A new study has found that, when pigeons sleep, they may experience visions of flight.
The research, published in Nature Communications, looked at brain activation patterns in sleeping pigeons, using functional magnetic resonance imaging. It found that most of the brain in the pigeons tested was highly active during rapid eye movement (REM) sleep, similar to mammals.
During sleep, the brain experiences a complex set of processes to ensure we wake up feeling refreshed. In humans, the different phases of sleep – REM and non-REM sleep – are associated with distinct changes in physiology, brain activity, and cognition.
The research aimed to discover whether similar processes also take place in birds. The researchers used infrared video cameras and functional magnetic resonance imaging (fMRI) to document the sleeping and wakeful states of 15 pigeons specially trained to sleep under experimental conditions.
The study used infrared video cameras and functional magnetic resonance imaging to document the sleeping and wakeful states of 15 pigeons (Barry Matlock).
The video recordings shed light on the sleep phases in the birds. "We were able to observe whether one or both eyes were open or closed, and to track eye movements and changes in pupil size through the pigeons' transparent eyelids during sleep," said Mehdi Behroozi from the research team. Simultaneously, the fMRI recordings provided information about brain activation and the flow of cerebral spinal fluid in the ventricles.
"During REM sleep, we observed strong activity in brain regions responsible for visual processing, including in those areas that analyse the movement of a pigeon's surroundings during flight. Based on these observations, we think that birds, just like humans, dream during REM sleep, and might be experiencing flight in their dreams."
Additionally, the scientists noticed activation of a particular brain area known as the amygdala during these phases. "This suggests that if birds experience something similar to our human dreams, pigeons' dreams might include emotions as well," says Gianina Ungurean from the Avian Sleep Group at the Max Planck Institute for Biological Intelligence. This hypothesis is supported by the fact that the birds' pupils contract rapidly during REM sleep, like they do during courtship or aggressive behaviours while awake.
Reference
Behroozi, M, Böger, L, Helluy, X, Güntürkün, O, Libourel, P-A, Rattenborg, N C, & Ungurean, G. 2023. Wide-spread brain activation and reduced CSF flow during avian REM sleep. Nature Communications. DOI: 10.1038/s41467-023-38669-1
