If you think you understand what’s going on in the mind of your teenager, think again.

Since 2002, the University of California at Davis’s Sleep Lab has been investigating exactly what changes the mind goes through during puberty. They’ve been scanning the brains of sleeping teens as they transition through an important stage of human development.

“Sleep is interesting because there are so many unanswered questions,” Dr. Ian Campbell, project scientist at UC Davis and study co-author, said in an interview with Healthline. “We still don’t know the purpose of sleep.”

Their latest study builds on their previous research and could provide important insight into how the mind remakes itself in preparation for adulthood.

A Sleeping Mind Says So Much

Scanning a sleeping brain, researchers say, is the best way to measure levels of “synaptic pruning,” the process during which the brain matures from childhood to adulthood.

Beginning even before birth, the human brain forms connections—called synapses—between neurons. During the maturation process, the brain decides which of these connections are important and which are superfluous. During childhood, the brain appears to use its synapses to heal and to adapt to its environment, but it later trades some of them in exchange for the problem-solving skills required as an adult. 

The team's previous studies show that the brain’s slowest waves—which appear during the most recuperative portions of sleep—decline consistently between ages nine and 18. However, the most rapid decline occurs between the ages of 12 and 16 ½, prompting researchers to conclude that most synaptic pruning occurs during puberty. 

“We knew there was going to be a change, but we didn’t know at what rate [the brain] would mature,” Campbell said.

The up side of synaptic pruning is that it leads to a more mature, better functioning brain capable of the decision-making needed in adulthood. The downside is that the adult brain can’t heal from injury as quickly. (Yet another reason for adults to wear helmets when playing high-risk sports.) 

In their latest study, published in the current issue of the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, the UC Davis researchers monitored the brain waves of 28 healthy, sleeping adolescents using an electroencephalogram, or EEG.

“With these pictures, we get a better idea of how the brain is developing during a crucial period of adolescence,” Campbell said.

Researchers noticed that the brain has the highest synaptic density at age eight and that this density slowly declines until at age 12, when it accelerates through age 16½.

The team’s next research goal will be to determine how much sleep is required during adolescence and how well the adolescent brain performs during testing.

Adolescence and Mental Illness

The outcomes of this field of research could prove beneficial for our understanding of mental illness, as puberty is often when mental problems arise.

For example, some children with ADHD grow out of it, but not all do. Studying these adolescent brain changes could lead to better screenings, treatments, and perhaps someday, a cure.

Schizophrenia is another condition that may benefit from this research. Because onset of scizophrenia is typically around 18 for men and 25 for women, Feinberg's research shows the brain may be cutting out the wrong synapses and re-organizing itself incorrectly.

“It’ pruning gone wrong,” Campbell said.

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