A group of scientists from the Sleep Team at the Lyon Neuroscience Research Center in France has concluded that lizards dream just like we do and that they also have two sleep states which is something they have in common with humans, birds, and mammals.
As Science Daily reports, these new findings have reaffirmed the conclusions of a 2016 study that was conducted on bearded dragons (Pogona vitticeps) while also tackling a whole new sleep investigation on a lizard that is known as an Argentine tegu (Salvator merianae) and coming up with the same results.
When we sleep at night, our bodies perform a myriad of different functions. These include temperature regulation, hormone production, giving us more energy stores for later, taking knowledge that has been amassed and consolidating it, and also removing metabolic waste from our brains. But up until fairly recently, scientists had only thought that birds and land mammals went through this process during their two sleep states.
These sleep states are known as slow-wave sleep and REM, and it is in REM, also known as paradoxical sleep, in which we dream. The previous study that was conducted on the bearded dragon showed that this lizard, like us, was also able to dream and exhibited two sleep states. It was suggested that these sleep states may have originally been present in an ancestor of both reptiles and mammals, with this common ancestor having lived perhaps 350 million years ago.
Do lizards dream like us? Two species of lizard exhibit two sleep states, just like humans, other mammals, and birds.— UAR: Animal Research (@animalresearch) October 11, 2018
PLOS Biology, 11 October 2018. DOI: 10.1371/journal.pbio.2005982 pic.twitter.com/3Okd09dnes
To corroborate the findings of the 2016 study on the bearded dragon, scientists conducted the entirety of the sleep experiment on the lizard all over again and after reaching the same conclusion as the previous study, looked more closely at the Argentine tegu to see if it too would exhibit two sleep states. Scientists from the Sleep Team found that this lizard also entered slow-wave and REM sleep and had dreams just like the bearded dragon, and determined that dreaming is something that lizards clearly have in common with humans, birds, and other mammals.
However, scientists were quick to point out that they did notice some differences in the sleep states of the lizards when compared with mammals and birds. Further, even the two lizards were found to have these differences also.
When humans enter REM sleep and dream, scans show that ocular and cerebral activity is markedly close to how it is when they are awake. But the REM state that the lizards entered was associated with very slow eye movement, unlike humans, and the Argentine tegu’s cerebral activity was not at all similar to how it was when it was awake. So while the findings show that lizards do indeed have two separate sleep states, these appear to be slightly different than ours.
The new study which reaffirms that lizards dream and enter two different sleep states has been published in PLOS Biology.