Mapping the Aging Brain: Insights from a Global Study
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Chapter 1: Understanding Brain Aging
Aging is accompanied by noticeable physical changes such as wrinkles and reduced muscle tone. However, beneath the surface, significant transformations occur within our brains as well.
In my prior writings, I've delved into the intricate relationship between aging and brain function. It's evident that even in the absence of dementia, our brains undergo considerable changes. They can shrink, become susceptible to strokes, and develop lesions. Additionally, gene activity can become erratic, fluid intelligence may decline, and certain memory and learning processes can become less efficient than we recall.
Nonetheless, the human brain stands as a testament to evolutionary resilience. Despite aging, it isn't entirely without defenses. Some individuals manage to maintain impressive cognitive function well into their later years. These so-called "cognitive superagers" exhibit subtle distinctions in their anterior cingulate cortex and brain networks that retain youthful connectivity. However, this ability is rare and not something most of us inherit genetically.
Fortunately, there are proactive steps we can take to support brain health. Adopting a balanced diet and engaging in regular physical activity are fundamental strategies. Consider trying the MIND or Mediterranean diets, keeping in mind the benefits of olive oil while being cautious about calorie intake. Other lifestyle adjustments can also be beneficial. Recent research involving mice suggests that stimulating brain activity in enriched environments enhances a gene regulator that promotes brain health. In humans, engaging in challenging work, maintaining social connections, and even utilizing the internet can help mitigate severe cognitive decline. Quality sleep is equally essential.
X Marks the Spot
A recent study has aggregated data from various international sources, analyzing brain MRI images from over 100,000 participants, ranging from infants just over three months old to centenarians.
(You can explore the data for yourself here.)
This extensive dataset has allowed researchers to create brain charts that illustrate changes throughout the human lifespan, akin to the growth charts we use for children, which help us compare their height and weight with peers. Now, we have analogous charts for brain development from birth to age 100.
The researchers concentrated on four primary metrics: cortical grey matter volume, white matter volume, subcortical grey matter volume, and ventricular cerebrospinal fluid volume.
To summarize these terms succinctly (for those less familiar with neuroscience terminology): cortical refers to the outer layer of the brain, where reasoning and abstract thinking occur. Grey matter consists of brain cells, while white matter comprises the myelin sheaths surrounding neuron axons, which facilitate signal transmission. Ventricles are the cavities in our brains filled with cerebrospinal fluid that serve protective roles.
The lifespan trajectories for these metrics are as follows:
- Cortical grey matter: Peaks around age 6, followed by a steady decline.
- Cortical white matter: Peaks around age 29, remains stable until about 50, then declines rapidly.
- Subcortical grey matter: Peaks between ages 14 and 15.
- Ventricular cerebrospinal fluid volume: Increases until age 2, stabilizes until around 30, then rises gradually until it accelerates after age 60.
The researchers also examined total cerebrum volume and surface area, along with cortical thickness:
- Volume and surface area: Peak between ages 11 and 12, then gradually decrease.
- Cortical thickness: Peaks early at age 2, followed by a steady decline.
This information is neatly summarized in the following figure:
Generalized chart of brain development across the human lifespan. (From Bethlehem et al. 2022. Brain charts for the human lifespan. Nature. Doi: 10.1038/s41586-022-04554-y)
In examining participants with specific brain conditions, researchers identified significant deviations from the general trajectory. The top three conditions observed were:
- Alzheimer’s disease: Notable reductions in grey, white, and subcortical volume, accompanied by substantial increases in ventricular volume.
- Mild cognitive impairment: Similar findings, albeit with less pronounced differences.
- Schizophrenia: Comparable to mild cognitive impairment.
The authors wisely caution that:
The analogy to pediatric growth charts does not imply that brain charts are immediately applicable for benchmarking or diagnosing individual patients in clinical contexts.
It's essential to remember that these findings reflect averages across a large group; there will be exceptions that are completely healthy. Additionally, while the dataset is international, it has a bias toward European and American populations, which is a common limitation in scientific research. Lastly, these metrics focus on large-scale, volume-based characteristics of the brain; many other factors such as activity, connectivity, and metabolism also play crucial roles in brain health.
Be a Positive Outlier
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Chapter 2: Visualizing the Aging Brain
The first video titled "The Aging Brain: Week by Week Time Lapse" illustrates the progressive changes in brain structure over time, providing a visual perspective on the aging process.
The second video, "Your Aging Brain: The Spectrum From Healthy to Alzheimer's Disease," offers insights into the range of cognitive health as we age, highlighting the differences between typical aging and the onset of Alzheimer's.