Do birds dream of flying? Scientists say they now know the answer

Sleep is a universal experience that encompasses complex biological functions. For us humans, it is divided into different phases – rapid eye movement (REM) and non-REM sleep. These sleep phases have unique associations with our physiology, brain activity, and cognition. 

During REM sleep, our brain activity peaks and ushers in vivid, peculiar, and emotional dreams. Meanwhile, non-REM sleep, a time of metabolic slowdown, enables the brain to flush out waste products. This cleaning mechanism plays a vital role in preventing neurological disorders like Alzheimer’s disease.

Despite the clarity in understanding human sleep, the question of whether birds undergo similar processes during sleep has been a mystery. However, new research led by Professor Onur Güntürkün, head of the Biopsychology Department at Ruhr University Bochum, has recently uncovered fascinating insights into avian sleep patterns.

What is happening in pigeon brains while they sleep?

“Birds and mammals share a common evolutionary ancestor dating back about 315 million years, yet their sleep patterns, including both REM and non-REM phases, are remarkably alike,” said Güntürkün.

In order to further investigate the intricacies of bird sleep, the research team combined cutting-edge technologies, namely infrared video cameras and functional magnetic resonance imaging (fMRI). They trained 15 pigeons to sleep under these experimental conditions, and closely observed their sleeping and wakeful states.

The video recordings revealed interesting details about avian sleep. “We observed whether one or both eyes were open or closed, tracked eye movements and changes in pupil size through the transparent eyelids of the pigeons during sleep,” explained Mehdi Behroozi, a member of the Bochum team.

Simultaneously, the fMRI recordings delivered insights about brain activation and cerebral spinal fluid flow in the ventricles.

Do pigeons dream of flying?

“During REM sleep, we observed strong activity in brain regions responsible for visual processing, including those areas analyzing the movement of a pigeon’s surroundings during flight,” said Behroozi. In addition, areas processing signals from the body, especially the wings, were also active.

Based on these observations, Behroozi suggests that birds may dream during REM sleep, possibly even reliving their flight experiences in their dreams.

Another intriguing finding was the activation of the amygdala during REM sleep. This implies that birds, like humans, may experience emotional content in their dreams.

“Pigeons’ dreams might include emotions as well,” said Gianina Ungurean from the Avian Sleep Group at the Max Planck Institute for Biological Intelligence. This theory is further supported by the birds’ rapid pupil contraction during REM sleep, similar to their reactions during courtship or aggressive behaviors.

How REM sleep helps birds

Just like in humans, non-REM sleep in pigeons is a period of enhanced cerebral spinal fluid flow through ventricles. However, a ground-breaking discovery was made: for the first time in any species, the researchers found that this fluid flow diminished significantly during REM sleep.

Niels Rattenborg, head of the Avian Sleep Group, explained this phenomenon: “The increased influx of blood into the brain during REM sleep, which supports the heightened brain activity, might obstruct the cerebral spinal fluid from moving from the ventricles into the brain. This implies that REM sleep and its functions might come at the cost of waste removal from the brain.”

Despite this, the team is contemplating that REM sleep might aid in waste removal in unexpected ways. “The surge of blood at the onset of REM sleep increases vessel diameter. This could push cerebral spinal fluid that entered the space during non-REM sleep into the brain tissue, promoting outflow of waste-laden fluids,” said Ungurean.

This cleaning process might be particularly critical for birds due to their higher neuronal density compared to mammals. As such, they might need more efficient, or more frequent flushing cycles to remove waste products. 

Birds’ sleep consists of more, but shorter REM phases compared to mammals. The frequent surges of blood associated with these REM phases might be instrumental in keeping their densely packed brains free of harmful waste products.

What the future holds for bird sleep research

The experts are enthusiastic about future research possibilities. They plan to delve further into the potential role of REM sleep in waste removal. Additionally, they hope to decode the content of a pigeon’s dream.

“We hope to train birds to report if and what they just saw upon awakening from REM sleep. That would be a crucial step towards confirming whether they dream,” said Ungurean.

Without the detailed analysis of bird dreams, these new findings already enhance our understanding of sleep’s role in birds and humans. The research, published in the journal Nature Communications, underscores the significance of sleep in sustaining a healthy brain and averting cognitive decline. It also suggests that dreaming, this peculiar yet universal phenomenon, has a deeply-rooted evolutionary history.

More about REM sleep

Rapid Eye Movement (REM) sleep is one of the five stages of the human sleep cycle, named for the characteristic rapid movement of the eyes that occurs during this phase. REM sleep is distinct from the four stages of non-REM sleep, characterized by unique physiological, neurological, and psychological features.

Physiologically

REM sleep is fascinating. While the brain shows activity levels similar to wakefulness, most of the body’s voluntary muscles are paralyzed. This phenomenon, known as REM atonia, is believed to be a protective mechanism that prevents us from acting out our dreams. Heart rate and blood pressure tend to fluctuate, and breathing can become irregular.

Neurologically

REM sleep is a period of high brain activity. Brain waves during this stage resemble those during wakefulness, which is why REM sleep is sometimes referred to as paradoxical sleep. Several neurotransmitters play pivotal roles in modulating REM sleep, including acetylcholine, which is particularly active, and monoamines (serotonin, norepinephrine, and histamine), which are almost completely inactive.

Psychologically 

REM sleep is the stage when the most vivid dreaming occurs. This is thought to be related to the high brain activity and the function of certain brain regions during REM sleep. The exact purpose of dreams is still a topic of ongoing scientific debate, but theories suggest they may help with processing emotions, consolidating memory, and learning.

Additionally, REM sleep is believed to play a crucial role in brain development. Infants, for instance, spend much of their sleep time in the REM phase. It’s also during REM sleep that proteins are synthesized, contributing to brain repair and growth.

Though it’s known that REM sleep is important, as evidenced by its conservation across many animal species and the negative health impacts linked to its deprivation, many aspects of REM sleep remain a mystery. Sleep, in general, is an active area of research as scientists continue to unveil its many complexities.

More about dreaming 

Dreaming is a fascinating and complex phenomenon that occurs during sleep, particularly during the Rapid Eye Movement (REM) phase, but also during certain stages of non-REM sleep. While we often associate dreams with vivid visual or auditory experiences, dreams can involve any of the senses and a wide range of emotions. Dream content can range from mundane daily activities to bizarre or surreal scenarios.

While everyone dreams, not everyone recalls their dreams. The ability to remember dreams varies greatly among individuals and can be influenced by a variety of factors including sleep stages, interruptions in sleep, stress, and certain lifestyle factors. Some people remember multiple dreams per night, while others recall their dreams infrequently.

There are many theories about why we dream, and understanding the purpose of dreams has been a subject of debate in the scientific and philosophical community for thousands of years. Here are a few key theories:

Emotional processing 

Some believe dreams are a way for the brain to process emotions and experiences from the day. This might explain why certain events or feelings from waking life often recur in dreams.

Memory consolidation

Another theory proposes that dreams play a role in consolidating and processing information gathered during the day, integrating it into long-term memory.

Problem-solving

Some theories suggest that dreams are a space where the brain can work on solving problems encountered during waking hours, without the constraints of reality.

Neural pathway stimulation

Dreams might serve as a means for the brain to stimulate and develop neural connections, especially during infancy and early childhood when brain development is most active.

Psychodynamic (Freudian) interpretation

Psychoanalyst Sigmund Freud posited that dreams are a reflection of repressed desires and unconscious thoughts. While this theory has been influential, it is not widely accepted in contemporary neuroscience.

It’s important to note that while these theories offer different perspectives, they’re not mutually exclusive, and the true purpose of dreams may encompass elements from each theory or be something yet undiscovered.

A relatively new field of research, dream science, employs various technologies such as electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to better understand the neurological underpinnings of dreaming. 

Despite advancements in this area, much about the nature and purpose of dreams remains enigmatic and continues to captivate both scientists and the general public.

The study represents the collective efforts of various researchers including the Bochum Biopsychology team, 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. This cross-institution collaboration adds further robustness and breadth to these intriguing insights into avian sleep processes.

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