Scans reveal the brain's early growth, late decline and surprising variability

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Scientists have analyzed a huge number of brain scans to learn more about how the brain develops, from infancy all the way until the end of life. / AP

The human brain starts with a bang and ends with a whimper.

That's the conclusion of a project that used more than 120,000 brain scans to chart the organ's changes throughout the lifespan. The results appear in the April 6 issue of the journal Nature.

Among the key findings:

• The brain reaches 80% of its maximum size by age 3.
• The volume of gray matter, which represents brain cells, peaks before age 6.
• The volume of white matter — a way of measuring the connections between brain cells — peaks before age 29.
• The loss of white matter accelerates after age 50.

The ongoing study could eventually lead to brain growth charts that would allow doctors to look for signs of atypical development in young patients. But for now, the results are meant for scientists who study typical brain growth or brain disorders like schizophrenia and Alzheimer's disease.

One goal is to "use this huge amount of existing data to help understand and treat psychiatric diseases," says one of the study's authors Dr. Aaron Alexander-Bloch, a psychiatrist at the University of Pennsylvania and Children's Hospital of Philadelphia.

The project began more than six years ago when two young researchers at a scientific conference began talking about a simple question: How does a person's brain change during their lifespan?

They realized there was no good answer because most studies that involved MRI brain scans had been limited to a small number of people at a single point in time. Also, the studies used different designs and kept their data in different forms.

So the researchers had an idea.

Researchers decided to turn more than 100 small studies into one big one

"We could just stitch together all these other studies and all these common data sets to create some sort of ground truth and a common language," says Richard Bethlehem, a research associate in the psychiatry department at the University of Cambridge.

Bethlehem and Jakob Seidlitz, a postdoctoral researcher at the University of Pennsylvania and Children's Hospital of Philadelphia, began asking other researchers if they would contribute their study data to the effort.

"And really everyone came back and said, 'This looks great, we should definitely be doing this,'" Seidlitz says.

The pair assembled an international team and began the hard work of turning more than 100 small studies into one big one.

"Richard and I spent months literally just curating a lot of these data sets," Seidlitz says.

They began to realize how different brains can be

Eventually, they had brain scan data from more than 100,000 individuals, ranging from a fetus to a centenarian. And when they analyzed the data, they began to realize how different brains could be.

"One of the fundamental things that we started to see was just the sheer variability of how big the brain gets throughout development," Seidlitz says.

The team also found variation in the growth patterns of several dozen different areas of the brain's outermost layer and in the volume of white matter, gray matter, subcortical gray matter and in the fluid-filled cavities known as ventricles.

Despite its huge size, the study still has gaps, the researchers say, including a lack of racial and ethnic diversity. "That's one of the things we've been humbled by," he says.

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