Dreams have captivated humanity for ages, sparking curiosity and countless interpretations. From ancient civilizations to modern science, the question “Why Do People Dream?” remains a profound enigma. While we may not have all the answers, compelling theories are emerging, suggesting dreams play crucial roles in our emotional well-being, cognitive functions, and even brain maintenance.
For a long time, dreams were relegated to the realm of the subconscious, often associated with hidden desires or unresolved conflicts. Some psychological theories proposed that dreams serve as a stage for processing emotions, working through problems, or grappling with suppressed wishes. Others hypothesized that dreams were simply byproducts of random brain activity during sleep, devoid of any inherent purpose. More recently, neuroscience is offering intriguing new perspectives, venturing into the biological necessity of dreaming. One such theory, championed by neuroscientist David Eagleman from Stanford University, proposes a fascinating idea: dreams might be essential for protecting our visual cortex.
Eagleman’s theory centers around the brain’s remarkable adaptability, a concept known as neuroplasticity. The brain is not a static organ; it’s constantly rewiring itself based on experiences. Neurons, the fundamental building blocks of the brain, are in a perpetual state of competition for resources and territory. Eagleman explains this as a “do-or-die competition” where sensory areas of the brain gain or lose neural territory depending on the input they receive. Throughout our lives, experiences mold and reshape the brain’s intricate map. Think of it like neighboring countries constantly vying for boundaries, neurons are perpetually defending their designated areas.
This concept of brain plasticity is vividly illustrated in cases of children who have undergone hemispherectomies, the removal of half of their brain, due to severe medical conditions. Remarkably, these children can often regain near-normal function as the remaining brain reorganizes itself to compensate for the missing hemisphere. Similarly, individuals who lose sight or hearing often exhibit heightened sensitivity in their remaining senses. This is because the brain regions that were previously dedicated to the lost sense are taken over and repurposed by other sensory inputs, enhancing their capabilities.
The speed at which this neural reorganization can occur is astonishing. Studies conducted by Lotfi Merabet and his team at Harvard Medical School in 2007 and 2008 demonstrated just how rapidly this sensory takeover can begin. Their 2008 study, involving blindfolded participants, revealed that the process of other senses seizing idle brain areas can commence in as little as 90 minutes. Further research even suggests this can happen within a mere 45 minutes of sensory deprivation.
Now, let’s connect this to sleep and dreaming. When we sleep, our senses, except for vision during REM sleep, are significantly reduced. About 90 minutes after we fall asleep, we typically enter REM (Rapid Eye Movement) sleep. This phase is initiated by neurons in the brainstem, the stalk-like structure at the base of the brain, triggering two crucial events. First, these neurons induce muscle paralysis, preventing us from physically acting out our dreams. Second, they send signals directly to the visual cortex, the brain region responsible for processing visual information, initiating the dream experience.
Eagleman argues that the timing of REM sleep – approximately every 90 minutes – aligns perfectly with the timeframe in which the visual cortex needs to defend itself. Brain scans of people during REM sleep reveal that the majority of brain activity is concentrated within the visual cortex. According to Eagleman’s theory, dreams are the brain’s ingenious mechanism to prevent sensory encroachment during sleep. REM sleep and the accompanying dreams are, therefore, internally generated activity within the visual cortex, acting as a safeguard for its territory. As long as the neurons in the visual cortex are actively engaged in their primary function – generating visual imagery, as they do in dreams – they are less likely to be co-opted by neighboring neurons processing other sensory information like sound or touch.
Eagleman further posits that the degree of brain plasticity is directly related to the necessity of REM sleep. The more adaptable the brain, the more crucial REM sleep becomes for this defensive action. Infants, with their highly plastic and rapidly developing brains, spend a significant portion of their sleep – almost 50% – in REM. As we age, and our brains become less malleable (think about the ease with which children learn languages compared to adults), the proportion of REM sleep decreases.
This correlation between brain adaptability and REM sleep extends across species. Eagleman points out that human brains are born “half-baked,” relying heavily on experience to shape their development. Species with less hardwired brains at birth, like humans, possess greater adaptability and learning capacity. However, this adaptability comes with trade-offs. For instance, newborn fawns and calves can walk within hours of birth because this behavior is hardwired into their brains. Human babies, with their more adaptable brains, require considerably more REM sleep than animals born with more pre-programmed instincts.
While Eagleman’s theory offers a compelling perspective on why we dream, it’s not without its critics within the dream research community. One point of contention is the existence of REM sleep in blind mole rats, animals that lack vision. If dreams are solely for visual cortex protection, why would a blind creature still experience REM sleep? However, Eagleman counters this by suggesting that some evolutionary traits can become vestigial, remnants of functions that were once crucial but have become less relevant over evolutionary time. Perhaps blind mole rats retained REM sleep as a leftover trait from sighted ancestors, even though it no longer serves a visual protective function.
Antonio Zadra, a dream researcher at the University of Montreal, is a prominent critic, asserting that Eagleman’s theory “has little to do with actual dreaming and explains almost nothing about dreams per se, as opposed to REM sleep.” He considers the theory “silly and overly reductionistic and simplistic,” arguing it focuses too narrowly on visual cortex protection and neglects other potential functions of dreams and REM sleep.
However, Deirdre Leigh Barrett, a psychologist at Harvard University and former president of the International Association for the Study of Dreams, offers a more nuanced perspective. While acknowledging some reservations about the singular focus on visual protection, she finds the correlation between brain complexity and REM sleep intriguing and “very convincing.” She is more open to considering Eagleman’s hypothesis as a potential piece in the larger puzzle of why we dream.
Eagleman himself acknowledges that his theory may not be the sole explanation for dreaming and that REM sleep likely serves multiple purposes beyond just safeguarding the visual cortex. He uses the analogy of a computer screensaver, activated periodically – in this case, every 90 minutes – not to prevent screen burn-in, but to prevent the visual cortex from being overtaken by other sensory functions during sleep. These nightly visual hallucinations we experience as dreams, therefore, might paradoxically be essential for maintaining our ability to see clearly during our waking hours. The mystery of why we dream continues to unfold, and Eagleman’s theory adds a fascinating and biologically grounded dimension to this age-old question.
