IB Psychology SLTopic 2 — Human DevelopmentPaper 1 & 2Biological approach~11 min read
Neuroplasticity in the Developing Brain
Maturation is the plan the brain is born with. Plasticity is the brain editing that plan as life happens. It is the reason a stroke patient can learn to speak again, and the reason a hard childhood can leave a physical mark on brain tissue.
📘 What you need to know
Neuroplasticity is the brain’s ability to change its own structure and function in response to experience, learning or damage.
Structural plasticity = the physical shape changes. Regions that get used a lot grow more grey matter.
Functional plasticity (also called functional recovery) = an undamaged area takes over a job the damaged area used to do.
The extra grey matter comes from increased synaptic connectedness — more and stronger links between neurons.
Changes are gradual, not instant. They depend on how much damage there was, or how much practice went in.
Plasticity works both ways: rich experience builds the brain up, and chronic stress or neglect can hold it back.
Key study: Luby et al. found childhood poverty was linked to reduced brain growth — unless caregiving was warm.
What plasticity actually is
Your brain is not a finished machine that slowly wears out. It is more like a path system in a park. Routes that people walk every day become wide and obvious. Routes nobody uses disappear under the grass. The layout keeps changing to match how the park is being used.
Definition
Neuroplasticity = the brain’s ability to reorganise itself — by forming, strengthening or losing connections — in response to experience, learning or injury.
Students often think plasticity is only about recovering from injury. It is not. Every time you actually learn something, your brain has physically changed. Plasticity is learning, seen from the biology side.
The two types you must be able to separate
A quick test in the exam: if the question mentions injury or recovery, it is usually functional. If it mentions practice, learning or grey matter, it is structural.
Structural plasticity
The physical tissue changes. Areas used heavily build up more grey matter because neurons there form more connections with each other.
Example: the back of the hippocampus, which handles spatial memory, is enlarged in people who spend years memorising complex street layouts.
Functional plasticity
The job moves house. When an area is damaged, nearby healthy areas gradually pick up the function it used to perform.
Example: after a stroke damages a speech area, other regions can slowly take over enough for speech to partly return.
Why “gradual” matters. Neither type happens overnight. Structural change needs repeated use over months. Functional recovery needs repeated attempts at the lost skill. That is exactly why rehabilitation after brain injury is slow, boring and repetitive — the repetition is the mechanism.
Plasticity can work against you
Here is the part that connects biology to the rest of this topic. If the brain is shaped by what it experiences, then a childhood with chronic stress, little stimulation and unpredictable care will also leave a physical trace. The same mechanism, pointing the other way.
Long-term stress floods the developing brain with stress hormones. Two regions are especially sensitive: the hippocampus (memory and learning) and the amygdala (emotion and threat detection). Both are still growing through childhood, which is precisely why they are vulnerable.
Notice the arrow going upward. Caregiving is not one more cause in the chain — it changes how strongly poverty affects the brain. That is called a mediating or protective factor.
The key study
KEY STUDY
Luby et al. — poverty, caregiving and brain growth
Aim
To find out whether growing up in poverty is linked to delayed brain development, and whether anything in the child’s life reduces that link.
Sample
145 children in the USA, taking part in a long-running study of preschool depression. Many were living in poverty.
Method
Longitudinal. Children were assessed once a year over several years for thinking, emotional and social skills.
Researchers also recorded the quality of the caregiver relationship and how many stressful life events the child had.
Each child then had MRI scans: one whole-brain scan, and one focused on the hippocampus and amygdala.
Findings
Children from poorer homes had less white and grey matter in the hippocampus and amygdala than expected for their age.
Children who had received warm, supportive care showed much less of this reduction, especially in the hippocampus.
Stressful life events made the pattern worse.
Conclusion
Poverty is linked to reduced brain development, but the quality of caregiving acts as a protective factor. The environment writes on the brain in both directions.
You may see this study dated 1998 in some revision notes. The well-known poverty-and-brain paper by Luby and colleagues was published in 2013. If a date is not required, just write “Luby et al.” and describe the study properly — that is what earns the marks.
Evaluating the research
Strengths
Limitations
Method triangulation. Behavioural, cognitive and social data were compared with MRI results, which strengthens internal validity.
Confounding variable. Some children already had depression, which can itself affect brain development. Poverty may not be the only cause.
Longitudinal design tracks real change over time rather than taking a single snapshot.
Correlational. No researcher assigned children to poverty, so a direct causal claim is not available.
Practical value. If caregiving buffers the effect, then parenting support is a realistic intervention.
Subjective measures. “Quality of caregiving” and “social skills” are hard to define and score consistently.
MRI gives an objective, physical measure that is hard to fake or misreport.
Sample bias. US preschoolers, many with depressive symptoms — low population validity for children elsewhere.
Link to concepts
Causality: pre-existing depression is a genuine confound. A stronger design would compare children in poverty who do and do not have depression.
Bias: the sample is narrow — American, preschool age, many with depressive symptoms. Results should not be stretched to all children in poverty everywhere.
Measurement: MRI tells you the size of a structure. It cannot tell you why the structure is that size, so the explanatory power is limited.
Exam practice
EXAM QUESTION
Evaluate one study of neuroplasticity in development. [22]
“Evaluate” means the marks live in the judgement, not the description. Aim for roughly one third describing and two thirds weighing up.
Opening
Define neuroplasticity in one sentence and say which study you will use and why it fits.
Description (keep it tight)
Luby et al. — 145 US children, longitudinal, MRI of hippocampus and amygdala, poverty linked to less white and grey matter, warm caregiving reduced the effect.
Evaluate the methodstrength: longitudinal + triangulation → strong internal validity.
weakness: correlational, and pre-existing depression is a confounding variable.
Evaluate the sample
Narrow US sample with depressive symptoms → limited population validity.
Evaluate what it can explain
MRI shows structure changed, not why it changed.
Finish with a judgement, not a summarye.g. “convincing that poverty and brain growth are linked; not yet convincing that poverty alone is the cause”
💡 Exam tips
Give a one-sentence definition of plasticity before anything else. It is an easy, guaranteed mark.
Always name which type you mean — structural or functional. Vague answers lose the detail marks.
Use the words grey matter and synaptic connectedness when describing structural change.
This study is perfect for essays on poverty too, so you get two topics out of one set of notes.
Have “confounding variable” ready for any correlational brain study. It is the fastest route to a critical point.
Mention that plasticity cuts both ways — it explains recovery and harm. That nuance reads as real understanding.
⚠ Common mix-ups
Thinking plasticity means growing new brain cells. It is mostly about connections between existing neurons changing, not new neurons.
Saying plasticity stops after childhood. It slows down, but adult brains still change — that is why rehabilitation works.
Swapping the two types. Structural = shape changed. Functional = job relocated.
Writing that poverty causes brain damage. The study shows an association with reduced growth, and caregiving weakens it.
Forgetting the protective factor. Leaving out the caregiving finding removes the most interesting part of the study.
Confusing plasticity with maturation. Maturation is the age-driven timetable. Plasticity is experience-driven change.
Up next: Vygotsky on How Children Learn — we move from the biology to the people around the child, and to the idea that thinking is something you first do with someone else.
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