The trouble with teens

They're moody, impulsive and they sleep till the afternoon. Now scientists say they can't help it - it's just the way their brains work

STAYING UP LATE AND LONG LIE-INS

When they rise at lunchtime on a Saturday and need a crane to get them up on school-day mornings, teenagers are not just being lazy. Their biological clocks run on a different time to those of adults, because the hormone melatonin, which promotes sleepiness, starts to be secreted in the brain much later at night and lingers later in the morning.

Researchers have found that students do worse in examswhen they sit them in the morning compared with in the afternoon. "Teenagers' body clocks can be delayed by between two and four hours, and they don't start to function until 10am or as late as noon," says Professor Russell Foster, a neuroscientist at Oxford University. "It is cruel to impose a cultural pattern on teenagers that makes them underachieve," he adds.

German and American schools that switched to later starts saw greater success in exams and reduced rates of truancy and depression. "Most schools' regimes force teenagers to function at a time of day that is sub-optimal, and many university students are exposed to considerable dangers from sleep deprivation," Foster says.

The time at which children become fully awake gets later as they get older. This continues until the age of 20, when it begins to reverse, making adults more alert in the mornings.

WHY THEY DRINK SO MUCH, AND WHY THEY CAN'T HANDLE IT

Researchers have found that alcohol is much less sedating in adolescents than in adults, so they can keep drinking. This can have serious consequences as they grow older, producing physical changes in the still-developing brain that can last a lifetime.

One study found that teenagers who drank excessively - an average of two drinks a day for two years - recalled 10 per cent less in memory tests than non-drinking teenagers, a rate that was even worse than that of adults with a history of alcoholism. In some cases the impact was still seen years later, when they had stopped drinking.

"Those who drink excessively when they are younger can't handle stresses well later on," says Barbara Strauch, author of Why Are They So Weird? What's really going on in a teenager's brain. "They find that they become heavy drinkers later on much more easily than others, and it may well be because of changes in the physical nature of their brains. If you drink a lot of alcohol as a teenager, it will shift the physical structure of the brain, so that it could be damaged."

Scientists found that a lot of the damage comes not just from alcohol, but from withdrawal after binges.

MOODINESS

Moodiness is often blamed on raging hormones, which can be very destabilising. Researchers have found that oestrogen, present in men and women, is connected to the mood systems in the brain and fluctuates a great deal. However, environment plays an important role. "We know that teenagers are dealing with a difficult environment and they may deal with it by sulking," Strauch says.

"If your teenager is sulking, you might look at whether they're getting enough sleep and whether they're drinking too much. A lot are chafing at the fact that some of the risks have become very boring; it's all drugs or alcohol. A lot of adolescents are watched every moment because of the increasing competition for college, and some of them get sulky because they have no way to be free." Scientists found that the brain works best if it is allowed to explore on its own at times, Strauch adds.

HIDING IN THEIR ROOMS

Teenagers who hide in their rooms may be overstimulated and just need to get away. "I don't think any of the neuroscience teaches us that we are supposed to let teenagers not be civil," Strauch says. "That doesn't mean we are not supposed to have them take out the trash and be part of the family. But it does teach us that there are enormous changes going on inside their brains.

"I think the most reassuring thing it teaches us is that they aren't finished yet. You don't have to take it so personally, and you realise that this is not a finished human being with a finished brain. That helps us to be a little bit more patient. Teenagers may look grown up but they are not grown-ups. There is still a lot of development taking place in their brains."

IMPULSIVE BEHAVIOUR

Teenagers experience enormous shifts in levels of dopamine, the neurochemical involved with the pleasure and reward circuit of the brain. It increases in middle and late adolescence, which prepares the front part of the brain for thinking and being alert.

The influx of dopamine may occur to push adolescents to take the risks needed for survival. "Scientists think there are some teenagers who may have a dysregulation of their dopamine systems. They may have too much, they may have too little, and it runs in families," Strauch says.

"Teenagers have temperaments, of course, but it may also very well be that the brain systems are developing differently because of dopamine and they may find themselves seeking out really high risks. For some, it might be trying out for the school play. For others, it might be jumping off a building while drunk. You have to figure out whether the risk is a normal part of their development, or is it destructive."

In adolescence, the prefrontal cortex (the part of the brain behind the forehead) is still developing. "This is the part that tells you to stop and not do that stupid thing. I think part of risk-taking behaviour is because that part of the brain is unfinished. Slamming doors is basically the teenager getting angry, and they don't have the developed prefrontal cortex to say, 'If I slam the door I'm just going to make my parents more angry.'"

INABILITY TO EMPATHISE

Teenagers become worse than younger children at recognising facial expressions and correctly identifying mood. This is also down to the development of the prefrontal cortex, which helps them to think about the emotions of others. "It's probably because of all the systems coming on in their brains, but later on it settles down and they go back to being able to figure out that a frown might mean 'sad'," Strauch says.

When the ability to empathise, think abstractly and understand the nuances of a poem or a joke switches on, many parents find it the most rewarding part of adolescence. "They develop an interest in other people. Many parents told me the best part of adolescence was that their teenager started to laugh with them about ironic, corny jokes, the kind you wouldn't understand when you're younger," Strauch says.

INFATUATION

Researchers have shown that people fall in love more readily if they are already in a physically aroused state - anything that gets the blood up. Teenagers fall in love fairly often because they are often in highly arousing situations - on an emotional roller-coaster, or even in a state of fear.

Helen Fisher, an anthropologist at Rutgers University in America, believes that love is rooted in brain systems that are still developing, so teenagers may be more impulsive - and get into more trouble - in this area. "The prefrontal cortex develops slowly," she said. "They have strong desires but not the brain power or experience to go with them."

Some scientists believe that sexual urges and brain development must be in synchronisation for things to work well. High dopamine levels push teenagers to find a mate. Oestrogen and testosterone also play a role. "During this period, the brain is actually preparing itself for the act of mating and pushing you out there to seek a mate, and to try to find a good one. It's a natural part of growing up and it's about being pushed by a developing brain," Strauch says.

Why Are They So Weird? What's really going on in a teenager's brain by Barbara Strauch is published by Bloomsbury, priced £10.99

Those raging hormones

* Growth in the brain's frontal lobes - involved in reasoning and judgement - peaks at puberty, at about age 11 in girls and 12 in boys.

* After rising in volume far beyond adult levels, the grey matter in the adolescent brain then decreases.

* The frontal lobes are one of the last areas of the brain to reach an adult state, perhaps not reaching full development until 20 or over.

* Some scientists believe that if the prefrontal cortex is still not fully developed in adolescence, teenagers may not be able to see the consequences of their actions.

* The hippocampus, where certain memories are formed, grows faster in adolescent girls than boys.

* The cerebellum, linked to movement and social cognition, is up to 14 per cent larger in adolescent boys than in girls.

* When parent-teenager relations are poor, sons with high testosterone levels are more likely to engage in risky behaviour, such as skipping school, having sex, lying, drinking and stealing.

* Low-testosterone sons with poor parental relationships are more likely to be depressed.

* Low-testosterone daughters who had poor relationships with their mothers are more likely to do risky things.

* Low-testosterone daughters who had bad relationships with their fathers are more likely to report signs of depression.

* Among teenagers with good relationships with their families, high and low testosterone levels, in either girls or boys, do not seem to matter at all.