Creating hibernation-like sleep with ultrasound

The Background

Whether it’s Avatar or Interstellar, we’ve all seen space movies with rows of people in “cryosleep” for a long journey. Putting people into an artificial “hibernation-like” sleep has always been a science fiction dream.

Hibernation is characterized by a slower metabolism and lower body temperature. It lets animals conserve energy in times of fatal conditions, like when food is scarce or in cold temperatures.

For us, there could be more benefits to induced hibernation than just scifi-style space travel. Organs could be better preserved for transplants, there could be less damage after heart attacks or strokes, and diseases could be slowed down during treatment.

Researchers previously figured out which part of the brain is responsible for hibernation, but not how to easily trigger the behavior.

The Solution

It turns out that the specific brain region that regulates hibernation can be activated with ultrasound (the hypothalamus preoptic area). This is super convenient because ultrasound is as non-invasive as it gets. 

No shots are required, just some mild sound waves that are already regularly used in humans and are completely safe. Ultrasound is quite specific and can be targeted to small regions of the brain without affecting other regions, limiting side effects.

This week's researchers found that applying ultrasound pulses to a specific brain region caused mice to enter a hibernation-like state. The mice’s temperature, metabolic rate, heart rate, and breath rate all fell after ultrasound exposure (plus they got sleepy).

The infrared images and the bottom left graph below show that the mice’s temperature drops after a brief ultrasound pulse, going down as much as 3ºC (~6ºF). The heart rate showed a similar trend, dropping almost 50% after ultrasound started.

Importantly, ultrasound pulses directed to other regions of the brain had no noticeable impact on the mice. Only targeted pulses to the area that controls hibernation made a difference. The researchers could control how much the mice’s vitals decreased based on how intense and long the ultrasound pulses were.

The researchers found that neurons in the hypothalamus preoptic area responded to ultrasound. Specifically, they saw that the ion channel TRPM2 on the cells was activated and led to downstream effects like body temperature decrease.

Mice enter hibernation-like states when they don’t get enough food. So they’re already prepared for the ultrasound-induced version. Would this work in a mammal that doesn’t ever enter a hibernation-like state? Like a human?

It turns out rats, like humans, don’t hibernate. The researchers took their findings from mouse models and repeated the experiments with rats.

Remarkably, they found the exact same thing! Despite rats not doing anything remotely close to hibernating, the researchers were able to put them in a hibernation-like state. The rats didn’t have as big of a drop in temperature (or other vital signs), but they still showed the same response as the mice.

This is an incredible start toward showing that ultrasound could be used to induce hibernation states in other mammals and eventually humans.

Before that, a lot more work needs to be done on how to “awaken” the subject from ultrasound-induced sleep and its long-term effects. Still pretty cool though.

See you next week for more science,

Neil

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