The Brain Development Myth

YOU HAVE probably heard the following claim: young people’s brains are not fully developed until age 25.

Advocates for juvenile justice reform have argued for several years now for reduced accountability for juvenile offenders based on this claim. Some even argue for reduced accountability for offenders up to age 25, labeling people ages 18 to 25 as “emerging adults.” The argument has been successful. Accountability for young people who break the law has been reduced across the country, including in Indiana. This has contributed to the surge in violence our nation and state has experienced.

The claim, though, that young people’s brains are not fully developed until age 25, is a myth.

A recent article in Slate magazine attempts to uncover the origin of this myth. You can read the article here.  

The article reveals that the myth started with the development of fMRI technology. In the early 1990’s scientists invented the fMRI machine. fMRI stands for functional magnetic resonance imaging. The machine detects the change in blood oxygenation and flow that occurs in response to neural activity. When a particular part of the brain is active, it requires more oxygen, and therefore more blood flows to that area. The fMRI basically makes a video of that happening.

Researchers started using this new technology to see what happens in the brain in various situations. For instance, scientists discovered that both physical pain and emotional pain register the same way in the brain. As happens frequently with new technology, though, the fMRI findings started to be used to bolster wider claims. One of those claims is that people’s brains aren’t fully developed until age 25.

The next piece of the myth development here is selection bias. Selection bias occurs when the makeup of a study’s participants impacts the outcome or the interpretation of the outcome. In this instance, some of the early participants in fMRI imaging studies were people 18 to 25 years old. Many studies involve this age range, and suffer this selection bias, because researchers have easy access to people that age. Most researchers are housed on college campuses with thousands of young people eager to be paid this weekend’s beer money to stick some sensors on their head for a few minutes.

When fMRI researchers looked at the brain scans of these college kids, they noticed that parts of their brains showed characteristics of continuing development. Papers were published saying that young people’s brains are still developing into their early twenties. These papers had caveats on them that warned against extrapolating too much from the results because they could be impacted by many factors, including selection bias. That’s too far in the weeds for most people, though, including science reporters.

It is also too far in the weeds for juvenile justice reform activists. Always on the lookout for ways to erode personal responsibility, justice reformers seized on the popular science reporting on young adults’ developing brains. If their brains aren’t fully developed, they argued, they shouldn’t be held accountable for their actions. This became a go-to argument for the movement, which is why you have heard it and likely seen it on PowerPoint slides at every juvenile justice conference you have ever been to.

Over time, later studies have demonstrated the fallacy of the age 25 myth, correcting for the overinterpretation and selection bias. One study that looked at people up to age 90 found that brain development continued throughout the entirety of life. Further, it turns out there is wide variability between individuals when it comes to brain development. In one study, researchers took fMRI scans of variously aged people then asked scientists to determine the age of the people based on their brain scans. They weren’t able to. Some 8-year-old brains exhibited more “maturity” than some 25-year-old brains.

One of the main researchers in this area, Psychologist Larry Steinberg, when asked where the age 25 claim came from, laughed and said, “I honestly don’t know why people picked 25. It’s a nice-sounding number? It’s divisible by five?”

Sadly, though, the myth moved faster than the research. Juvenile justice reform spread across the country and our communities have suffered as a result.

It is curious that our courts are so quick to embrace unsound scientific assertions in the name of reform like this. It is emblematic of a broader erosion of standards whereby judges and lawyers have deferred to social workers and justice reformers instead of insisting on evidence. As Judges, why don’t we apply the same standards in the conference room that we apply in the courtroom?

In the courtroom, the judge must be persuaded by the evidence. And not just any evidence. The evidence must be relevant and reliable, especially when it comes to scientific evidence. We even have formal rules about it. For instance, Indiana Rules of Evidence Rule 702(b) states that “Expert scientific testimony is admissible only if the court is satisfied that the expert testimony rests upon reliable scientific principles.” This is commonly referred to as the Daubert test, referencing the name of a case where it was first applied.

The myth that our brains are not fully developed until age 25 would not meet the test for admissibility under Indiana Evidence Rule 702(b). It fails the Daubert test. It should not, then, be used to form the basis of public policy that decreases accountability in the criminal justice system, especially in the face of mounting evidence that the reform movement is damaging our communities. Just because someone enthusiastically puts it on a PowerPoint slide, doesn’t make it true. It is well past time for judges and policymakers to insist on relevant and reliable evidence when making decisions about our justice system.