Ultrasound can trigger a hibernation-like state in mice and rats

Focused ultrasound waves targeting a certain area of the brain can lower body temperature in rodents, showing a possible way to put people in suspended animation

By Michael Le Page

25 May 2023

A common dormouse in a state of torpor

Simon Phillpotts/Alamy

Zapping part of the brain with focused ultrasound can put mice in a hibernation-like state called torpor for at least 24 hours. The same approach can also induce the state in rats, which, unlike mice, don’t naturally enter torpor.

“That has huge implications,” says Hong Chen at Washington University in St. Louis, Missouri. “The thinking is that, if we show that in animals that don’t normally enter the torpor state we can still induce a similar phenomenon, maybe we can scale up the technology to larger animals.”

If this can be done in people, too, it could have medical uses among other things. For instance, inducing torpor in people who have had strokes could buy them time and help limit the damage, says Chen.

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Many warm-blooded animals lower their body temperature and slow down their metabolism to save energy, entering torpor. Some bats and birds go into torpor at night. Others, such as mice, enter it only when food runs low. Hibernation involves extended periods of torpor interrupted by occasional returns to normal body temperature.

In 2020, two teams independently discovered that stimulating part of the hypothalamus in the brains of mice can induce torpor. However, they used complex methods, including genetic engineering, to activate this “brain switch”.

Chen wondered if ultrasound could be used instead. Her team has been developing a method called focused ultrasound for treating brain diseases.