I once dreamed of a kiss that hadn't happened yet. Not long after, on a cold morning, I saw a young night heron sleeping on a branch above the pond in New York's Brooklyn Bridge Park, his head resting on her chest, and I wondered: Do birds dream?
In 1861, a fossil was discovered in Germany with the tail and jaws of reptile and wings and furcula of a bird, leading to the revelation that birds had evolved from dinosaurs.
We now know that, although birds and humans have not shared a common ancestor in more than 300 million years, a bird's brain is much more similar to ours than that of a reptile. The neuronal density of their forebrain—the region responsible for planning, sensory processing, and emotional responses, and on which the state of sleep rich in rapid eye movement, or REM, dreams largely depends—is comparable to that of the primates.
At the cellular level, the brain of a songbird has a structure, the dorsal ventricular crest, similar in function, if not shape, to the neocortex of mammals. (The neocortex is the most evolutionarily nascent outer layer of the brain, responsible for complex cognition and creative problem solving.)
The first electroencephalogram of electrical activity in the human brain was performed in 1924, but it was not applied to bird sleep until the 21st century., with the help of the even more nascent functional magnetic resonance imaging, developed in the 1990s. EEG tracks what neurons do more directly. But MRI can map brain activity more precisely via blood oxygen levels. Scientists have used these technologies together to study cell activation patterns during REM sleep in an effort to deduce the content of dreams.
An MRI of pigeons found that brain regions responsible for visual processing and spatial navigation were active during REM sleep, as were regions responsible for wing action, even when the birds were asleep: They seemed to be dreaming of flying.
The amygdala—a group of nuclei responsible for emotional regulation—was also active during REM sleep, hinting at feelings-filled dreams. My night heron was probably dreaming, too—a bent neck is a marker of atonia, the loss of muscle tone characteristic of REM sleep.
But the most disturbing hint from the research is that without birds' dreams, we too might not have dreams.
There are two main groups of living birds: the flightless paleognaths, such as the ostrich and the kiwi, which have preserved certain ancestral reptilian traits, and the neognathas, which include all other birds. EEGs from sleeping ostriches have found REM-like activity in the brainstem—an older 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 such as the platypus and echidna, the evolutionary link between us and birds—also reveal REM-like activity in the brain stem, suggesting that this was the ancestral crucible of REM before slowly migrate towards the forebrain. If so, the bird's brain could be the place where evolution designed dreams.
Dmitri Mendeleev came to his periodic table in a dream. “All the elements were arranged as necessary,” he recounted in his diary. For Einstein, the central revelation of relativity took shape in a dream in which cows simultaneously jumped and moved in wave-like motions.
What happens with the mind also happens with the body. Studies have shown that people who learn new motor tasks “practice” them while they sleep and then perform better while awake. This line of research has also shown how mental visualization helps athletes improve their performance.
It may be that in REM, we practice the possible to the real. It may be that the kiss in my dream was not a nocturnal fantasy but, like the heron's dreams of flight, the practice of possibility. Perhaps we have evolved to become reality via dreams—a laboratory of consciousness that began in the bird's brain.
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