Why is it that cats prefer to sleep on one side? I’ve said it before, and I’ll keep saying it again and again and again: who knows why cats do anything? Just over the course of today, my cat purred at me, bristled at me and attacked a paperclip as if it had offended her honour.
Putting this fundamental truth to one side, recent research published in Current Biology suggests that cats have a preference for sleeping on their left side. Of course, they do. That’s exactly the sort of contrary, counterintuitive stunt that cats would pull.
Only, there could actually be a good reason for it. Cats sleep. A lot. And people like taking films of them. A lot. So, there’s no shortage of sleeping cat videos on YouTube. Taking advantage of this fact, researchers from Europe and Canada analysed 408 films of sleeping cats, and found that in two-thirds of them, the left side was favoured.
Lots of animals have a consistent preference for one side of the body. This is known as behavioural lateralisation. Most people, for example, are right-handed, while most kangaroos are left-handed. Asian elephants often have a preferred forefoot and also, a preferred direction of trunk curl.
Brains are also lateralised, physically and to some degree, functionally. Vertebrate brains have a left and a right side (known as hemispheres), which work together but have their own specialisations.
This is more nuanced than the popular idea of the ‘creative right brain’ and ‘logical left brain’. But in humans, the left hemisphere does play a dominant role in processing language, while the right hemisphere plays a dominant role in processing shapes.
Nerve fibres travelling from the brain to the body have to physically cross over at the base of the brain. For this reason, the right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body.
So, when cats wake up from a lefty-biased slumber, they see a left visual field of view that‘s processed by the right side of the brain. In cats, this hemisphere is specialised in spatial awareness, processing threats and the coordination of rapid escape movements.
Domestic moggies may sleep on our radiators, but their ancestors slept in the wild, where their survival depended on the ability to quickly dodge danger when they woke. Sleeping on their left side, to activate the right hemisphere on waking, therefore makes sense as a potential survival strategy.
Domestic cats may have inherited this behaviour. Although they’re less likely to get pounced on by a coyote, there’s still danger out there. Just think of how many cats you’ve seen snoozing in the middle of the road.
But there’s another reason why cats may favour their left side for snoozing. According to the study’s authors, the right hemisphere not only reacts faster to threats, but it also reacts faster to emotionally arousing objects, such as toys, potential fast-moving prey and food. All of this could help to explain how my cat switches from being dead to the world to scarfing down her breakfast in less than the blink of an eye.
This article is an answer to the question (asked by Natasha Rita, Truro) 'Why do cats prefer to sleep on their left?'
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