Teenage kicks in the hormones

Thu, Oct 4, 2012, 01:00

What makes the teenage years so awkward for everyone? A lot has to do with maturing and the wiring processes in the teenage brain, writes CLAIRE O’CONNELL

SLEEPING UNTIL lunchtime at weekends. Spot creams in the bathroom cabinet. The occasional slammed door and maybe even risky behaviours, such as e experimenting with drugs or driving too fast.

Teenagers are all individuals but if there’s one in your household – or maybe you are one yourself – at least some of the above is probably familiar.

Still, between the refrains of “turn down the volume” and “what did you do to your hair?”, spare a thought for the underlying biology of that transition between childhood and adulthood.

Hormones are one of the most famous game-changers, and they start to make their presence felt during puberty, says Dr Sinead Murphy, a lecturer in paediatrics at University College Dublin and a consultant paediatrician at Temple St Hospital.

“Puberty is basically controlled by the hypothalamus, which releases a hormone that acts on the ovaries in females and the testes in males. That causes them to produce the sex hormones, which can affect behaviour,” she says.

However, it’s not all even-keeled: the hormones tend to get released in pulses during adolescence, and girls could experience the cyclical nature of hormones even before menstruation starts, she adds.

Meanwhile, growth hormone, which pretty much does what it says on the tin, gets secreted mainly during sleep, which might be a reason to be lenient about the long lie-ins.

Puberty hormones may also affect brain development, but we still have plenty to learn about that. Dr Anne-Lise Goddings at University College London is studying the links.

“We now know that how the brain functions when asked to do tasks on a computer and in a brain scanner changes not just with age in adolescence, but also with their levels of androgens and oestrogens,” she says. “And how the structure changes across adolescence is related to puberty and the hormones that cause it too.”

For now though, the mechanisms are unclear. “So far, we can’t be sure exactly how the hormones cause these changes,” says Goddings, who is a Medical Research Council clinical training research fellow and paediatric specialty registrar at UCL’s Institute of Child Health and Institute of Cognitive Neuroscience. “They may act directly on the brain using hormone receptors, or might work by changing our behaviour, which in turn changes the structure and function of the brain.”

More generally, magnetic resonance imaging (MRI) has been highlighting that in the adolescent and teenage years the brain is quite distinct from childhood and adulthood.

During adolescence the volume of white matter, which contains the fibres connecting different brain regions, gets larger. Meanwhile, the volume of grey matter, which contains the “bodies” of brain cells and their connections to each other, gets smaller, explains Dr Iroise Dumontheil, formerly at UCL and now a lecturer at the Department of Psychological Sciences, Birkbeck, University of London.

“Grey-matter volume decreases during adolescence and this is thought to reflect the elimination of unnecessary connections between neurons, to adapt to experiences and the environment and only maintain the connections that are useful and thus obtain a more efficient, less noisy system,” she says. “So these [imaging] studies suggest that adolescence is an important period where the brain continues to be shaped by our experience and environment.”

Functional MRI studies have also compared which parts of the adult and adolescent brains become active during the same task. “In some cases, there is greater activity in adults, for example, in working memory tasks, which require participants to remember something for a few seconds. In other cases, there is reduced activity in adults, for example, in response inhibition,” says Dr Dumontheil. “We are still trying to understand what these changes in activation reflect, whether they reflect the structural changes or how different regions of the brain collaborate together, or different strategies used by the participants during the tasks.”

Brain imaging may also offer some possible clues about the potential for risk-taking during the teenage years. During adolescence there are changes in an area of the brain called the prefrontal cortex, which is an important region for “executive functions” involved in making judgments, planning, inhibiting actions and making decisions, says Goddings.

“We know that the structure of the prefrontal cortex is continuing to mature during adolescence, and that some of the most dramatic changes that happen in adolescence affect the prefrontal cortex,” she says.

“The connections between brain cells – the synapses – which increase in number throughout childhood, start to decrease in adolescence. This is thought to be because some of the synapses are being pruned, to make the brain more efficient.”

As well as the structural changes, the prefrontal cortex also seems to become activated differently during a number of tasks in adolescence, compared with adults and children, she adds. So can we make a link with behaviour?

“We think that this prolonged development of the prefrontal cortex might mean that adolescents’ abilities to make judgments and decisions isn’t yet fully mature,” says Goddings.

“In contrast, other brain regions may be more functionally developed in adolescence, meaning that teenagers may be particularly sensitive to the environment they are in but less able to make adult-like decisions within it.”

The emerging science should give us pause for thought about the teen years, says Dr Dumontheil. “I think it’s important to consider the positive aspects, that research [has] shown that adolescence is a period of continuing brain plasticity, and maturation of higher cognitive processes,” she says.

“This has implications in terms of education and potentially training or treatment interventions that may be more successful during adolescence than later in life.”

We should have some empathy for young people undergoing the transition, adds Dr Murphy.

“Sometimes teenagers are not given credit for the fact that this is all happening to them – they were possibly quite happy in their childhood state, childhood body and childhood mind and this is being foisted upon them,” she says. “Plus it is there for all to see – the spots and the breast development or facial hair and breaking voice.

“Yet people are giving out to them for being a bit stroppy. I think we need to be a bit more positive and understanding.”

Focus on healthy habits

TEENAGE YEARS can be an ideal time for developing healthy habits that will stand to you in adulthood, and consultant paediatrician Dr Sinead Murphy has some pointers.

One is around sleep. Teens may love to sleep all morning, and to some extent this is normal behaviour for the age-group, she explains. But it’s important to draw the line.

“It’s not okay for kids to be staying up until 5am on the laptop or phone and then getting up in the afternoon,” she says, pointing out that there could be long-term impacts. “Children and teens whose sleep cycle is disrupted have more of a tendency to put on weight or become overweight, just like adults do.”

While it’s important to avoid excess, some weight gain in adolescence is normal and in girls it is linked to the hormones that drive puberty, explains Dr Murphy.

“The change from the childhood to adult body in girls is mostly a gain of fat and they need that to maintain a normal menstrual cycle and subsequent fertility, so there’s a certain amount of appropriate weight gain in puberty,” she says.

Keeping the focus on a healthy lifestyle is important, according to Murphy, and she advises that, if possible, getting the family to eat together, without the TV on, is a smart move in that direction.

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