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Study unravels mystery of brain-cell connections

August 15, 2005
By Lee Bowman

Brain-cell connections that were the last to form in adulthood are also the first to fail as we age, according to a study at the University of California-Los Angeles.

Neuroscientists used a computer analysis of magnetic resonance images to examine the fatty sheaths that insulate the brain's wiring.

That insulation, called myelin, is a coating of fat with a very high cholesterol content that allows it to wrap tightly around the "cables" that send messages through the brain. Over time, it makes functions of the brain more precise and efficient. These connections and their coatings continue to form in some parts of the brain well into middle age.

As myelin is produced in ever-greater quantities, however, cholesterol levels in the brain also continue to grow, and eventually promote production of toxic proteins. The toxins disrupt the brain connections and eventually lead to the neuron-destroying plaques and tangles visible in the cortex of Alzheimer's disease patients.

"The brain is not a computer. It is much more like the Internet," said Dr. George Bartzokis, lead investigator of the study, published in the August issue of the journal Neurobiology of Aging. "The speed, quality and bandwidth of the connections determine the ability to process information, and all these depend in large part on the insulation that coats these connecting wires."

They also found that myelin deterioration was greater throughout the brains of patients diagnosed with Alzheimer's than in healthy older adults, supporting Bartzokis' theory that the disease is driven by myelin breakdown.

"Myelin and the cells that produce it are the most vulnerable component of our brain - the human brain's Achilles' heel," said Bartzokis, a professor of neurology and director of the UCLA Memory Disorders and Alzheimer's Disease Clinic.

Since it's apparent that the late-myelinating regions are the first to go in Alzheimer's, this helps explain why the highest levels of reasoning and newer memories are the first to fail, while more basic functions like movement and vision are unaffected until late in the disease.

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