Dreams have been considered a hallmark of human sleep for a long time. Latest findings, however, suggest that when pigeons sleep, they might experience visions of flight. Researchers at Ruhr University Bochum and at the Max Planck Institute for Biological Intelligence studied brain activation patterns in sleeping pigeons, using functional magnetic resonance imaging. The study revealed that similar to mammals, most of the brain is highly active during REM sleep. However, this wake-like state might come at a cost of reduced waste removal from the brain. The researchers published their findings in the journal Nature Communications on 5 June 2023.