Replenishing a brain chemical that helps neurons focus has improved higher brain functions in the world’s oldest monkeys.

Led by neuroscientist Audie Leventhal, researchers at the University of Utah School of Medicine studied macaque monkeys and found that those with an age equal to 90 in humans performed more poorly than younger monkeys in visual tests.

They found that the cause was differences in amounts of the inhibitory neurotransmitter Gamma-aminobutyric acid, which helps neurons stay focused by calming them and making them more selective.

Higher brain functions such as visual processing and understanding language rely on this selectivity, and such functions decline as people age.

The researchers found that monkeys given drugs to increase GABA levels improved vastly in mental ability.

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