Brain size increases. And it matters
Be that as it may, the larger the size of the brain, the better its general condition and the “purity” of cognitive functions. The following article will provide evidence that the human brain has been gradually increasing in size since the 1930s. New research shows how this affects the risk of developing dementia, particularly Alzheimer's disease.
Brain size increases. Statistics
In 2020, 55 million people were diagnosed with dementia and this number is expected to rise double every 20 years. It seems that after the death of Gordon Moore, some kind of incorrect law for carbon computing systems began to apply. But, puns aside, the situation is quite optimistic, and here’s why.
Why is dementia not as scary as it seems?
The increase in the number of people with this disease is a reflection of the general aging population and the fact that humanity is starting to live longer. Research conducted in 2016 The National Institutes of Health (NIH) has shown that since the 1970s there has been a gradual decline in the number of new cases of dementia, averaging 20% per decade.
But what is driving this decline? A 2016 study examined the influence of education, among other factors, on the risk of dementia and found that by the 2000s, the incidence had dropped by 44% among people with at least a high school diploma, compared with the 70s. Although the study noted a link between education and dementia, the study did not examine potential causes.
New research UC Davis has a simpler explanation: our brains are simply bigger now.
The size of the modern human brain and the subtleties of statistics
It appears that the decade in which a person is born influences brain size and potentially long-term brain health. Genetics plays an important role in determining brain size, but our results suggest that general health, social, cultural and educational factors also play a significant role.
Charles De Carli, professor of neurology, director of the Alzheimer's Disease Research Center at the University of California, Davis, and lead author of the study.
UC Davis researchers used the same data set in the new study as their previous one, the Framingham Heart Study (FHS). Begun in 1948, the population-based study of more than 15,000 people in Framingham, Massachusetts, followed three generations of participants to explore trends in heart and brain health.
FHS participants underwent brain MRIs between 1999 and 2019, and researchers examined images from 3,226 people (53% women, 47% men) born between 1930 and 1970. None of the participants had a history of cognitive impairment or stroke, which defines a reduced risk of dementia. Perhaps, to get rid of dementia, it is worth focusing not only on growing new tissue for the brainand on the lifestyle?
The brain is changing and it shows
When the researchers compared MRI scans of people born in the 1930s with a sample from the 1970s, they found a gradual but consistent increase in the size of some brain structures.
First, intracranial volume (ICV), or the volume inside the skull, increased decade after decade from an average of 1234 ml in the 30s to 1321 ml in the 70s. On average, it grew by 6.6%. Although people were taller in the 1970s than in the 1930s, after adjusting for height, the differences in ICV remained the same. Research showed that a larger ICV indicates the presence of “brain reserve”, which can protect against dementia.
Increases in size were also observed in white and gray matter. Gray matter is the cerebral cortex and is important for mental functions: memory, emotions and movement. Some conditions, including stroke, Parkinson's disease and Alzheimer's disease, can affect the overall health of gray matter.
The white matter runs underneath the gray matter and contains millions of bundles of nerve fibers. The white color comes from myelin, thin layers of fat that protect neurons the way a layer of insulation protects wires. Myelin thinning is one of the biomarkers of brain aging and the body as a whole.
Between the 1930s and 1970s, researchers observed an increase in the volume of white matter by 7.7% and gray matter by 2.2%. The volume of the hippocampus, whose main task is to store short-term memories and transfer them to long-term storage, also increased by 5.7%. And the surface area of the cerebral cortex, that is, the wrinkled visible layer of gray matter, increased by 14.9%.
Why does the brain size increase?
Larger brain structures like those observed in our study may reflect improved brain development and health. Greater brain structure represents greater brain reserve and may mitigate the effects of age-related brain diseases such as Alzheimer's disease and related dementias later in life.
Charles De Carli, professor of neurology, director of the Alzheimer's Disease Research Center at the University of California, Davis, and lead author of the study.
While acknowledging the significant influence of genetics, researchers point out that environmental influences early in life are more likely to increase brain structure and reduce the risk of dementia.
They say the increase in brain size they observed likely reflects improvements in health, education and sociocultural factors since the 1930s, as well as improvements in modifiable risk factors for dementia, from attention to exercise and lifestyle to self-education, diet and interest in self-development.
However, a limitation of the study is that the FHS sample is predominantly white, English-speaking, healthy, and well-educated. Therefore, the sample is not representative of the general U.S. population. However, this is offset by the study design, which followed a huge number of people for most of their lives, spanning almost 80 years from birth.
So does this mean brain size is increasing?
If you lead a healthy lifestyle, received enough nutrition as a child, plus load your brain with tasks and work, then you create an excellent foundation for the development of the brain as a whole, and protection against possible neurodegenerative diseases. It may well be that an adequate healthy lifestyle and cognitive load will be excellent protection against the development of neurodegenerative diseases in the future. And there is no hope for a magic pill that will set everything in the brain itself.
