Inventing Ourselves

1. Adolescence is a Crucial, Biologically Distinct Developmental Stage

Adolescence isn’t an aberration; it’s a crucial stage of our becoming individual and social human beings.

Universal Stage. Adolescence is not merely a Western construct but a biologically distinct period observed across cultures and species. Behaviors like risk-taking, self-consciousness, and peer influence are common across diverse human societies, suggesting a fundamental developmental process. This challenges the notion that adolescence is a recent or culturally specific phenomenon.

Animal Parallels. Evidence of adolescent-typical behavior in non-human mammals, such as increased risk-taking and novelty-seeking in adolescent mice and the rebellious phase of adolescent wombats, further supports the biological basis of this developmental stage. These parallels across species suggest that adolescence serves an evolutionary purpose.

Historical Consistency. Descriptions of adolescent behavior throughout history, from Socrates to Shakespeare, reveal consistent patterns of risk-taking, questioning authority, and seeking peer approval. This historical consistency suggests that adolescent-typical behavior is not a recent invention but a long-standing aspect of human development.

2. Self-Identity Formation Intensifies During Adolescence

The development that adolescents go through is central to human experience.

Evolving Sense of Self. Adolescence marks a period of intense self-discovery and identity formation. Teenagers become more aware of how others perceive them, leading to increased self-consciousness and a desire to fit in. This is the time when personal values, beliefs, and social affiliations are actively explored and defined.

Looking-Glass Self. The "looking-glass self" becomes particularly influential during adolescence, as teenagers imagine how others view them and internalize these perceptions. This can lead to feelings of contentment, embarrassment, pride, or shame, depending on the perceived judgments of others. Social media amplifies this effect, providing constant opportunities for self-comparison and evaluation.

Introspection and Intentionality. Adolescents also develop a greater capacity for introspection, reflecting on their own emotions, thoughts, and actions. They begin to understand their motivations and intentions, considering alternative possibilities for their behavior in different situations. This increased self-awareness contributes to a more complex and nuanced sense of self.

3. Peer Influence Peaks, Shaping Adolescent Behavior

In adolescence, friends matter.

Heightened Peer Sensitivity. Adolescents place a greater emphasis on peer acceptance and are more susceptible to peer influence than either children or adults. This heightened sensitivity to social exclusion can drive decision-making, leading to both positive and negative behaviors. The desire to fit in with their peer group often outweighs considerations of long-term consequences.

Risk-Taking Context. Adolescents are more likely to engage in risky behaviors, such as smoking, drinking, or reckless driving, when in the presence of their peers. This is because the social rewards of peer acceptance can outweigh the perceived risks of the behavior. The "see-saw" model illustrates how social factors can tip the balance in favor of risky decisions.

Social Norms. Adolescents are particularly attuned to social norms and cultural expectations, making them more likely to adopt the behaviors and attitudes of their peer group. This cultural susceptibility can be harnessed for positive change, as demonstrated by anti-bullying programs that leverage peer influence to promote prosocial behavior.

4. Brain Development Continues Well Beyond Childhood

Contrary to the received wisdom up to the late twentieth century, we now know that our brains are dynamic and constantly changing into adulthood.

Challenging Old Dogma. Contrary to previous assumptions, the human brain continues to develop and change throughout adolescence and into the early twenties. This protracted development is particularly evident in the prefrontal cortex, the region responsible for decision-making, planning, and self-control. This discovery has revolutionized our understanding of adolescent behavior and its underlying neural mechanisms.

Synaptic Pruning. One key process driving brain development during adolescence is synaptic pruning, the elimination of unused neural connections. This process refines brain circuitry, making it more efficient and specialized. Environmental experiences play a crucial role in determining which synapses are pruned and which are strengthened.

Myelination. Another important process is myelination, the coating of nerve fibers with myelin, a fatty substance that speeds up neural transmission. Myelination increases white matter volume and improves the efficiency of communication between different brain regions. These structural changes contribute to enhanced cognitive abilities and behavioral control.

5. The Prefrontal Cortex Undergoes Protracted Development

The prefrontal cortex is bigger in humans than in any other species (relative to body size), and the cells it contains look different in humans from how they look in other animals.

Executive Functions. The prefrontal cortex, located at the front of the brain, is responsible for executive functions such as planning, decision-making, impulse control, and working memory. These functions are essential for goal-directed behavior and adapting to complex situations. Damage to the prefrontal cortex can impair these abilities, leading to difficulties in planning, problem-solving, and social behavior.

Introspection and Self-Reflection. The prefrontal cortex also plays a key role in introspection, the ability to reflect on one's own thoughts, feelings, and actions. This self-awareness is crucial for developing a sense of identity and understanding one's place in the world. Brain-imaging studies have shown that the prefrontal cortex is activated when people think about themselves and their relationships with others.

Training Potential. The protracted development of the prefrontal cortex during adolescence suggests that this period is a sensitive time for shaping executive functions and self-awareness. Training programs that target these skills may have a particularly beneficial impact during adolescence, helping young people develop into responsible and well-adjusted adults.

6. Social Understanding Evolves Through Adolescence

Adolescents are more likely than younger children to compare themselves with others and to understand that others are making comparisons and judgements about them; they also begin to place higher value on these judgements.

Mentalizing Network. Social understanding relies on a network of brain regions known as the social brain, which includes the dorsomedial prefrontal cortex (dmPFC), temporo-parietal junction (TPJ), posterior superior temporal sulcus (pSTS), and anterior temporal cortex (ATC). These regions work together to enable us to recognize faces, interpret emotions, and understand other people's thoughts and intentions.

Theory of Mind. A key component of social understanding is theory of mind, the ability to attribute mental states to others. This allows us to predict their behavior and understand their perspectives, even when they differ from our own. Children typically develop a basic understanding of theory of mind by age 4 or 5, but this ability continues to evolve throughout adolescence.

Developmental Shifts. Brain-imaging studies have shown that the pattern of activity within the social brain network changes during adolescence. As individuals mature, activity shifts from the dmPFC to other regions, such as the temporal cortex, suggesting a change in cognitive strategy from conscious self-reflection to more automatic social processing.

7. Risk-Taking is Influenced by Both Brain and Social Factors

To understand why adolescents take risks, we have to look at the contexts in which risk-taking occurs.

Dual Systems Model. The dual systems model proposes that adolescent risk-taking is driven by a developmental mismatch between the limbic system, which processes reward and emotion, and the prefrontal cortex, which regulates self-control. The limbic system matures earlier, leading to heightened sensitivity to rewards, while the prefrontal cortex develops more slowly, resulting in reduced impulse control.

Hot vs. Cold Contexts. Adolescents are more likely to take risks in "hot" contexts, where emotions are running high or peers are present. In these situations, the rewarding aspects of risk-taking are amplified, while the inhibitory control of the prefrontal cortex is diminished. In contrast, adolescents may avoid risks in "cold" contexts, where emotions are less intense and social pressures are absent.

Counterfactual Emotions. The ability to think counterfactually, imagining alternative outcomes of decisions, also develops during adolescence. This may influence risk-taking by affecting the intensity of emotions like regret and relief, which play a role in decision-making.

8. Mental Health Vulnerabilities Emerge During Adolescence

What is it about late adolescence that makes some brains particularly vulnerable to debilitating delusions and hallucinations?

Onset of Mental Illness. Adolescence is a critical period for the onset of many mental illnesses, including schizophrenia, depression, anxiety disorders, and eating disorders. This suggests that the brain undergoes changes during adolescence that make some individuals more susceptible to psychiatric disturbance. Understanding these changes is crucial for developing effective prevention and treatment strategies.

Genetic and Environmental Factors. Mental illness is often the result of a complex interplay between genetic predisposition and environmental factors. Individuals with a family history of mental illness may be more vulnerable to developing these conditions, especially if they experience stressful life events or other environmental risk factors.

Brain Development Differences. Studies have shown that adolescents who develop mental illnesses may exhibit differences in brain structure and function compared to their peers. These differences may involve alterations in grey matter volume, white matter connectivity, and activity patterns in brain regions involved in emotion processing and self-control.

9. Neuroscience Can Inform Education and Juvenile Justice

Understanding brain development in adolescence has profound implications for social and education policy.

Tailored Education. Neuroscience research can inform educational practices by identifying optimal times for teaching specific skills and tailoring interventions to the developmental stage of the adolescent brain. For example, training programs that target executive functions may be particularly effective during adolescence, when the prefrontal cortex is still developing.

Reconsidering Juvenile Justice. Findings about the adolescent brain have implications for the juvenile justice system. The fact that adolescents are more susceptible to peer influence, act impulsively, and have less developed self-control should be considered when determining culpability and sentencing. Rehabilitation and restorative justice approaches may be more effective than punitive measures for young offenders.

Addressing Myths. It is important to dispel common myths about the brain, such as the notion that people are "left-brained" or "right-brained" or that we only use 10% of our brains. These misconceptions can lead to ineffective educational practices and misguided interventions. Evidence-based approaches, grounded in sound scientific research, are essential for promoting optimal brain development and learning.

Last updated: May 29, 2025