Sunday, March 2, 2008

The white matter matter

The brain is divided into two main regions: the superficial gray matter, and the white matter below. Gray matter is the surface control center; the nerve cell bodies in this layer connect to one another via long extensions called axons. These electrical connectors travel through the white matter, so-named because a white, fatty material called myelin surrounds and insulates the axons, one from another.

We have long known that damage to the gray area through stroke or injury results in devastating paralysis and loss of physical functions such as speech. Through the fancy radiological technique of magnetic resonance imaging (MRI), we now know that the white matter is also vulnerable to a patchy sort of damage which, over time, can have a cumulative effect on motor, speech, and thinking skills.

These damaged areas appear on MRI scanning as small bright spots within the large body of white matter. The number of these 'white matter hyperintensities' (WMH) increases with age. WMHs have also been linked to a history of hypertension, migraine, and depression. Microscopic studies done on brains whose owners no longer need them confirm that these areas represent ischemic damage due to a loss of blood supply and fresh oxygen to the tissue. Many bright spots in the brain do not foreshadow a bright future for cognitive functioning. The following two studies have aided researchers in understanding the significance of such MRI findings.

Maryland researchers at Johns Hopkins University scanned the aging brains of 3600 individuals and graded the white matter abnormalities from 0 (no white matter matters to speak of) to 9 (a huge load of stressed-out white matter). Over the next five years, they followed the group for the occurrence of stroke. The higher the grade, the more the brains failed to age in good style. Those whose white matter was heavily spotted and bright (grade 5 or higher) had triple the stroke incidence compared to those whose white matter was scarcely spotted at all.

In 1932, public health authorities in Scotland administered the "Scottish Mental Survey" to all the resident 11 year olds. In 1999, scientists at the University of Edinburgh rounded up a bevy of 78 year olds and compared their current cognitive ability to their pre-teen mental testing as well as their current brain MRI scans.* The scientists found that the amount of white-matter lesions in their subjects' aging Scottish noggins was a better marker for present mental functioning than the early-age IQ scores. Furthermore, the impact of the white matter changes was independent of youthful mental ability.

Don't take it's 'just age' for an answer if bright spots are spotted on your MRI scan. Get cardiovascular risk factors such as elevated blood pressure, cigarette use, elevated blood sugar, and high cholesterol out of your life.
*Leaper, SA et al. Radiology. 2001 Oct;221(1):51-5.Click here to read

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