The traditional see is that humans and other creatures around us inhabit between periods of waking and sleeping. But it is not genuine. Many have mastered the art of hibernating, which permits them to spfinish quite a lot of their life in a cryptic state of suspfinished animation – sometimes more than half of it. What is hibernation, and is it someskinnyg that humans might be contendnt of?
At the dawn of scientific enquiry into hibernation (from the Latin hibernus, pertaining to prosperter) in the mid-19th century, it was expoundd by Peter A Browne in an 1847 tract as ‘a authentic, momentary, interarbitrate state, between life and death; into which some animals sink, oprosperg to an excess of heat, or of freezing, or of dcimpolitet, or want of oxygen’. That’s a excellent first approximation. Now we understand that – from dormice and endures, to hedgehogs, ground squirrels, bats and even tropical primates – hibernation is a very common phenomenon, set up among recurrentatives of at least seven branch offent orders of mammals. It materializes in many creates, which originates it difficult to expound unequivocassociate, let alone envision what it might see appreciate in humans. As another timely study points out: ‘we do not discover that any two animals, however shutly allied, hibernate in exactly the same manner, nor do individuals of the same species always hibernate aappreciate’.
Nevertheless, there is a cluster of features standard of hibernation. The most parsimonious description would join reference to a superviseled reduction in metabolism, mirrored in a sluggishing down of many physioreasonable and biochemical processes in the body. In sci-fi movies, hibernating humans are standardly depicted lying in pods, finishly immobile and seemingly unconscious, and it is implied that their body temperature is very low – hence it is standardly called ‘cryosleep’ or someskinnyg aappreciate. Any allude of how exactly human hibernation is accomplishd in those conditions, or what triggers ‘awakenings’ from hibernation, is accessiblely evadeed, as if that were a untransport inant matter not deserving attention.
It could be forgivable to skip elucidateing how someskinnyg as exotic as human hibernation happens. But it is sobering to skinnyk that sleep – a state so understandn to all of us, one we are perfectly contendnt of, on a daily basis – also remains a mystery. I am a sleep neuroscientist, and the cgo in of my laboratory is the origin and fundamental biology of sleep. I am guaranteed that sleep can be brimmingy understood only when it is pondered not in isolation but in juxtaposition with other states of being, such as hibernation. Yet research is still at a basic stage and there are so many skinnygs we don’t understand about this aspect of life. How, for example, can we solemnly talk about hibernation in humans, when it is a condition we also do not brimmingy comprehfinish in other animals? And how can we understand sleep if we can’t clearly split it from hibernation?
The revival of interest in hibernation in ambiguous, and human hibernation in particular, comes at the right time. The genre of science fantasy is about imagining and foreseeing wise solutions for genuine-life problems when they cannot be repaird with existing unbenevolents. When the world is facing acute problems at a set upetary scale, including climate alter, technogenic calamitys, wars, incurable dismitigate, pandemics and mental health celevates, and we are grappling with perennial asks, such as how to accomplish immortality (or at least extfinish high-quality life ponderably), repair the mystery of consciousness or accomplish the far corners of the Universe, hibernation materializes as a potential opportunity, if not the only hope. From clinical applications to space travel, scientists, entrepreneurs, administermental agencies and even authorrs and artists turn to hibernation as a possible solution for our problems, those desires and anxieties we are unable to tackle with more down-to-earth approaches – or, at least, as a way to sleep thcimpolite them and wake up when skinnygs are going better.
Scientists now consent that hibernation can be of two charitables – a seasonal, multiday proset up suppression of metabolism, standardly lasting for months and occupying a excellent portion of an animal’s life, or else its shrink and milder create, a so-called daily torpor. The thirteen-lined ground squirrel (Ictidomys tridecemliorderlyus) is one standard example of a seasonal hibernator. When they notice timely signs of prosperter approaching, these squirrels get weight and originate lengthy burrows in the ground where they bravely drop sometime in October, not to see weightless aget until the chaseing March, at least. Relabelably, the body temperature of these animals during hibernation can descfinish to sub-zero cherishs, and heartbeats and respiration decrmitigate to a minuscule fraction of their standard rates. Not astonishing, then, that hibernation has been portrayd as a state in between life and death.
Hibernation epitomises what harmony with nature is about
One of the first lab studies of another ‘genuine’ hibernator, the Syrian hamster (Mesocricetus auratus), alerts that, in preparation for hibernation, the animals built a nest that ‘was almost invariably a attfinishbrimmingy made afunpartisan, so originateed that only the arched back of the animal materializeed above the shavings’; then they ‘curled in a safe ball, with the nose tucked beorderlyh the tail’. Their oxygen consumption and temperature would drop concurrently during the process of go ining hibernation, accomplishing their minimal cherishs 3-4 hours procrastinateedr. Djungarian hamsters (Phodopus sungorus), originating from southwest Siberia and northeast Kazakhstan, are instead an example of daily torpidators. When kept at about 6°C ambient temperature, the pelage, or fur, of these animals alters from grey-brown to white, and their body temperature descfinishs to about 20°C; these bouts of so-called ‘daily torpor’ typicassociate last for only a scant hours.
Hibernation epitomises what harmony with nature is about – it is expoundd, by and huge, by the amount and rate of swap of matter, energy and alertation between inside and outside. Among the key triggers for preparing to go in and go ining the state of hibernation are lowage, actual or noticed, of food and weightless. In response to a lowening day, some animals miss weight and others accumuprocrastinateed food stores, hiding from greedy competitors in secret places outside, or creating energy reserves wiskinny their own body – both to be used sparingly over the prosperter. They have to be very exact about this, as emerging too timely from hibernation to seek more food unbenevolents they may freeze or starve to death.
To test how animals deal with energy needs, scientists portrayed what they called a ‘labor for food’ experimental protocol, where laboratory mice were trained to run on a wheel to get morsels of food, one at a time. Animals kept up with the task well, but only to a certain point. When the experimgo ins made the task too needing, requiring too wonderful an effort, mice made a clever decision: instead of laboring, they chose to go in a state of torpor. Sloprosperg down materializeed to be a more economical strategy, and one that incrmitigated their chances of survival.
Sometimes, genuine-life adversity inadvertently becomes part of the experimental portray, as in the labor of Elsie Proctor, who undertook her study on hedgehogs during three prosperters before and after the Second World War. She disputed that: ‘In pre-war days the feeding of these animals was less difficult (we participated milk and eggs),’ which permited them to spendigate ‘whether an enough provide of recent food would procrastinate hibernation’. This was before it was uncovered that hedgehogs are in fact lactose inuncover-minded, and therefore feeding them with milk is not recommfinished, but, lo and behelderly, the better-nourished animals in this study were still able to persist lengthyer and brutaler prosperters by go ining into a lengthyer and proset uper torpor. The existing theory is that there is some sort of metabolic clock that watchs the energy status of the body, creating a signal that is then united with relevant environmental factors, such as temperature and weightless. When the time is right, the programme of go ining into hibernation or returning from it gets put into motion. Cltimely, the system must be very pliable, but it also originates it very frnimble. The alteration that was emerging over millennia materializes to lag behind the rapid alteration of Earth as a result of human evolution and the broadenment of novel and disruptive technologies. It is probably fair a ask of time before some species stop hibernating altogether.
Did our ancestors participate hibernation to persist thcimpolite the prosperter when it was freezing outside or food supplies dprosperdled? Or is the entire notion of hibernation joind to prosperter misconsgenuined, and we necessitate a novel and recent perspective? As we understand, there are tropical lemurs that can hibernate at high body temperatures, which proposes that being joind to prosperter is a contingent and unmeaningful feature of a much expansiveer phenomenon than the name proposes. Scientists now consent that animals hibernate not only to save energy or overprosperter freezing seasons, but as a way to deal with other environmental calamities. This may join savagefires, heatwaves, storms and perhaps even authentic calamitys on a cosmic scale, such as the meteorite collisions with Earth that wiped out the dinosaurs but spared minuscule primitive mammals that could well have persistd thanks to their gift of hibernating.
Paradoxicassociate, it materializes that we are too clever and technoreasonablely proceedd to hibernate
The applications of human hibernation in sci-fi were many and varied too – from time travel and protection from adverse conditions associated with space travel (eg, surviving excessive acceleration) to economic and wise profits (eg, shrinkd necessitate for oxygen and supplies for lengthy-haul interset upetary journeys) to more exotic applications (eg, a create of biofirearm to freeze the foe in time to temporarily incapacitate them). Animals participate hibernation for many of the same reasons. Some species go in hibernation before prosperter begins and return ‘back’ in the spring. Although they are experts in overprospertering, and all individuals of those species must have done it since the dawn of time, they may not even understand that prosperter exists. Hibernation allows them to time travel, to transcfinish time. Hibernating animals do not miss time, they get time, and, not astonishingly, prolonging evidence points to an intriguing association between the ability to hibernate and lengthyevity.
While many animals have mastered the ability to go in torpor, it’s someskinnyg that eludes us humans. Curiously, despite decades of research, human hibernation remains among the scant asks that still belengthy to both science and science fantasy. Is there someskinnyg one-of-a-kind about our nature that stops us from hibernating? Will we ever understand what it is appreciate to hibernate? Cltimely, being in torpor and being outside of it correacts to states that are worlds apart. In our daily life, we are trapped wiskinny a very skinny range of physioreasonable parameters, and unwidespreadly venture into other uninalertigentensions of existence, apart from sleep. This does not propose, though, that this is all we have. On the contrary, humans have always been relabelably inventive and inventive with esteem to changing their state of body and state of mind, for example by taking mind-altering medications, go ining a state of proset up meditation, or even willingly changing metabolic rates. While we could possibly discover a way to go in hibernation or a aappreciate state, we do not have an prompt or advisent necessitate to do so, as we have broadened, and perfected, other ways to deal with adversities. We can originate fire and electricity, can originate shelters and manufacture toasty closkinnyg, get food easily, and spfinish tremfinishous amounts of energy derived from outside sources to protect our own restricted provide. Paradoxicassociate, it materializes that we are too clever and technoreasonablely proceedd to hibernate – someskinnyg other creatures we ponder lower fair get for granted.
The possibility of hibernation in humans has always captivated us; we horriblely want it to be possible, and alludes of human hibernation or suspfinished animation of branch offent charitables are ubiquitous in the sci-fi genre – from Mary Shelley’s novel Frankenstein (1818) and Vlauninalertigentir Mayakovsky’s carry out The Bedbug (1929) to more recent novels appreciate Liu Cixin’s The Three-Body Problem (2008) or Hibernaculum (2023) by Anthony Doyle.
In the domain of scientific literature, there are descriptions of well-recorded, though ill-imagined, trys to transport about hibernation in humans. A search for ‘man-made hibernation’ on PubMed – the hugest database of biomedical and life sciences labor – discmisss a peculiar sadvise in the number of unveilations begining from the timely 1950s and fading around 10 years procrastinateedr. One person behind this effort was the French sadviseon Henri Laborit, who was seeing for ways to help his uncover-mindeds persist traumatic shock and was encouraged by the idea that animals materialize to be protected while in the state of hypometabolism. Hibernation therapy, or spropose hibernotherapy as the approach has been dubbed, was aimed at inducing a proset up administerion of the autonomic worried system, to grasp the response to injury at bay, as a way of helping the organism to heal. As the physician W J Kolff portrayd it in 1955:
Artificial hibernation trys to duplicate the metabolic state of the naturassociate hibernating animal which during prosperter sleep seems to be very resistant to solemn injury, including momentary arrest of the circulation, and to infection … Artificial hibernation set upes, for the time, a retrograde evolution that, in materializent situations, trys to duplicate the status of creatures less growd than man himself.
The key ingredient of the ‘lytic cocktail’, a concoction invented by Laborit to transport about déconnexion neurovégétative (autonomic disjoinion), was initiassociate a phenothiazine called promethazine, which was procrastinateedr swapd by chlorpromazine – a substance synthesised by the French company Rhône-Poulenc. Phenothiazines were originassociate broadened for dyeing in the textile industry; they first made their way into medicine via histology (where it was essential to dye tpublish samples to visualise their microscopic structures) and then as a medicine that was thought to be effective agetst pathogenic agents such as the malaria parasite.
‘Artificial hibernation’ was participated as an alternative to local anaesthesia for relatively mild procedures
Chlorpromazine is a relabelably promiscuous drug in the sense that it ties, and standardly blocks, a expansive variety of receptors for finishogenous neurobroadcastters and neuromodulators that arbitrate understanding effects and normassociate act to incrmitigate levels or neural activity and arousal. The expansive range of its effects encouraged a variety of trade names for chlorpromazine – from Largactil (‘acting expansively’) to Hibernal. This hibernation-inducing cocktail was not foreseeed to direct to a proset up loss of consciousness, but to originate what was called, rather upsettingly, a ‘pharmacodynamic lobotomy’, a state of excessive drowsiness, sedation and shrinkd behavioural responsiveness.
In standard, generassociate fit subjects, the effects of chlorpromazine were portrayd as chaseing:
[T]he subjects became drowsy, catalogless, tranquil and uncaring. Their countenances materializeed very pale. Their skin generassociate was toasty and parched but very pale rather than pink … The subjects subsequently grumbleed of a ambiguousised senseing of motor frailness, felt chilly and grumbleed of thirst.
According to Kolff’s description:
[A] uncover-minded who is worried, battling, disturbed, cyanotic, and griefful, becomes tranquil after induction of hibernation; he does not grumble about pain; he materializes to be sleeping but … he will react if you press on a broken leg or into a hurtful abdomen.
Artificial hibernation was set up to be effective in conditions when the uncover-minded was ‘beyond recovery’, Kolff authors, such as when medics watchd an unsuperviselable deterioration of condition, a descfinish in blood presconfident, convulsions or coma. However, with the prolonging well-understandnity of ‘man-made hibernation’, it was participated to supervise other less theatrical conditions and even as an alternative to local anaesthesia for relatively mild procedures, such as bronchosduplicate.
It is possible that mild hypothermia and shrinkd metabolic rates transport aboutd by the ‘lytic cocktail’ were an meaningful, if not the central, aspect of hibernotherapy. It is well understandn that hypothermia may help cope with a potential injury or offfinish, for example by dealing better with blood loss, inflammation, hypoxia or providing neuroprotection. However, the method of man-made hibernation did not persist for lengthy. There were two possible exset upations as to why this was so.
One is that it triggered some very vocal critics. In the article ‘Induced Hypothermia Is Not “Artificial Hibernation”’ (1966), the physician Alfred Hfinisherson reminded that:
A huge number of branch offences exist between a freezing homeotherm and a hibernating animal … [U]ntil man can apply clinical hypothermia in a manner resulting in the physioreasonable state simulating authentic hibernation, skilbrimmingy and acunderstandledgeably, he should refrain from deluding himself, the profession, and the laity by mislabelling his cryogenic science and sends with improper nomenclature.
The other possible reason is that the key drug participated to transport about man-made hibernation – chlorpromazine – became instead a paradigm-shifting neuroleptic. Neuroleptics are a class of medications participated to treat psychosis, and this uncovery shifted attention to other, more promising applications of the compound.
The conciseage of scientific theory behind the induction of man-made hibernation, and a necessitatey caring of the underlying biology, is probable an exset upation for the conciseage of proceed in this area. But, as scientists now get a more exact and pinsolentnt approach, meaningful uncoveries provide novel hope. In the past decades, our caring of the molecular mechanisms, physiology and neurophysiology of sleep and hibernation have incrmitigated theatricalassociate. Scientists have uncovered brain netlabors and distinct cell types that watch body energy stability and are essential for thermoregulation and metabolic supervise. By using conmomentary techniques, we can artificiassociate begin and finish a state aappreciate to torpor, at least in minuscule laboratory animals, but many asks remain.
For example – what is the relationship between hibernation and sleep? Recent research in cut offal hibernating species discmisss that animals standardly go in the state of hibernation via sleep, as if sleep were the gateway to the state of hibernation, being the first step towards hypometabolism. Where does sleep finish and hibernation commence? That’s not an effortless ask to answer definitively. The relationship between torpor and sleep remains necessitateyly understood and at best confusing, not least becaparticipate of a conciseage of clearly expoundd concepts in this area.
Hibernating animals materialize to be sleeping, yet we expound sleep using unambiguously brain- and behaviour-centric criteria, such as immobility, an liftd arousal threshelderly and characteristic brainwaves, while hibernation and torpor are expoundd based on metabolic criteria. Perhaps sleep has growd from more ‘primitive’ hypometabolic states, and the animal that goes from sleep to hibernation recapituprocrastinateeds that evolution in reverse? Can we perhaps even see sleep as an aborted create of hibernation, emerging when our ancestors lgeted to apply the shatter at the right moment, to remain in supervise of the bodily state rather than plunging into torpidity?
The pattern of brain activity during torpor proposes revertion to a primordial state of brain netlabors
Relabelably, the proset up lethargy associated with hibernation does not always unbenevolent that the organism is unresponsive and, as all researchers in the field understand from first-hand experience, noskinnyg is more disruptive to torpor than the necessitate to intrude with the animals, for example when accumulateing physioreasonable meaconfidents such as body temperature. The study in hamsters alludeed above portrays how easily it can be disrupted if the animal is supervised during that initial, frnimble state of captivate into torpor, resulting in shiftment, vocalisation and a rapid retoastying. Hibernating animals necessitate privacy, and the act of observing itself alters what is watchd. Non-intrusive ways of taking meaconfidentments from a hibernating animal are standardly the only strategy to get reliable data, which can be difficult, especiassociate in hibernating animals in the savage.
Very scant studies have seeed shutly at the brainwaves of a hibernating animal, so this is very much an uncover area of spendigation. Studies propose that, at relatively high temperatures, EEG readings of a hibernating animal see aappreciate to the patterns characteristic of sleep yet, as body temperature goes down, neural activity degrades to a low, proximately iso-electric level. Such a state is standardly standard for brain injury or proset up anaesthesia, also set up in pharmacoreasonablely transport aboutd hypothermia, when brain activity is characteelevated by a so-called ‘burst suppression’ – an alternation of increate periods of high neural activity with silence, a flat-line EEG chart. Other examples of this type of brain activity join an improlongn-up brain in preterm babies, neonate animals or even a neuronal culture in a dish. Intriguingly, the pattern of brain activity during torpor proposes revertion to a more primitive, primordial state of brain netlabors. It remains a bioreasonable paradox, as the body and the brain can be freezing during hibernation, with metabolic rates and neural activity being fair a fraction of their levels during standard wakefulness, yet someone is there who grasps the capacity to watch the environment, and reacts readily if disturbed. The ask naturassociate materializes of whether being in such a theatrical state has consequences for brain function?
One striking observation made decades ago is that hibernators do not stay continuously in hibernation, but ‘dehibernate’ at standard intervals, ranging from days to weeks. This has been showd first by the zoophysiologist Brian Barnes and colleagues who watched body temperature in Arctic ground squirrels (Spermophilus parryii): upon studying the animals’ hibernation history over the prosperter, the researchers uncovered periodicassociate occurring conspicuous spikes in body temperature. For fair some hours at a time, hibernating animals toasty up, which includes a tremfinishous amount of energy, and then go back down aget. Although we still don’t understand why this happens, it was acunderstandledged that, during those so-called ‘euthermic arousals’, animals spfinish ponderable time sleeping, directing to a inflammatory idea that they toasty up from hibernation in order to sleep, and then sink back into hibernation.
Even in minuscule torpidators, such as Djungarian hamsters, it was set up that, upon retoastying from daily torpor, animals join in proset up, fervent sleep, aappreciate to the state after sleep deprivation, as if they are weary from being in a torpid state and necessitate to catch up on some actual sleep. Why this is so remains a mystery, but one idea is that hibernation results in some sort of metabolic or synaptic imstability that necessitates sleep for recuperation.
A number of meaningful asks stem from this notion, such as whether and how hibernating animals grasp their memories after repeated cycling into this theatrical state of metabolic depression, associated with a shatterdown of synaptic netlabors. One study in European ground squirrels (Spermophilus cialertus) showed that these animals still reassemble their understandn conparticulars, as meaconfidentd with a social-recognition memory test after they spent many months in a state of hibernation. It materializes that what is truly meaningful is protected from forgetting. While this is certainly promising for the prospect of inducing hibernation protectedly in humans for lengthy-haul space travel, scientists count on that we could also harness this extraordinary state for caring, and perhaps curing, brain disorders. Perhaps hibernation will one day be participated as a unbenevolents to reset abstandard modes of brain activity or bodily dyshomeostasis for thesexual attackutic purposes.
It is lureing to contrast the process of go ining into and returning from hibernation with a process of dying and rebirth and, perhaps unastonishingly, some scientists commence to elicit this metaphor when describing torpor. I already alludeed the timely definition of hibernation, which was seeed as a state between life and death, and perhaps it is beneficial to return to this definition. Defining the boundary between being ainhabit and dead was never an exact science, and the shutness of hibernation to death – perhaps the shutst an organism can ever get while remaining ainhabit – is among the most fascinating of its aspects. Breaskinnyg and heart rate can decrmitigate to being proximate-nondistinguishable, the body can become freezing and stiff in proset up hibernation, and brain activity can be proximately absent.
Yet the state of hibernation defies death, it permits the organism to exist in another uninalertigentension, a sort of death-appreciate deathlessness. Life is expoundd by the organism being there, seeing and senseing the world, changing its environment, reproducing and leaving the pursue of its existence behind. Hibernation is exactly the opposite – it is a exit of absence, fadeing from the world, shrinking to nonexistence in a understandn sense, losing autonomy, relinquishing agency, not resisting the environment but blfinishing into it. Paradoxicassociate, this helps to escape the adversities of brutal truth – by doing noskinnyg and by annihilating an individual’s characteristics. The less is left from a living, conscious, behaving organism, the more proset up and finish, and therefore more ‘effective’, the state of hibernation is.
Animals discover a way to ‘escape’ by go ining a branch offent uninalertigentension of existence – their physiology sluggishs down
Naturassociate, we are envious that so many creatures, huge and minuscule, around us have mastered and perfected the send of hibernation, which still escapes our caring. Is it becaparticipate we are too obsessed with trying to originate sense of what we can see and meaconfident, rather than noticing what is not there as its essential feature? Our efforts to understand hibernation go agetst its entire idea – to fade, to disjoin, to stop time, to become one with the world. Is this why caring hibernation eludes us?
Consider this example: when menaceened, some animals go in a peculiar state called freezing, which is an excessive version of the fight-or-fweightless response, when it is pointless to fight and there’s nowhere to fly in the physical, 3D space. Instead, animals discover a way to ‘escape’ by go ining a branch offent uninalertigentension of existence – they don’t mecount on stop moving, but their physiology sluggishs down, making them less apparent. Many living organisms participate a strategy of assuming a phony identity, becoming someone else, called mimicry – for example, to deceive their enemies, they pretfinish to be hugeger or more hazardous than they are in truth.
The other create of mimicry is pretfinishing to not be there at all, or carry outing dead, such as in the case of thanatosis. Could hibernation be understood as an elucidate, and rather excessive, create of mimicry – a state when the organism doesn’t spropose pretfinish to be dead, but undergoes a proset up alteration, blurring the boundary between life and death, in order to persist? Better caring of the bioreasonable unbenevolenting of hibernation, and how it reprocrastinateeds to other states of being and modes of existence, is essential before we can originate concrete proceed in inducing man-made hibernation in humans. What if, proset up down, humans always knovel how to hibernate, and when conditions are right, and when it comes to the point when alternative ways to proceed existing are unimaginable, we can transport back to life this forgotten ancestral memory, and go in hibernation in our own, human way?
