brain aging, MRI, gray matter

Tracking How the Brain Grows and Shrinks Over Time

By Simon Spichak, MSc | April 27th, 2022

Analyzing more than 120,000 brain scans, researchers mapped the way the brain grows — and shrinks — over time. 

What happens to the adult brain as you grow and age? According to new research, it changes not only in its functionality, but in its size.

While pediatricians have charts to track a child’s physical growth — height and weight — there are no charts, metrics or tools for tracking brain growth. Jakob Seidlitz, a neuroscientist at the University of Pennsylvania and father of a small child, first noticed this peculiarity at a check-up.

“It is shocking how little biological information doctors have about this critical organ,” Seidlitz told Nature. Along with his co-author Richard Bethlehem, a neuroscientist at the University of Cambridge, Seidlitz led a massive study to characterize the brain’s growth over time.

“The charts are already beginning to provide interesting insights into brain development,” Bethlehem said in a news release. “You could imagine them being used to help evaluate patients screened for conditions such as Alzheimer’s.”

The results of the study were published in Nature. To shed a little more light on the research, the authors also shared the brain growth charts generated in the study online. Seidlitz, Bethlehem and their team didn’t do any of the brain imaging themselves — instead, they contacted dozens of scientists requesting brain scans from their databases. In total, they amassed more than 120,000 MRI brain scans  from more than 100,000 individuals ranging from 16 weeks old to 100 years.

Some of the brain scans came from people with specific medical conditions or diseases, including Alzheimer’s. 

In part, the researchers’ results confirmed what scientists had expected: The amount of the brain’s gray matter volume (representative of the amount of cells in the brain), as well as its width, peaked early in development. The amount of white matter  (associated with improved mental speed) peaked around the age of 30. Interestingly, though the amount of white matter might decline after 30, another study found that mental speed only begins to decline in your 60s.

The charts are already beginning to provide interesting
insights into brain development. You could imagine them
being used to help evaluate patients screened for
conditions such as Alzheimer’s.

What surprised some scientists was the data Bethlehem and Seidlitz obtained on the amount of cerebrospinal fluid in the brain. It was previously thought that this volume increased with age as other parts of the brain began to shrink. Bethlehem and Seidlitz showed that this volume grew extremely fast in late adulthood, but the health implications of this finding are still unknown.

The majority of brain scans included in the study came from North America and Europe with an overrepresentation of white, university-aged, urban and affluent people. This means that the results might not completely generalize to the rest of the world, according to Sarah-Jayne Blakemore, a cognitive neuroscientist at the University of Cambridge who was not involved in the study. Additionally, most of these brain scans were one-time snapshots from one person. 

As the project continues to expand, Bethlehem and Seidlitz will add new brain scans to their website to generate updated growth charts. 

With more information, it could be possible to determine whether someone is at risk for neurodegeneration based on their brain’s growth trajectory, as compared to others, Bethlehem said. Clinicians and researchers will continue adding to the database which will hopefully lead to a better understanding of age-related diseases like Alzheimer’s and dementia. 

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