Can humans really hibernate? Exploring the feasibility of "cold sleep"

When you hear the awakening from a cold sleep device, it's a classic scene from a science fiction story. We even have the odd confidence that if we are going to travel interstellarly, we must have a cold sleep device. But if you think about it calmly, this is strange. People whose body temperature drops in snowy mountains and suffers from hypothermia, will be struck by sleepiness and die?

While thinking about this, I caught up with information that an institution researching "technology to artificially hibernate humans" existed in Japan.

It is said that it has been successful in artificially bringing mice that do not hibernate into a state close to hibernation. I immediately decided to contact Dr. Sunagawa Genshiro, a research team at the Hibernation Biology Research Team at the RIKEN Institute for Life and Functional Sciences, who is currently conducting this research.

First, let's talk about definitions. We call it cold sleep, but is there a difference between "sleep" and "hibernation" that the doctor has been researching?

"Hidden and sleep are actually completely different physiological phenomena. Sleep is a physiological state of rest that regulates brain activity, organizes and recovers memories. Usually, body temperature is maintained even during sleep and does not drop significantly. Hibernation is a function that dramatically reduces energy expenditure in the whole body.

Organisms that live in harsh environments survive by significantly lowering their metabolism. Body temperature also drops depending on the environment. Hibernating animals spend a long period of time with little to eat during the winter, as their bodies keep their energy expenditure to the limit. The brain activity is also significantly reduced, and the heartbeat and breathing are also extremely slow.

Unlike sleep, it takes time to wake up, and external stimuli cannot be awakened immediately. "Hidden" is a special state that helps maintain life for a long period of time."

When compared to a PC, it seems that sleep is defragmented and hibernation is in energy-saving sleep mode. However, humans do not hibernate. Why did the doctor come to the idea that humans can also hibernate?

"The trigger was to learn about monkeys that can hibernate. I intuitively thought that if monkeys, a primate, could hibernate, humans could also hibernate. If humans could use similar functions, my dream was to see a groundbreaking progress in medicine and space exploration."

Controlling metabolism brings a future where patients with severe illnesses slow the pace at which they deteriorate, and that allows for long-term space travel, the doctor says.

Regarding hibernation, there are many unexplained parts of mammals, such as the reasons why some species can and cannot, and details of how they hibernate, and the mechanisms for hibernating, and the fundamental mystery of life itself is also very appealing, the doctor added.

By the way, there are still questions about advances in medicine. Anesthesia is already a technique for slowing down metabolism and treating it. What are the benefits of choosing to hibernate?

"Both are "a state where consciousness is reduced," but they are fundamentally different in terms of metabolism control. Since anesthesia acts on the brain, it suppresses various functions of the brain besides consciousness. When general anesthesia is applied, consciousness and pain will disappear, but if left as is, it will no longer be possible to control other physical functions.

Metabolism is reduced, and body temperature and blood pressure are also reduced. The patient is at risk. In hibernation, on the other hand, we are unconscious, but not all functions of the brain are suppressed. It is a controlled, low metabolic state, so it can be maintained without any special support.

Hibernation is originally a controlled, low-metabolic state that allows for long-term life support, so there is no need to use drugs or stimuli for awakening. When applied to medical or space exploration, hibernation is likely to be more sustained and less risky."