Sleep is a phenomenon that is observed across nearly all organisms within the animal kingdom, ranging from mammals to flight-based organisms such as canaries and eagles; this bodily state serves an essential role in the preservation of the body in manners such as replenishing hormones and energy used up throughout the day as well as the storing of memories that have been processed throughout the previous day. Additionally, REM sleep allows for a regulation of body temperature and the systematic removal of waste from the brain. In humans, this bodily state is often broken down into two main sub-states: slow wave sleep, a primitive and initial state of rest, and REM sleep, a more vivid and active state of sleeping often identified by rapid eye movements and increased cerebral activity. REM sleep is often associated with dreaming, a phenomenon that is experienced by nearly all of humanity every night.
Up until recent discovery, REM sleep was thought to be a sleep stage exhibited only by humans and a select few other species; however, recent research conducted at the Lyon Neuroscience Research Center has disproved this statement entirely. Through prior experimentation done on the bearded dragon as well as new studies on the sleep habits of the Argentine tegu, researchers have been able to confidently establish that many lizards exhibit the exclusive and dream-inducing REM sleep that was previously believed to be limited mostly to humans. Replicating sleep studies done in 2016 on the bearded dragon and applying similar studies to the Argentine tegu, a noticeably different lizard, revealed to the French researchers brain activity that closely mirrors that of humans that are actively undergoing slow wave and REM sleep. This profound set of data not only presents the possibility that REM sleep is present in more species of animals than was previously believed, but also suggests to researchers that lizards and humans shared a common ancestor as soon as 250 million years ago, noticeably sooner than previously believed.
A pair of Argentine tegus as seen in their natural habitat.
Image from Wikimedia Commons
More specific to lizard species such as the Argentine tegu and the bearded dragon, eye movement and cerebral activity observed in sleep studies strongly contrasts behaviors observed in these lizards while they were fully conscious and awake; while sleeping, bearded dragons and Argentine tegu displayed low eye movement and low cerebral activity, strongly opposing the normal behaviors exhibited in conscious tegus and bearded dragons. This contrast in brain behavior and ocular activity between sleep and consciousness is a new phenomenon when compared to sleeping humans; while humans undergo REM cycles in their sleep, brain activity and eye movement is often observed to be on par with (and in some cases surpassing) normal cerebral and ocular activity observed while the subject is awake and functioning completely. This suggests that REM cycles, while now known to be present in more animals than previously thought, is individualized and unique to many different species in terms of ways in which the sleep cycle can be identified. This may provide an explanation for why scientists have previously failed to identify distinct sleep cycles in other species prior to recent studies: those conducting experimentation and research on sleep in other animals were looking for indicators of REM found in humans, such as rapid eye movement, rather than unique indicators of separate sleeping stages like those found in the Argentine tegu.
A pair of bearded dragons in a
domesticated and controlled environment.
Image from Wikimedia Commons
These studies allow researchers to delve deeper into the possibility of REM sleep being a universal state shared by countless numbers of members of the animal kingdom, possibly shared through a common ancestor as soon as 250 million years ago. Furthermore, researchers now have a more dynamic and complex understanding of REM sleep that can be applied to studies of human sleep cycles themselves; perhaps human sleep is more complex than two basic sleep cycles, with what is referred to as REM sleep in humans representing more than one sleep cycle in and of itself, for example. Unfortunately, this research may take anywhere from a short few years to literal decades to transpire, and even more time for this new research to have any significant impact in modern society outside of the scientific community. In any case, we now know that lizards dream like us. But who knows? Maybe one day we’ll have completely mapped and discovered all that there is to know about lizards. Maybe they can talk like humans, too…