How our brain develops

How big is the brain of a normally developing six-year-old? When in life do certain areas of the brain develop particularly strongly? And to what extent does brain mass decrease with age? For the first time such questions can now be answered from a large database. Using more than 100,000 brain scans of people of all ages, scientists created standardized reference charts. They provide information on the typical development of our brain throughout life and also provide insight into pathological changes. The publicly available database is to be an important research resource in the future, and with subsequent additions, it may become a standard tool in clinical practice.

Growth curves have been standard in pediatrics for over 200 years. With their help, you can quickly and easily check whether, for example, your child’s height, head circumference and weight are within the range that can be expected at this age. Our brain also undergoes major changes throughout our lives. How and when exactly this usually happens has so far been unclear. Although MRI images provide insight into the living brain, the database has so far been too small to derive general standards from it.

Data from over 100 studies

A team led by Richard Bethlehem of the University of Cambridge has closed this research gap. To this end, scientists used a complex process to collect brain scans from over 100,000 people worldwide, which were published in over 100 studies. The age of the subjects ranged from unborn fetuses 115 days after conception to 100-year-old seniors. “That way, we were able to document the very early, rapid stages of brain development as well as a slow decline with age,” says Bethlehem.

The challenge for scientists was the high methodological variability of various studies. “With brain imaging data, it’s a bit more complicated than simply measuring a tape measure and measuring the height or circumference of a person’s head,” says co-author Jakob Seidlitz of the University of Pennsylvania. First, scientists had to standardize the data. They started with simple properties such as gray matter and white matter volume, and then expanded their work to more detailed information such as the thickness of the cortex and the volume of specific areas of the brain.

Milestones in brain development

In doing so, they documented important milestones in brain development, some of which were already suspected and some were newly discovered. The data shows that the brain grows particularly rapidly from mid-pregnancy to age three – from ten percent of its later size to 80 percent. Gray matter, which is made up of brain cells, reaches its maximum volume by the age of six and then shrinks. White matter, which is made up of connections between brain cells, grows until the age of 29. Then the brain begins to contract very slowly again and the decrease in volume accelerates slightly from around age 50.

Since the dataset also includes numerous recordings of brains that have undergone pathological changes, scientists were also able to see how diseases such as Alzheimer’s dementia affect our thinking organ. For example, the brain volume of Alzheimer’s patients decreases much faster than is actually the case for the respective age of the affected people. “In the future, our reference framework can be used to evaluate patients who are screened for diseases such as Alzheimer’s,” says Bethlehem. “By comparing how quickly the volume of a patient’s brain changed with that of their peers, doctors were able to identify possible signs of pathological neurodegeneration.”

Growing database

According to the researchers, however, before the newly created reference diagrams can actually be used in clinical practice, they should be supplemented with further data. For example, it would be helpful to include more brain scans of non-Westerners as they have so far been under-represented in the dataset. “We’re still at a very early stage in creating brain diagrams,” explains Bethlehem. “But our work shows that it is possible to create these tools by combining big data sets.”

To allow other researchers to contribute their data to the project, his team made all the data available free of charge on a website and provided a tool with which to adapt and integrate further datasets. “We expect to update the charts and build on these models as new data becomes available,” says Seidlitz. “By creating a common brain imaging language, we provided the necessary bridge to help transfer insights from imaging to clinical practice.”

Source: Richard Bethlehem (University of Cambridge) et al., Nature, doi: 10.1038 / s41586-022-04554-y

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