At first glance, pigeons may not appear to be the brightest of birds. With their bobbing heads, clumsy gaits and dull-sounding "coo" noises, pigeons are often mistaken for being downright stupid pests. Yet a recent study in the journal Nature Communications suggests that pigeons may be more sophisticated than humans often assume.
The reason is simple: This study provides the first evidence ever that pigeons — and by implication other birds — are capable of dreaming.
"The study of dreaming has captivated scientists since the early days of sleep research."
To learn this, German researchers raised a group of 15 pigeons to be comfortable around functional magnetic resonance imaging (fMRI) as well as infrared video cameras. By doing so, the scientists were able to closely monitor the pigeons brains as they slept — a feat that was easier for the birds because they were used to machines that would likely otherwise keep them awake.
With that problem out of the way, they monitored a number of biological functions that help us understand sleep. The fMRI provided information about their brain activity while sleeping and about the flow of their cerebral spinal fluid (CSF), which is thought to flush toxic proteins and other wastes out of the brain during sleep through the glymphatic system. The scientists likewise tracked the birds' eye movements and pupil size, which can also be used to determine their sleep state.
Gianina Ungurean, a researcher at the Avian Sleep Group for the Max Planck Institute for Biological Intelligence, was a corresponding author on the study. Ungurean spoke to Salon by email about the team's most significant findings. The broader goal of the research was not, after all, merely to learn about bird dreaming. Scientists want to understand how all organisms, including humans, engage in the act of dreaming.
"The study of dreaming has captivated scientists since the early days of sleep research," Ungurean explained. "However, our understanding of the brain processes behind dreaming remains limited," particularly because every dreaming animal other than humans cannot verbally communicate their subjective experiences to researchers.
Despite these limitations, however, the scientists learned that "birds, like humans, experience REM sleep, which is the sleep stage associated with the most vivid dreams." Similarly they learned that many of the same brain regions which are active in humans during REM sleep, "including visual and higher associative areas," are also active in birds. The same was true for the avian amygdala, which is believed to regulate emotions in birds just as in humans; it likewise is active in sleeping birds just as it is in sleeping humans. Finally, by building on previous research which showed that birds constrict their pupils while awake when they experience strong emotions (such as those involved in courtship), the researchers found that birds "exhibit the same pupil constriction during REM sleep."
Because "birds rely heavily on their vision... birds might experience visual dreams like humans do."
"In summary, our results do not provide definitive evidence that pigeons dream, but they lay the foundation for future research aimed at addressing this fascinating question," Ungurean concluded. "Exploring whether birds and other animals experience dreaming would open up new avenues for investigating the purpose, if any, that dreams serve."
When asked what pigeons might dream about, Ungurean replied that because "birds rely heavily on their vision, and that large portions of the visual system were active during REM sleep, birds might experience visual dreams like humans do."
This is not the first study to dive into the science behind non-human dreaming. In 2022, Chinese researchers publishing a study in the journal Neuron revealed that they had exposed various species of sleeping animals to a chemical called trimethylthiazoline, which is strongly associated with predators. When they did this, they discovered that animals were more quick to wake up from their sleeping states if they were in a REM cycle than if they were in a non-REM cycle. Moreover, they found that neurons in a brain region called the medial subthalamic nucleus gave their animals a lower threshold for waking up during REM cycles and were more likely to be defensive once awakened.
"Together, our findings suggest adaptive REM-sleep responses could be protective against threats and uncover a critical component of the neural circuitry at their basis," the authors concluded at the time.
Humanity's knowledge of birds has also seen some important strides in recent years. Vinciane Despret, a Belgian philosopher of science and associate professor at the University of Liège, recently wrote a book called "Living as a Bird" that synthesized our current scientific knowledge to speculate about how birds process reality.
"I think that time is really not the same for birds as it is for us humans," Despret explained, latter adding that. "We don't live in the same time all the time: If you are in difficult trouble or sick, the time will seem long, and other times when you are just enjoying something, the time seems too short. It seems, for example, that when you get older, the time we live in is not the same — that when we were young the years did not pass so fast, but when you are past 60, the years start coming at you faster."
Birds, by contrast, have a perception of time that "is very, very different," Despret said. "Sometimes they live in the pure present, but when they sing, for example, they have to negotiate and manage the time. Because what is song? It's music. And music is a question of managing time."
At the same time, Ungurean's study also shows that bird brains are much more similar to human brains than people might realize. If nothing else, the study suggests that birds may perhaps replay consolidated memories from their experiences while sleeping, just as humans do.
"Although it remains to be proven, it is possible that cortical replay could be associated with, or even take place during, dreaming," Ungurean told Salon. "This suggests that birds may have comparable requirements for memory consolidation and could potentially employ similar mechanisms as mammals."
