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Lizards share sleep patterns with humans | Lizards share sleep patterns with humans |
(35 minutes later) | |
Lizards share sleep patterns with humans, according to scientists. | Lizards share sleep patterns with humans, according to scientists. |
Until now, it was thought features of human sleep such as rapid eye movements were seen only in mammals and birds. | Until now, it was thought features of human sleep such as rapid eye movements were seen only in mammals and birds. |
Now, a study of the bearded dragon - a popular pet - suggests these distinctive sleep rhythms emerged hundreds of million of years ago in a distant ancestor. | Now, a study of the bearded dragon - a popular pet - suggests these distinctive sleep rhythms emerged hundreds of million of years ago in a distant ancestor. |
They could even have been present in dinosaurs, say scientists. | They could even have been present in dinosaurs, say scientists. |
Some form of sleep has been described in everything from worms to people. | Some form of sleep has been described in everything from worms to people. |
But the sleep phases of humans and birds are very distinctive, involving cycles of deep (slow-wave) sleep, followed by awake-like brain activity and rapid eye movement (REM). | But the sleep phases of humans and birds are very distinctive, involving cycles of deep (slow-wave) sleep, followed by awake-like brain activity and rapid eye movement (REM). |
Faster rhythm | Faster rhythm |
German researchers recorded the brain activity of bearded dragons when they were sleeping. | German researchers recorded the brain activity of bearded dragons when they were sleeping. |
They found that similar to humans and other mammals, the reptiles showed cycles of eye movements and deep sleep. | They found that similar to humans and other mammals, the reptiles showed cycles of eye movements and deep sleep. |
However, while humans typically go through four or five 90-minute cycles of slow-wave sleep and REMs, the lizard sleep rhythm is faster and more regular, resulting in hundreds of much shorter cycles. | However, while humans typically go through four or five 90-minute cycles of slow-wave sleep and REMs, the lizard sleep rhythm is faster and more regular, resulting in hundreds of much shorter cycles. |
And in lizards the activity seems to originate from a different brain area from mammals. | And in lizards the activity seems to originate from a different brain area from mammals. |
"Although similar to mammalian sleep, lizard slow-wave sleep and REMs resemble a stripped-down version of the richer mammalian repertoire," the scientists write in the journal Science. | "Although similar to mammalian sleep, lizard slow-wave sleep and REMs resemble a stripped-down version of the richer mammalian repertoire," the scientists write in the journal Science. |
Common ancestor | Common ancestor |
The fact that reptiles, birds and mammals share similar sleep patterns suggests these evolved in a common ancestor some 300 to 320 million years ago. | The fact that reptiles, birds and mammals share similar sleep patterns suggests these evolved in a common ancestor some 300 to 320 million years ago. |
At the time, the land was ruled by amniotes - a class of four-legged, backboned animal that laid eggs protected by amniotic membranes. | At the time, the land was ruled by amniotes - a class of four-legged, backboned animal that laid eggs protected by amniotic membranes. |
"Those were probably small and lizard-like animals," said lead researcher Dr Gilles Laurent of the Max Planck Institute for Brain Research in Frankfurt, Germany. | "Those were probably small and lizard-like animals," said lead researcher Dr Gilles Laurent of the Max Planck Institute for Brain Research in Frankfurt, Germany. |
"They lived between 300 and 320 million years ago, at a time when the earth's continents formed a single land mass." | "They lived between 300 and 320 million years ago, at a time when the earth's continents formed a single land mass." |
It could be that the true source was even more ancient, he added. | It could be that the true source was even more ancient, he added. |
"This would require evidence of REMs and slow-wave sleep from amphibians or fish, which has so far been negative," he said. | "This would require evidence of REMs and slow-wave sleep from amphibians or fish, which has so far been negative," he said. |
"But it may be worth checking again." | "But it may be worth checking again." |
Ancient origin | |
Lizard sleep may be similar to the sleep patterns of our ancestors, said Dr Laurent. | Lizard sleep may be similar to the sleep patterns of our ancestors, said Dr Laurent. |
And lizards might even dream in a rudimentary way. | And lizards might even dream in a rudimentary way. |
Asked if dinosaurs slept, he said: "I wish I knew but it seems likely that they expressed REM and slow-wave sleep." | Asked if dinosaurs slept, he said: "I wish I knew but it seems likely that they expressed REM and slow-wave sleep." |
Thanos Siapas, professor of computation and neural systems at Caltech, California, who was not involved in the research, said it shed new light into how the architecture of 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," he said. | |
"Comparing the circuit mechanisms and role of these network events across species may provide critical new insights into their function." |
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