As far as brain regions go, the hypothalamus is something of a multi-tasker: it helps control our temperature, hunger, sleep, emotions, and sex drive.

But that's not all. A new study suggests it's also responsible for keeping us young, thanks to a supply of neural stem cells that regulate our ageing.

Sadly, these disappear with time – which could be why we get old – but tests with mice show that implanting new cells to replace them can actually extend lifespan.

"Our research shows that the number of hypothalamic neural stem cells naturally declines over the life of the animal, and this decline accelerates ageing," says molecular pharmacologist Dongsheng Cai from the Albert Einstein College of Medicine in the Bronx.

"But we also found that the effects of this loss are not irreversible. By replenishing these stem cells or the molecules they produce, it's possible to slow and even reverse various aspects of ageing throughout the body."

Cai and his team discovered back in 2013 that the hypothalamus plays a role in ageing, and that by reducing inflammation in the brains of mice, the animals were able to live longer lives.

Now, in a follow-up study, the researchers think they've pinpointed the particular cells in the hypothalamus that matter here: neural stem cells, which serve to generate replacements for dead and damaged cells.

In mice, these cells start to disappear when the animals are about 10 months old (mice middle age), and are largely gone by the time they turn two (elderly).

To figure out if this reduction is what helps cause ageing – as opposed to just a correlation – the researchers disrupted the neural stem cells in a group of mice, using a toxin to destroy around 70 percent of the cells.

Doing so not only caused the mice to live a few months less than naturally ageing control animals, but it also increased the effects of ageing while they still lived.

"There was a decline in learning and memory, coordination, muscle mass, endurance, and skin thickness," Cai explained to Jessica Hamzelou at New Scientist.

To see if an opposite effect was also possible – in other words, whether stocking up on neural stem cells could produce youthful vigour and longevity – the team injected hypothalamic stem cells taken from newborn mice into the brains of two groups of mice.

One of these groups was made up of normal old mice; the other consisted of animals that had had their hypothalamus disrupted by the toxin. The treated animals lived significantly longer than untreated animals, enjoying a lifespan up to 15 percent longer than the controls.

The team thinks that the longevity provided by these neural stem cells comes down to molecular secretions called microRNAs (miRNAs), which help to regulate gene expression.

Scientists uninvolved with the research have described this ageing mechanism as "totally novel and quite unexpected", although there's no guarantee the same physiological function is at work in people.

Finding out whether it is will be on the horizon for the researchers, who now want to launch clinical trials to see if neural stem cells implanted into human volunteers acts like some kind of elixir of youth.

"Of course humans are more complex," Cai explained to Ian Sample at The Guardian.

"However, if the mechanism is fundamental, you might expect to see effects when an intervention is based on it."

The findings are reported in Nature.