The challenge of defining maturity when the brain never stops changing

December 21, 2016

Neuroscientists don't know when your brain is a legal adult. While the law has to draw a line between adolescence and maturity, ranging globally from 10 to the early 20s, different parts of the brain mature at different rates, rather than growing up entirely overnight. In an Opinion published December 21 in Neuron, Harvard psychologist Leah Somerville argues that using current neuroscience tools to define when a brain "reaches maturity" is much trickier than it may seem. First, researchers would have to agree about what would characterize a brain as "mature" in the first place.

"In the last 10-15 years, neuroscience evidence that, for example, the brain is still maturing, is a very persuasive type of data that policy makers, even up to the US Supreme Court, weigh in their thought process," says Somerville (@leahsom), who directs Harvard's Affective Neuroscience & Development Lab. "Neuroscientists aren't too concerned with trying to pinpoint the age of maturity -- because we see plenty of problems with doing that--but policy has really dragged us into the conversation, which is making the community question how we can translate the research responsibly."

Research has shown that while there are clear structural differences between an adolescent and adult brain (these include a reduction in gray matter and increases in white matter), brain maturation does not map on to a single developmental timeline, and it differs by individual when different parts of the brain develop. In one large study, several regions of the brain had not yet plateaued even by the age of 30.

The plasticity of the brain -- its ability to interact with the environment, add new connections and grow new neurons over time--also makes it so that change is constant throughout life. A simple look at the volume of white matter or connection patterns between brain cells would not be an effective way to identify a static baseline that defines maturity or immaturity. For example, one study found that some 8-year-old brains exhibited greater brain-connectivity maturation measures than some 25-year-old brains.

"When considering whether an individual brain can diagnose someone as mature or immature, neuroscientists have deep concerns about trying to make those kinds of inferences," Somerville says. "The very idea that we could come up with some number that would encompass all of the complexity involved in brain development is a challenge. While there are decades of evidence that adolescents behave differently from adults, the age of 18 doesn't have any biological magic to it."

Somerville is a member of a working group on translating neuroscience at the Massachusetts General Hospital Center for Law, Brain, and Behavior. They hope to take their discussions on how brain development can inform when a person should be responsible for their actions and generate papers for legal audiences. The Center also holds regular events on these issues, including free public lectures and panel discussions.

"We want to help policymakers understand that the idea of maturity itself just can't be static," she says. "The brain is constantly changing, but in ways that are more subtle than the major developmental events that we think about in childhood and adolescence."
This material is based upon work supported by the National Science Foundation and the American Psychological Association F. J. McGuigan Early Career Investigator Research Prize for Understanding the Human Mind.

Neuron, Somerville, Leah: "Searching for signatures of brain maturity: What are we searching for?"

Neuron (@NeuroCellPress), published by Cell Press, is a bimonthly journal that has established itself as one of the most influential and relied upon journals in the field of neuroscience and one of the premier intellectual forums of the neuroscience community. It publishes interdisciplinary articles that integrate biophysical, cellular, developmental, and molecular approaches with a systems approach to sensory, motor, and higher-order cognitive functions. Visit: To receive Cell Press media alerts, contact

Cell Press

Related Brain Articles from Brightsurf:

Glioblastoma nanomedicine crosses into brain in mice, eradicates recurring brain cancer
A new synthetic protein nanoparticle capable of slipping past the nearly impermeable blood-brain barrier in mice could deliver cancer-killing drugs directly to malignant brain tumors, new research from the University of Michigan shows.

Children with asymptomatic brain bleeds as newborns show normal brain development at age 2
A study by UNC researchers finds that neurodevelopmental scores and gray matter volumes at age two years did not differ between children who had MRI-confirmed asymptomatic subdural hemorrhages when they were neonates, compared to children with no history of subdural hemorrhage.

New model of human brain 'conversations' could inform research on brain disease, cognition
A team of Indiana University neuroscientists has built a new model of human brain networks that sheds light on how the brain functions.

Human brain size gene triggers bigger brain in monkeys
Dresden and Japanese researchers show that a human-specific gene causes a larger neocortex in the common marmoset, a non-human primate.

Unique insight into development of the human brain: Model of the early embryonic brain
Stem cell researchers from the University of Copenhagen have designed a model of an early embryonic brain.

An optical brain-to-brain interface supports information exchange for locomotion control
Chinese researchers established an optical BtBI that supports rapid information transmission for precise locomotion control, thus providing a proof-of-principle demonstration of fast BtBI for real-time behavioral control.

Transplanting human nerve cells into a mouse brain reveals how they wire into brain circuits
A team of researchers led by Pierre Vanderhaeghen and Vincent Bonin (VIB-KU Leuven, Université libre de Bruxelles and NERF) showed how human nerve cells can develop at their own pace, and form highly precise connections with the surrounding mouse brain cells.

Brain scans reveal how the human brain compensates when one hemisphere is removed
Researchers studying six adults who had one of their brain hemispheres removed during childhood to reduce epileptic seizures found that the remaining half of the brain formed unusually strong connections between different functional brain networks, which potentially help the body to function as if the brain were intact.

Alcohol byproduct contributes to brain chemistry changes in specific brain regions
Study of mouse models provides clear implications for new targets to treat alcohol use disorder and fetal alcohol syndrome.

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.

Read More: Brain News and Brain Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to