Understanding Brain Maturity Beyond Adolescence
Craig Bolan
When do we transition into adulthood? For some, it’s the day they turn 18 and leave home, while for others, it’s a realization that no one else is handling their responsibilities, like making dental appointments. Yet, many, like my father, may still feel like they haven’t fully entered adulthood, regardless of the evidence of age visible in the mirror.
While adulthood is recognized legally at ages 18 or 21 in many countries, the neurological journey is more complex. Unlike a fixed timeline, different networks in the brain mature at varying rates. Some circuits reach adult-like functionality in the early teens, while others evolve well into the 20s and beyond.
So when can we hold ourselves accountable for our brain’s immature behavior? The answer is more gradual than you might think.
Up until recently, neuroscientists largely agreed that brain maturity is achieved by age 25; however, this figure lacks a definitive biological marker. This estimate surfaced from influential studies at the start of the 21st century which primarily tracked brain development up to age 20. As a result, the age of 25 was adopted as a conventional baseline.
Since then, researchers have been probing further for clarity by examining behaviors linked to the maturation of specific brain structures. For instance, a 2017 study by Christian Tamnes from the University of Oslo indicated that gray matter thickness generally decreases throughout the teenage years and levels off in the 20s.
This trend is not alarming; during childhood, the brain is densely interconnected with neurons, creating a complex web of possibilities. As adolescents progress, redundancies are eliminated to make neural networks more efficient—imagine replacing tangled backroads with sleek highways.
Nevertheless, gray matter does not develop uniformly, indicating that a universal turning point for maturity remains elusive. Personal circumstances like socioeconomic status and stress during adolescence can accelerate gray matter thinning, while nurturing environments can foster growth.
Ultimately, the core question might not be about when our brains appear mature, but rather when they start behaving like adults. Adult behavior correlates closely with executive functions—our capacity to make sound decisions, control impulsive actions, and plan for the future. “Executive function is a key metric for assessing brain maturity,” states Brenden Tervo-Clemens from the University of Minnesota.
To further investigate, Tervo-Clemens and his team examined data from four extensive datasets, combining information from over 10,000 individuals aged 8 to 35. Their analysis revealed that executive functions mature quickly between ages 10 and 15, plateauing with minor adjustments until about age 20, suggesting that adulthood is approached around this age.
In parallel, a crucial factor in defining adulthood may lie in the development of social cognition—mental processes essential for interpersonal interaction. A 2017 study led by Philip Jackson at Université Laval tracked individuals ages 12 to 30, revealing that various aspects of social functioning mature at different intervals. Skills like social understanding emerge early, while empathy continues to develop post-18.
Nonetheless, concentrating solely on one capability may oversimplify the complex nature of the brain. “The brain operates as a multifaceted system with intricate interactions,” notes Tervo-Clemens. “Selecting a single marker for brain age is, therefore, an oversimplification.”
To paint a more comprehensive picture, a team led by Alexa Mousley from the University of Cambridge assessed brain scans from infancy to age 90. Their study, published last year, focused on white matter—connections enabling communication among brain regions.
The research identified four significant developmental changes occurring around ages 9, 32, 66, and 83. The span from ages 9 to 32 appears particularly pertinent for defining adulthood. Childhood and adolescence witness a fragmented brain, gradually becoming more integrated and efficient—this global efficiency peaks around age 29.
A separate study in May echoed these findings, analyzing over 35,000 brain scans to illustrate that some white matter tracts reach peak development in our 20s and 30s, while others continue to mature into our 40s. This suggests that the brain’s refinement is a prolonged process that extends well beyond the legal age of adulthood.
Despite the absence of consensus, these studies underline the reality that the brain is not fully matured by age 18, leading to tangible real-world implications, argues Katia Rubia, a Professor of Cognitive Neuroscience at King’s College London.
Rudimentary brain regions responsible for emotions and reward systems continue developing through adolescence, while the frontal lobes—critical for emotional regulation, planning, and impulse control—lag behind. This developmental imbalance explains why adolescents often engage in impulsive behaviors such as shoplifting, reckless driving, and risky sexual activities. “This occurs because their frontal lobes are not yet fully developed, impairing their foresight regarding consequences,” Rubia notes.
Rubia advocates for policymakers to consider brain development in decisions about adulthood. “In my view, we should postpone driving privileges,” she remarks, emphasizing that young drivers tend to exhibit more dangerous behavior due to incomplete frontal lobe development.
Some scientists propose creating benchmarks to track brain maturation akin to the way doctors measure height and weight. Such normative comparisons could prove useful in various contexts, including criminal justice. However, current practical limitations impede this approach. According to a 2020 report by the Scottish Sentencing Council, a widespread application of brain imaging remains impracticable. Yet, as research into brain development expands, these avenues may become feasible in the future.
Ultimately, a clear definition of adulthood from legal, medical, and societal perspectives is vital. Neurology, however, presents a nuanced picture—brain maturation varies individually. Factors such as genetics, culture, and life experiences shape this complex process. Some brain functions mature quickly, while others lag, and certain pathways may even not peak until one reaches their 40s. Moreover, adulthood is a continuous journey rather than a fixed endpoint.
As for emotional growth, that’s another layer. Research shows that individuals typically feel they’ve transitioned into full adulthood by age 29. Thus, while the legal age for adulthood is often cited as 18 and neuroscience points to a range between 20 and the mid-40s, the subjective experience of maturity unfolds at its own unique pace. As for my father at 81, he continues to wait.
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Source: www.newscientist.com