Adolescent Development

Abstract

Adolescent development, which MeSH classifies under human development, is the course of biological, psychological and social change across adolescence, the phase of life between childhood and adulthood. This article covers how adolescence is bounded by puberty and by social role transitions, the structural development of the brain between childhood and adulthood, the dual-systems account of adolescent risk taking and the criticisms of it, the effect of peers on risky decisions, social development and the social brain, the early onset of mental disorders, the proposal of emerging adulthood as a further period, and current large-sample research. The central debate concerns whether adolescent behavior is best explained by an imbalance between an early-maturing reward system and a later-maturing control system.

Keywords: adolescence, puberty, brain development, dual systems model, peer influence

Adolescence has been described as the phase of life stretching between childhood and adulthood, encompassing elements of biological growth and major social role transitions, both of which have changed in the past century (Sawyer et al., 2018). One review of the field identified adolescent problem behavior, parent-adolescent relations, puberty, the development of the self, and peer relations as topics that had dominated recent research (Steinberg & Morris, 2001).

What Adolescent Development Is

Adolescence is a period of formative biological and social transition, and social cognitive processes involved in navigating increasingly complex and intimate relationships continue to develop throughout it (Blakemore & Mills, 2014). Puberty is accompanied by physical, psychological and emotional changes, and human puberty stands out in the animal world for its association with brain maturation and physical growth (Patton & Viner, 2007). A review covering research since 1988 also identified research on diverse populations, contextual influences on development, behavioral genetics and siblings as important new directions (Steinberg & Morris, 2001).

Figure 1

Two Proposed Age Ranges for Adolescence

Puberty and the Boundaries of Adolescence

Earlier puberty has accelerated the onset of adolescence in nearly all populations, while understanding of continued growth has lifted its endpoint age well into the 20s (Sawyer et al., 2018). Delayed timing of role transitions, including completion of education, marriage and parenthood, continues to shift popular perceptions of when adulthood begins (Sawyer et al., 2018). On that basis, the same authors proposed that a definition of 10 to 24 years, rather than 10 to 19 years, corresponds more closely to adolescent growth and popular understandings of this life phase (Sawyer et al., 2018).

The effects of puberty on health and wellbeing have been described as profound and paradoxical: physical maturation brings peaks in strength, speed and fitness, yet puberty marks a transition in risks for depression and other mental disorders, psychosomatic syndromes, substance misuse and antisocial behaviours (Patton & Viner, 2007). The same review noted that recent secular trends in these psychosocial disorders coincide with a growing mismatch between biological and social maturation and with the emergence of more dominant youth cultures (Patton & Viner, 2007).

Brain Development

Brain development in the first two decades generally involves early cortical grey matter volume increases followed by decreases, and monotonic increases in cerebral white matter volume (Mills et al., 2016). Repeating the same analyses in four separate longitudinal samples (391 participants; 852 scans) between ages 8 and 30 years, one study found that cortical grey matter volume is at its highest in childhood, decreasing steadily through the second decade with deceleration in the third decade, while cerebral white matter volume increases until mid-to-late adolescence before decelerating (Mills et al., 2016). The same study showed that accounting for cranial and brain size affects models of regional brain development, particularly with respect to sex differences (Mills et al., 2016).

Areas of the social brain undergo both structural changes and functional reorganization during the second decade of life, possibly reflecting a sensitive period for adapting to one's social environment (Blakemore & Mills, 2014).

Dual-Systems Models and Their Critics

One framework holds that risk taking increases between childhood and adolescence as a result of changes around the time of puberty in the brain's socio-emotional system, leading to increased reward seeking, especially in the presence of peers, and that it declines between adolescence and adulthood because of changes in the brain's cognitive control system that improve individuals' capacity for self-regulation (Steinberg, 2008). On that account, the differing timetables of these changes make mid-adolescence a time of heightened vulnerability to risky and reckless behavior (Steinberg, 2008). A related review proposed a model of the differential development of bottom-up limbic systems, implicated in incentive and emotional processing, relative to top-down control systems during adolescence (Casey et al., 2008).

A later review of the dual systems model reported that psychological and neural manifestations of reward sensitivity increase between childhood and adolescence, peak sometime during the late teen years and decline thereafter, whereas psychological and neural reflections of better cognitive control increase gradually and linearly throughout adolescence and into the early 20s, although there are occasional exceptions to these general trends (Shulman et al., 2016). The authors described the model as admittedly an oversimplification, but argued that as a heuristic device it provides a far more accurate account of adolescent risk taking than prior models that attributed adolescent recklessness to cognitive deficiencies (Shulman et al., 2016). The same review conceded that some forms of real-world risky behavior peak at a later age than predicted, which the authors said likely reflects differential opportunities for risk taking in late adolescence and young adulthood rather than neurobiological differences, and it noted critiques that adolescence may not actually be a peak period of vulnerability to risk taking (Shulman et al., 2016).

Critics have argued that recent evidence inconsistent with dual-systems models illustrates the complexity of developmental and clinical variations in brain function, and that building new models will be facilitated by network-based approaches that map relationships between structure and function, and between brain and behavior, over time (Pfeifer & Allen, 2012). Another review argued that developmental neuroimaging studies do not support a simple model of frontal cortical immaturity, and that growing evidence points instead to changes in social and affective processing, which begin around the onset of puberty, as crucial to understanding adolescent vulnerabilities (Crone & Dahl, 2012). The same review proposed that these changes may also confer adaptive advantages, such as greater flexibility in adjusting one's intrinsic motivations and goal priorities amidst changing social contexts (Crone & Dahl, 2012).

Peers and Risk Taking

In an experiment with 306 participants in three age groups, adolescents (13 to 16), youths (18 to 22) and adults (24 and older), participants were randomly assigned to complete risk measures either alone or with two same-aged peers (Gardner & Steinberg, 2005). Participants took more risks and made riskier decisions when in peer groups than alone, and peer effects on risk taking and risky decision making were stronger among adolescents and youths than adults (Gardner & Steinberg, 2005).

Social Development

The changes in social environment that occur during adolescence might interact with increasing executive functions and heightened social sensitivity to influence a number of adolescent behaviors, and one review emphasized the importance of considering the social environment and social rewards in research on adolescent cognition and behavior (Blakemore & Mills, 2014). Personal autonomy and relations with parents and peers are covered further under adolescent psychology.

Mental Health

In a nationally representative United States household survey of 9,282 respondents aged 18 years and older, the median age of onset was much earlier for anxiety (11 years) and impulse-control (11 years) disorders than for substance use (20 years) and mood (30 years) disorders (Kessler et al., 2005). Half of all lifetime cases started by age 14 years and three fourths by age 24 years, and the authors concluded that interventions aimed at prevention or early treatment need to focus on youth (Kessler et al., 2005). A later meta-analysis of 192 epidemiological studies (n = 708,561) reported that the proportions of individuals with onset of any mental disorder before the ages of 14, 18 and 25 were 34.6%, 48.4% and 62.5%, and that the peak age at onset was 14.5 years (Solmi et al., 2022).

The widespread use of digital technologies by young people has spurred speculation that their regular use negatively impacts psychological well-being (Orben & Przybylski, 2019). Applying specification curve analysis across three large-scale social datasets (total n = 355,358), one study found the association between digital technology use and adolescent well-being to be negative but small, explaining at most 0.4% of the variation in well-being (Orben & Przybylski, 2019).

Emerging Adulthood

Emerging adulthood has been proposed as a new conception of development for the period from the late teens through the twenties, with a focus on ages 18 to 25, distinct demographically, subjectively and in terms of identity explorations (Arnett, 2000). Its proponent specified that emerging adulthood exists only in cultures that allow young people a prolonged period of independent role exploration during the late teens and twenties (Arnett, 2000). A critical examination of the concept, reviewing elements of its theoretical framework and relevant empirical studies, found several limitations to the model and offered an alternative perspective that might complement the stage theory (Hendry & Kloep, 2007).

Worked Example

The proposed change in definition can be expressed as a span of years. The conventional range of 10 to 19 years covers 10 years of age, and the proposed range of 10 to 24 years covers 15 (Sawyer et al., 2018), so the expanded definition is 15 / 10 = 1.5 times as long.

The onset figures can be read the same way. If half of all lifetime cases start by age 14 years and three fourths by age 24 years (Kessler et al., 2005), then 75% - 50% = 25% of lifetime cases start between those two ages, an interval that falls within the expanded 10 to 24 year definition of adolescence.

Discussion

Proponents of the dual-systems account report that reward sensitivity increases between childhood and adolescence, while critics have contended that the model inadequately accounts for studies that do not find adolescents to be particularly sensitive to reward (Shulman et al., 2016), and one critical review points instead to changes in social and affective processing (Crone & Dahl, 2012). Its proponents present the model as a heuristic that they argue is more accurate than accounts based on cognitive deficiencies (Shulman et al., 2016), while critics point to evidence inconsistent with it and call for network-based models (Pfeifer & Allen, 2012).

Current Directions

Most tests of the dual systems model have been conducted in the United States or Western Europe, and an international study of more than 5000 individuals between ages 10 and 30 years from 11 countries in Africa, Asia, Europe and the Americas found that sensation seeking increased between preadolescence and late adolescence, peaked at age 19 and declined thereafter, whereas self-regulation increased steadily from preadolescence into young adulthood, reaching a plateau between ages 23 and 26 (Steinberg et al., 2018). Although there were some variations in the magnitude of the observed age trends, the developmental patterns were largely similar across countries, with exceptions: sensation seeking did not vary with age or increased linearly in some countries, such as Sweden and Jordan, and self-regulation did not increase with age in Jordan and India (Steinberg et al., 2018). The Adolescent Brain Cognitive Development (ABCD) study was described in 2018 as recruiting and following the brain development and health of over 10,000 9 to 10 year olds through adolescence, with imaging methods harmonized across 21 sites to measure brain structure and function relevant to adolescent development and addiction (Casey et al., 2018).

Common Misconceptions

Adolescent risk taking is simply a matter of an immature frontal cortex.

One review argued that developmental neuroimaging studies do not support a simple model of frontal cortical immaturity (Crone & Dahl, 2012).

Every definition of adolescence ends at 19.

One proposal holds that a definition of 10 to 24 years corresponds more closely to adolescent growth than 10 to 19 years (Sawyer et al., 2018).

Glossary

Adolescence.

The phase of life stretching between childhood and adulthood.

Cerebral white matter volume.

The volume of white matter in the cerebrum, which increases until mid-to-late adolescence before decelerating.

Cognitive control system.

In the dual systems account, the brain system whose changes improve individuals' capacity for self-regulation between adolescence and adulthood.

Cortical grey matter volume.

The volume of grey matter in the cerebral cortex, as measured with magnetic resonance imaging.

Dual systems model.

The account that pairs an early-maturing socioemotional-incentive processing system with a still immature cognitive control system to explain adolescent risk taking.

Emerging adulthood.

A proposed period of development from the late teens through the twenties, with a focus on ages 18 to 25.

Peer effects.

Differences in risk taking and risky decision making between completing measures with same-aged peers and completing them alone.

Puberty.

The developmental process that is accompanied by physical, psychological and emotional changes adapted to ensure reproductive and parenting success.

Self-regulation.

In the dual systems model, the still-maturing capacity paired with sensation seeking, which increases steadily from preadolescence into young adulthood.

Sensation seeking.

An affinity for exciting, pleasurable and novel activities, one of the two constructs of the dual systems model.

Sensitive period.

A developmental window; adolescence has been proposed as a sensitive period for adapting to one's social environment.

Social brain.

The brain areas involved in social cognition, which undergo structural changes and functional reorganization during the second decade of life.

Socioemotional system.

In the dual systems account, the brain system whose changes around the time of puberty lead to increased reward seeking, especially in the presence of peers.

Specification curve analysis.

The analytic approach one study applied across three large-scale social datasets to examine correlational evidence for the effects of digital technology on adolescents.

Key Researchers

Jeffrey Jensen Arnett

. Psychologist at Clark University; proposed emerging adulthood as a distinct period of development from the late teens through the twenties. Wikidata - Wikipedia - Google Scholar - Faculty Page

Sarah-Jayne Blakemore

. Psychologist at the University of Cambridge; with Kathryn Mills reviewed whether adolescence is a sensitive period for sociocultural processing. ORCID - Wikidata - Wikipedia - Google Scholar - Faculty Page

B. J. Casey

. Neuroscientist at Barnard College, Columbia University; co-authored a model of the differential development of limbic and control systems in adolescence and the overview of the ABCD study imaging procedures. ORCID - Google Scholar - Faculty Page

Eveline A. Crone

. Psychologist at Erasmus University Rotterdam and Leiden University; with Ronald Dahl argued that changes in social and affective processing are crucial to understanding adolescent vulnerabilities. ORCID - Wikidata - Wikipedia - Faculty Page

Ronald E. Dahl

. Developmental scientist at the School of Public Health, University of California, Berkeley; with Eveline Crone proposed that adolescent social-affective changes may confer greater goal flexibility. ORCID - Google Scholar - Faculty Page

Laurence Steinberg

. Psychologist at Temple University; proposed a social neuroscience framework for adolescent risk taking and co-authored a review and reappraisal of the dual systems model. ORCID - Wikidata - Wikipedia - Google Scholar - Faculty Page

Frequently Asked Questions

What is adolescence?

Adolescence is the phase of life stretching between childhood and adulthood, and its definition has long posed a conundrum (Sawyer et al., 2018).

How does the brain change during adolescence?

Cortical grey matter volume is at its highest in childhood and decreases steadily through the second decade, while cerebral white matter volume increases until mid-to-late adolescence before decelerating (Mills et al., 2016).

What is the dual systems model?

According to the dual systems perspective, risk taking peaks during adolescence because an early-maturing socioemotional-incentive processing system is active at a time when a still immature cognitive control system is not yet strong enough to consistently restrain potentially hazardous impulses (Shulman et al., 2016).

Do peers make adolescents take more risks?

In one experiment, peer effects on risk taking and risky decision making were stronger among adolescents and youths than adults (Gardner & Steinberg, 2005).

When do mental disorders usually begin?

A meta-analysis of 192 epidemiological studies reported that 34.6% of individuals with any mental disorder had its onset before age 14, 48.4% before age 18 and 62.5% before age 25, with a peak age at onset of 14.5 years (Solmi et al., 2022).

Are these age patterns the same in every country?

In a sample from 11 countries, the developmental patterns of sensation seeking and self-regulation were largely similar across countries, but sensation seeking did not vary with age or increased linearly in some countries, such as Sweden and Jordan, and self-regulation did not increase with age in Jordan and India (Steinberg et al., 2018).

Does digital technology harm adolescent well-being?

In one study across three large-scale social datasets, the association between digital technology use and adolescent well-being was negative but small, explaining at most 0.4% of the variation in well-being (Orben & Przybylski, 2019).

What is emerging adulthood?

Emerging adulthood is a proposed conception of development for the period from the late teens through the twenties, with a focus on ages 18 to 25 (Arnett, 2000).

References