The brain is in a process of continuous alteration throughout the lifespan; it is in a constant state of change between the influence of biological factors and the physical and social environment. However the process is not linear. There are surges of growth and change in different parts of the brain, and in different processes within it, at different times. The timing of this is a function of the interplay between the environment and the genetic programme.
The brains of young people are not radically different from adults in structure. There is no great difference in the capacity between young people and adults. There is a difference however, in the degree of myelination (an insulating layer around the axon), which makes brains more reliable and efficient in their reactions and responses but less flexible and less available for new learning. The major brain development in the adolescent years is the increase in myelination which then levels off to some degree in the mid-twenties.
'It’s sort of unfair to expect (teens) to have adult levels of organisational skills or decision making before their brains are finished being built.'
Jay Giedd, MD, NIH (2002)
The primary difference between the brain of an adolescent and an older person’s brain then is not a ‘difference in capacity’ but in the selection of capacities. Adolescents are not passive victims of brains that are out of control. Youth is not separate from adulthood. It is the becoming of adulthood. There is no ‘next stage’ of adulthood, which is qualitatively different from being a young person and adulthood is not, itself, a destination. You don’t learn what you need for adulthood by being excluded from it until you can demonstrate that you have got the right circuits.
A smart society would engage young people progressively in adult processes as they demonstrate their readiness. Our society does this a little but mostly we exclude young people until a certain arbitrary age is reached and then bestow the right to participate - mostly without guidance and support. It should be no surprise that it does not work too well. We respond to this failure usually by increasing the age at which responsibility will be granted.