New study says brain stays in adolescent stage until age 32

Scientists have published a new study that says, generally, brain development moves out of the adolescent phase only by around age 32, and that this stage begins at 9 years old. 

According to researchers at the University of Cambridge, the brain moves through five structural phases, contrary to the findings of older studies, which say the brain follows only one smooth structural curve as it grows. 

In a study published in the journal Nature Communications, researchers wrote that the brain typically reaches turning points at ages nine, 32, 66, and 83. 

The study was based on input from brain scans taken from around 4,000 people with ages reaching up to 90. 

In an interview with ABC News Live, neurologist Dr. Leah Croll, who is not connected to the study, said, "This study...is not saying that the brain of a 30-year-old and a 10-year-old are exactly the same. It's more that in those years, the brain is undergoing a general pattern of reorganization and development."

"But certainly, adolescence, as it pertains to our biology and our bodies and our psychological development, remains the same. It's more just that the brain is still fine-tuning those connections beyond the mid-20s," she added. 

While the neuroscientists involved in this new study agree that the brain constantly changes depending on experiences and knowledge acquired, they say brain development follows more of a jagged path than a smooth pattern throughout one's lifetime. 

In an interview with the BBC, lead researcher Dr. Alexa Mousley said, "The brain rewires across the lifespan. It's always strengthening and weakening connections, and it's not one steady pattern—there are fluctuations and phases of brain rewiring."

According to the study, the five stages of a brain's development are:

Childhood—from birth to age 9. At this inefficient stage, the brain rapidly increases in size while thinning out synapses, or connections between brain cells, which are overabundant at birth. 

Adolescence—from ages 9 to 32. Between the ages of nine and 32, the inefficiency pans out, backing up the numerous measures of brain function, said Mousley. 

Earlier studies suggested this stage lasted only within the teenage years, but apparently, according to these new findings, it continues into the early 30s. 

Neuroscientists also found that these are the ages that carry the greatest risk of mental health disorders developing.

Adulthood—from age 32 to 66. This long period of stability shows brain efficiency very slowly degrading. According to Mousely, the reversal of efficiency "aligns with a plateau of intelligence and personality" that many experience in the adolescent stage.

Early aging—from age 66 to 83. While there is generally no abrupt decline, there will be noticeable shifts in brain activity patterns. 

This is the age when the effects of dementia and high blood pressure may begin to show. 

The brain slowly stops functioning as one team of cohesive parts and, instead, begins to move like a dysfunctional family, with each member going their own way. 

Late aging—from 83 onward. While there is less data on this final stage, the researchers found that the brain changes here are similar to those in early aging, but more distinct. 

In a University of Cambridge article, Mousley said that these eras or phases "provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives."

"It could help us understand why some brains develop differently at key points in life, whether it be learning difficulties in childhood, or dementia in our later years.”