There's a lot of information around about what happens when humans sleep, from rapid eye movements (REM) to dreaming. But the research involving the electrophysiological characteristics of sleep has mostly been limited to mammals and invertebrates.
Now, the lizard is having its time in the spotlight; interestingly, their sleep patterns are similar to humans. According to researchers from the Max Planck Institute for Brain Research in Frankfurt, Germany, the Australian dragon Pogona vitticeps exhibits sleep patterns that are very similar to humans, right on down to the fact that they too, experience REM.
The findings were published in the journal Science under the title, "Slow waves, sharp waves, ripples, and REM in sleeping dragons." It states the following:
Most animal species sleep, from invertebrates to primates. However, neuroscientists have until now only actively recorded the sleeping brains of birds and mammals. Shein-Idelson et al. now describe the electrophysiological hallmarks of sleep in reptiles. Recordings from the brains of Australian dragons revealed the typical features of slow-wave sleep and rapid eye movement (REM) sleep.
So, what does that really mean? Science states that, "These findings indicate that the brainstem circuits responsible for slow-wave and REM sleep are not only very ancient but were already involved in sleep dynamics in reptiles."
Yes indeed, it looks as though our sleep patterns may have evolved from reptiles upwards of 320 million years ago.
Now, before we get too excited about this finding, it should be noted that the sleep cycles between humans and lizards are not precisely the same. Humans usually experience about four or five 90-minute cycles of slow-wave (SW) sleep and REMs. In contrast, the lizard sleep rhythm is faster and more regular; they have hundreds of shorter cycles.
The Science abstract provides elaboration on these cycles:
Recording from the brain of a lizard, the Australian dragon Pogona vitticeps, we identified SW and REM sleep patterns, thus pushing back the probable evolution of these dynamics at least to the emergence of amniotes. The SW and REM sleep patterns that we observed in lizards oscillated continuously for 6 to 10 hours with a period of 80 seconds.
As the importance of sleep continues to remain an essential factor in overall health and well-being, it's necessary to stay on top of emerging information that comes from studies like this. The more that's discovered and shared, the more we can understand, and appreciate, the pivotal role of sleep in our lives.
This particular study brings us closer to how sleep evolved. "The data and analysis are very compelling and suggest an ancient origin of the two alternating stages of sleep, REM and slow-wave sleep," says Thanos Siapas. The professor of computation and neural systems at Caltech, California, who was not involved in the research, says that "comparing the circuit mechanisms and role of these network events across species may provide critical new insights into their function."