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Mice, like people, like to be rocked to sleep

Forget the running wheel. If your pet mouse is an insomniac, what it really needs is a hammock. New research shows that mice, just like humans, fall asleep faster with a gentle sway.

Mild rocking helps both adults and children fall asleep faster and experience deeper, longer sleep. Scientists have suspected that the human vestibular system—the bits of the inner ear that keep us balanced and oriented in space—are involved, but there’s been no solid proof.

So, in the new study, researchers put mouse cages on rocking platforms, monitored the animals’ brain activity, and measured how well they slept. The rodents slept 12% longer with rocking than without, and they fell asleep 51% faster if they had been sleep-deprived. But their brain signals did not indicate a deeper sleep.

The researchers did not look for a benefit of rocking on memory, which a related study suggests is a benefit for humans. The mice showed other differences from people as well; the rodents like to be rocked about four times faster than we do, for example. These differences might reflect the fact that mice carry their pups around in their mouths, which has a lulling effect, rather than rocking them in their arms like humans. But the researchers say it’s too early to speculate on shared evolutionary mechanisms.

More intriguingly, mice that lacked a key part of the vestibular system called otoliths—teensy stones that sense linear acceleration—did not get any benefit at all from being rocked at bedtime, confirming the vestibular system’s central role in the effect, the team reports today in Current Biology.

The results might lead to better noninvasive treatments for sleep disorders, the researchers say. For example, understanding how the brain uses the “rocking signal” to promote sleep might usher in alternatives such as transcranial magnetic stimulation, which uses electrical impulses to stimulate nerve cells and has been used to treat other brain disorders such as depression. But for now, you’re probably fine with a hammock.