Vladyslav Vyazovskiy, Associate professor of neuroscience, University of Oxford
On cold, dark days it is tempting to imagine shutting yourself away until the warmer weather returns. Many animals do just that by entering a state known as torpor, which reduces their bodily functions to a minimum and uses fat stores in their body for energy. Could humans ever hibernate in the same way?
Aside from providing a convenient way to avoid winter, one reason to find out might be the advent of long-distance space travel. A journey to our nearest planet Mars would take around eight months using current technology. If we one day hope to visit another star system, even if we could travel at the speed of light, the journey would take years. Being able to go into a state of long-term torpor would make such distances considerably less tedious for the astronauts and conserve vital resources.
As a neuroscientist, I am currently part of a team of experts organised by the European Space Agency to work out whether and how we might be able to put humans into a state of stasis. It’s still an open question but, at least in theory, we can’t exclude that it might be possible.
Body temperature and metabolism
When and for how long animals enter torpor can vary hugely, from many months of the year, to just a few hours a day over a period of a few months. Some animals, such as mice and hummingbirds, enter a state of torpor on a daily basis if they need to save energy. Others, such as hedgehogs and bears, go into prolonged periods of torpor, usually during the winter (this is what we call hibernation). Those species that go into torpor every year, even if the conditions outside are stable, are called obligatory hibernators.
The fact that large mammals such as bears and even primates, such as the fat-tailed dwarf lemur of Madagascar, can hibernate means that theoretically humans aren’t too big or energy-hungry to enter torpor. Nor does our evolutionary origin prevent us from doing so, as hibernating animals have been found widely across all types of mammal.
Controlled hypothermia and metabolism are already widely used in clinical practice, such as during cardiac surgery and to protect tissues from damage when blood flow is reduced, such as after a stroke. Lowering body temperature and metabolism mean cells need less oxygen, enabling their survival in conditions when oxygen cannot be delivered. This process of artificial cooling in humans appears similar to spontaneous torpor in animals in that it includes reduced breathing, heart rate and metabolism. But the key difference is that animals seems to “know” the way to safely and spontaneously enter torpor. Lowering a human’s body temperature by blocking their natural thermoregulation requires the aggressive use of drugs.
One of the difficulties with replicating torpor is that we don’t really know how animals start and maintain the process. Much research has been devoted to investigating it but few conclusive answers have been obtained so far. On the one hand, it’s possible that torpor is triggered in a “bottom up” fashion, starting with changes occurring in individual cells of the body at a molecular level. But a “top down” approach that involves signals from the nervous system or hormones may also play a role.
Protecting the brain
There’s another key issue with the idea of human hibernation, and that’s what it might do to the brain. Animal hibernators regularly come out of torpor for a period of hours or days but often spend that time asleep, before returning to hibernation Similarly, animals emerging from daily torpor also usually enter a deep sleep.
This has led some scientists to suggest that, although we tend to think of hibernation as being like a long sleep, torpor actually creates a sleep-deprived state and the animals need to regularly compensate for this. We can see this in the way animals’ brainwave patterns are similar when they emerge from torpor to when they have been sleep deprived.
This maybe because the low metabolism and body temperature of torpor are associated with activity in those brain regions, which are typically associated with sleep regulation. But it may also be because torpor changes the brain in a way that could damage it if it wasn’t restored by the mechanisms of sleep. The brain is highly sensitive to a lack of oxygen and so needs to be protected during the time when blood and nutrients supply is reduced.
Another way that torpor affects the brain is by reducing and reorganising the synaptic connections that are the basis of our memories. Research in animals such as bats shows that most memories are preserved even after many months in a state of almost complete neuronal depression. But some memories seem to be taken better care of than others, such as the ability to remember close kin. So if we wanted to induce human hibernation it would be vitally important to investigate further how memories are retained over a long period of torpor.
While we’re still unsure whether safe prolonged human hibernation is possible, research looking at potential mechanisms may provide the novel insights needed for this to become a reality. Recent technological advances and new pharmacological and genetic tools have already shown great potential to induce or manipulate sleep. But to fully understand how we could safely induce human hibernation, we will likely need to dissect key brain circuits and identify the key molecular pathways that regulate our sleep functions.
This article was originally published on The Conversation. Read the original article.
If humans and other animals were living in the same environment, why didn’t other animals evolve like us? – Sami, aged 13, London, UK
This is a brilliant question. Humans have evolved differently to other animals. We have much bigger brains relative to body size and in absolute size than other mammals, and have a level of intelligence that other animals don’t.
There are many advantages to intelligence, such as the ability to plan and cooperate, innovate new techniques and share information about what works.
The reason that living things evolve certain features, like stripes on a tiger, bright colours on a butterfly or a big brain in humans, is that these features have benefits that help them survive. The living things with these beneficial features then pass them on to their offspring.
There are a number of hypotheses – ideas – about the origins of human intelligence. The one I do my research work on is called biocultural reproduction.
Having big brains allows humans to keep more babies alive than other animals. According to the biocultural reproduction hypothesis, how intelligence helps us to keep babies alive comes down to how we care for each other – and especially how we look after children.
Helping each other
Many animals live in small or large social groups, and some social species of birds and mammals, such as meerkats, help each other to feed and protect their babies. This is called cooperative breeding. The helper animals don’t have any babies of their own. They give up their own reproduction to assist a dominant family member, such as their mother or older sister.
People are different. Anyone who wants to and is able to have a baby can do so. Not all human parents can or will care for their own babies, but other people often take care of the children of others.
Parents and other carers may invest in young people for many years, sometimes for all their life. I am a parent and I continue to help my grown-up offspring, and their offspring – my grandchildren. This helping is what scientists call biocultural reproduction.
The carers may be genetically related to the child they look after, but they also may not be. The rules for how people care for each other are not set by genes, but by the names we give each other. These are not names like Sami or Barry, but things like “daughter”, “auntie”, “grandfather”, “cousin” or “friend”.
Using names like these requires symbolic language. This means that the names we call each other represent ideas about how we should treat each other. Only humans and some of our ancestors evolved this kind of symbolic communication.
We might call our friends “sister”, “brother” or “cousin”. In many human societies, younger people refer to older people they are not genetically related to as “auntie” or “uncle”. Some religious leaders are called “father”, “mother” or “sister”. These names are used as a sign of respect and also give us information about our relationships with these people.
Big brains needed
This naming thing that people do is complicated. Big-brained intelligence is needed to remember all the names and the lifelong history of interactions that we have with family and friends.
Our closest biological cousins, such as chimpanzees, have brains only one-third the size of ours. They do not use symbolic language or call each other by names. Mother chimpanzees care for their own infants and no other chimps help, not even fathers or grandparents. Only one-third of chimpanzee babies survive to adulthood.
In contrast, the wide range of people who provide care – including feeding, care when ill, education, money and love – means that human babies are more likely to survive and thrive. Big-brained intelligence helps us care for each other and helps to explain, in part, why the human population is approaching eight billion people.
If so, you’ll be interested in our free daily newsletter. It’s filled with the insights of academic experts, written so that everyone can understand what’s going on in the world. With the latest scientific discoveries, thoughtful analysis on political issues and research-based life tips, each email is filled with articles that will inform you and often intrigue you.
Editor and General Manager
Find peace of mind, and the facts, with experts. Add evidence-based articles to your news digest. No uninformed commentariat. Just experts. 90,000 of them have written for us. They trust us. Give it a go.
If you found the article you just read to be insightful, you’ll be interested in our free daily newsletter. It’s filled with the insights of academic experts, written so that everyone can understand what’s going on in the world. Each newsletter has articles that will inform and intrigue you.
Comment on this article