Dormouse in a coma
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Zapping parts of the brain with focused ultrasound can put mice into a hibernation-like state called diapause for at least 24 hours. The same approach can induce this state in rats, which, unlike mice, do not spontaneously enter coma.
“This means a lot,” says Hong Chen of Washington University in St. Louis. “If we show that we can induce similar phenomena in animals that don’t normally go into a coma, perhaps we can scale up the technique to larger animals.”
If this can be done in humans, it could have particular medical applications. For example, inducing a coma in someone who has had a stroke could buy them time and limit the damage, says Chen.
Many warm-blooded animals cool down, slow their metabolisms, and go into diapause to conserve energy. Some bats and birds go into a coma at night. Other animals, such as rats, enter there only when food is low. Hibernation involves long periods of sleeplessness interrupted by the occasional return to normal body temperature.
In 2020, two teams independently discovered that stimulating a portion of the hypothalamus in the mouse brain can induce insomnia. But they used complex methods, including genetic engineering, to activate this “brain switch.”
Chen wondered if ultrasound could be used instead. Her team is developing a method called focused ultrasound to treat brain disorders.
Chen’s team found that a 10-second pulse of ultrasound focused on the switch region of the mouse brain lowered the body temperature of the mice by about 3 degrees Celsius (5.4 degrees Fahrenheit). The mouse recovered completely after 2 hours, but by repeatedly pulsing each time his body temperature began to rise, he was able to maintain this condition for 24 hours with no signs of adverse effects.
It may be possible to maintain this state longer, Chen says, but her team has yet to try it.
The technique also works in rats, but they only lowered their body temperature by about 1.3°C (2.3°F).
“This is important because rats are non-hibernating animals and are closer to humans in that regard,” says Matteo Celli, a professor at the University of Bologna in Italy. His team induced coma in rats and pigs by chemically inhibiting parts of the brain. brain stem.
Lowering body temperature with ultrasound could be useful for medical purposes, but interplanetary travel may require more powerful methods to curb metabolism, Selly said.
It’s unclear exactly how focused ultrasound induces coma, says Takeshi Sakurai of Japan’s University of Tsukuba, one of the two discoverers of the hypothalamic switch.
That may be what causes the brain to switch, says Sakurai. “But there are also other neuronal groups in nearby regions that play a role in thermoregulation, making it more likely that they are also involved.”
Chen believes that a combination of localized heating and physical movement induced by focused ultrasound waves opens ion channels on neurons, activating them. However, this has not yet been established.
Human exploitation is still a long way off, she says. “Safety is a big concern.” experiment had to be done.
But developing a helmet that can send focused ultrasound pulses to equivalent parts of the human brain is entirely feasible, she says.
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