Lateralized sleeping positions in domestic cats.

Both vertebrates and invertebrates show a multitude of left-right asymmetries of brains and behaviors¹. For example, cats, dogs, and many other species have a preferred paw when handling food². But why should humans and other animals have lateralized brains? Based on a large comparative approach¹, it is likely that asymmetries serve several purposes. First, by specializing on one limb or one side of its sensory system, the contralateral hemisphere goes through life-long cycles of motor and perceptual learning, thereby increasing the speed of processing and motor efficacy, decreasing reaction time, and enhancing discrimination ability. Second, by having two complementary, specialized hemispheres, neural processes are computed in parallel, thereby reducing cognitive redundancy¹. For example, the right hemisphere excels in processing threat-related stimuli, providing the left visual field an advantage in reacting to a predator approaching from the left³. Here, we report that two-thirds of cats prefer a leftward sleeping position, giving their left visual field and thus their right brain half a privileged view of approaching animals without being obstructed by their own body. VIDEO ABSTRACT.