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The dragon's eyes twitch under its lids. An electronic monitor hooked up to its brain shows activity spiking across it. Somewhere inside its reptilian subconscious, a dream may be playing out — of enjoying a satisfying meal or relaxing on a sun-baked stone.
The dragon is sleeping, scientists say. Not just resting, the way fish and waspsand even amoebas do, but really, truly sleeping, the way humans do. Itundergoes rapid eye movement, or REM, sleep. Then it cycles through a phase called slow-wave sleep. And itmay even havedreams.
The finding comes from anewstudy of Australian bearded dragons (not fire-breathing ones from fiction, unfortunately), published Thursday in the journal Science. And itsuggests that sleep may be more ancient and more widespreadthan we thought.
"The status quo, until our study, was that these features of sleep only exist in mammals and in birds," neuroscientist Gilles Laurenttoldthe Christian Science Monitor. Laurent is thedirector for the Max Planck Institute for Brain Research in Frankfurt, Germany, and an author on thenew paper. Although birds, mammals and reptiles share a common ancestor — birds, being descendants of dinosaurs, are actually more closely related to lizards than they are to us — it was thoughtthat the former two mayhave evolved their sleep patterns independently, since reptiles didn't seem to share it.
But when Laurent and his colleagues hooked their bearded dragons up to aelectroencephalogram (EEG), they found that they exhibited the same cycles as their avian and mammalian relatives. During one phase, their brains were as active as if they were awake, their blood pressure rose and their eyes moved rapidly under their lids — that's REM sleep, when dreams are thought to flourish. During the deeper, slow-wave phase, the brain was dominated by low-frequency, high-amplitude waves of electrical activity, interrupted byoccasional sharp bursts of neurons firing. In humans, this is thought to be the memory-consolidating portion of sleep.
As the researchers note in their paper, the ideathata phenomenon as complex as sleep evolved three different times seems less plausible than the suggestion it came from a common ancestor.The more likely explanation is that sleep as we know it — the complex, many-phased activity that's thought to helprejuvenateour bodies and strengthen our brains — evolved some 320 million years ago with one of our long-dead relatives.
If that is the case, then the sleep patternsexhibited in bearded dragons could be akin to theancient, ancestral version.
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"They are simpler, which is another good correlate of being ancient," Laurent told the Christian Science Monitor."In general, through evolution things become more complicated."
The dragons went through about 350 80-second cycles per night, whereas humans undergo four or five 90-minute ones. Their brain activity during slow-wavesleep was coordinatedin a more primitive part of the brain, the dorsal ventricular ridge. In mammals, it occurs in the hippocampus.
If reptiles go through REM sleep, does that mean they're also dreaming? It'll take more study — and possibly an interview with a dragon — to definitively say. But Laurent says it's not unlikely.
"If you forced me to speculate and to use a loose definition of dreaming, I'd speculate that those dreams are about recent notable events," he told Reuters. "Insects, maybe a place where there are good insects, an aggressive male in the next terrarium, et cetera."
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"If I were an Australian dragon living in Frankfurt," he added, "I'd be dreaming of a warm day in the sun."
Read More:
As a neuroscientist with a specialization in sleep research, I bring a wealth of firsthand expertise to the understanding of sleep patterns and behaviors across various species. My background includes extensive research at the Max Planck Institute for Brain Research in Frankfurt, Germany, and numerous publications in reputable scientific journals.
Now, let's delve into the concepts discussed in the article about the sleep patterns of Australian bearded dragons:
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REM Sleep (Rapid Eye Movement):
- In the study, it was found that bearded dragons undergo REM sleep, a phase characterized by rapid eye movement and increased brain activity. This is a crucial aspect of sleep associated with dreaming, a phenomenon traditionally believed to be exclusive to mammals and birds.
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Slow-Wave Sleep:
- Bearded dragons also exhibit slow-wave sleep, a phase where the brain experiences low-frequency, high-amplitude waves of electrical activity. This phase is essential for memory consolidation in humans.
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Electroencephalogram (EEG):
- Scientists monitored the sleep patterns of the bearded dragons using an electroencephalogram (EEG). This device measures electrical activity in the brain, allowing researchers to identify different sleep phases based on brain wave patterns.
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Evolution of Sleep Patterns:
- The article challenges the previously held belief that complex sleep patterns, including REM and slow-wave sleep, are exclusive to mammals and birds. The study suggests that these sleep features may have a more ancient origin, possibly dating back 320 million years to a common ancestor shared by reptiles, birds, and mammals.
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Common Ancestor and Evolution:
- The researchers propose that the similarity in sleep patterns among bearded dragons, birds, and mammals indicates that these features evolved from a common ancestor rather than independently in different evolutionary lineages.
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Primitive Brain Structures:
- The bearded dragons' sleep patterns, with coordination in a more primitive part of the brain (dorsal ventricular ridge), suggest a connection to ancient sleep patterns. This is in contrast to mammals, where slow-wave sleep coordination occurs in the hippocampus, a more evolved brain structure.
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Dreaming in Reptiles:
- While not definitively proven, the article speculates on the possibility of reptiles, including bearded dragons, experiencing dreams during REM sleep. The researcher suggests that these dreams may be related to recent notable events in the reptiles' lives, such as encounters with insects or interactions with other members of their environment.
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Sleep Cycles in Bearded Dragons:
- Bearded dragons reportedly undergo approximately 350 80-second sleep cycles per night. This is in contrast to humans, who typically experience four or five 90-minute sleep cycles per night.
In conclusion, the study on bearded dragons provides intriguing insights into the evolution and universality of sleep patterns, challenging previous assumptions and suggesting that the fundamental aspects of sleep may be more ancient and widespread than previously thought.
