Evolving brain size from 1930 to 1970 may indicate reduced dementia risk, researchers say

The development and maintenance of the human brain is influenced by both genetic factors and environmental conditions, which can influence the risk of dementia later in life. Therefore, in recent studies, JAMA Neurology They assessed whether there were changes in skull and brain size and cortical thickness in individuals born between 1930 and 1970.

study: Trends in intracranial volume and cerebral volume in Framingham Heart Study participants born between 1930 and 1970. Image credit: Gorodenkoff/Shutterstock.com

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Advances in medical diagnostics and treatment strategies have significantly improved the health of the American population, resulting in longer life expectancy. However, this increased longevity also increases the likelihood of encountering Alzheimer's disease and other dementias, as well as the various conditions prevalent in the elderly.

Fortunately, the incidence of dementia is on the decline, likely due to more education and better precautions against cardiovascular risks. Another important factor may be the initial environment.

The Framingham Heart Study Cohort (FHS) includes many generations of people who have been followed over several decades. The difference between the first and newest subjects enrolled in the cohort is more than 80 years.

For this reason, the researchers in this study decided to draw a cohort from this study group to examine trends in cardiovascular and brain health across successive generations.

The aim was to investigate the predicted increase in brain development in the US population due to changing trends in early life living environments. This will be reflected in an increase in brain volume.

About research

All participants were born between 1925 and 1968. None had been diagnosed with dementia or stroke, and all had undergone magnetic resonance imaging (MRI) between 1999 and 2019. The average age at which people underwent an MRI scan varied by decade of birth, but there was some overlap between the decades.

What was the result?

There were more than 3,200 participants, and the average age at which they underwent an MRI scan was 58 years. Imaging revealed that multiple brain volume measurements showed an upward trend in later birth cohorts.

The researchers measured intracranial volume (ICV), hippocampal volume (HV), cortical surface area (CSA), cortical gray matter volume (CGMV), and white matter volume (WMV). On average, women were observed to be 5.5 inches shorter and have lower HV, CGMV, and WMV.

The difference in hippocampal volume was -0.64 mL, whereas men's gray and white matter volumes were approximately 54 mL and 63 mL larger, respectively.

The average height of the 1930s birth cohort was 66 inches, while the average height of the 1970s birth cohort was 68 inches. The average ICV was 1,234 mL in the 1930s cohort compared to his 1,321 mL in the 1970s, an increase of more than 6%, respectively. This is after adjusting for confounding factors such as age, gender, and height.

Regional measures also vary by birth cohort, showing clear trends. Both HV and WMV increased with the birth decade. CSA was similar, but cortical thickness was reduced, suggesting cortical atrophy.

Comparing the 1930s and 1970s cohorts, the largest increase was in CSA, which increased by 15%. WMV and HV increased by 8% and 6%, respectively, while CGMV increased by 2%. Cortical thickness decreased by more than a fifth, from 2.3 mm to 1.9 mm, respectively. There were no significant differences between men and women.

The same trend, although the difference was smaller, was observed after restricting the analysis to only those born in the 1940s and aged 55 to 65. For example, WMV and CGMV increased by only 0.2% and 0.1%, respectively.

What is the impact?

The findings show that later generations experience increases in brain volume both globally and locally. When comparing the 1930s and his 1940s cohorts, the differences were greatest in his ICV, WMV, and HV.

“We found that larger brain volume indicates greater brain development and potentially greater 'brain reserve', which may explain lower rates of dementia. We hypothesize that there is a sex.”

ICV reflects normal brain development and does not decline with age or diseases that affect volume. Indeed, her ICV in adults predicts cognitive level in old age and provides a reliable and consistent biomarker of brain size.

HV loss can occur early in neurodegenerative diseases such as Alzheimer's disease.

Larger cortical WMV in later cohorts may lead to larger CSA as a result of greater rotation. Increased WMV indicates higher neuronal connectivity, mitigating the effects of age-related brain tissue loss. The increase in CSA with decreasing cortical thickness supports this explanation.

The presence of gyri in the brain increases brain CSA by 1,700-fold compared to the shrew brain, but limits the increase in cortical thickness to 6-fold. Genes regulate different brain regions differently, causing gyri to develop to different degrees.

The increase in greater brain structure is due to changes in early life experiences, such as better education, social environment, and health status. Better prevention of cardiovascular disease may also be a cause. Therefore, modifying these factors may also improve resistance to late-life dementia.

At a population level, these effects are extremely important, helping to optimize brain development and build cognitive resilience over decades.