Brain scans prove teenagers are children at heart

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The Independent Online

The terrifying transition from angelic child to stroppy teenager is the result of a blip in the brain, a scientist has concluded.

The terrifying transition from angelic child to stroppy teenager is the result of a blip in the brain, a scientist has concluded.

She found that part of the brain involved with higher reasoning is the last to mature, which could explain teenage angst and sullen behaviour. Scans carried out over 10 years on children from the age of four to adults as old as 25 revealed that the brain matures in a gradual wave of development travelling from the back of the head to the front. The last parts to develop fully are the frontal lobes,which are involved in reasoning and problem-solving.

Judith Rapoport of the US National Institutes of Mental Health in Bethesda, Maryland, who did the research, said: "One could speculate that some of the more immature aspects of adolescent behaviour may be due to the lack of maturity of some parts of the frontal lobes of the brain."

It is now well established that babies are born with practically all of their complement of brain nerve cells, which gradually diminish after early adulthood. In the first 18 months of life a vast number of connections are formed between cells.

The study monitored 13 individuals, looking at the changes in the density of the "grey matter", the tissue between nerve cells. As teenagers developed, the grey-matter density decreased, indicating that the number of connections had become fewer, in line with the theory that a mature brain involves the "pruning" of some nerve connections in order to strengthen the connections that remain.

"Everybody recognises that children's brains overproduce the connections between nerve cells and that these connections get pruned down as the children get older," Professor Rapoport said. "What's new about this is a painstaking method of seeing the adolescent brain mature. What you see is a wave of loss of nerve connections sweeping from the back of the brain to the front." The last part of the brain to undergo the process was the temporal lobes of the outer cortex, she said.

The order in which the brain developed over a period of 10 years roughly matched the order in which these regions evolved over millions of years, she said. The oldest parts of the brain in evolutionary terms were the first to mature and the most recent parts, such as the temporal lobes, were the last. The first areas of the brain to mature were those directly involved with the basic functions of life such as controlling the movement of limbs, and the last to mature were those controlling thoughts and reasoning.

Professor Rapoport's team also found that the left side of the brain, which is responsible for controlling the right-hand side of the body, tended to mature more quickly than the right. This may reflect the fact that the majority of the children in the study were right-handed, which triggers the early maturity of the brain's left hemisphere, the researchers say in the journal Proceedings of the National Academy of Sciences.

One of the practical benefits of understanding the way the adolescent brain matures is that it can shed light on mental problems such as schizophrenia and autism, the researchers say. "Alterations either in degree or timing of [the] basic maturational pattern may at least partially be underlying these neurodevelopment disorders," they say.

Professor Rapoport said that further work on how the healthy brain matures would be crucial for understanding what could go wrong. "To interpret brain changes we were seeing in neurodevelopmental disorders, we needed a better picture of how the brain normally develops," she said.