June 8, 2001 CHAMPAIGN, Ill. — Next time an older person says that thinking is exhausting, believe it. Concentration, researchers say, drains glucose from a key part of the brains of young and old rats, but dramatically more from older brains, which also take longer to recover. The findings, detailed in two studies published in May, are part of research that eventually may impact how schools schedule classes and meals as well as our understanding of age-related deficits in memory and learning, said lead researcher Paul E. Gold of the University of Illinois. "The brain runs on glucose," said Ewan C. McNay of Yale University. "Young rats can do a pretty good job of supplying all the glucose that a particular area of the brain needs until the task becomes difficult. For an old rat given the same task, the brain glucose supply vanishes out the window. This correlates with a big deficit in performance. A lack of fuel affects the ability to think and remember."
Glucose is a naturally occurring sugar in the blood and the primary source of energy in human brain metabolism. Last year, Gold, a professor of psychology, and McNay broke ground when they reported declines of hippocampal extracellular glucose concentrations in rats as they went through a maze. Their findings challenged conventional thinking about levels and stability of glucose in the brain. It has long been thought that the brain always has an ample supply of glucose short of starvation.
"While this is the case in terms of consciousness, the new findings suggest that glucose is not always present in ample amounts to optimally support learning and memory functions," said Gold, who also is director of the Medical Scholars Program in the UI College of Medicine at Urbana-Champaign.
In the May issue of Neurobiology of Learning and Memory, Gold, McNay and Richard C. McCarty, formerly at the University of Virginia, reported that glucose drainage during a task is site specific. Hippocampal extracellular levels fell by 30 percent, but that in other brain areas remained stable. "Only the part of the brain involved with what the animal is asked to do is affected by changes in glucose usage," Gold said. "This is not simply a reflection of changes in circulating blood levels or drainage in other areas."
In May’s Journal of Gerontology, McNay, a postdoctoral researcher in psychology, and Gold reported that 24-month-old rats had a 48 percent decline in hippocampal extracellular glucose levels and needed 30 minutes to recover from a maze-related task. Three-month-old rats had a 12 percent decline and recovered quickly. Older rats given injected glucose supplements prior to testing did not show the drainage of glucose and performed at the same levels as the younger rats.
"Glucose enhances learning and memory not only in rats but also in many populations of humans," Gold said. "For schoolchildren, this research implies that the contents and timing of meals may need to be coordinated to have the most beneficial cognitive effects that enhance learning."
The National Institute on Aging, National Institute on Neurological Disorders and Stroke, U.S. Department of Agriculture and Alzheimer’s Association provided funding for the studies.
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