Birds Dream, Much Like We Do

I once dreamed a kiss that had not yet happened. Not long after, I watched a young night heron sleep on a branch over the pond in New York’s Brooklyn Bridge Park, head folded into chest, and wondered: Do birds dream?

In 1861, a fossil was found in Germany with the tail and jaws of a reptile and the wings and wishbone of a bird, leading to the revelation that birds had evolved from dinosaurs.

We have since learned that, although birds and humans have not shared a common ancestor in over 300 million years, a bird’s brain is much more similar to ours than to a reptile’s. The neuron density of its forebrain — the region engaged with planning, sensory processing and emotional responses, and on which the dream-rich sleep state of rapid-eye movement, or REM, is largely dependent — is comparable to that of primates.

At the cellular level, a songbird’s brain has a structure, the dorsal ventricular ridge, similar to the mammalian neocortex in function if not shape. (The neocortex is the more evolutionarily nascent outer layer of the brain, responsible for complex cognition and creative problem-solving.) In pigeons and barn owls, the dorsal ventricular ridge is structured like the human neocortex, with both horizontal and vertical neural circuitry.

The first electroencephalogram of electrical activity in the human brain was in 1924, but EEG was not applied to avian sleep until the 21st century, aided by the even more nascent functional magnetic resonance imaging, developed in the 1990s. In recording the electrical activity of large populations of neurons near the cortical surface, EEG tracks what neurons do more directly. But fM.R.I. can pinpoint the location of brain activity more precisely through oxygen levels in the blood. Scientists have used these technologies together to study the firing patterns of cells during REM sleep in an effort to deduce the content of dreams.

A study of zebra finches — songbirds whose repertoire is learned, not hard-wired — mapped particular notes of melodies sung in the daytime to neurons firing in the forebrain. During REM, the neurons fired in a similar order: The birds appeared to be rehearsing the songs in their dreams.

An fM.R.I. study of pigeons found that brain regions tasked with visual processing and spatial navigation were active during REM, as were regions responsible for wing action. The birds appeared to be dreaming of flying. The amygdala — a cluster of nuclei responsible for emotional regulation — was also active during REM, hinting at dreams laced with feeling.

My night heron was probably dreaming too — the folded neck is a marker of atonia, the loss of muscle tone characteristic of REM.

But the most haunting intimation of the research is that without the dreams of birds, we too might be dreamless.

There are two primary groups of living birds: the flightless Palaeognathae, including the ostrich and the kiwi, which have retained certain ancestral reptilian traits, and Neognathae, comprising all other birds. EEG studies of sleeping ostriches have found REM-like activity in the brainstem — a more ancient part of the brain — while in modern birds, as in mammals, this REM-like activity takes place primarily in the more recently developed forebrain.

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

If so, the bird brain might be where evolution designed dreams — that secret chamber adjacent to our waking consciousness where we continue to work on the problems that occupy our days.

Studies have shown that people learning new motor tasks “practice” them in sleep, then perform better while awake. This line of research has also shown how mental visualization helps athletes improve performance.

It may be that in REM, we practice the possible into the real. It may be that the kiss in my dream was not nocturnal fantasy but, like the heron’s dreams of flying, the practice of possibility. It may be that we evolved to dream ourselves into reality — a laboratory of consciousness that began in the bird brain.

Practicing the possible into the real, while sleeping.