IB Psychology HLTopic 2 — Models of DevelopmentPaper 1 & 2Biological approach~9 min read
Brain Maturation and Development
A baby is not born with a small, finished brain that simply gets bigger. The brain is born unfinished on purpose, and it finishes itself by reacting to the world around it. Once you understand the order in which it finishes, a lot of odd things about children and teenagers stop being odd.
📘 What you need to know
Maturation means development that follows a biological timetable — it unfolds with age, in a fairly fixed order.
In the first years of life the brain makes new neural connections at an enormous rate.
Connections that get used repeatedly are strengthened (neural branching); ones that are not used are cut away (neural pruning).
The brain matures back to front: movement and the senses first, planning and self-control last.
Some skills have a window of opportunity — a period when the brain learns them most easily.
Chugani et al. (1998) tracked this using PET scans of glucose use in the brain from birth to late adolescence.
Evaluation words to have ready: reductionist, individual differences, correlation not cause.
What maturation actually means
When psychologists say development is maturational, they mean it is driven mainly from the inside. The order of the stages and roughly when they happen are set by biology, not by how much teaching a child gets. Experience still matters enormously — but experience works on top of the timetable, it does not replace it.
Definition to learn
Maturation = physical and neurological development that follows a genetically set sequence, so it happens in the same order for almost everyone, at roughly the same ages.
Think of it like teeth. You cannot teach a six-month-old to grow molars. The order is set. But whether those teeth stay healthy depends completely on what happens around them. Brain areas are the same.
Build a lot, then cut back
In the first few years of life the brain forms new connections between neurons at a staggering rate — more than a million a second at the peak. That sounds like a design for a genius, but a brain with connections running everywhere is slow and noisy. It has too many possible routes for every signal.
So the brain does two things at once:
Neural branching — connections that get used again and again grow stronger and spread out. Repetition is the signal that says “keep this”.
Neural pruning — connections that are hardly used are removed. About half of them go during adolescence.
Pruning is not damage. It is editing. The brain ends up with fewer connections but much faster, cleaner ones — the paths the child actually uses.
Notice the third cell has thicker lines, not more of them. Efficiency comes from strong, well-used routes — which is why what a child repeatedly does matters so much.
Back to front: the order of maturation
The areas that mature first are the ones handling the most basic jobs: movement and the senses. A baby can see, grip and kick long before it can wait its turn. Language and emotion come next. The prefrontal cortex — planning, weighing consequences, holding back an impulse — is last, and it keeps maturing into the mid-twenties.
This single fact explains a lot. A fifteen-year-old can understand perfectly well that a risk is dangerous, and still take it, because the reasoning system is fully online while the braking system is not yet finished.
The bars show roughly when each system reaches maturity, not when it starts working. All three are running from very early on.
Key study: Chugani et al. (1998)
How would you actually watch a brain mature? You cannot open one up. Chugani used a clever proxy: glucose metabolism. Brain areas that are working hard burn more glucose, and a PET scan can show where that is happening.
🧩 The study in four steps
Aim — to track how glucose use in the brain changes from birth to late adolescence, and match that to cognitive development.
Method — a review article pulling together many PET scan studies of human brain development, rather than one new experiment.
Findings — newborns show low activity in the cerebral cortex but clear activity in the amygdala, suggesting emotion drives the earliest interactions. From around 6–9 months activity rises in the frontal lobes, alongside better thinking skills.
Conclusion — there are windows of opportunity for particular skills, and a critical period across the first ten years, especially for the structure of language (grammar more than vocabulary).
Skill
Window of opportunity
What that means in practice
Motor skills
Before birth to 6 months
Movement patterns are laid down extremely early
Vision
0 to 6 months
The visual system needs real light and shapes to tune itself
Emotion regulation
0 to 3 years
Calm, responsive care in these years matters more than later
Vocabulary and speech
0 to 3 years
Being talked to, not just talked at, builds language
Logic, including maths
0 to 4 years
Early play with number and pattern is not wasted time
Careful with the word “window”. Missing one makes a skill harder to pick up later — it does not make it impossible. Say “more difficult” rather than “never”, or you will overstate the evidence and lose marks in an evaluation.
Evaluating this model
Strengths
Replicable. PET scanning follows a set procedure, so other teams with the equipment can repeat it and check the findings.
Supported by other work. Separate studies also identify the prefrontal cortex as the last region to finish, which raises reliability.
Useful. Knowing the normal timetable lets doctors spot developmental delay early, which means earlier intervention.
Limitations
Biologically reductionist. Explaining development purely by brain maturation leaves out upbringing, peers, schooling and poverty, all of which shape cognition.
Individual differences. Real children do not line up neatly with the windows. Averages hide a wide normal range.
Correlational. A scan can show that frontal activity rises as thinking improves. It cannot show which one caused the other.
Link to concepts
Measurement — PET lets researchers “look inside” a living, developing brain, something impossible a few decades ago. But it measures glucose use, and then we infer maturity from that. The measure and the concept are not the same thing.
Causality — scanning is objective and controlled, which fits the features of science, but the artificial setting costs ecological validity, and correlation still is not cause.
Exam practice
WORKED EXAMPLE
Outline one study of brain development. [3 marks]
1. Name it and give the aim
Chugani et al. (1998) set out to track glucose use in the brain from birth to late adolescence.
2. One line on methodA review of PET scan studies of human brain development.3. One finding plus what it shows
Frontal lobe activity rises from about 6–9 months, alongside better thinking — so cognitive gains track brain maturation.
3 marks: aim + method + findingThree marks means three moves. Do not spend all your words on the aim.
WORKED EXAMPLE
Explain one limitation of using brain scans to study development. [3 marks]
1. State the limitation
Scanning studies are biologically reductionist.
2. Explain why that matters
A scan shows the brain changing but cannot capture upbringing, poverty or schooling, which also shape thinking.
3. Tie it to the study
So Chugani’s timetable describes what develops, not the whole of why one child develops differently from another.
Point → explain → applyNever leave a criticism as one word. The marks are in the explanation.
💡 Exam tip
Learn the study as aim, method, findings, conclusion. Examiners are looking for those four things and nothing else.
Say “a review article”, not “an experiment”, for Chugani. Getting the method wrong costs easy marks.
Use the exact terms: neural branching, neural pruning, prefrontal cortex, critical period.
Pair every strength with a limitation in an essay. A one-sided evaluation caps your band.
The back-to-front order is a brilliant example to use in questions about adolescent behaviour or risk-taking.
If you need a second study for support, mention that other research also finds the prefrontal cortex develops last — that is evidence of reliability.
⚠️ Common mix-up
Pruning is not damage. Losing connections here is efficiency. Students often write about it as if the brain is breaking.
More connections does not mean smarter. A toddler has more than you do.
Maturation is not the same as learning. Maturation is the biological timetable; learning is what experience adds on top.
Critical period does not mean “now or never”. It means “easiest now, harder later”.
PET is not MRI. PET tracks activity through glucose use; MRI images structure. Mixing them up in a study description looks careless.
Do not claim a scan proves cause. Write “is associated with” or “coincides with”.
Up next: Neuroplasticity in the Developing Brain — maturation is the timetable the brain follows, and plasticity is how it rewrites that timetable when life demands it.
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