Published: May 5, 2016
A recent study has found that Australian bearded dragons may sleep like humans do. Researchers at the Max Planck Institute for Brain Research in Germany studied Pogona vitticeps, Australian bearded dragons (a species of lizard), and found brainwave patterns that mirrored those of mammals (including humans) and birds.
When mammals and birds sleep their brains alternate between two states: rapid eye movement (REM) sleep and slow-wave sleep. During slow-wave sleep, brain waves (electrical impulses in the brain) are synchronized, but during REM sleep, the brain is very active. During this time, the eyes move rapidly (hence the name of the sleep state) and the brain generates high-frequency waves.
It has long been thought that reptiles do not experience sleep in the same way that mammals and birds do. The researchers who discovered the interesting new trend about the lizards’ sleep habits did not originally plan to study sleep. They were studying how the lizards used visual information to chase treats. Part of their study involved continuous observation of the dragons’ brain waves with electrodes. However, the pattern of brain waves at night fascinated the researchers, who decided to study it further.
They saw evidence that the dragons experienced a two-state sleep. For short periods, the dragons’ brains exhibited brain waves at a slow frequency. This sleep state was followed by one in which the dragon’s brain exhibited brain waves at a much higher frequency. Each period was short, only about 80 seconds, compared to the 90 minute sleep cycle in humans. Researchers also used an infrared camera to observe the eye motions of the lizards during sleep. They observed the characteristic eye-twitching movements representative of REM sleep.
Such results were replicated across multiple lizards across several weeks and have important implications. It was thought that only mammals and birds experienced a two-state sleep and that this sleep pattern evolved after the mammals and birds diverged from reptiles. However, this new evidence suggests that the sleep pattern evolved in a common ancestor of mammals, birds and reptiles. The results also suggest that there is an unknown component of sleep that is important to all animals.
Scientists have pointed out that more evidence is required to confirm the sleeping patterns of dragons. It is possible that the dragons were awake but immobile when the researchers studied them. However, the researchers noted that the lizards exhibited other physiological signs of sleep including a low heart rate, and they could be moved without waking them up.
Despite some doubts, researchers are excited by the possibility that the dragons do experience sleep cycles. By studying these cycles, researchers can learn more about sleep in different animals including humans.
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