Old age may have its downsides, but losing the ability to grow new brain cells isn鈥檛 one: healthy people in their seventies seem to produce just as many new neurons as teenagers.
The discovery overturns a decades-old theory about how our brains age and could provide clues as to how we can keep our minds sharper for longer.
In mammals, most brain cells are created at or soon after birth and are not renewed. Recently, it was discovered that the human hippocampus, associated with learning and memory, produces new neurons throughout life. However, it was thought that this ability, called neurogenesis, severely declines after middle-age.
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To investigate, at Columbia University in New York, and colleagues removed the hippocampus from 28 people, aged between 14 and 79, soon after their death.
They analysed the number of new neurons, the number of glial cells, which support neurons, as well as molecular markers that are expressed when brain cells form new connections or migrate around the brain 鈥� a sign of neuroplasticity.
They found similar numbers of new neurons throughout the hippocampus, as well as comparable numbers of glial cells, regardless of the age of the person the sample had come from. The team estimates that each person was producing about 700 new neurons per day when they died.
New for old
Studies in animals suggest that older mammals don鈥檛 have the capacity to grow new neurons and experiments in older humans have appeared to confirm this theory. However, these human studies only included diseased brains, or used tissue removed more than a day after death, says Boldrini.
鈥淣ew neuron growth has never been studied before in people who didn鈥檛 have any brain disease or end of life stress, with tissue taken within 24 hours of death,鈥� she says. 鈥淥ur results show that healthy older people can form just as many new neurons as younger people. If we know what is happening in these people to keep their neurons forming then maybe we can use it to help others age more healthily too.鈥�
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There were some differences between the ages 鈥� in part of their hippocampus, older people had less neuroplasticity, meaning their brain was less able to rearrange its connections in this area. It is not yet clear the impact of this age-related change.
, associate professor of molecular neurobiology at Swansea University, points out that the number of new neurons may still be a lot higher in newborns and young children. 鈥淭herefore, decreased neurogenesis across the life-span cannot be ruled out,鈥� he says.
He says it would be interesting to see the study repeated in people who exercised versus people who did not. 鈥淭his would provide some insight into whether the production of new neurons can be modified by environmental factors in humans to promote healthy brain ageing.鈥�
