Narcissistic, lazy, impulsive and rude - adolescents can be infuriating. But it's just the way their brains are wired, doctors now believe

Teenagers, parents endlessly moan, seem designed to infuriate any sane person condemned to live with them. Diva-scale sulks, rooms in which the floor is invisible, an inability to remember anything that involves anyone else, and a refusal to get out of bed until lunchtime are just a few familiar symptoms. And the anti-social behaviour is not limited to the home. Truanting children between the ages of 10 and 16 are said to be responsible for 40 per cent of street crime, 25 per cent of burglaries and 33 per cent of car thefts.

Teenagers, parents endlessly moan, seem designed to infuriate any sane person condemned to live with them. Diva-scale sulks, rooms in which the floor is invisible, an inability to remember anything that involves anyone else, and a refusal to get out of bed until lunchtime are just a few familiar symptoms. And the anti-social behaviour is not limited to the home. Truanting children between the ages of 10 and 16 are said to be responsible for 40 per cent of street crime, 25 per cent of burglaries and 33 per cent of car thefts.

"When they shout, you want to shout the same thing back," says Kate Figes, the journalist and author of The Terrible Teens, a book on raising teenagers. "When they are out having a good time with their friends and complain that home or family commitments are boring, parents easily feel rejected, unloved and misunderstood."

Of course, patience and humour and good communication skills on the adult side can do much to reduce the conflict, but for those of us not blessed with saintly virtues, science has been coming to our aid recently. Whereas it was once thought that the brain was fully formed by late childhood, latest research suggests this is far from true.

By and large we handle the outbursts of smaller children more effectively because we know they are children, they are not mature. Teenagers can be so infuriating and hurtful because both sides assume they are virtually adults. But what if much of classic teen behaviour is because their brains still aren't wired up properly? "If we understand the way that the adolescent mind works, we stand a better chance of understanding why teenagers can be so sensitive and irrational. We are then less likely to overreact or blame them when they appear to be unreasonable or contradictory," according to Figes.

A report out in May described how the brain matures in a gradual wave of development that travels from the back of the head to the front. The last bit to be fully wired up are the frontal lobes, the part that decides to hold off sex tonight because you don't have a condom or finish your homework before going to the party. But the job isn't completed until you're age 20 or later.

"One could speculate that some of the more immature aspects of adolescent behaviour," says lead scientist Judith Rapoport of the American National Institutes of Health in Bethesda, Maryland, "may be due to the lack of maturity of some parts of the frontal lobes of their brains." This research is just the latest of a series of findings in the last few years showing that teenage brains are far more plastic than we used to think.

This can be seen as a great opportunity. "The research shows just how hopeless we are at giving teenagers what they really need," says Figes, whose novel What About Me? Diaries and e-mails of a Menopausal Mother to her Teenage Daughter (McMillan) has just been published.

"Just at the time when the finishing touches are being put to the control of their motor skills and they are at their most passionate and vulnerable, what do we do? We warehouse them all together in schools and cram them full of second-hand facts. Instead they could be doing much more active learning, be much more involved with adults. We should also be much better at handling their need for risk and rites of passage."

So what exactly is this research that seems to have the potential to transform the stereotype of teenagers for ever? For the last 13 years Dr Jay Giedd has been peering into the brains of teenagers, using an MRI (magnetic resonance imaging) scanner at the National Institutes of Health in Bethesda. Taking neural snapshots every two years, he is building up a library of how the brain changes and grows.

"We started out trying to find out if there were brain markers for ADHD (Attention Deficit Hyperactive Disorder)," he says, "but we soon found we knew so little about how the brain developed normally that it was impossible to figure out where things might be going wrong." Before Dr Giedd started his research the general view was that brain growth was over by the age of 12. Some academics even claimed that adolescence was a cultural phenomenon that only emerged in the wake of the industrial revolution.

What has become clear, however, is that adolescents repeat a process that they went through in the period immediately before and after birth. Babies emerge from the womb with their brains only half finished. Over the first three years the brain continues to wire itself up at a furious pace, forming hundreds of thousands of new synapses a second. A two-year-old has more neural connections than an adult. Then between about three and five comes the purge. Circuits that aren't used are ruthlessly excised.

Giedd's remarkable discovery was that far from being finished at 12, the process of brain consolidation has an Act II. Between about six and 12 there is not much change in the number of neurons, but a big increase in the number of connections between neurons, which shows up as a thickening of grey matter on the scans.

Then as you enter adolescence the brain embarks on a second round of pruning, only this time it is the connections rather than brain cells that go at the rate of about 0.7 per cent a year until the early Twenties. At the same time there is a thickening of the white matter (the myelin sheath) that insulates the fibres linking nerve cells, speeding up transmission. "The result of all this," says Giedd "is that you get fewer but faster connections in the brain."

The new "wiring" theory could well help parents and others to become more understanding. "If you know all this is going on," says Figes "it makes it easier to step back and not become quite so infuriated at the narcissistic, self-obsessed behaviour of your children. Instead, you can concentrate on how to help them through it. Our culture has a tendency to abandon teenagers, to assume they don't want anything to do with "wrinklies", but actually the new picture of more hormones and less control means they need our support and love even more."

Suddenly, the inability of teenagers to plan to get their homework done before settling into an hour-and-a-half-long phone call seems more comprehensible. The executive functions that make those kinds of choices aren't fully complete. The apparently wilful refusal to solve simple organisational problems - how to book cheaper train seats for a trip as well as getting clothes for the weekend party - doesn't look quite so hopeless either. One of the brain parts that doesn't completely connect till later is the corpus callosum - the bridge that links the two halves of the brain - which is involved in creativity and problem solving.

The ability to ignore obvious risks - from smoking to unsafe sex - begins to make more sense, too. Sex hormones, the usual culprits responsible for teenage bad behaviour in the past, still play a major role. But in the new model, while hormones provide the engine, the problems arise because the wiring for the control systems is still not in place. Take the feel-good brain chemical dopamine. The hormonal rush increases its levels and so feelings of pleasure become more intense. Without fully developed neuronal brakes, why put off the pleasures of sex, drugs or risk taking?

Even the business of endless lazing in bed turns out to have a biological basis. One of the less appreciated effects of the rise in sex hormones is the effect it has on the rhythm of the sleep hormone melatonin. Teenagers go to bed and get up later because that is what their body clocks are telling them to do. A society that requires them to turn up at school at 8am or 9am in the morning may be a recipe for mass teenage sleep deprivation.

However, these brain scans studies fit into a wider social picture, as shown in a review of scientific theories of teen behaviour conducted by researchers at University of Wisconsin in 1987. They found that in times of war and employment booms, scientists pronounced adolescents as being "capable and adult-like" but during peacetime and economic downturn they characterised them as "psychologically incapacitated and slow to develop".

We may have got it right this time around, but its worth considering whether our simultaneous demonising and infantilising of adolescents tells us more about our society's need for good consumers than it does about the true nature of our children.

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