There are times when hibernating would be useful, like surgery or space travel, and we’re getting closer to being able to do so on demand in humans. Scientists have now demonstrated a way to induce a hibernation-like state in mice and rats using non-invasive ultrasound pulses to the brain.
Torpor is a sleep-like state that animals such as mice and birds can go into to conserve energy, by bringing their body temperature and metabolism right down. It’s thought to be a survival mechanism for when food is scarce, allowing them to simply snooze through tough times.
In 2020, scientists identified a set of neurons in the hypothalamus that allows mice to enter torpor, and found that they could stimulate them using light or chemical signals to induce hibernation on demand. Better yet, the same thing worked in rats, which don’t naturally go into torpor, suggesting it could work in other mammals and maybe even humans. A follow-up study in 2022 demonstrated how the technique could be used to prevent tissue damage during heart surgery.
The problem is that triggering the neurons required animals that were genetically engineered to respond to the triggers, which included implanted fiber optics. That’s not the most comfortable or practical method, so for the new study scientists at Washington University developed a non-invasive way to induce torpor.
The team created an ultrasound emitter small enough to be mounted on the heads of mice as they went about their day. This could fire off 10-second pulses of ultrasound directed at the preoptic area of the hypothalamus, which instantly triggered symptoms of torpor in the animals. That includes a drop in body temperature by 3 to 3.5 °C (5.4 to 6.3 °F), as well as reduced heart rate and oxygen consumption. The animals woke up naturally after a few hours.
In another experiment, the researchers hooked the ultrasound emitter up to an automated system that would deliver further pulses whenever the body temperature started to rise again. Through this, they were able to keep the mice in torpor for 24 hours at a time, with no visible damage to the brain and no apparent discomfort to the animals.
The team repeated the experiments with rats, and again found that it worked much the same, albeit with a smaller drop in body temperature of 1 to 2 °C (1.8 to 3.6 °F). This adds evidence to the idea that the metabolic response is still present in mammals that don’t naturally hibernate, suggesting it could potentially work in humans.
Of course, that’s a long way off yet, but having a non-invasive way of triggering the state is an important step. If we could get it to work, the team suggests ultrasound-induced torpor could save lives during medical emergencies, or eventually help future astronauts hibernate on long space voyages.
The research was published in the journal Nature Metabolism. The team describes the work in the video below.
