The slowdown of the brain with old age is due to the lack of a brain chemical which helps neurons to be selective about what they respond to, reveals research involving the world’s oldest monkeys.

Higher brain functions, such as visual recognition or understanding language, require the processing of information in the brain but decline as people get older. This decline appears to be due to a reduction in a neurotransmitter called GABA, say researchers, which means neurons with specific tasks become more easily fired by some other stimulus.

Macaque monkeys, with an age equivalent to 90-years in humans, were not as sharp as their younger counterparts in visual tests despite having perfect eyesight. But when they were given drugs to increase levels of GABA in the brain they improved vastly, say the team.

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