves of thought that resist change.

Rigidity at the neural level breeds rigidity at the civic level. Economists studying East Germany, including Harvard’s Alberto Alesina, found that decades of socialist rule left scars on behavior: Citizens became more cautious, less entrepreneurial, and slower to trust. A society that punished initiative and rewarded conformity trained its population to avoid novelty. Those scars of enforced consensus outlasted the Berlin Wall.

Neuroscience also shows that cognitive flexibility isn’t automatic. Like any skill, it must be trained. In a paper titled “One cannot simply ‘be flexible,’ ” Ghent University cognitive scientist Senne Braem and colleagues showed that when people are rewarded for switching tasks, they later switch more readily—even without realizing why. When switching is discouraged, they become more rigid. Flexibility is like a muscle: It grows with practice, feedback and time.

This helps explain why rigid beliefs can turn dangerous. Dogmatism and extremism go hand in hand with low cognitive flexibility and thinking that resists correction. Political psychologist and neuroscientist Leor Zmigrod has shown that people who score high in political dogmatism also perform poorly on tasks that require mental flexibility. Studies of radicalization likewise find that when opponents are cast as monsters—“Nazi,” “racist,” “enemy of democracy”—the capacity to see those opponents as human diminishes. Threat responses flare and ordinary moral limits fall away, making violence seem justified.

As Cass Sunstein argued in his book “Going to Extremes,” when like-minded people talk only with one another, they grow more extreme. But head-on clashes with opponents don’t necessarily soften rigidity. Brain scans by psychologist Jonas Kaplan and colleagues showed that when subjects’ political beliefs were challenged, the brain’s default mode network—which anchors our sense of self—lit up alongside threat circuits like the amygdala. At the same time, prefrontal regions that normally support flexibility fell quiet.

In other words, once convictions are woven into our sense of self, challenge doesn’t loosen them—it locks them in. Reports suggest Kirk’s accused killer clashed with his conservative family. But it seems that those grooves had formed, so that argument and discussion left him unmoved. Online, voices that amplified his anger were easy to find. Those spaces reward outrage and punish doubt, driving minds deeper into extremism.

People point to social media as the trigger, but the narrowing of perspective often starts much earlier—in classrooms. The glee some teachers expressed after the killing revealed how easily bias can masquerade as neutrality. Studies find educators lean heavily to one side politically, yet many sincerely believe they’re impartial—the “bias blind spot” in action. From primary school through college, dissent is rare and pressure runs mostly one way, etching patterns that are hard to undo. China has long understood this: It now pulls Tibetan children into state-run schools from the age 4, stripping away language and culture so Communist Party ideology can fix identity before anything else can take root.

In U.S. schools, the scientific method—once taught as a clear, step-by-step framework for testing evidence—has been set aside in favor of looser “inquiry” or “science practice” approaches. Education researcher Markus Emden cautions that when schools drop explicit instruction in the method, students lose practice in the disciplined testing of claims—leaving them unprepared when they encounter opposing views.

All of this is why free speech matters. It is an indispensable check on one-sided teaching that can begin from even the earliest years of school, when authority figures can easily shape children’s habits of thought. Free speech works upstream, before grooves harden, by giving parents the right to challenge and by ensuring children hear more than one voice.

This lesson should guide our educational institutions. From kindergarten through college, schools should be the places where young people learn mental flexibility: weighing opposing arguments, wrestling with uncomfortable facts, and practicing civil disagreement. Too many schools trade that mission for the promise of “safe spaces.” The result is fragility, not the strength of mind a free people needs.

Neuroscience offers a blunt warning. The basal ganglia—working with prefrontal circuits that normally support flexibility—can turn repetition into habit, in our thoughts as well as our movements. If we repeatedly avoid dissent, we become expert at avoidance, sometimes at any cost. When young minds are enclosed in like-minded circles, convictions can harden until pushback strengthens them instead of loosening them. That is why exposure to difference must begin early and run deep.

Only the difficult habit of listening to contrary voices can make our minds—and our democracy—strong enough to endure.

Ms. Oakley is a distinguished professor of engineering at Oakland University and creator and co-instructor of the Coursera course “Speak Freely, Think Critically.”