The science of sleep

The recent birth of my first baby has inevitably got me thinking about sleep.

Since I have spent the past couple of weeks away from Robson & Prescott, I don’t have much news worthy of reporting in a column about the life of a vet. So I thought I’d have a look into the subject of sleep.

Apparently, a human baby can sleep 16 hours a day. On the past three weeks’ evidence, this sounds unlikely to me. This (mythical) figure puts them alongside lemurs in the animal kingdom.

While I’ve been discovering why sleep deprivation is a form of torture, it’s not been especially comforting to discover during the preparation of this missive that there are many animals that happily spend more than 80 per cent of their time asleep.

Giraffes, for example, enjoy only about 30 minutes a day of deep sleep split into several separate sessions. Conversely, brown bats average close to 20 hours a day.

Most mammal species need significantly more sleep when they’re young, although baby orcas and baby bottlenose dolphins appear to not sleep at all during the first few months of life, which makes me feel a bit better.

Sleep might seem pretty simple, but scientists are still scratching their heads over questions surrounding this slumbering state. It’s unclear exactly why organisms need to sleep, let alone whether every last species actually settles down for a good kip. Defining sleep itself isn’t all that straightforward, but it’s typically said to be a reduction in physical activity and a decreased response to outside stimuli.

Sleeping creatures often assume a customary posture – whether that’s lying down for people, hanging upside down for bats, or standing up, as is sometimes the case for horses, giraffes and elephants.

Sleep is also easily reversible, meaning it’s a relatively simple matter to wake up, specially when compared to other states along the continuum of reduced consciousness, such as hibernation or coma.

There are examples of animals that can disrupt their normal sleeping patterns for certain events, such as migratory birds which can survive with significantly less sleep during migration without building up any sleep debt. Some have been shown to take extremely brief power naps of just a few seconds, sometimes using a special ‘unihemispheric’ sleep to remain semi-alert to their surroundings.

During this sleep, which is also practised by some marine mammals like whales and dolphins, half the brain powers down while the other half remains ready for action. Now that’s a trick I’d like to learn!

Fish and amphibians are among the creature types for whom it’s still a little unclear whether actual sleep occurs, or if they’re simply exhibiting signs that suggest a resting state. Insects, on the other hand, do set aside time to slumber.

At the top of the tree, often quite literally, are koalas – probably the sleepiest animals in the world. Living entirely on eucalyptus trees, whose leaves have incredibly low nutritional value, they sleep for an astonishing 22 hours a day. When awake, they spend quality time only on eating.

Right now, the life of a koala (or my own cats for that matter, who survive on a comparatively pathetic 14 hours sleep a day) seems enormously appealing.

In fact, I’d even settle for a hectic weekend on call.

Sam Prescott,

Director and Senior Vet