Torpor is a physiological state similar to hibernation, in which mammals inhibit metabolism, lower body temperature, and slow down other physiological processes to conserve energy. This state is believed to be controlled by the central nervous system (CNS). Ultrasound can penetrate the skull in a non-invasive manner and focus on the brain, and if focused on nerves, it has been shown to activate animal nerve cells.

On May 25, 2023, the team led by Hong Chen from Washington University in St. Louis published a research paper titled "Induction of a torpor like hypothalamic and hypometabolic state in rodents by ultrasound" in the Nature Metabolism journal.

This study shows that ultrasound pulses directed towards the head can induce reversible hibernation like states in mice and rats. This non-invasive method temporarily activates nerve cells in the brain, leading to a decrease in body temperature, slowing metabolism, and may be applied in future medical or potential long-distance spaceflight.

▲ Schematic diagram of experimental setup

The research team has developed an ultrasound transmitter that can be installed on the head of freely moving mice. They applied 10 second ultrasound pulses to the preoptic area of the hypothalamus, which is known to regulate hibernation activity. This activity triggered an immediate temperature drop of several degrees (average 3-3.5 ° C) in both female and male mice, accompanied by a decrease in heart rate and oxygen consumption, and these animals fully recovered within 2 hours.

The research team then combined an ultrasound transmitter and an automated system to emit repeated ultrasound pulses when body temperature began to rise, thereby maintaining this type of hibernation state in the experimental animals for up to 24 hours without any signs of injury or discomfort. The study also showed that this technique worked on 12 rats (which typically do not hibernate naturally), although their body temperature only dropped by 1-2 ° C. The research team believes that this suggests that the physiological process of regulating metabolic reactions may also exist in non hibernating mammals.

Although more research is needed to investigate whether this method is safe for humans, the research team suggests that this non-invasive, reversible technology that delays metabolism and lowers body temperature may be applicable in medicine for emergency treatment or acute illness, or could be helpful for future long-distance interstellar travel.