Newest neural links go first in Alzheimer's patients
"Last hired, first fired" may apply to our brain functions. Myelin sheaths insulating neural connections that were developed last in life are the first to degenerate in people with Alzheimer's disease, according to research from the University of California, Los Angeles. Typically, patients with AD lose fresh memories, decision-making abilities, and impulse control before they lose movement and visual capabilities. The former functions are associated with neural connections developed relatively recently, while the latter are controlled by connections developed much earlier in life, said lead author Dr. George Bartzokis, a visiting professor of neurology at UCLA.
In a study published in the August issue of the Neurobiology of Aging, MR imaging was used to examine the deterioration of myelin in the brain's splenium and genu regions of the corpus callosum. The genu connects the two frontal lobes, where human thinking and planning occur, and the splenium connects adjacent occipital lobes, where vision is processed.
The genu was found to be more adversely affected, Bartzokis said.
The structural makeup of newer myelin sheaths differs from that of sheaths developed earlier in life. The MR convention of converting transverse relaxation time into transverse relaxation rates can exploit these differences, providing researchers with a calculated rate of change.
The UCLA group imaged 34 AD patients aged 59 to 85 years and 250 normal controls aged 19 to 82 years. The rate of decline was three times faster in the genu of all subjects than in the splenium. The deterioration of myelin was far greater across the board in the Alzheimer's patients compared with the normal subjects.
The study suggests that the loss of myelin sheath, which occurs naturally with age, could be a risk factor for AD as well.
"The study demonstrates the usefulness of this MRI method for examining the single most powerful risk for Alzheimer's disease by far: age," Bartzokis said.
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