Opinion
Adolescence as a Sensitive Period of Brain Development

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Trends

Recently the idea that adolescence may be a sensitive period of development has gained traction in the literature.

Adolescence is characterised by changes in brain structure and function, particularly in regions of the cortex that are involved in higher-level cognitive processes such as memory, for which capacity may be heightened in adolescence.

Heightened plasticity may not only result in increased opportunities for development but also in increased vulnerabilities. Data from rodents show effects of social isolation and reduced fear extinction that are consistent with adolescence as a sensitive period for the development of mental illness.

Adolescent sensitive periods are likely to be characterised by large individual differences. Rodent data indicate that individuals who are exposed to drugs such as cannabis during adolescence may experience detrimental effects on cognitive functioning.

Most research on sensitive periods has focussed on early sensory, motor, and language development, but it has recently been suggested that adolescence might represent a second ‘window of opportunity’ in brain development. Here, we explore three candidate areas of development that are proposed to undergo sensitive periods in adolescence: memory, the effects of social stress, and drug use. We describe rodent studies, neuroimaging, and large-scale behavioural studies in humans that have yielded data that are consistent with heightened neuroplasticity in adolescence. Critically however, concrete evidence for sensitive periods in adolescence is mostly lacking. To provide conclusive evidence, experimental studies are needed that directly manipulate environmental input and compare effects in child, adolescent, and adult groups.

Section snippets

Defining Plasticity and Sensitive Periods

In the 1960s, Wiesel and Hubel investigated the effect of monocular deprivation for 1–4 months after eye opening. Neurons in the corresponding visual cortex subsequently lost responsiveness to stimuli directed towards the previously deprived eye and started responding preferentially to the nondeprived eye 1, 2. Monocular deprivation in the first 3 months of life was also associated with atrophy in cells in the thalamus receiving input from the deprived eye. Recovery from this atrophy was very

What Evidence Would Be Consistent with Adolescence Being a Sensitive Period?

If adolescence were indeed a sensitive period, certain patterns in the developmental data would be expected. First, the impact of a specific stimulus on brain and behaviour should be higher in adolescence than before or after. For that reason, studies comparing children, adolescents, and adults are needed. Only if all of these age groups are considered is it possible to assess whether adolescence is a stand-alone period of heightened plasticity (Figure 1, Model A), a continuous sensitive period

Adolescence as a Sensitive Period for Memory

At age 35, we are more likely to recall autobiographical memories from ages 10 to 30 years than memories prior or subsequent to this period, a phenomenon referred to as the ‘reminiscence bump’ [26]. The reminiscence bump is remarkably robust and shows a similar pattern when tested with different mnemonic tests and in different cultures 26, 27. In addition to autobiographical events, the recall of music, books, films, and public events from adolescence is also superior compared with from other

Adolescence as a Sensitive Period for the Effects of Stress on Mental Health

Many mental illnesses have their onset in adolescence and early adulthood 38, 39. A longitudinal study showed that 73.9% of adults with a mental disorder received a diagnosis before 18 years of age and 50.0% before 15 years of age [40]. It is thought that psychiatric disorders may in part be triggered by stress exposure in childhood or adolescence [41]. Social stress in particular is thought to have a disproportionate impact during this time [41]. The experience of acculturation stress

Adolescence as a Sensitive Period for the Effects of Drug Use

Adolescence is a time of heightened engagement in risky health behaviours, such as unsafe sexual behaviour, dangerous driving, and experimenting with alcohol and other drugs 52, 53. This increase in risk-taking behaviour might be partly mediated by the increase in time spent with friends rather than family [54]. When together with their friends, adolescents are more likely to engage in risky behaviour than when alone [55]. Young adolescents appear to be particularly susceptible to peer

Concluding Remarks

Evidence for plasticity in memory and the effects of social stress and drug use is consistent with the proposal that adolescence is a sensitive period for certain areas of development. The strongest evidence for sensitive periods to date comes from rodent studies showing a heightened vulnerability to the disruptive effects of social isolation and cannabis use, as well as reduced fear extinction learning. There is little conclusive evidence for human adolescence, however. Studies are needed on

Acknowledgments

We would like to thank Kathryn Mills for helpful comments on the manuscript. D.F. is funded by the UCL Psychology and Language Sciences Department. S.J.B. is funded by a Royal Society University Research Fellowship. Our research is funded by the Nuffield Foundation and the Wellcome Trust.

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