Young People
 
 
Caution! Mind under construction

It’s not just the hormones, says Vivienne Parry. During puberty teenagers’ brains are undergoing a radical readjustment

Times Online
Nov 2005

When the hormones start to arrive by the truckload at puberty, something very strange happens to children. They can turn overnight from sweet, adorable creatures into an unpredictable and combustible blend of know-it-all arrogance and furious leave-me-alone vulnerability. They are spotty, moody, truculent and can’t concentrate for more than two minutes at a time. They also become hugely self-conscious, suddenly finding everything, including their parents “sooo embarrassing”.

And there is a darker side too. Soaring rates of death, three quarters of which result from accidents or “misadventure”, illicit use of drugs or alcohol, risky sexual behaviours and the first signs of emotional disorders which may be lifelong. Hormones have a lot to answer for — or have they? Puberty is undoubtedly an extraordinary hormonal event and humans are lucky that they on have to go through it only once, unlike most animals which go through this hormonal onslaught with every breeding season.

The first hormone event takes place, unseen, between age 6 and 8 and involves the adrenal glands, which sit atop each kidney. They step up production of male hormones, particularly one called DHEA, which the body uses as construction material for other hormones. These androgens prime follicles for pubic hair growth and make the skin greasy.

The next big step is when the brain begins production of a key hormone called GnRH (gonadotrophin releasing hormone). This is the true onset of puberty, although what triggers it is unknown. It’s not just age because age at puberty varies worldwide. Nutritional status is important, with percentage body fat especially so for girls. Pulses of GnRH then make the pituitary gland produce the hormones which will act on ovary and testes to produce sperm and eggs.

The effect is dramatic. In boys, up to 50 times more testosterone is available than before puberty. It sculpts their bodies and jawlines, increases their muscles and makes them think about sex every other minute (as little as that? is the reaction of most 13-year-old boys). In girls, oestrogen rearranges body fat, and stimulates the growth of womb and breast. They begin to have periods and to ovulate, although very irregularly at first. In both sexes, body-hair growth is promoted.

A range of teen traits is directly influenced by hormones. Spots, for instance, are caused by skin sensitivity to testosterone. Fridge-raiding is caused by higher levels of the hormone cortisol, which sharpens the appetite and makes adolescents seek the food that they need for growth. Not getting up until lunchtime is caused by alterations in the secretion of melatonin (see page 11).

We can see what surges of reproductive hormones do to rutting stags or nesting birds in the mating season, so there’s no doubt that these hormones can affect behaviour, but they have never seemed adequately to explain the complexities of human teenage behaviour. Neither has anyone managed to correlate degree of teenage angst with hormone levels. But recently a whole new explanation has emerged.

It was always thought that the brain stopped developing within a couple of years of birth. During pregnancy and early life, a huge number of nerve connections (synapses) are formed, but these are then pruned radically. “It’s a way of making the brain more efficient,” says Dr Sarah-Jayne Blakemore, a research fellow at the Institute of Cognitive Neuroscience at University College London and an expert on the adolescent brain. She gives the example that, worldwide, all babies can distinguish the difference between the sound of the letters R and L. In the Japanese language however there is no difference and, after about a year, Japanese babies lose the ability to distinguish these sounds. They don’t need it.

This example relates to the sensory areas of the brain and was long assumed to be true of the entire brain — that “plasticity” as it is called, was lost by about 3 years old. But post-mortem work in the Eighties on adolescent brains suggested something very different. It wasn’t confirmed until just a few years ago, when MRI scans of adolescent brains revealed the stunning truth. Not only is there major reorganisation in the teenage brain but it continues to develop until the early twenties.

Puberty coincides with two brain events. A process called myelination, which massively increases brain activity. There is also a pruning exercise among synapses which have proliferated during childhood as the brain is fine-tuned in response to the environment: strengthening synapses used frequently, ditching the rest. The pruning takes place mainly in the pre-frontal cortex. This part of the brain is responsible for executive action — a shopping list of the things that teenagers struggle with: priority setting, impulse inhibition, planning and organisation.

The changes in the adolescent brain primarily affect motivation and emotion, which manifest themselves as mood swings and conflict with authority. The combination of a hormone such as testosterone, which drives bravado, with an impaired ability to reason, is an explosive one.

The pre-frontal cortex is also responsible for our self-identity and for socialisation and empathy. Research has already shown that one effect of this brain reorganisation is a 20 per cent dip at puberty in the ability to gauge emotions from faces. This is likely to make teenagers less able to read social situations or recognise when they are treading on dangerously thin ice with authority figures.

Dr Blakemore is currently researching empathy in teenagers, and her work suggests that this also seems to dip at puberty. “It would mean they are less able to put themselves in other people’s shoes and imagine how they feel.”

One aspect of teenage brains is that they get a bigger reward from nicotine and alcohol than adults. As a result, those who begin drinking before the age of 15 are four times more likely to develop alcohol dependence than than those who begin drinking later.

Teenagers are by turns maddening and glorious. But, as they are caught in limbo between adult and child, we should treasure and understand them. Blame their brains, not them.

If your child is between the age of 10 and 16 and would like to volunteer for a brain scan (in Central London) please contact Dr Sarah-Jayne Blakemore by e-mail at s.blakemore@ucl.ac.uk.

The Truth about Hormones by Vivienne Parry (Atlantic Books, £9.99) is available from Times Books First at £9.49, p&p is free: 0870 1608080: www.timesonline/booksbuyfirst

King of chemistry

ALEXANDER MAYALL: “I like science because it has a proper right or wrong answer. Chemistry is my favourite because it’s about what everything in the universe is made from and you get to look at the way it all fits together. I also find it quite easy.

In my last project, for my Standard Assessment Tasks, I got a level 7 (the national average is 5 to 6). I found that memorising the symbols for all the different chemicals is the hardest thing — it’s best to approach that like having to learn spellings.

Experiments are fun. Something always happens and you’re never sure what. We did quite a good one with magnesium and steam; it made hydrogen. You can set that alight and then watch it burn. You learn the reaction that the metals have towards the steam. The teacher told us that the test tube might break — and it did.

I know that there are some moral issues involved in science. One of them is playing God — now that reseachers are able to create life in an unnatural environment. Some people are taken aback at the idea of duplicating people.


I haven’t made up my mind completely on this yet — but if it helps keep people alive, I’m all for it.

I think that science plays a big role in the world today. Especially in the discovery of new medicines. If a scientist creates a new medicine then that’s something that they deserved to be praised for.”

Adolescent genius

The fact that teenagers’ brains are busy re-organising connections gives them a brilliant advantage over adults. Their thinking is unconventional, they are more open to ideas and change.

It’s no accident that teenagers are behind some of the world’s great discoveries, particularly in technology:

Take Ada, Countess of Lovelace, the daughter of Lord Byron. She was just 17 when she met Charles Babbage, the inventor of the difference engine, an elaborate calculating machine and forerunner of modern computers. It was Ada, not Babbage, who saw that his machine could be used to manipulate symbols. Her contribution to computing has been recognised by Microsoft — her image is on their product-authenticity hologram stickers.

Bill Gates, of Microsoft, began to program computers at 13. He started up his company when he was just 19.

Aidan Macfarlane is co-author of the book series based on questions sent to the TeenageHealthFreak.org website and is a cheerleader for teens: “Teenagers see the world in a different way. Their brain is still plastic and disconnecting, so they question everything. They’re wonderful.”