A recent study published on Thursday, which involved 5 Australian bearded dragons, determined that this lizards may sleep and dream as birds, people and other mammals do. This discovery could establish an important discussion about the evolution of sleep.

The team from a German laboratory documented for the first time that reptiles experienced rapid eye movement (REM) and another sleep stage called slow-wave sleep that was just known to be present in a few animals, as reported by Reuters.

Eastern Bearded Dragon (Pogona barbata), Victoria, Australia. Credit: Wikipedia/jjron

REM sleep normally occurs when dreams are present in the subconscious, and this is the reason that let scientists believe the possibility for lizards to dream, something that has been previously suspected by common non-scientific lizard pet owners but not officially confirm.

“If you forced me to speculate and to use a loose definition of dreaming, I would speculate that those dreams are about recent notable events: insects, maybe a place where there are good insects, an aggressive male in the next terrarium,” said Gilles Laurent, director of the Max Planck Institute for Brain Research in Germany.

For the study published in the journal Science, researchers placed probes inside the lizard’s brain to measure electrophysiological activity during sleep. They found that while people often experience four or five long slow wave and REM sleep cycles nightly, the 5 tested lizards experienced on average 350 80-second-long cycles.

An evolutionary timeline

This discovery of the sleep in lizards suggested that the sleep traits known in the mammals emerged far earlier than previously suspected in the common evolutionary ancestor of the groups. Gyorgy Buzsaki, a professor of neural sciences at New York University, said that the findings were evidence of an early evolutionary timeline for stage sleep.

However, according to Matthew Wilson, a professor of neuroscience at M.I.T. who has studied sleep and learning, it is possible in an evolutionary sense that there might be a deep, common mode of off-line procession that got elaborated and refined in these other vertebrate systems like mammals, expanding into the hippocampus, as reported by the New York Times.

Source: Science