Do dragons dream of something when they fall asleep? It sounds like a question for Game of Thrones fans, but it is an interesting issue from an evolutionary point of view. All animals sleep, but not everyone does it the same way.

An exclusive of ours? Scientists have long held that mammals and birds were the only ones to experience, in sleep, the REM phase (Rapid eye movement, that accompanied by dreams and rapid eyelid movements) and the slow-wave sleep stage, a phase in which brain activity is lowered and brain waves become regular and synchronized. This "slower" and deeper sleep is considered indispensable for the consolidation of memories of the experiences lived during the day.

Pure coincidence. Until now, attempts to track both phases in the reptiles proved to be confused. But an experiment by the Max Planck Institute for Brain Research in Frankfurt (Germany) on bearded dragons (Pogona vitticeps), saurians typical of the Australian deserts, has left scientists speechless.

A strange resemblance. The team was studying how these common reptiles use visual information to find food. He monitored their brain electrical activity 24 hours a day: at night the dragons' brains produced two different types of waves, one at low frequency (4 Hz) and one at higher frequency (20 Hz), alternating every 40 seconds . A rhythm and alternation very similar to those of the REM, high frequency, and slow-wave sleep of mammals and birds.

Ancient origins. Infrared cameras have also shown that, in conjunction with high-frequency waves, the pupils of saurians moved as ours move when we dream. This seems to suggest that the origin of these two stages of sleep goes back to a distant, common ancestor of reptiles, birds and mammals. And that the function of these two phases is so important as to have been favored by evolution: perhaps, even reptiles while they sleep revive the experiences of the day ended, and fix in their memory the best places to find food.