Exploring the Dreaming Lives of Animals: A Scientific Insight
Written on
Even though animals often face injustice, there is much we misunderstand about their intelligence. Traditionally, birds, such as chickens, are seen as lacking smarts. However, recent research contradicts this notion. For instance, crows can strategize and utilize tools, while pigeons are capable of letter recognition and can even identify tumors from X-ray images. Studies show that chickens possess logical reasoning similar to some primates and can demonstrate empathy. A recent study published in Nature Communications has revealed that pigeons can experience the REM phase of sleep, akin to humans, suggesting they may also have vivid dreams. The complexity of dreams and sleep in animals is a captivating subject, with this study merely scratching the surface of extensive research conducted over decades. To gain insights, we consulted Laura Beani, a zoologist and associate professor at the University of Florence, who has explored this topic for many years.
A Brief Historical Context
“It all began in 1913,” Beani noted, “when Henri Pieron described sleep as a 'necessary, periodic, and rhythmic change in brain activity that disconnects it from the environment.' For many years, sleep was regarded merely as a passive state marking the end of wakefulness. However, in 1953, a groundbreaking study by Eugene Aserinsky and Nathaniel Kleitman revealed the existence of REM sleep, an active process with distinct characteristics that can be identified through electroencephalogram recordings.” This led to the understanding that sleep comprises both non-REM phases with slow waves and REM phases, which feature fast, low-voltage waves associated with vivid dreams. Beani explains that both mammals and birds exhibit this REM phase. “Current theories suggest that slow-wave sleep is crucial for consolidating declarative memories, while the REM phase supports the retention of emotional experiences.”
Why Do Animals Experience Dreams?
Let's consider an example. “If we take a 30-year-old individual,” Beani states, “who has lived around 11,000 days and sleeps an average of eight hours a night, including two hours of REM sleep, they have spent nearly a thousand days dreaming since birth.” Interestingly, the duration of REM sleep varies among species and doesn't necessarily correlate with intelligence. Research by Jerome Siegel in 2001 indicated that species known for longer REM durations are not necessarily the most intelligent. For instance, the platypus, a primitive mammal with a lengthy REM phase, is less developed at birth, while mature species like whales and dolphins exhibit shorter or no REM sleep. Regardless, all animals dream to some extent. “Sleep fulfills several functions such as conserving energy, regulating brain temperature, and clearing waste from the brain,” Beani explains. “Dreaming, however, is linked to memory consolidation and learning.”
Examples of Animal Dreams
As Aristotle noted in History of Animals, “It seems that not only humans dream, but also horses, dogs, oxen, sheep, and goats; dogs even express their dreams through barking in their sleep.” Cognitive scientist Jason Goldman from the University of Southern California explains that there are two main methods to investigate dream activity in animals: observing physical behaviors during sleep and comparing brain activity patterns during sleep to those during wakefulness. Studies in the 1960s showed unusual movements in sleeping individuals, which is surprising since muscle paralysis typically occurs during REM sleep. Research by Michel Jouvet and J. F. Delorme in 1965 demonstrated that removing part of a cat's brainstem allowed them to move during REM sleep, leading to the phenomenon known as REM-without-atonia. Subsequent studies confirmed this, showing that cats in this state exhibit movements as if hunting.
The second method involves applying non-invasive electrodes to monitor brain activity in sleeping animals. For instance, in 2007, MIT scientists recorded hippocampal activity in mice navigating a maze and found similar patterns during sleep, suggesting the mice were dreaming of their maze experiences. Similarly, Amish Dave and Daniel Margoliash from the University of Chicago observed that zebra finches exhibited identical neuronal activation patterns in their sleep, indicating they might be dreaming of their songs. The examples continue to surprise: Beani mentions that “during sleep, octopuses may change color, likely dreaming of hunting or impressing a mate. Even jellyfish, lacking a true brain, display different pulsation patterns at night.”
Sources: - Thinking chickens: a review of cognition, emotion, and behavior in the domestic chicken - Wide-spread brain activation and reduced CSF flow during avian REM sleep - The REM sleep-memory consolidation hypothesis - What do animals dream about? - Behavioural and EEG effects of paradoxical sleep deprivation in the cat - REM sleep without atonia — from cats to humans - Mechanisms underlying oneiric behaviour released in REM sleep by pontine lesions in cats