A new study by UC Davis Health researchers has found that the human brain is getting bigger. Study participants born in 1970 had 6.6% more brain volume and almost 15% more brain surface area than those born in 1930.
The researchers suggest that increased brain size may lead to increased brain reserve, potentially reducing the overall risk of age-related dementias.
The findings are published in JAMA Neurology.
“The decade in which a person is born appears to influence brain size and potentially long-term health,” said Charles DeCarli, first author of the study. DeCarli is a distinguished professor of neurology and director of the Alzheimer’s Disease Research Center at UC Davis. “Genetics play a major role in determining brain size, but our findings show that external influences – such as health, social, cultural and educational factors – may also play a role.”
75-year study reveals brain changes between generations
The researchers used brain magnetic resonance imaging (MRIs) of participants in the Framingham Heart Study (FHS). The community-based study began in 1948 in Framingham, Massachusetts, to analyze patterns of cardiovascular and other diseases. The original cohort consisted of 5,209 men and women aged between 30 and 62 years. The study has been going on for 75 years and now includes second and third generation participants.
MRIs were conducted between 1999 and 2019 on FHS participants born in the 1930s to 1970s. The brain study consisted of 3,226 participants (53% women, 47% men) with an average age of about 57 years at the time of the MRI.
The study, led by UC Davis, compared MRIs of people born in the 1930s with those born in the 1970s. He found a gradual but consistent increase in several brain structures. For example, a measure that looks at the volume of the brain (intracranial volume) shows a steady increase decade after decade. For participants born in the 1930s, the average volume was 1,234 milliliters, but for those born in the 1970s, the volume was 1,321 milliliters, or about 6.6 percent more volume.
Cortical surface area – a measure of the surface of the brain – shows an even greater increase decade after decade. Participants born in the 1970s had an average area of 2,104 square centimeters compared to 2,056 square centimeters for participants born in the 1930s—almost a 15 percent increase in volume.
The researchers found that brain structures such as white matter, gray matter and the hippocampus (a brain area involved in learning and memory) also increased in size when they compared participants born in the 1930s to those born in The 70s.
Bigger brains may mean lower rates of dementia
According to the Alzheimer’s Association, approximately 7 million Americans are currently living with Alzheimer’s disease. This number is expected to grow to 11.2 million by 2040.
Although their numbers are increasing as America’s population ages, the incidence of Alzheimer’s — the percentage of the population affected by the disease — is declining. A previous study found a 20% decrease in dementia cases per decade since the 1970s. Improved health and brain size may be one reason for this.
“Larger brain structures like those observed in our study may reflect improved brain development and improved brain health,” DeCarli said. “Larger brain structure represents greater brain reserve and may buffer the late-life effects of age-related brain diseases such as Alzheimer’s and related dementias.”
One of the study’s strengths is the design of the FHS study, which allowed researchers to examine brain images of three generations of participants with birth dates spanning nearly 80 years. A limitation is that non-Hispanic white participants made up the majority of the FHS cohort, which is not representative of the US population.
Additional authors: Pauline Maillard and Evan Fletcher of UC Davis; Matthew Pass of Monash University, Australia; Alexa Beiser, Daniel Kojis, and Hugo Apparicio of Boston University; and Claudia Satizabal, Jayandra Himali and Sudha Seshadri of UT Health San Antonio.
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The Alzheimer’s Center at UC Davis
The Alzheimer’s Center at UC Davis is one of only 33 research centers designated by the National Institute on Aging. With locations in Sacramento and Walnut Creek, the center is focused on turning research findings into better tools for diagnosing dementia and treating patients, while focusing on the long-term goal of finding a way to prevent or treat Alzheimer’s disease . Also funded by the state of California, the center allows researchers to study the effects of the disease on a uniquely diverse population. For more information, visit ucdavis.edu/alzheimers/.