The reshaping of the brain
At the age of two, Ben began to see nothing in his left eye and was taken to the hospital by his mother. Doctors found that both of his eyes had developed retinal cancer. After the failure of radiation and chemotherapy, the surgeon removed his eyes. Since then, Ben has lost his vision forever.
However, at the age of seven, the invention developed a trick to decode the world around it: make a "clicking" sound similar to when locking a door with your mouth, and listen to the echo. In this way, it would have been possible to locate objects such as doorways, people, parked cars, and trash cans. His behavior is known as echolocating: emitting sound waves to objects in the environment and capturing reflected echoes to build a mental model of the surrounding environment.
While echolocation sounds like a skill that humans can't possibly master, thousands of blind people are just as proficient at it as Ben. This phenomenon has been documented as early as the 1940s – an article published in Science titled "Echolocation by Blind Men, Bats, and Radar" first coined the term "echolocation."
How does blindness give a person the amazing ability to understand their surroundings with both ears? The answer lies in one of the gifts that evolution has given to the human brain—adaptability.
- Pablo Ruiz T. -
Every time we learn something new, acquire a new skill, or develop a new habit, the physiology of our brain changes. Neurons are cells in the brain responsible for processing information quickly, thousands of them connected to each other, but like the friendships of people in every small group, the connections between them are constantly changing: they will strengthen, they will weaken, and they will find new partners. In neuroscience, we call this phenomenon "brain plasticity," which refers to the brain's ability to take on new shapes like plastic and hold on. However, the latest research has found that the brain's flexibility is far more subtle and complex than its ability to maintain a certain shape. To describe this feature, we use the term "livewiring" to describe brain plasticity to highlight how the brain, a vast system of 86 billion neurons and 200 trillion connections, is rewire all the time.
Neuroscientists once thought that different regions of the brain were born to perform specific functions, but this old paradigm has now been overturned by new discoveries. A certain area of the brain may initially be assigned to handle a particular task. For example, the back of our brain is called the "visual cortex" because it processes vision so often, but this area can also be reassigned to other tasks. Neurons in the visual cortex are nothing special, and in people with normal vision, they just happen to be used to process shape or color, but in blind people, the same neurons can be reshaped to process other forms of information.
Nature gives the human brain full flexibility to adapt to the environment. The brain's ability to reconfigure, like sharp teeth and flying legs, is good for survival. The living threads of the brain make it possible for us to learn, memorize, and develop new skills.
Vova Brown -
In this example, due to the flexible remodeling of the brain, the visual cortex is instead used to process sound. As a result, Ben has more neurons that can be used to process auditory information, and this enhanced processing power also allows Ben to interpret the amazing details of sound waves. Ben's super hearing shows a more general pattern: the more brain areas occupied by a particular sense, the better that sense performs.
There have been some important discoveries about livelines in recent decades, but perhaps the most surprising one is its rapidity. The reorganization of brain circuits occurs not only in people who have just gone blind, but also in visually normal people who are temporarily blind. In one study, visually impaired participants were on a surprise note about how to read Braille, and half of the participants were blindfolded in the process. After five days of study, the blindfolded participants were better able to discern the nuances between Braille symbols than the non-blindfolded participants. Even more striking, the blindfolded participants' visual areas, which react to touch and sound, are activated by them. When the activity of the visual cortex was temporarily interrupted, the braille reading advantage of the blindfolded participants also ceased to exist. In other words, blindfolded participants performed better on tasks involving touch because their visual cortex was recruited to help. After the eye mask is removed, the visual cortex returns to normal within a day and no longer responds to touch and sound.
But such a change doesn't have to take five days, it's just the exact amount of time to measure. When we took continuous measurements of blindfolded participants, within about an hour, activities involving touch were observed in the visual cortex.
- Tang Yau Hoong -
Dreaming – The Battle of the Visual Zone
What does the flexibility of the brain and the rapid takeover of the cortex have to do with dreaming? There may be more connections than we previously thought. Apparently, by redistributing the visual cortex to the other senses, Ben benefited greatly, as he permanently lost both eyes, but what about the blindfolded participants in the experiment? If the loss of one of our senses is only temporary, then the rapid occupation of brain regions by other senses may not be so beneficial.
And we think that's why we dream.
In the endless scramble for brain regions, the visual system faces a unique problem: every 24 hours, every 24 hours, all animals are shrouded in darkness for an average of 12 hours (this, of course, refers to most of the evolutionary process, excluding our current electrified world). Every night of our lives, our ancestors actually became uninformed blindfolded experiment participants.
So, how did the visual cortex of the ancestors' brains guard their territory in the absence of information input from both eyes?
We believe that the way the brain holds the visual cortex brain area is by keeping it active at night. According to our "defensive activation theory," dream sleep exists to keep neurons in the visual cortex active and thus fight against the occupation of neighboring senses. From this point of view, dreams are predominantly visual, precisely because vision is the only sense that is disadvantaged by darkness. Therefore, only the visual cortex is fragile to some extent, and it is necessary to guard its brain area through internally generated activity.
- Dan Gartman -
evidence
1. As we age, the flexibility of the human brain gradually decreases, and the proportion of RAPID EYE movement sleep decreases
In human sleep, there is a period of rapid eye movement (REM) sleep every 90 minutes, and most dreams occur at this time (although some forms of dreams also occur in non-REM sleep, these dreams are abstract and lack the visual vividness of REM dreams).
REM sleep is triggered by a specific set of neurons that directly activate the brain's visual cortex, allowing us to experience vision even when we close our eyes. It can be speculated that this activity of the visual cortex is the reason for the painting-like and cinematic nature of dreams (in the reM movement sleep state, the circuits that trigger the dream also paralyze your muscles so that the brain does not move the body while simulating the visual experience). The anatomical precision of these circuits means that dream sleep is of biological importance—without important functions, such precise and universal circuits would be difficult to evolve.
Regarding dreams, the defensive activity theory makes some clear predictions. For example, if the flexibility of the brain decreases with age, the proportion of REM sleep throughout the sleep cycle should also decrease year by year throughout the person's lifetime. And that's exactly what happened: REM sleep in human babies accounts for about 50 percent of sleep time, but in older adults that percentage drops to about 18 percent. As the brain's flexibility decreases, REM sleep also seems to become less necessary.
- Veronika Stehr -
2. The more flexible the brain, the longer the time spent on REM sleep each night
Of course, the connection between the two is not enough to prove the defensive active theory. To further validate this theory, we expanded our investigation to include animals other than humans. The defensive activity theory makes a clear prediction: the more flexible the brain of an animal, the more REM sleep it should need to protect its sleeping visual system. So we looked at the degree of "pre-programmed" brains of 25 primates at birth and how flexible they are. How can the degree of pre-programming be measured? We studied the time it takes for these animals to develop: how long it takes to wean, how long it takes to learn to walk, and how many years it takes to enter puberty. The faster an animal develops, the higher the degree of preprogramming of the brain, that is, the less flexible it is.
The study found that species with more brain flexibility also spent more time each night on REM sleep, which was consistent with the predictions. Brain flexibility and RAPID EYE movement sleep, two indicators that initially seem unrelated, are actually related.
Incidentally, two of the primates we studied were nocturnal. But that doesn't change the hypothesis: whether animals sleep at night or during the day, the visual cortex is at risk of being taken over by other senses. Nocturnal primates are equipped with powerful night vision abilities, using their vision at night to find food and avoid predation. But then when they sleep during the day, their eyes are closed and they can no longer have visual input, so their visual cortex also needs to be defended.
- Dominik Mayer -
3. People who are born blind (or who are blind at an early age) do not experience visual images in their dreams
Dream circuits are so important that people who are born blind also dream. But people who are born blind (or young) experience visual images in their dreams, but rather other sensory experiences, such as fumbling through a rearranged living room or hearing a strange dog bark. This is because other senses have occupied their visual cortex. That is to say, blind and sighted people have the same brain area that is active when dreaming, but the senses processed in this brain area are different. It is worth noting that people who are blind after the age of 7 have more visual content when they dream than people who are blind at an early age. This is also consistent with the theory of defensive activity: the brain's flexibility decreases with age, so if you are older when blind, the non-visual senses cannot completely conquer the visual cortex.
4. Visual illusions occur when visual input is denied
If dreams are visual hallucinations triggered by a lack of visual input, it can be expected that similar visual hallucinations may also be found in people who are slowly deprived of visual input while awake. And this is true for people with degenerated eyeballs, patients immobilized in the tank-respirator*, and prisoners in solitary confinement. In all these cases, one sees things that do not exist.
*Translator's Note
Tank-respirator: Also known as iron lung, or iron lung, is a medical device that assists patients who have lost the ability to breathe on their own. Most of the users are patients with polio and severe muscle weakness that cause respiratory muscle paralysis. The iron lung is a tightly enclosed metal cylinder connected to the pump, and the patient lies inside the cylinder, leaving only the head exposed. When the iron lung pump inhales and extracts air, due to the change of air pressure in the cylinder, the patient's chest is expanded or compressed accordingly, allowing the patient to carry out passive breathing exercises.
We developed the theory of defensive activity to explain visual illusions that occur in the dark for long periods of time, but the theory may represent a more general principle: the brain has evolved specific circuits that generate activity during periods of input deprivation as compensation. This can occur in several situations: (1) deprivation is regular and predictable (e.g., dreaming while sleeping) ;(2) sensory input pathways are impaired (e.g., tinnitus or phantom limb syndrome) ;(3) deprivation is unpredictable (e.g., hallucinations caused by sensory deprivation). From this perspective, hallucinations during periods of deprivation may actually be a feature of the system, rather than a malfunction.
- lipika S -
Current research and conclusions
We are now working to complete a systematic comparison of species throughout the animal kingdom. For now, the evidence is encouraging. Some mammals are immature at birth, unable to regulate their body temperature, food or self-protection (such as kittens, puppies, and ferrets); while some mammals are born mature, grow teeth and hair in the womb, can open their eyes, have the ability to regulate body temperature, walk less than an hour after birth, and can eat solid foods (such as guinea pigs, sheep and giraffes). ReM sleep in immature animals at birth is up to 8 times higher than in mature animals at birth. Why? Because when the pups' brains are highly flexible, the system requires more activity to protect the visual system during sleep.
Ever since humans had language, dreams have puzzled philosophers, priests, and poets. What is the meaning of dreams? Do dreams herald the future? In recent decades, as one of the core unsolved mysteries in the field of neuroscience, dreams have been in the attention of neuroscientists. Do dreams have a more practical, functional purpose? We believe that dream sleep exists, at least in part, to prevent other senses from occupying the visual cortex of the brain when vision is not being used. Dreams are too high balance for the flexibility of the brain. So, although dreams have long been the subject of ballads and stories, perhaps dreams can also be better understood as the crystallization of the strange love of brain plasticity and the rotation of the earth.
By David Eagleman & Don Vaughn
Translation: Tooth tooth | Reviewed: Sixin | Cover: lipika S
Edit: Pheasant | Typography: Light and shadow
Original: https://time.com/5925206/why-do-we-dream/