Scientists Reveal Why Cats Always Sleep on Their Left Side
Many cats appear to favor resting on their left side, according to a recent study conducted by an international team of researchers. The group reviewed several hundred YouTube videos featuring cats in side-sleeping positions, the journal Current Biology reported.
They propose that this side-sleeping preference may have evolved as a survival mechanism, enhancing the animal’s ability to hunt or flee quickly after waking.
The study was carried out by scientists from the University of Bari Aldo Moro (Italy), Ruhr University Bochum, Medical School Hamburg, and collaborators from Germany, Canada, Switzerland, and Turkey.
Because sleep is a period of heightened vulnerability for all animals, cats tend to sleep between 12 and 16 hours a day in elevated locations where threats from below are less likely. Curious about whether felines display a preference for sleeping on one side over the other, Dr. Sevim Isparta of the Animal Physiology and Behaviour Research Unit in Bari and Professor Onur Güntürkün of the Biopsychology group at Bochum launched the investigation.
“Asymmetries in behavior can have advantages because both hemispheres of the brain specialize in different tasks,” explains Güntürkün.
The researchers examined 408 publicly available YouTube videos that showed a single cat lying on one side with its full body visible for a minimum of ten seconds. To maintain accuracy, they only included unaltered footage, excluding any content that had been edited or mirrored. Their analysis revealed that approximately two-thirds of the cats were sleeping on their left side.
The explanation: Cats that sleep on their left side perceive their surroundings upon awakening with their left visual field, which is processed in the right hemisphere of the brain. This hemisphere is specialized in spatial awareness, the processing of threats, and the coordination of rapid escape movements. If a cat sleeps on its left shoulder and wakes up, visual information about predators or prey goes directly to the right hemisphere of the brain, which is best in processing them.
“Sleeping on the left side can therefore be a survival strategy,” the researchers conclude.
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