A theory suggests that dreams are a way for the visual cortex of the brain to defend itself against being “taken over” to process inputs from other senses.
Visual Cortex Defense Theory
David Eagleman, a neuroscientist at Stanford University, proposes the idea that dreaming is essential for protecting the visual cortex – the part of the brain responsible for processing vision. Eagleman’s theory takes into account that the human brain is highly adaptable, with some regions capable of taking on new tasks, and this ability is called neural plasticity. Eagleman states that neurons compete for survival. The brain, according to Eagleman, allocates its resources by “performing a critical competition” for the sensory areas of the brain, where regions can gain or lose neural territory “when input slows down, stops, or shifts.” Experiences over a lifetime reshape the brain’s map. “Just like neighboring countries, neurons define their territories and continuously defend them,” says Eagleman.
Rapid Reorganization
Reorganization can occur quickly. Studies published in 2007 and 2008 by Lotfi Merabet from Harvard Medical School and colleagues demonstrated how quickly this takeover happens. A 2008 study where participants were made blind showed that the takeover of an inactive area by other senses begins in just 90 minutes. Other studies found that this can occur in as little as 45 minutes.
The Role of Dreaming in Defending the Visual Cortex
When we sleep, we can smell, hear, and feel, but visual information is absent – except during REM sleep. About 90 minutes after dozing off, one enters REM sleep. This begins when neurons in the brainstem, the stalk-like part at the base of the organ, send a signal to start two important tasks. The activity of these neurons, for instance, paralyzes the major muscles, preventing the sleeper from acting out what happens in the dream. These neurons also send direct messages to the visual cortex, initiating the dreaming process.
Adaptation and REM Sleep
Eagleman states that the more flexible the brain, the more REM sleep is necessary for defense. For children to develop properly, they must sleep a lot, spending nearly 50 percent of their time in REM sleep. However, as we age, the brain becomes less flexible. At the same time, adults spend less time in REM sleep.
Harmony Between Adaptability and REM Sleep
The harmony between adaptability and REM sleep appears to apply to all species. According to Eagleman, “Mother Nature gives human brains half-cooked to the world and allows experience to take control and shape them.” He states that the less practiced the brains of species at birth, the greater their adaptability and ability to learn from experience. But this has its downsides. For instance, deer and calves can walk within hours of birth because the behavior is hardwired. Human infants, with their more adaptable brains, need significantly more REM sleep than animals born with more adaptable brains.
Differences in Opinion
Opinions among researchers, especially dream researchers, differ regarding Eagleman’s hypothesis. Antonio Zadra, a dream researcher at the University of Montreal, points out that Eagleman’s theory “has little to do with actual dreams and explains almost nothing about dreams themselves, as opposed to REM sleep.” He asserts that the theory is “silly and overly simplistic.” Meanwhile, Deirdre Leigh Barrett, a psychologist at Harvard University and a former president of the International Association for the Study of Dreams and author of the book “The Committee of Sleep,” is more willing to consider Eagleman’s hypothesis. “It’s very compelling that there is a connection between smarter animals and more complex brains,” she says. Regarding the theory that dreams defend the brain, “I have some issue with the visual argument, but it’s an interesting one.”
The Role
REM Sleep in Protecting the Visual Cortex
Eigman says his theory could expand to encompass other explanations for dreams and that REM sleep may serve multiple purposes in addition to protecting the visual cortex. Think of dreaming like a protected computer screen that operates every 90 minutes – except instead of shielding against frozen images, dreaming prevents the visual cortex from being taken over by other functions. These visual hallucinations at night may allow us to see better during the day.
Roberta McLain is a teacher, freelance writer, and teacher at a boarding school based in Boston. She has become increasingly aware of the need for better scientific communication while teaching high school science for multiple decades. She holds a bachelor’s degree in biological sciences and psychology and a master’s degree in biological sciences. She is a graduate student in the science writing program at Johns Hopkins University. Follow her on LinkedIn and Twitter @MclainRoberta or email her at [email protected]
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