It turns out that we have more in common with dinosaurs and birds than previously thought. In the study, which was published last week in the journal Science, scientists tracked brain activity in sleeping lizards. As it turned out, reptile sleep goes through the same phases that are observed in mammals and birds. Apparently, dinosaurs slept in the same way.
“The findings suggest that sleep phases appeared in animals much earlier than previously thought. The results of the work are really surprising, because until now scientists have agreed that the phases of REM and slow sleep are characteristic only of mammals and birds. According to these ideas, sleep phases emerged simultaneously with the appearance of birds (about 100 million years ago) or placental mammals (about 65 million years ago),”says Dr. Gilles Laurent, director of the Center for Brain Research at the Max Planck Institute.
However, new data indicate that the phases of REM and slow sleep appeared even in the common ancestors of mammals, birds and reptiles - amniotes, which lived about 300 million years ago, when the modern continents were part of a single supercontinent Pangea.
The researchers implanted special silicon probes into the forebrains of five bearded agamas (Pogona vitticeps), which recorded the activity of the reptile's brain during sleep. According to Laurent, the work used a new type of probes that more accurately tracked the state of the animal's brain.
Scientists also recorded eye movements of sleeping lizards using infrared cameras and computer analysis of video. Records showed that the lizards had two phases of sleep. The first of them was characterized by a low frequency and high amplitude of brain activity. The second, by the type of brain activity, resembled awakening and was accompanied by rapid eye movements. This sleep dynamics is common in mammals and birds.
Laurent draws attention to the fact that, despite the similarity in the phases of sleep, mammals, birds and reptiles have strongly diverged in evolutionary development. The differences between the two relate largely to sleep. So, the duration of one sleep cycle in lizards is only about 80 seconds. But in humans, this parameter reaches 60-90 minutes. For cats, 30 minutes. In addition, in lizards, REM sleep and slow-wave sleep were about the same duration, but in humans, REM sleep is usually shorter. In birds, the relationship between sleep phases is unstable.
"If the division of sleep into phases happened as long ago as we think, the dinosaurs of the Mesozoic era (230-65 million years ago), most likely had similar dynamics of sleep," - said Laurent.