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‘Birds Experience Something Similar to Human Dreams’ During REM Sleep, Suggests New Study

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There’s a Surprising Similarity Between The Dreams of Humans And Birds

For many years, dreams have been viewed as a unique characteristic of human slumber. Yet, recent research indicates that pigeons may also envision flight while asleep. A team of scientists from the Ruhr University Bochum and the Max Planck Institute for Biological Intelligence used functional magnetic resonance imaging to analyze the brain activity patterns of pigeons during sleep.

Their investigation showed that the pigeon brain, much like that of mammals, exhibits significant activity during REM (rapid eye movement) sleep. Nonetheless, this state of heightened activity resembling wakefulness may limit the brain’s ability to eliminate waste.

These research findings were reported in the Nature Communications journal on June 5, 2023.

Sleep is a multifaceted process in our brains, ensuring we wake up revitalized. In humans, the sleep cycle includes different stages, namely REM and non-REM sleep, each related to various physiological alterations, cerebral activities, and cognitive shifts. For instance, the REM sleep stage is marked by intense brain activity, leading to vivid, strange, and emotional dreams.

On the contrary, non-REM sleep stage sees a decrease in brain metabolic activity, aiding in the clearance of waste materials. This is accomplished by circulating cerebral spinal fluid within the brain’s ventricles—interlinked cavities that envelope brain structures—and then throughout the brain. This mechanism is believed to facilitate the removal of damaging protein accumulations linked to diseases like Alzheimer’s.

The inner workings of a pigeon’s brain during its slumber had remained a mystery until now. Professor Onur Güntürkün, the Head of the Biopsychology Department at Ruhr University Bochum, points out that the last shared evolutionary ancestor of birds and mammals goes back about 315 million years to the dawn of land-dwelling vertebrates.

Interestingly, the sleeping patterns of birds exhibit significant similarities with those of mammals, encompassing both REM and non-REM stages.

To uncover the intricate details of avian sleep, the scientists employed infrared video cameras and functional magnetic resonance imaging (fMRI) to monitor and document the sleep and wakeful states of 15 pigeons, uniquely conditioned to sleep under these experimental circumstances.

The video footage offered insight into the birds’ sleep stages.

“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,” adds Mehdi Behroozi from the Bochum team.

Concurrently, the fMRI data contributed valuable knowledge regarding brain activity and cerebral spinal fluid movement in the ventricles.

“During REM sleep,” as explained by Mehdi Behroozi, “we observed strong activity in brain regions responsible for visual processing, including in those areas that analyze the movement of a pigeon’s surroundings during flight.

The researchers further observed noticeable activity in the regions responsible for interpreting sensory information from the body, particularly signals stemming from the wings.

Based on the findings, the researchers “think that birds, just like humans, dream during REM sleep, and might be experiencing flight in their dreams,” according to Mehdi Behroozi.

Moreover, the researchers identified the activation of a specific brain region, the amygdala, during these stages.

“This suggests that if birds experience something similar to our human dreams, pigeons’ dreams might include emotions as well,” points out Gianina Ungurean from the Avian Sleep Group at the Max Planck Institute for Biological Intelligence.

Support for this theory comes from the observation that the birds’ pupils swiftly constrict during REM sleep, mirroring the pattern seen during mating or confrontational behaviors when the birds are awake, as recently shown by Gianina Ungurean and team.

Similar to humans, pigeons exhibit an increased flow of cerebral spinal fluid through their ventricles during non-REM sleep. Yet, the team found that this flow surprisingly decreases considerably during REM sleep – a first-ever discovery for any creature.

Niels Rattenborg, the head of the Avian Sleep Group, explains, “We think that the increased flood of blood into the brain during REM sleep, which supports the elevated brain activity, might block the cerebral spinal fluid from moving from the ventricles into the brain. This suggests that REM sleep and its functions might come at the expense of waste removal from the brain.”

However, the team is also contemplating the possibility that REM sleep could aid waste elimination in ways not previously considered

“At the onset of REM sleep, the influx of blood increases vessel diameter,” explains Gianina Ungurean.

“This might force cerebral spinal fluid that entered the space surrounding the vessels during non-REM sleep to flow into the brain tissue, and enhance the outflow of fluids carrying waste products.”

The team hypothesizes that sleep-associated brain cleansing could be particularly vital for birds. Given that bird brains contain a higher density of neurons compared to mammals, the process of waste disposal might necessitate more efficient—or more regular—flushing cycles. Since birds undergo more frequent and shorter REM phases during sleep than mammals, the repeated increase of blood flow might help keep their densely populated brains clear of harmful waste products.

Looking ahead, the team aims to investigate further into the potential role of REM sleep in waste removal. They are also keen on understanding what pigeons may dream about.

“We hope to train birds to report if and what they just saw upon awakening from REM sleep. That would be an essential step towards establishing whether they dream,” shares Gianina Ungurean.

Even without an in-depth dream analysis, these fresh insights significantly enhance our understanding of the role of sleep in both birds and humans. The findings underscore the significance of sleep in maintaining a healthy brain, preventing cognitive deterioration, and suggest that the phenomenon of dreaming has ancient origins.

Image Credit: Getty

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