How does the human brain structurally change as we grow up?
Brain structures change significantly from childhood to adulthood, but the way researchers adjust for overall brain size can dramatically alter their conclusions about these developmental patterns.
Source
Structural brain development between childhood and adulthood: Convergence across four longitudinal samples
What they did
Researchers analyzed structural brain scans from four separate longitudinal datasets collected across three countries to track physical brain changes from childhood to early adulthood. They examined how measures like intracranial volume and whole brain volume change, and tested how different statistical methods of adjusting for overall brain size affect regional developmental curves. The scans were processed uniformly using either 1.5-T or 3-T MRI machines across the different study sites.
What they found
They found that intracranial volume increases by approximately 1% annually until mid-adolescence, whereas whole brain volume decreases during adolescence. Cortical grey matter volume was highest at around 8 years of age and steadily declined, while white matter volume grew until mid-to-late adolescence. Crucially, correcting regional volumes using whole brain volume flattened differences between males and females, whereas using intracranial volume as a covariate did not.
The limits
What it doesn't show
This study cannot determine the biological cause behind these volume changes, such as whether grey matter reduction reflects synaptic pruning or changes in myelination. Furthermore, the results are sensitive to the specific age ranges of the cohorts; for instance, the site studying a narrow range of 10 to 16 years showed linear trajectories rather than the non-linear patterns found in broader cohorts. Additionally, because the study focused on gross cortical measures, it does not show how these size-correction methods impact smaller subcortical structures.
Key terms
- Intracranial Volume (ICV)
- The total volume inside the skull cavity, including brain tissues, meninges, and cerebrospinal fluid.
- Whole Brain Volume (WBV)
- A composite structural measure representing the combined volume of grey and white matter across the entire brain, including the cerebellum.
- Cortical Grey Matter Volume (CGMV)
- The volume of the brain's outer layer containing neuronal cell bodies, dendrites, and synapses.
- Cerebral White Matter Volume (CWMV)
- The volume of deep brain tissue containing myelinated nerve fibers that transmit signals between different brain regions.
- Proportional Method
- A size-correction technique where a regional brain volume is divided by a global brain measure to yield a ratio.
- Covariate Method
- A statistical technique that controls for overall brain size by entering it as a covariate in a regression model.
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Quiz yourself
What was the primary objective of this collaborative study on brain development?
Common questions
Why does cortical grey matter volume decrease during adolescence if the brain is still developing?
The decrease in grey matter volume does not mean the brain is deteriorating; rather, it is thought to reflect processes like synaptic pruning (refining neural connections) and increased myelination of white matter, which changes how grey and white tissue boundaries appear on MRI scans.
How does the choice of correction method affect sex differences in brain studies?
Using the proportional method to adjust regional volumes by overall size eliminates apparent sex differences, whereas using intracranial volume as a covariate still leaves significant sex differences, showing how statistical choices shape our scientific conclusions.
Why did a specific sample show linear trajectories while the others showed non-linear ones?
The Pittsburgh sample had a narrower age range of 10 to 16 years, which made its developmental trajectory appear linear, while the studies covering wider age ranges captured the non-linear curves of earlier childhood and later adulthood.
Should researchers use intracranial volume or whole brain volume to control for brain size?
The study suggests whole brain volume might be a more stable correction factor across different samples, but recommends that researchers always show uncorrected results and justify their chosen method.
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