How Evolution Created REM in the Bird Brain to Rehearse What Happens in Our Sleep – The Marginalian

This article first appeared in The New York Times

I once dreamed of a kiss that had never happened. I dreamed of the angle at which our heads were tilted, the fit of my fingers behind her ear, the precise pressure released from the lips by this transfer of trust and compassion.

Freud, who founded the study of dreams in his seminal 1899 book, would not discount this as a mere chimera of the wishful unconscious. But what we have discovered since then about the mind – especially about the dream-rich state of rapid eye movement, or REM, unknown in Freud's day – suggests another possibility for the working conditions of these same nocturnal lives.

One very cold morning after a dream about kissing, I watched a little starling at night lying naked on a branch over a pond in Brooklyn Bridge Park, head curled against my chest, and I found myself wondering if birds dream.

The recognition that non-human animals dream dates back at least to the days of Aristotle, who observed a sleeping dog barking and took it as vague evidence of mental activity. But by the time Descartes promoted the Enlightenment in the 17th century, he had reduced other animals to mere automatons, defiling centuries of science with the idea that anything unlike us is inherently inferior.

In the 19th century, when the German naturalist Ludwig Edinger made the first anatomical studies of the bird's brain and found the absence of the neocortex – the outer layer of the brain that is still growing in evolution, responsible for complex understanding and solving creative problems – he dismissed birds as Cartesian puppets of the reflex. This idea was reinforced in the 20th century by the deviation, led by BF Skinner and his pigeons, in behaviorism – a school of thought that considered behavior as a Rube Goldberg machine of stimulus and response controlled by reflex, ignoring internal attitudes and emotional responses.

In 1861, just two years after Darwin's publication On the Origin of Speciesdebris was found in Germany containing the tail and jaws of a reptile and the wings and bone of a bird, which led to the revelation that birds had turned to cages. We have since learned that, although birds and humans have not shared a common ancestor for more than 300 million years, the brain of a bird is more similar to ours than that of a reptile. The neuron density of its forebrain – the region involved in planning, sensory processing, and emotional responses, and on which REM sleep is most dependent – ​​is comparable to that of animals. At the molecular level, the songbird's brain has a structure, the ventricular ridge, that resembles a functional mammalian neocortex if not more so. (In pigeons and owls, the DVR is shaped like the human neocortex, with horizontal and vertical nerve circuits.)

However, bird brains are also profoundly different, capable of doing unimaginable things, especially during sleep: Many birds sleep with one eye open, even when flying. Migratory animals that travel long distances at night, like the bar-tailed godwit, which covers 7,000 miles between Alaska and New Zealand in eight days of continuous flight, sleep in unusual ways, blurring the line between our normal sleep and wake stages.

But while sleep is an outwardly visible behavior, dreaming is an inward phenomenon as mysterious as love – a mystery where science has brought brain imaging technology to light the innermost realms of a sleeping bird's mind.

The first electroencephalogram of electrical activity in the human brain was recorded in 1924, but EEG was not used in bird sleep research until the 21st century, aided by the still emerging functional magnetic resonance imaging, developed in the 1990s. These two technologies complement each other. By recording the electrical activity of a large number of neurons near the left hemisphere, EEG tracks what the neurons are doing specifically. But fMRI. can pinpoint brain function more accurately through blood oxygen levels. Scientists have used this technology together to study cell firing patterns during REM sleep in an attempt to discover the content of dreams.

A study of zebra finches – birds that sing their own song learned, not hard-wired – mapped the specific notes of songs sung during the day to neurons firing in the forebrain. Then, during REM, the neurons fired in the same sequence: The birds appeared to repeat the songs in their dreams.

An fMRI study of pigeons found that the brain regions tasked with visual processing and spatial navigation were active during REM, as were the regions responsible for wing function, even when the birds were silent due to sleep: They seemed to be dreaming of flying. The amygdala – a cluster of nuclei responsible for emotional regulation – was also active during REM, identifying dreams that are associated with emotion. My night heron was probably dreaming, too – a folded neck is a classic sign of atonia, the loss of muscle tone characteristic of the REM state.

But the most alarming tip of the research on bird sleep is that without bird dreams, we may not be dreaming either. No heron, no kiss.

There are two main groups of living birds: the flightless Palaeognathae, including the ostrich and kiwi, which have retained some reptile characteristics, and the Neognathae, which includes all other birds. EEG studies of sleeping ostriches have found REM-like activity in the brainstem – an ancient part of the brain – while in modern birds, like mammals, this REM-like activity occurs primarily in the newly developed forebrain.

Several studies of sleeping monotremes – egg-laying mammals like the platypus and echidna, the evolutionary link between us and birds – also revealed REM-like activity in the brainstem, suggesting that this was the ancestral crucible of REM before it gradually migrated towards the forebrain.

If so, the bird's brain may be where evolution designed dreams — that secret chamber near our waking hours where we continue to work on the problems that occupy our days. Dmitri Mendeleev, after a long and difficult confusion about the arrangement of atomic weights in his waking state, came to his table of dates in a dream. “All the elements went as they should,” he recounted in his diary. “When I woke up, I immediately wrote it down on a piece of paper.” Cosmologist Stephon Alexander dreamed up his approach to fundamental understanding about the role of equilibrium in the devaluation of the universe which earned him a national award from the American Physics Society. For Einstein, the central revelation of relativity came from a dream of cows simultaneously jumping and moving in a wave-like motion.

As with the mind, so with the body. Studies have shown that people who learn new motor tasks “practice” them while asleep, and then perform better while awake. This line of research has also shown how visualization helps athletes improve performance. Renata Adler touches on this in her book A fast boat: “That was a dream,” he writes, “but many of the most important things I find, are those that are learned in your sleep.”

It may be that in REM, this blurring between wakefulness and unconsciousness, we make that possible real. It is possible that the kiss in my dream was not a dream of the night but, like the dreams of a flying crocodile, a habit of possibility. We may have evolved to dream into reality – a laboratory of consciousness that began in the bird's brain.