If you scroll through TikTok or Instagram long enough, you’ll inevitably stumble across the line: “Your frontal lobe isn’t fully developed yet.” It’s become neuroscience’s go-to explanation for bad decisions, like ordering an extra drink at the bar or texting an ex you swore not to.

The frontal lobe plays a central role in higher level functions like planning, decision-making and judgment.

It’s easy to find comfort in the idea that there’s a biological excuse for why we sometimes feel unstable, impulsive or like a work in progress. Life in your 20s and early 30s is unpredictable, and the idea that your brain simply isn’t done developing can be oddly reassuring.

But the idea that the brain, particularly the frontal lobe, stops developing at 25 is a pervasive misconception in psychology and neuroscience. Like many myths, the “age 25” idea is rooted in real scientific findings, but it’s an oversimplification of a much longer and more complex process.

In reality, new research suggests this development actually extends into our 30s. This new understanding changes how we view adulthood and suggests that 25 was never meant to be the finish line in the first place.

Where did the ‘age 25’ myth come from?

The magic number stems from brain imaging studies in the late 1990s and early 2000s. In one 1999 study, researchers tracked brain changes through repeated scans in children and teens. They analyzed gray matter, which consists of cell bodies and can be thought of as the “thinking” component of the brain.

Researchers found that during the teenage years, gray matter goes through a process called pruning. Early in life, the brain builds an enormous number of neural connections. As we age, it gradually trims back the ones that are used less often, strengthening those that remain.

This early work highlighted that gray matter volume growth and loss is key for brain development.

In influential follow-up work led by neuroscientist Nitin Gogtay, participants as young as four had their brains scanned every two years. The researchers found that within the frontal lobe, regions mature from back to front.

More primal regions, like areas responsible for voluntary muscle movement, develop first, while more advanced regions that are important for decision-making, emotional regulation, and social behaviour had not fully matured by the final brain scans around age 20.

Since the data stopped at age 20, researchers couldn’t say precisely when development finished. The age of 25 became the best estimation for the assumed endpoint, and eventually became enshrined in the cultural consciousness.

What newer research reveals

Since those early studies, neuroscience has moved on considerably. Rather than looking at individual regions in isolation, researchers now study how efficiently different parts of the brain communicate with one another.

A recent major study assessed efficiency of brain networks, essentially how the brain is wired, through white matter topology. White matter is made up of long nerve fibres that link different parts of the brain and spinal cord, allowing electrical signals to travel back and forth.

Researchers analyzed scans from more than 4,200 people from infancy to 90 years old and found several key periods of development including one from age nine to 32, which they coined the “adolescent” period.

For anyone well into adulthood, it may feel jarring to be told that your brain is still an “adolescent,” but this term really just signifies that your brain is in a stage of key changes.

Based on this study, it seems that during brain adolescence, the brain is balancing two key processes: segregation and integration. Segregation involves building neighbourhoods of related thoughts. Integration involves building highways to connect those neighbourhoods. The research suggests this construction doesn’t stabilize into an “adult” pattern until the early 30s.

The study also found that “small worldness” (a measure of network efficiency) was the largest predictor for identifying brain age in this group. Think of this like a transit system. Some routes require stops and transfers. Increasing “small worldness” is like adding express lanes. Essentially, more complex thoughts now have more efficient paths throughout the brain.

However, this construction doesn’t last forever. After around the age of 32, there is a literal turning point where these developmental trends switch directions. The brain stops prioritizing these “expressways” and shifts back to segregation to lock in the pathways our brains use most.

In other words, your teens and 20s are spent connecting the brain, and your 30s are about settling down and maintaining your most used routes.

Making the most of a brain under construction

If our brains are still under construction throughout our 20s, how do we make sure we are building the best possible structure? One answer lies in boosting neuroplasticity — the brain’s ability to rewire itself.

While the brain remains changeable throughout life, the window from age nine to 32 represents a prime opportunity for structural growth. Research suggests there are many ways to support neuroplasticity.

High-intensity aerobic exercise, learning new languages and taking on cognitively demanding hobbies like chess can bolster your brain’s neuroplastic abilities, while things like chronic stress can hinder it. If you want a high-performance brain in your 30s, it helps to challenge it in your 20s, but it’s never too late to start.

There is no magical switch that turns on at age 25, or even 32 for that matter. Like your brain, you’re in a decades-long construction project. Stop waiting for the moment you become an adult and start making active choices about how to support this project. Make mistakes, but know that the concrete hasn’t set quite yet.

Taylor Snowden is a postdoctoral fellow in Neuroscience at the University of Montreal.

This article was originally published in The Conversation.

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