IFA DOCTOR If she wants to know how well a child is growing, she can access clinically validated charts that show exactly how that child compares to the norm for their age and gender. Not only can the doctor look up how many inches shorter or taller the child is than the average age, they can also look up what height percentile they fall in. Medical diagnoses can then be made on the basis of an absolute comparison with the statistical norm.
Reference charts are an important tool in modern primary medicine and cover many aspects of a person’s healthy development. However, there is one major gap in their coverage: the human brain. Richard Bethlehem and Simon White from the University of Cambridge and Jakob Seidlitz from the University of Pennsylvania want to remedy the situation. registered mail natureThe neuroscientists describe the most comprehensive effort to date to create a standard against which a person’s brain development can be measured over the course of their life.
Her brain diagrams were compiled from more than 120,000 three-dimensional brain scans from more than 100,000 patients who participated in more than 100 different research studies. The dataset included people of all ages, from babies still developing in the womb a little over 100 days after conception to adults over 100 years old.
Using this data, the scientists cataloged how the average human brain evolved from cradle to grave, focusing on three types of brain tissue: gray matter (made up of cell bodies of neurons), white matter (the filaments that make up the neurons). connect) and tissue that transports cerebrospinal fluid (the brain’s tubing system). The scientists paid particular attention to the cerebral cortex, the outermost layer of the brain, which is responsible for superordinate brain functions. They observed that gray matter in the cortex peaked at 5.9 years, 2 to 3 years later than previously thought.
After characterizing the development and aging of the average human brain, the scientists modeled the distribution around it and plotted the percentage variation in the structure of human brain tissue. This allowed them to study how the brains of patients with various developmental or degenerative disorders behave compared to more typical brains. “Our study confirmed that Alzheimer’s disease, mild cognitive impairment and schizophrenia show significant restructuring of brain tissue compared to a more typical brain of the same age and sex,” says Dr. Seidlitz.
The catalog also held some surprises. For example, it is commonly believed that autism occurs differently in male and female patients, but there is little evidence of this difference in their brain tissue. In contrast, attention-deficit hyperactivity disorder (ADHD)—which is similar by gender—shows the largest average difference in brain structure between male and female patients of all the diagnoses they analyzed. Over the course of a lifetime, men’s brains change ADHD Patients appear to be prone to below-average gray matter, white matter, and CSF volumes. The woman’s brain ADHD Patients, on the other hand, tended to have slightly higher volumes of the same tissues.
What these differences in brain size mean is not yet clear. And the authors point out that their brain diagrams are not yet ready for clinical use, not least because the data set they use has several limitations. “Unfortunately, the data we have compiled reflects the demographic bias of neuroscientific research in general, ie most studies are from Europe or North America and overrepresent patients of European ancestry,” says Dr. Bethlehem.
To reflect the full diversity of the normative development of the human brain, a more representative dataset is needed. Once this is achieved, the usefulness of brain maps can be tested in a clinical setting. One day, hopefully, these charts could become a useful tool for tracking a person’s brain health or spotting the earliest physical signs of brain disorders like Alzheimer’s disease. ■
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This article appeared in the Science & Technology section of the print edition under the heading “Frames of Mind”