Immature brain in adolescence

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The period of adolescence has increased over the past century with earlier onset of puberty and with recognition that brain maturation extends into the mid-20s. Initially regarded as a fairly abrupt transition from childhood to adulthood on a particular birthday, currently 18, adolescence is now acknowledged as a specific and unique period of development and many of the problems presenting to health professionals at this age relate to brain immaturity, including the management of chronic medical conditions such as diabetes, pervasive developmental disorders, behaviour disturbance that may reflect immaturity or the emergence of adult psychiatric disorders, and drug- and alcohol-related psychological problems. Adolescence is also a period of achievement, of learning and social development, a time for determining a career and embarking on appropriate training. It has been a period of artistic creativity, particularly in music. But society has expected much more of this age group. In the past, adolescents (physically mature people in their late teens and 20s) were responsible for defending their country at war, of initiating and supporting a family But the cultures of youth, and the expectations held for them, have changed in our society. It was the very characteristics of adolescent boys, the feeling of immortality, of taking risks without fear of consequences that made them fearless fighters and hunters, and their sexual drives that committed them as parents. These are no longer relevant for most young people, but may lead to risky behaviour affecting safety and health. To a large extent, culture determines adolescence, both in its social expression and in its duration. It is a period when sense of self develops and this is susceptible to peer influence.1 The changing culture has contributed to the problems in behaviour and mental health that present at this age, but what is particularly relevant is understanding the immaturity of the adolescent brain. It has become increasingly important for the profession, both as paediatricians and medical practitioners in general to recognise this. Research in the psychology of adolescents and structural and functional brain development at this age has advanced over the last two decades with understanding of the immaturity of the brain,2, 3 together with determining the relationship between early experience and genetics.4 There is now considerable knowledge on the development of the brain during adolescence and the relation of this to behaviour.5, 6 This includes in particular the relation of prefrontal cortex and limbic development. From the onset of puberty until the mid-20s, there is protracted development of neural circuitry, especially in the prefrontal cortex and limbic system structures and white matter-associated fibres. The process to achieve maturity proceeds at different rates and regions of the brain, concluding in the dorso-lateral prefrontal cortex. This process involves thinning of the grey matter of the brain from early puberty with concurrent growth of white matter volume with synaptic proliferation, myelination and pruning. This is most prominent in the frontal regions and shows differences between the sexes. These developments influence attentional control, the manipulation of stored knowledge and the modulation of complex actions, cognition and emotional behaviour. Neurotransmitter changes, especially the dopamine pathway, occur in synchrony with the changes in the prefrontal cortex. Maturity of the limbic system occurs in conjunction with the prefrontal cortex, and in each area, the influence of maturity (and delayed maturity) is relevant to behaviour. The components of the limbic system include the hypothalamus, which is responsible for homeostasis, and in particular for general body function with recognition of body signals, endocrine function, sexuality and the circadian rhythms. It is therefore expected that the developing maturity and vulnerability imposed by change may be expressed by disordered behaviour at this age. The confusion in recognition of body signals may be expressed in disturbed perception of body image and lead to eating disorders. Some confusion in sexuality and sexual behaviour is also to be expected as the limbic system develops. Altered sleep patterns are seen commonly in adolescents and may relate to development of circadian rhythms at this age. The amygdala is responsible for reaction to the environment with fear and anxiety as a protective response. In adolescence, there may be a weaker sensitivity in considering harmful behaviour.7 The hippocampus relates to memory functions and the prefrontal cortex to reward response and to susceptibility to drugs of addiction and mood, also placing the vulnerable adolescent at risk. The prefrontal cortex matures later the other areas, affecting attention, reward evaluation and behaviour that is directed to specific goals. Male and female brains differ in architecture and functional activity in limbic cortex and frontal cortex at this age. It is likely that these are innate biological differences started in utero. There are differences in the neurobiology of learning.8 Male and female response to stress differs at adolescence and there may be differences in response to selective serotonin reuptake inhibitor antidepressants. This may also explain differences in presentation of psychiatric disorders in males and females in adolescence.2, 9, 10 At this stage of development, there is increased drive to seek rewarding outcomes of behaviour, especially immediate rewards which may include response to alcohol and recreational drugs, sexual activity and to fast-food intake. This also relates to the characteristic behaviour we associate with adolescents. It is a critical period in the development of skills and sophisticated cognitive functioning, together with changes in emotional processing. It also poses a window of vulnerability to the unhealthy environmental influences such as adverse social pressures, aggressive marketing, the media, the Internet, alcohol, pornography, altered relationships with parents in a dysfunctional family or social environment. Teenagers may be well aware of risks but weigh these against the much more desirable quick rewards from their impulsive behaviour. This may explain the poor results of most efforts of health education to influence behaviour at this age. It is also suggested that there is increased vulnerability to neurotoxic substances and possible change in response to psychoactive medication drugs. Behaviour driven by emotion and seeking immediate rewards (e.g. social, sexual, risk-taking) is influenced by biological factors of puberty. At best, this is shown by creativity and sporting prowess and leadership. At worst, it leads to drug seeking, alcohol abuse, eating disorders, inappropriate sexual activity, antisocial activity and excessive Internet commitment, especially to gaming and virtual social interaction, for example, with hundreds of ‘friends’ on Facebook. These drives have both societal and personal outcomes, but with maturity of the prefrontal region, there is development of a stronger regulatory control which inhibits impulses and leads to delay in gratification and allows for long-term planning. Further, it recognises experience and benefits from this. Adolescence could be regarded as a critical period for reorganisation of regulatory systems for behaviour.11 For some adolescents, maturation of these areas of the brain may be disordered. An example is a mismatch between prefrontal cortical areas responsible for self-control and consideration of consequences of one's actions on the one hand, with areas influencing spontaneous behaviour directed to quick rewards (fun, social satisfaction) without considering the consequences, on the other. Problems of behaviour may arise if these areas are out of balance, or the area for control is significantly delayed in development in relation to the imme

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