I was a medical student when the first computed tomography (CT) scanner was installed in our university hospital. I vividly remember looking at those fuzzy (by current standards) pictures with awe. These were brain images of living people, seen for the first time. Despite the limitations of that early technology, we could actually see how the brain changes due to stroke, brain hemorrhage, and tumors.
Our story on brain imaging in this issue of Neurology Now (“Picture the Brain,” page 28) chronicles our steady progress since the early days of CT scanners, and highlights the importance of brain imaging techniques of all kinds to diagnose and treat a variety of neurologic conditions. Research using these techniques has also allowed us to learn more about how the brain functions—in disease and in health.
Neuroscientists have been trying to disentangle the effects of “normal” wear and tear on the brain over time from the effects of disease. We know that age is the biggest risk factor for dementia, which is the most common neurodegenerative disease. The question is: why does dementia occur, and can we do anything about it?
It turns out that the brain regions affected by neurodegenerative diseases such as Alzheimer's disease are the same areas that are vulnerable to changes in healthy aging. The most commonly affected regions are those that underlie cognitive function. Studying how the brain changes over the life span in healthy people could give us clues about how to keep the brain functioning normally for a longer period of time.
CT and magnetic resonance imaging (MRI) scans have shown us that the brain gets smaller (atrophies) in patients with dementia. This loss of brain tissue is associated with the cognitive and behavioral symptoms seen in these patients. Several groups have used brain MRI to measure brain size and volume over the age spectrum. Brain volume is at its peak at around 10 years of age for girls and 14 years for boys. The brain size then stabilizes until about 35 years of age, and shrinks by 0.2 percent per year thereafter until age 60. After age 60, the rate of shrinkage increases to 0.5 percent per year.
Along with this loss in brain volume, the networks that link different parts of the brain together also change with age. An MRI technique called diffusion tensor imaging, which allows us to see the fiber tracts that make up these networks, have shown that the size of the tracts increases until about 35 years of age, and then drops off steadily with advancing age. A number of medical conditions—such as hypertension, diabetes, heart disease, and stroke—seem to accelerate this decline.
Some scientists speculate that diagnosis and effective treatment of these disorders in people in their 30s and 40s is crucial for preventing brain damage and cognitive problems later in life. In fact, maintaining good general health seems to be the most important prevention strategy to fight unhealthy brain aging, and to preserve normal cognitive function.
The field of brain imaging continues to advance and become more elegant and sophisticated. While many of these techniques are already invaluable in the clinics and hospitals, the research being done with these tools holds promise to help us all live healthy and productive lives.
Take good care,
Robin L. Brey, M.D.