Contact: Kara Villamil, or Mona S. Rowe
Released March 2, 1998
image of brain scans from study
image of area of the brain studied
UPTON, NY - Two of the most common signs that a person is growing old - diminished motor skills and decreased mental agility - are directly connected to a reduced capacity to absorb a key "communications chemical" in the brain, a new study has found.
But, the study's authors say, the effect may be preventable, raising the possibility of future means of improving the quality of life for the nation's growing elderly population.
The finding is reported in the March issue of the American Journal of Psychiatry by a team of researchers from the U.S. Department of Energy's Brookhaven National Laboratory, the State University of New York at Stony Brook and the University of Pennsylvania School of Medicine.
"This is the first study to look at the significance - both for motor function and cognitive function - of the normal changes in brain chemistry that occur in healthy people as we age," said Nora Volkow, the leader of the team.
"And while we don't know for certain what might be able to prevent these changes and slow these universal effects of aging, we think it should be possible," Volkow continued. For example, she said, exercise and varied daily activity may help preserve the brain's chemistry.
Making the Dopamine Connection
Volkow and her colleagues focused their study on dopamine, a type of brain chemical called a neurotransmitter that sends signals between brain cells, or neurons. The signal is sent when dopamine molecules released from the end of one neuron attach to docking ports called receptors on a neighboring neuron.
Previous studies had shown that the number of dopamine receptors in the brain decreases with age, and that the symptoms of Parkinson's disease are caused by dopamine problems. But none had ever looked at the physical and mental result of that decrease in healthy people.
Volkow's team was able to make that connection using a sophisticated brain scanning technique called positron emission tomography, or PET, in combination with simple, standardized motor function and cognitive tests.
PET scans were made of the brains of 30 healthy volunteers, ranging in age from 24 to 86, to show the concentration of dopamine receptors in parts of the brain. Then, the scientists correlated each person's brain scans with their performance on an extended battery of cognitive and motor skills tests.
Among other skills, the tests measured the speed with which the subjects were able to tap their fingers on a table, their ability to learn and remember the rules of a card-sorting game, and their success at sorting out contradictory stimuli - for example, fulfilling a request to read out loud the printed name of a color, such as "red", even though the word was printed in a different color, such as green.
The study included only right-handed subjects who had shown no evidence of disease, including psychiatric disorders, and who had no history of alcohol or substance abuse. The group was made up of people of many races and educational levels.
Overall, the results showed that the people with the best performance on the finger-tapping tests also had the highest concentration of dopamine receptors in two areas of the brain, called the putamen and the caudate, that control motor function. Those with best scores on the card-sorting game and the word-color test also showed higher dopamine receptor concentrations in these brain regions. The researchers adjusted the results to correct for differences in education and age.
Groundwork for More Study and Prevention
The results of the study should encourage future studies on the association between the dopamine system and physical and mental agility.
And, said Volkow, further research might suggest ways to improve dopamine system function and therefore the motor and cognitive performance of older people. Already, researchers have shown that a lower-calorie diet slowed the loss of dopamine receptors in laboratory animals, and that a shift from a sedentary lifestyle to an exercise-rich lifestyle increased the number of dopamine receptors.
"Using PET in conjunction with standardized neuropsychological tests opens up a whole new way to study the dopamine system," said Volkow. "We know that sedentary people who start exercising improve their performance on such tests, but using PET, we could find out if this improvement is somehow connected with dopamine. We know that people with Parkinson's disease have a severe deficiency of dopamine, but we need to better understand their decrease in cognitive ability."
The research was sponsored by DOE and the National Institute on Drug Abuse.
Brookhaven National Laboratory carries out basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. Brookhaven is operated by Brookhaven Science Associates, a nonprofit research management organization, under contract with the U.S. Department of Energy.
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A comparison of PET scans from three subjects who participated
in the study, showing
the concentration of dopamine receptors and dopamine transporters
in the brain. Red indicates highest concentrations, purple indicates lowest.
The regions of the brain studied in the research.