Y11W06VC The brain still being built

Here's something that changes how you think about adolescence once you hear it. The human brain doesn't finish developing until somewhere around the mid-twenties. The last parts to come online are the regions responsible for long-term planning, impulse control, and resisting peer influence. This week's article looks at what that means for teenagers, for parents of teenagers, and for anyone still remembering what those years felt like.

Core Vocabulary

audacious

/ɔːˈdeɪʃəs/|au·da·cious

adjective

Daring, bold, or adventurous; showing courage or willingness to take risks despite potential danger.

Word Breakdown: From Latin "audax" (bold, daring), from "audere" (to dare). Related to "audacity" (boldness).

Word family: audacious (adj), audaciously (adv), audacity (n)

Synonyms: bold, daring, courageous, fearless, adventurous

Collocations: audacious claim, audacious idea, audacious behaviour, audacious move

Example: It seems audacious to claim that adolescent risk-taking is largely structural, yet brain science supports this view.

In the articleGiedd had a simple and audacious idea: scan the brains of hundreds of healthy children, adolescents and young adults, and see how the structure changed over time.

pruned

/pruːnd/|pruned

adjective/verb (past)

Cut away unnecessary parts; selectively removed or eliminated to improve efficiency or growth.

Word Breakdown: From Old French "pruigne" (plum), from Latin "pruna". Metaphorically extended to mean cutting away excess.

Word family: prune (v/n), pruned (adj), pruning (n), pruner (n)

Synonyms: trimmed, cut away, eliminated, removed, reduced

Collocations: pruned away, pruned connections, pruned synapses, pruned back, heavily pruned

Example: During adolescence, synaptic pruning eliminates weak neural connections while strengthening frequently-used ones.

In the articleGrey matter — the part of the brain where most computation happens — peaked in volume around age eleven for girls and age twelve for boys, and then slowly declined as the brain pruned unused connections and reinforced used ones.

reckless

/ˈrɛkləs/|reck·less

adjective

Without care or caution; heedless of consequences; dangerously disregarding danger or propriety.

Word Breakdown: From Old English "recceleas" (careless), from "reccan" (to care) + -less (without).

Word family: reckless (adj), recklessly (adv), recklessness (n)

Synonyms: careless, heedless, rash, irresponsible, dangerous

Collocations: reckless behavior, reckless driving, reckless abandon, reckless risk

Example: Adolescents often display reckless behaviour because their limbic systems are mature while their prefrontal cortex is still developing.

In the articleThe same adolescent brain that was sensible in solitude became reckless in company.

intensity

/ɪnˈtɛnsəti/|in·ten·si·ty

noun

The quality of being intense; great strength, force, or degree of something.

Word Breakdown: From Latin "intensus" (stretched tight, strained), from in- (in) + tendere (to stretch). -ity is a noun suffix.

Word family: intense (adj), intensity (n), intensely (adv), intensify (v), intensive (adj)

Synonyms: strength, force, magnitude, power, vividness

Collocations: emotional intensity, intensity of experience, intensity level, high intensity, low intensity

Example: The intensity of emotional experiences during adolescence can lead to more vivid but sometimes poor decision-making.

In the articleWhat's changed, as a result, is how researchers think about nearly everything associated with the teenage years: risk-taking, emotional intensity, the weight of social acceptance, the tendency to act in ways that older adults find baffling.

override

/ˌoʊvərˈraɪd/|o·ver·ride

verb

To set aside, disregard, or supersede; to use power or authority to cancel or bypass something.

Word Breakdown: From over- (above, beyond) + ride (to travel on). Metaphorical extension from physically riding over something.

Word family: override (v/n), overrides (v), overridden (v), overriding (adj)

Synonyms: overrule, supersede, disregard, cancel, bypass

Collocations: override decision, override system, override control, cannot override, override instinct

Example: The developing prefrontal cortex gradually gains ability to override impulsive urges from the limbic system.

In the articleIt was that the reward system in the adolescent brain responds more intensely to social approval than the adult brain does — and the still-developing prefrontal cortex isn't yet able to reliably override those intense signals.

calibrated

/ˈkælɪbreɪtɪd/|cal·i·brat·ed

adjective/verb (past)

Adjusted precisely to ensure accuracy or proper functioning; finely tuned or matched.

Word Breakdown: From French "calibre" (diameter) + -ate (verb suffix) + -ed (past/adjective). Related to precision measurement.

Word family: calibrate (v), calibrated (adj), calibration (n), calibrator (n)

Synonyms: adjusted, tuned, aligned, balanced, regulated

Collocations: calibrated response, well-calibrated, carefully calibrated, finely calibrated, recalibrated

Example: Adolescent brains are not yet calibrated for adult risk assessment; the balance between reward-seeking and caution remains misaligned.

In the articleA brain calibrated to feel social rejection intensely was a brain that worked hard to avoid producing it.

predispose

/ˌpriːdɪˈspoʊz/|pre·dis·pose

verb

To make someone susceptible or inclined toward something; to create a tendency toward a particular outcome.

Word Breakdown: From pre- (before) + dispose (to arrange, incline). Pre- means "before" and -pose relates to "position" or "inclination".

Word family: predispose (v), predisposed (adj), predisposition (n), predisposes (v)

Synonyms: incline, make susceptible, make prone, create tendency, make liable

Collocations: predispose toward, predispose to, genetically predisposed, predisposed condition

Example: Brain changes during adolescence predispose teens toward seeking novel experiences and social connection.

In the articleThe honest picture, integrating the main research and Romer's critique, is probably this: the adolescent brain really is structurally different from the adult brain; the differences really do predispose toward specific patterns of behaviour; but those differences also produce real strengths; and how adolescents actually behave depends heavily on the social environment surrounding them, not just their internal neurobiology.

affordances

/əˈfɔːrdənsɪz/|af·for·danc·es

noun (plural)

Qualities of an object or environment that suggest how it can be used; possibilities for action or interaction.

Word Breakdown: From afford (to provide, allow) + -ance (noun suffix meaning state or condition). Originally a psychological term by James Gibson.

Word family: afford (v), affordance (n), affordances (plural), affords (v)

Synonyms: opportunities, possibilities, features, attributes, capabilities

Collocations: environmental affordances, action affordances, perceptual affordances, offer affordances

Example: Adolescent social environments present affordances for risky behaviour that developing brains are not yet equipped to navigate safely.

In the articleIt's a stage, with its own logic, its own affordances, and its own limits.

Technical Terms

prefrontal cortex

/ˌpriːˈfrʌnt(ə)l ˈkɔːtɛks/|pre·fron·tal cor·tex

noun phrase

the front region of the brain responsible for planning, impulse control and long-term thinking

Synonyms: PFC, executive control region, higher-order reasoning centre

Collocations: prefrontal cortex develops, activation of the prefrontal cortex, prefrontal cortex and impulse control

Example: The prefrontal cortex, still maturing through the mid-twenties, is the region most responsible for weighing long-term consequences before acting on immediate impulse.

In the articleBut the prefrontal cortex — the newer, executive part of the brain responsible for planning, impulse control, and weighing long-term consequences — wasn't fully developed until the mid-twenties.

amygdala

/əˈmɪɡdələ/|a·myg·da·la

noun

the brain region most involved in emotional responses, particularly fear

Synonyms: emotional processing centre, fear centre, limbic alarm structure

Collocations: amygdala activation, amygdala response, amygdala and emotional memory

Example: When a student faces unexpected public criticism, the amygdala fires before the reasoning regions of the brain can assess the threat — producing a fast defensive emotional reaction.

In the articleThe amygdala and limbic system — the older, emotionally-loaded parts of the brain responsible for feelings and drives — were largely mature by early adolescence.

limbic system

/ˈlɪmbɪk ˈsɪstəm/|lim·bic sys·tem

noun phrase

the network of brain regions handling emotion and drives

Synonyms: emotional brain, affective system, subcortical emotion network

Collocations: limbic system response, limbic system and emotion, regulate the limbic system

Example: The limbic system's drive for immediate reward often conflicts with the prefrontal cortex's capacity to evaluate long-term outcomes — a tension especially visible in adolescent risk-taking.

In the articleThe amygdala and limbic system — the older, emotionally-loaded parts of the brain responsible for feelings and drives — were largely mature by early adolescence.

dual-systems model

/ˈdjuːəl ˈsɪstəmz ˈmɒd(ə)l/|du·al-sys·tems mod·el

noun phrase

Casey's framework of an early-maturing 'hot' system and late-maturing 'cool' system in adolescence

Synonyms: two-process model, System 1/System 2 framework, dual-process theory

Collocations: within the dual-systems model, dual-systems model of cognition, dual-systems framework

Example: The dual-systems model predicts that fast emotional responses will dominate under pressure unless slow deliberate reasoning is consciously engaged — a pattern visible in the adolescent brain.

In the articleAdolescence is a period of unusual neural plasticity, openness to new experiences, and capacity for fast learning.

neural plasticity

/ˈnjʊərəl plæˈstɪsɪti/|neu·ral plas·tic·i·ty

noun phrase

The brain's capacity to change, reorganise and form new connections in response to experience, learning and environment.

Word Breakdown: neural (relating to nerves or the brain) + plasticity (capacity to be shaped or changed)

Word family: neural (adj.), neuroplasticity (n.), plastic (adj.), plasticity (n.)

Synonyms: brain adaptability, neuroplasticity, neural flexibility

Collocations: period of neural plasticity, adolescent neural plasticity, high neural plasticity

Example: Adolescence is marked by neural plasticity, which means habits, experiences and learning can strongly shape the developing brain.

In the articleAdolescence is a period of unusual neural plasticity, openness to new experiences, and capacity for fast learning.

Figurative Phrases

come online

become operational

Etymology/Type: metaphor from technology, brain regions aren't literally networked online

Synonyms: become active, become operational, come into function

Example: The prefrontal cortex does not fully come online until the mid-twenties, meaning adolescent decision-making relies more heavily on emotional, reactive processing.

In the articleThe last parts to come online — the regions responsible for long-term planning, impulse control, weighing risks against rewards, and resisting peer influence — are still under construction well past the age at which society tends to assume a person should be acting like a fully-formed adult.

under construction

still being built

Etymology/Type: metaphorical use; the brain isn't literally a building site

Synonyms: still developing, not yet complete, in the process of being built

Example: The teenage brain is genuinely under construction — a neurological fact with real consequences for how adolescents assess risk and respond to peer pressure.

In the articleThe last parts to come online — the regions responsible for long-term planning, impulse control, weighing risks against rewards, and resisting peer influence — are still under construction well past the age at which society tends to assume a person should be acting like a fully-formed adult.

the accelerator has arrived before the brakes

vivid metaphor

Etymology/Type: emotional system matures before regulatory system

Synonyms: impulse precedes control, drive outpaces regulation, motivation without restraint

Example: Neuroscientists describe adolescent risk-taking as a situation where the accelerator has arrived before the brakes — the reward circuitry matures earlier than the impulse-control mechanisms.

In the articleThe accelerator has arrived before the brakes.

the tail of the distribution

the extreme minority

Etymology/Type: statistical metaphor; not a literal tail

Synonyms: the extreme end, the outlier range, the far end of the range

Example: Most teenagers make reasonably cautious decisions, but the tail of the distribution — those who take serious risks — tends to dominate public discussion about adolescent behaviour.

In the articleThe popular narrative often conflates the tail of the distribution — the minority taking serious risks — with the average teenager, who is mostly quite cautious and rule-following.

rise to those expectations

meet the level of what's expected

Etymology/Type: figurative 'rise', not physical

Synonyms: meet those expectations, fulfil those standards, live up to them

Example: Research suggests that students treated as capable of self-regulation often rise to those expectations — behaviour shaped as much by what is assumed of them as by what they feel.

In the articleWhen adults treat teenagers as incapable of responsible judgement, teenagers often rise to those expectations in the negative direction.

shrug off

dismiss without effect

Etymology/Type: idiomatic; not literal shrugging

In the articleThe same snub that a forty-year-old can shrug off will keep a fifteen-year-old awake, genuinely suffering, in a way that's often invisible to the adults around them.

Confusing Words

reckless vs fearless

Both words describe a relationship to risk, but the internal states they imply are very different — one involves the absence of appropriate caution, the other involves the absence of fear.

  • reckless — acting without adequate thought for the consequences; heedless of risk in a way that suggests poor judgement or impulsivity. A reckless decision is one where the risk was either ignored or not properly weighed. The word carries a negative judgement about the quality of the reasoning behind the action.
  • fearless — without fear; willing to face danger or difficulty without being deterred. Fearlessness does not imply recklessness: a fearless person may still assess risk carefully and choose to proceed. A skilled surgeon can be fearless under pressure while being methodical and precise.

If describing a failure to consider consequences appropriately, use reckless. If describing the absence of fear or intimidation in the face of a genuine challenge, use fearless.

override vs overrule

Both verbs involve one force or authority taking precedence over another, but they apply in very different contexts.

  • override — to set aside or take control of an automatic process, mechanism, or prior decision. A pilot overrides the autopilot; System 2 thinking can override an impulsive System 1 reaction. The word suggests cancelling something that was operating automatically, or asserting control over a system.
  • overrule — to reverse a decision made by a person or body in a formal, authority-based context. A judge overrules an objection; a senior manager overrules a team's recommendation. The word implies an explicit hierarchy and a deliberate reversal of a stated position.

If cancelling an automatic process or mechanism, use override. If reversing a formal decision made by a person or institution with authority, use overrule.

predispose vs determine

These near-synonyms differ in the strength of the causal claim they make — one suggests a tendency, the other suggests a certainty.

  • predispose — to make more likely; to create a tendency or inclination toward a particular outcome without guaranteeing it. Biology may predispose someone to risk-taking, but environment and choice still shape the result. Predisposition is probabilistic: it tips the scales without fixing the outcome.
  • determine — to fix the outcome completely; to be the decisive cause of what results. If brain development determined behaviour entirely, individuals would have no meaningful agency. The word implies full causal control, leaving no room for variation or choice in the outcome.

If describing something that makes an outcome more likely without making it inevitable, use predispose. If describing something that fully causes or fixes an outcome, use determine.