Unlocking the Enigma of Pigeon Dreams: A Fascinating Flight of Fancy

Unlocking the Enigma of Pigeon Dreams: A Fascinating Flight of Fancy

Groundbreaking research has unveiled a captivating discovery suggesting that birds, including pigeons, may partake in the realm of dreams, potentially featuring flight experiences during their slumber. Employing advanced techniques such as fMRI scans and video surveillance on dozing pigeons, scientists have observed sleep phases akin to those observed in mammals, including REM and non-REM sleep. Notably, the study revealed that during REM sleep, the avian brain regions responsible for visual processing, particularly those linked to flight, exhibit activity. Additionally, the amygdala, a key player in emotions, demonstrates activation during these dream-like episodes.

These findings shed light on the intriguing possibility that birds, much like humans, engage in dreams, with flight taking center stage in their REM sleep experiences. The parallels between avian and human sleep patterns are striking, further accentuating the captivating nature of birds’ dreamscapes.

Dreams have long been considered a quintessential element of human slumber. However, recent revelations indicate that pigeons, while asleep, may embark on flights of fancy. Researchers from Ruhr University Bochum in Germany and the Max Planck Institute for Biological Intelligence undertook a study to unravel the mysteries concealed within the pigeon’s sleeping mind. Utilizing functional magnetic resonance imaging (fMRI), the team explored brain activation patterns during the birds’ slumber. Remarkably, the study divulged that, much like mammals, pigeons exhibit heightened brain activity during REM sleep. However, this heightened state of consciousness may come at the cost of reduced waste removal from the brain. The study, published in the journal Nature Communications on June 5, 2023, opens up new avenues of inquiry into the role of REM sleep in waste removal and the content of avian dreams.

Sleep encompasses a complex interplay of processes aimed at rejuvenating the mind and body. In humans, distinct phases of sleep, such as rapid eye movement (REM) and non-REM sleep, correspond to physiological, cognitive, and brain activity changes. REM sleep, characterized by intense brain activity, offers a playground for vivid, surreal, and emotional dreams. On the other hand, non-REM sleep involves diminished metabolic brain activity and facilitates waste removal by flushing cerebrospinal fluid through the interconnected chambers known as ventricles, which encase the brain’s structures. This process aids in the elimination of potentially detrimental protein deposits, like those associated with Alzheimer’s disease.

Pigeons, too, take flight in the realm of dreams during their slumber. Researchers have made intriguing observations to support this notion. Credit: © RUB, Marquard

What transpires within a pigeon’s brain during sleep?

The question of whether similar processes unfold in birds has long remained unanswered—until now. Professor Onur Güntürkün, head of the Biopsychology Department at Ruhr University Bochum, explains, “The last common evolutionary ancestor of birds and mammals dates back about 315 million years, to the early days of land vertebrates. Yet the sleep patterns in birds are remarkably similar to those in mammals, including both REM and non-REM phases.”

To unravel the mysteries concealed within avian slumber, the researchers meticulously observed and recorded the sleep and wakeful states of 15 pigeons trained to sleep under experimental conditions. Infrared video cameras and fMRI provided invaluable insights into the birds’ sleep phases. “We monitored whether the pigeons’ eyes were open or closed, tracked eye movements and pupil size changes through their transparent eyelids, both during sleep,” explains Mehdi Behroozi, a member of the Bochum team. Simultaneously, fMRI recordings provided valuable information about brain activation and the flow of cerebrospinal fluid within the ventricles.

Onur Güntürkün, Mehdi Behroozi, and Xavier Helluy from the Bochum research team (left to right). Credit: © RUB, Marquard

Dreams of Soaring through the Skies

Mehdi Behroozi highlights the team’s discovery: “During REM sleep, we observed robust activity in brain regions responsible for visual processing, including areas that analyze the motion of a pigeon’s surroundings during flight.” Furthermore, the researchers observed activity in areas that process signals from the body, particularly the wings. “Based on these findings, we posit that birds, much like humans, experience dreams during REM sleep, potentially involving flight experiences,” adds Behroozi.

Moreover, the scientists detected activation in a specific brain region called the amygdala during these dreamlike states. Gianina Ungurean from the Avian Sleep Group at the Max Planck Institute for Biological Intelligence suggests, “This implies that if birds undergo experiences akin to our human dreams, pigeons’ dreams might involve emotions as well.” This notion gains support from the rapid contraction of the birds’ pupils during REM sleep, similar to their behavior during courtship or when engaged in aggressive acts while awake, as recently revealed by Gianina Ungurean and her colleagues.

Cleansing the Day’s Dust

Similar to humans, cerebrospinal fluid flow through the ventricles in pigeons intensifies during non-REM sleep. However, the researchers have made a groundbreaking discovery: cerebrospinal fluid flow dramatically diminishes during REM sleep—a first-of-its-kind finding across all animals. “We believe that the increased influx of blood into the brain during REM sleep, which supports heightened brain activity, may impede cerebrospinal fluid flow from the ventricles into the brain,” explains Niels Rattenborg, head of the Avian Sleep Group. “This suggests that REM sleep and its functions might come at the expense of waste removal from the brain.”

Nevertheless, the researchers are also contemplating the possibility that REM sleep contributes to waste removal through unexpected mechanisms. “At the onset of REM sleep, the blood influx causes vessel dilation. This might facilitate the flow of cerebrospinal fluid that entered during non-REM sleep into the brain tissue, thereby enhancing the removal of fluids carrying waste products,” proposes Gianina Ungurean.

The researchers hypothesize that the process of cleaning the brain during sleep may be particularly critical for birds. Due to their higher density of neurons compared to mammals, birds may require more efficient or frequent flushing cycles to eliminate waste products. As birds experience more frequent and shorter REM phases during sleep compared to mammals, the associated surges of blood may aid in maintaining their densely packed brains free of harmful waste products.

Share Your Dreams with Us!

In future endeavors, the research team plans to explore the potential role of REM sleep in waste removal. Additionally, they aim to devise methods to glean insights into the contents of a pigeon’s dream. Gianina Ungurean explains, “We hope to train birds to communicate their observations upon awakening from REM sleep. This crucial step would help determine whether they dream.” Even without a comprehensive analysis of avian dreams, these new findings already deepen our comprehension of sleep’s significance for birds and humans alike. They underscore the crucial role of sleep in sustaining a healthy brain and averting cognitive decline, while also suggesting that dreams have an extensive evolutionary history.

Reference: “Wide-spread brain activation and reduced CSF flow during avian REM sleep” by Gianina Ungurean, Mehdi Behroozi, Leonard Böger, Xavier Helluy, Paul-Antoine Libourel, Onur Güntürkün, and Niels C. Rattenborg, 5 June 2023, Nature Communications.
DOI: 10.1038/s41467-023-38669-1

The study was conducted by the Bochum Biopsychology team in collaboration with researchers from the Max Planck Institute for Biological Intelligence, the Max Planck Institute for Neurobiology of Behaviour, the Neurophysiology Department at Ruhr University Bochum, and the Université Claude Bernard Lyon.

Funding for the project was provided by the Max Planck Society and the German Research Foundation – project no. 316803389 – SFB 1280, as well as AVIAN MIND, ERC-2020-ADG, LS5, GA No. 101021354.

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More about pigeon dreams

• “Wide-spread brain activation and reduced CSF flow during avian REM sleep” (Nature Communications): Link
• Ruhr University Bochum: Link
• Max Planck Institute for Biological Intelligence: Link
• Max Planck Society: Link