Sunday, March 06, 2005
It's not just the hormones ...
Guardian Unlimited.: "Another clue that testosterone is not the whole story here is that teenage girls, while not as violent, certainly rival boys for downright bloody-mindedness during their adolescent years. Worse, I can hear some parents say.

The thing that is really irritating about teenagers (and by now you will have guessed that I have two teenage boys) is that one moment their behaviour is that of adults, while the next it is that of a not very bright three-year-old, or possibly, a retarded chimpanzee. Or an amoeba. The rapid oscillation between child and adult is one of the hallmarks of the teenager.

In fact teenage brains are going through a process of maturation, and it is this maturation which many now believe to be responsible for much of the behaviour that we classically attribute to hormones. These changes are independent of hormones and are a function of age.

It has only been discovered very recently that there are two main features of brain maturation that happen to coincide with puberty. Previously it was believed that the brain was pretty well set by adolescence but only in the last couple of years, and to everyone's surprise, it has been realised that maturation is not completed until late teens or even early 20s. One feature is that myelin, a sort of fatty insulating material, is added to axons, the main transmission lines of the nervous system, which has the effect of speeding up messages. The other feature is a pruning of nerve connections, the synapses, in the pre-frontal cortex. This is an area of the brain which is responsible for what is called executive action, which is a shopping list of the things that teenagers lack - such as goal-setting, priority-setting, planning, organisation and impulse-inhibition. During childhood, for reasons that are not clear, a tangle of nerve cells sprout in this brain area, which lies behind the eyes, but during puberty, these areas of increased synaptic density are then reduced by about half, presumably to increase efficiency.

These changes in the adolescent brain that occur around the time of puberty primarily affect motivation and emotion, which manifest themselves as mood swings, conflict with authority and risk taking. This new information has altered thinking about the effect of hormones on teenagers, because it has been realised that what we would call typical adolescent behaviour is not actually the result of hormones alone. For example, it is not just testosterone that drives risk taking, but the inability of the immature brain to assess risk properly that gets them into trouble."

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