Blame my brain: the amazing teenage brain by Nicola Morgan. Walker Books, 2013.
The human brain contains about 100 billion nerve cells (neurons). Each neuron has a long tail-like part (axon) and many branches (dendrites). A neuron sends super-fast messages to other neurons by passing a tiny electrical current along its axon and across very tiny gaps (synapses) into the dendrites of other neurons. Every single thing you do - thought, action, sneeze, emotion - happens when the neurons send the right messages, very fast, through the complicated web of branches.
Every time you repeat an action, or thought, or recall the same memory, that same web is activated and the web of connections becomes stronger, and the better you are at that specific task. But if you don't use those connections again, they may die off and you forget a fact or a name, or how to do something. To relearn something, you need to rebuild the web of connections by practicing again. If someone has a brain injury (e.g. a stroke) they might need to relearn how to walk or speak.
At birth a human baby has almost all of its neurons but few dendrites and therefore few synapses connecting them - so can't do very much. But their brains develop fast with new dendrites and synapses, as they learn to recognise people, talk and walk. There are also critical periods in brain development. If you don't learn a foreign language before the age of about seven, you can still learn to speak it fluently but probably always speak with the wrong accent, having passed the age when the brain can pick up accents. But most skills can be picked up at any age.
One type of neuron is called a mirror neuron. These neurons fire up when we watch someone else do something. If we watch several times, it may be easier for us to do the same thing because we have watched someone else do it. And it might be these neurons that help us feel what other people are feeling (empathy).
It was thought that all important development takes place in the first three years of life, but now we know that: (1) We can grow more neurons after we are born. (2) The brain grows and develops even into later life. (3) While some neurons die, we sometimes grow new ones. Adolescence is a time of major change in the volume of grey matter in the brain, and some parts of the brain are affected more than others. Not all teenagers show this in their behaviour, but some do.
The part of the brain used for thinking, reasoning, logic and decision making gets bigger mainly just before puberty (usually 11 to 12 years). But the pre-teen brain grows far too many connections and synapses, and during the teenage years these are cut back: dendrites that don't get used fall away and those that do get used get fewer and thicker.
Body clock: The adult human body clock is 'on' for for about 16 hours of the day when we are awake and it is difficult to sleep in this period. While babies need a lot of sleep, by the age of 9 or 10, we tend to have reached the adult pattern of eight hours of sleep. But research shows that teenagers need around nine hours, at the point they also stay up later - so they are not ready to wake at 7am.
Sleep: If they are woken too early they risk losing REM (rapid eye movement) sleep which is particularly deep sleep, and seems to be important for memory and learning. Trying to catch up by sleeping more at weekends does not help the body clock and may even disrupt it further. And there is now evidence that the sleeping brain practises the things that you did when you were awake. And the brain is also changing physically by pruning some connections and strengthening others.
Risk taking: Surviving risks means the brain releases dopamine so activating the feelings of pleasure, otherwise we become lazy. But some people's brains are more geared to this than others and adolescents in general do take more risks. Also the pleasure reaction is often stronger than the rational (pre-frontal cortex) part of the brain that logically looks at the risks. The need to impress friends is important for getting on in life, so teenagers often take different decisions when friends are present. And with puberty starting around 2 years earlier than 50 years ago, alcohol is more widely used, as are (increasingly stronger) drugs. 2013: Rates of sexually transmitted diseases have increased, almost a quarter of 15 year olds smoke regularly and a third have tried cannabis, and a fifth are classified as obese. And around 60% of teenage girls are on diets (often not healthy ones). But remember if a quarter of UK teens get drunk at least three time a month - three quarters don't.
Female and male brains: [The following statements are averages and not everyone's brain behaves in the same way; the brains of some girls work more in a male way, and vice versa. and it's not about being homosexual or heterosexual.] Boys tend to be interested in technical details of (e.g. a mobile phone) and girls more in the appearance and how useful it is. Boys are more likely to be diagnosed with autism, lacking understanding of social skills and bonding mechanisms. However, this may be less so as if is now being recognised that girls can mask the symptoms of autism by copying behaviour to 'fit in'.
The male brain is typically 10% heavier than a female brain but female brains have a greater proportion of the information-processing grey matter. Women are less likely to have dyslexia, language difficulty, colour blindness, schizophrenia, ADHD, Tourette's and other brain disorders. In later life, men lose brain cells faster and are more likely to develop memory problems.
Sex Hormones: these are chemicals that affect many aspects of our lives. When a sperm fertilizes an egg, the resulting embryo always starts out female. During week 6 or 7 the sex hormones either turn the embryo into a male (testosterone) or keeping it as female (oestrogen). Normal males will have a small amount of female hormones and females a small amount of male hormones. Hormone levels change during our lifetime and are especially active at puberty. They also change with the season and, for women, during the menstrual cycle.
Oestrogen: One effect of this hormone is to boost dopamine, which can make the world seem rosier, brighter but can also make it feel darker and sadder, and it can cause mood swings. But not all females have mood swings. And mood swings are not only causes by sex hormones. Boys have mood swings too.
Testosterone: Increased testosterone causes aggressive behaviour. Testosterone increases during and after intense sport, especially if you are on the winning side - and also if you are a spectator. Females with the condition 'congenital hyperplasia' have too much testosterone; they show more aggressive behaviour and better spatial skills - both of which are more common in males.
Learning: Different sexes may learn better with different teaching methods. For languages, some pupils (especially boys) may need the rules and grammar explained in a very structured way. In science subjects, some pupils (perhaps more often the girls) may need more rote learning, practical examples or a using comparisons or analogies.
Emotional behaviour: Girls start to use their pre-frontal cortex to control emotional behaviour sooner than boys, who may take longer to develop self-control.
Risk behaviour: Boys seem to take more risks and more dangerous ones - not wearing seat belts or helmets, driving while drunk, binge drink and drink heavily, use and deal drugs, smoke, fight and carry weapons, have sex before 13, overeat and so be overweight. Girls' risk taking is more often having sex when they hadn't intended to, fast or vomit to lose weight or avoid physical exercise.
Body changes: Girls start to look like women before boys start to look like men. This sometimes makes girls feel they are fat. Research using pictures shows that women think men like thinner women, while men didn't choose the same photos.
Developing early or late: Either is difficult for both sexes. Early development in girls creates an extra risk of early sex and alcohol addiction, depression, anxiety and eating disorders. For boys, while they may be more popular and given leadership roles, adults may expect them to be advanced in school work too which is unlikely as their frontal cortex is not mature.
Clumsiness: One the areas of the brain that grow the most in adolescence is the cerebellum, which is important in controlling large movements. However the brain may not have completely rewired itself as fast as the body growth. Stress can also cause clumsiness.
Social: Girls are likely to hit puberty just as they start secondary school, while boys have time to settle in before puberty starts. Both sexes may feel less comfortable with their other-sex parent and argue more with opposite sex siblings. It is thought that this is a biological way of preventing incest which can lead to deformities in offspring.
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