Suspended animation shows up early in science fiction after a long history in prior literature. In Shakespeare, it’s the result of taking a “distilling liquor” (thus Juliet’s ‘sleep,’ which drives Romeo to suicide). In the SF realm, an early classic is John Campbell’s 1938 story “Who Goes There?”, which became the basis for the wonderful “The Thing from Another World” (1951). Here an alien whose spacecraft has crashed remains in frozen suspension for millennia, only to re-emerge as the barely recognizable James Arness. In the essay below, Don Wilkins points us toward a new study that could have implications for achieving the kind of suspended animation that one day might get a crew through a voyage lasting centuries. A frequent contributor to Centauri Dreams, Don is an adjunct instructor of electronics at Washington University, where the work took place. Echoes of van Vogt’s “Far Centaurus”? Read on. I’ll have another take on this topic in the next post.
by Don Wilkins
Humans have often observed with envy the ability of certain animals to extend sleeping periods from mere hours to months. If bears can do it, why cannot a suitably prepared person do it? Artificial hibernation is often used in science fiction to transport an individual into a distant future without the bother of aging or achieving relativistic speeds or conserving scarce resources. A practical hibernation system, in a more terrestrial function, provides medical support, improving survival by decreasing metabolic activity of a critically ill patient. Some writers hypothesize that a certain number of sleepers, particularly hibernations of decades or more, will suffer disabilities or death.
Research has focused on inducing torpor, a condition of significantly decreased metabolic rates and body activity, producing hibernation without adverse side-effects or horrifying experiments with cryogenics. A practical system remains within the realm of science fiction.
Torpor, like hibernation, is a physiological state in which various animals, including certain fish, reptiles, insects and mammals, actively suppress metabolism, lower body temperature and slow other life processes to conserve energy and survive fatal conditions and cold environmental temperatures.
A research team led by Yaoheng Yang (Washington University, St. Louis) has demonstrated a novel method for inducing torpor in rodents: Deep ultrasonic stimulation of a mammal’s brain [1]. Animals in torpor states experience reduced metabolism and body temperatures. Ultrasound was selected as the stimuli as it noninvasively and safely penetrates bone, and can be tightly focused with millimeter precision. The team hypothesizes that the central nervous system organizes the multitude of reactions needed to induce torpor.
In the experiments, as shown in Figure 1, a mouse wore a tiny “hat”, a lead zirconate titanate ceramic piezoelectric ultrasonic device with a center frequency of 3.2 MHz. The output was focused on the animal’s brain in the hypothalamus preoptic area (POA). Activating the POA neurons induced a torpor state for periods greater than 24 hours.
Fig. 1: Ultrasound device for inducing a torpor-like hypothermic and hypometabolic state. a, Illustration of ultrasound (US)-induced torpor-like state. b, Illustration of the wearable US probe (top). The probe was plugged into a baseplate that was glued on the mouse’s head. MRI of the mouse head with the wearable US probe shows that ultrasound was noninvasively targeted at the POA (insert). Photograph of a freely moving mouse with the wearable US probe attached is shown at the bottom. c, Illustration of the US stimulation waveform used in this study. ISI, inter-stimulus interval; PD, pulse duration; PRF, pulse repetition frequency. d, Calibration of the temperature (T) rise on the surface (top) and inside (bottom) the US probe. The temperature inside the probe was measured between the piezoelectric material and the mouse head when US probes were targeted at the POA or the cortex.
When the POA was stimulated, the body temperatures of the test animals dropped approximately three degrees C, although the environment was held to room temperature. Metabolism switched from carbohydrates and fat to solely fat. Heart rates declined about 47%.
The system used an automatic closed-loop feedback controller with the animal’s body temperature as the feedback variable. Tests which kept the subject’s body 32.95 ℃ for 24 hours were successfully concluded when the ultrasonic influence was removed and the animal returned to normal body temperature. According to previous studies, the body temperature must be below 34 ℃ to induce torpor.
Increasing the acoustic pressure and duration of the ultrasound stimulus further lowered body temperature and slowed metabolism. Each ultrasonic pulse produced consistent neuronal activity increases together with body temperature reductions in the test subjects.
The team, through genetic sequencing, discovered ultrasound could restrain the TRPM2 ultrasound-sensitive ion channel in the POA neurons. The precise mechanism providing the torpid state is unknown.
In a rat, which does not naturally enter torpor or hibernation, ultrasound simulation of POA neurons reduced skin temperature and core body temperature.
Ultrasonics can, with great spatial accuracy, reach deeply within the brain to stimulate the POA neurons. This approach could serve as the foundation of a system providing long term, noninvasive, and safe induction of torpor.
Reference
1. Yang, Y., Yuan, J., Field, R.L. et al., “Induction of a torpor-like hypothermic and hypometabolic state in rodents by ultrasound,” Nature Metabolism 5, 789–803 (2023). Full text.
Next, the experiments need to be on rats that do not naturally hibernate and determine what side effects appear over prolonged induced torpor. Prior experiments have resulted in bowel damage. Then there is the issue of whether this approach is in any way similar to medically induced on the patient’s mental state while unconscious. I am not certain, but don’t bears periodically wake during the hibernation period to eat before going back into a torpor state?
Certainly, safe hibernation would be a useful method to reduce life support requirements on long journeys, but for an interstellar trip, it would mean many controlled hibernation and waking periods. AFAIK, hibernation doesn’t extend life, so the crew would just experience less waking life, and watch themselves grow older. Therefore useful for a trip to Mars or Venus, but not to the stars, as the crew might still die on the way just as if they are on a generation ship. If so, how does the next generation handle induced hibernation?
Perhaps rather than trying to induce hibernation by machine, we find a way to genetically engineer the human to hibernate naturally in response to an environmental factor, such as air temperature or light cycle length.
Perhaps we need to let go of the idea of biological humans star travelling. Robotic minds are far more adapted to such journeys, If we could make electronic copies of human minds, that copy could experience star travel, even if the biological consciousness stays in the solar system. That won’t happen any time soon, perhaps never, but it strikes me as a more viable way to make the journey at any velocity, even tiny fractions of lightspeed.
Alex beat me to most of the points I was going to make. Then there was this:
“Perhaps we need to let go of the idea of biological humans star travelling. Robotic minds are far more adapted to such journeys,”
Since hibernation doesn’t extend life, and is in fact likely to be injurious, humans on stellar trips will first need anti-aging and rejuvenation technology (no, they’re not the same thing). That may be a bit of a reach, however it may very well arrive before we are capable of reasonably rapid interstellar travel.
Then there’s the matter of boredom. That assumes the spacecraft is rudimentary and solely designed for economy and getting from here to there (wherever “there” is that’s worth the effort by biological humans). Too boring? Have a nap.
Alternatively you build an ark with a viable human society so that boredom is no longer a problem. But if we do that, “there” may not matter since they don’t necessarily require a physical destination. And there is no need for stasis, hibernation or other means to avoid a ship full of monkeys constantly shouting: “are we there yet?” A sufficiently intelligent robot will also quite likely be susceptible to boredom and other similar behavior when faced with centuries of tedium.
These topics come up again and again. Mostly it comes down to a proposed interesting technical or biological solution to long interstellar journeys that is likely not going to be a problem.
A machine brain can artificially slow its operational speed or turn itself off. IOW, a robot can go into the very stasis that currently eludes us. Its longevity will depend on engineering and how easy it is to manufacture and replace parts.
Just as the tv version of Foundation has Demelza living for many millennia, I see no fundamental reason a machine cannot be maintained for very long periods, with or without an active mind.
I am skeptical about life on Arks.I know living on a small island can feel very restrictive, especially having little privacy. humans living on a space island may have to be selected to like this. Can that be ensured in each generation, or will every possible individual need to be engineered to be comfortable with that life? Can a trip lasting millennia be possible both for maintaining the internal biosphere as well as the human passengers?
IDK the answers, but I do suspect that it will prove far easier to send robots to the stars than biological humans.
I was thinking along the same lines, robotic replicas of those who wish they could have gone to the stars i.e. we download our minds into a silicon/meat unit with swappable parts. Worn out parts are replaced and sleeping long periods is as simple as switching ourselves off for a time.
In Richard K Morgan’s Altered Carbon and other Takeshi Kovacs stories, human consciousness is put into “cortical stacks. Almost everyone has them. When you die you can be re-sleeved into another body. Star travel is achieved by sending just the stack and re-sleeving at the destination.
This keeps the biological human, although it does require the infrastructure to have human bodies available at the destination.
It is a clever twist on the idea of mind-uploading (and downloading), but I don’t think Morgan has truly thought out the reintegration issues of re-sleeving, even if the cortical stack was a viable technology.
Robert Sawyer’s “Mindcan” has dying humans’ minds transferred to humanoid robot bodies. The caveat is that these robotic versions cannot claim the legal status of the original. Eventually, the robotic protagonist lives on a non-terraformed Mars. Clearly, this version could also go on a long starflight and live on a suitable exoplanet.
IMO, the most likely scenario is that we will have “good enough” AGI long before mind uploading is possible. Robots will be able to do most of the exploration and economic exploitation of space, especially in other star systems. They do not need complex biological life support, just a source of power. They can work in vacuum for their ships need to be nothing more than open frameworks to tie together propulsion and control systems. For rockets and beamed sails, this is a huge mass saving over human-crewed ships, and therefore far more economic, not to mention more suited to long mission durations. The only issue is can we pack an AGI mind into a volume comparable to a human brain and with a similar low power requirement. I think we will, but that roadmap is not clear to me at the moment.
Hi Paul & Don
The introduction reminds me of Van Vogt, of course, and his Eternity drug. But a side thought occurred to me of an Earthly application – weight-loss. Resting metabolism burns about 2,000 calories a day, which is about 1 kg of fat reserves. Even if an induced torpor halves this, the weight-loss potential is still incredibly effective. Just ‘sleep’ off the excess weight. The trick will be keeping the body from cannibalising useful protein, like cardiac muscle.
Fat grams & (kilo)calories:
1……………….9
10……………..90
100……………900
200……………1800
⅕ of a kilogram: close enough for government work.
Only if cellular molecular machinery can be completely halted or altered, the short, intermediate and long term changes leading to senescence and mortality can be arrested.
Most hibernators have deep adaptations to it. I am unaware of hibernating primates (except for an occasional student in school).
Frozen frogs waking after winter snooze.
So it’s possible (as show by frozen frogs), wonder what the longest shelf life is?
“During this period, the liver produces large amounts of glucose to increase blood-sugar levels, which functions like a natural “antifreeze” by limiting the formation of ice crystals in the body. A high concentration of glucose or sugar in the frog’s vital organs inhibits freezing and without this physical process, the ice crystals would damage tissue and result in the frog’s death.
As much as 70 percent of the water in a frog’s body can be frozen. However, if it does get too cold, the frog can die.”
Hi Robin
Fat Tailed Lemurs go into torpor, so it was potentially present in primates at quite an early divergence point of our lineage.
Does a bear sleep in the woods?
Some kind of suspended animation technology has always been the Plan B if FTL or advanced fusion/matter-antimatter conversion doesn’t work out. Although this is known to occur naturally in a handful of vertebrates, and even a few mammals, whether we can adapt the technique reliably to humans is not clear. Nature has had a long time to work the bugs out. Then there’s always the problem of the wake-up procedure. Can we trust our AI to resuscitate the crew if the re-animation protocol is complex and requires intense monitoring and supervision?
One alternative is to divide the crew into watches, so that a certain percentage would be awake at any one time to keep an eye on their shipmates, as well as do routine shipboard navigation and maintenance. If the hibernation procedure is fairly simple, and if the previous watch can put their fellow crewmen “under”, then each watch could be awakened, and after a time, the next watch would be awakened and the preceding watch be put into deep sleep until the next was ready, and so on.
At any one time, part of the crew would be in stasis, and a few would be on duty, monitoring their condition and operating the ship. This solves the problem of the human body being only able to tolerate periods of hibernation much shorter than the total mission time, or the hibernation tech itself requiring full time human operators. It also presupposes that each astronaut could survive multiple episodes of cryogenic stasis.
That’s if human suspended animation is even possible. Personally, I’m not too optimistic. Sure, bears do it, but they’ve evolved the ability over thousands, maybe millions, of years; and they have to stuff themselves to obesity in order to pull it off. Its not clear we could reverse engineer that capability into the human physiology.
The whole concept is great for science fiction writers. You might be forced to wake up the sleeping crew prematurely to deal with a shipboard emergency, or one watch could mutiny and deep-six the rest!. And what if the freezing process is not perfect, and a certain percentage of the sleepers is lost during each iteration of the cycle?
Then again, consider the plot of the film “Passengers”, where one of the sleepers is awakened accidentally, and another deliberately, long before the ship arrives at its destination.
https://en.wikipedia.org/wiki/Passengers_(2016_film)
Hi Henry
“Passengers” many old SF fans suspect, is a retelling of “50 Girls 50” from the “Weird Science” comic book in the 50’s. Here’s a link.
The proverbial 100 year flight, 100 passengers, a guy waking early to take advantage of the sleepers… pretty creepy scenario, especially since you can only survive one freeze/thaw cycle. Hopefully, if we ever manage actual suspended animation, it’s as easy to initiate and reverse as in Karl Schroeder’s “Lockstep”.
Schroeder has written some great stuff, hasn’t he? I loved Lockstep.
” horrifying experiments with cryogenics.”
What’s more horrifying about experiments with cryonics, than with torpor? Genuine question.
This is an interesting technical achievement with medical potential, but for interstellar journeys refrigeration may not be enough. I think we need the sort of vitrification shown by tardigrades or the resurrection plant, in which much of the water of the cell is replaced by trehalose (a disaccharide: glucose dimers bound together at the aldehyde positions to make them nonreactive). Strangely, though vertebrates lost the ability to make trehalose, it seems to have mostly beneficial effects ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7277924/ ). It would take much more engineering to arrange for cells to dehydrate themselves while filling themselves with this sugar, but this could allow outright freezing of the passengers. (Technically, without many water molecules, their cells would not “freeze”, but low temperatures should reduce oxidation and other undesired reactions) Then again, a thousand years of exposure to cosmic rays and other background radiation will also require souped-up DNA repair mechanisms akin to Deinococcus, and as always it would be nice to have improved p53 paralogs to prevent cancer akin to those of elephants.