October 7, 2019
Sensory Information in Dreams: Sighted vs Blind
Abstract lip drawingSource: Impressions | Penelope Peru Photography
Vivid, colorful imagery; stomach-dropping falls; jumbled conversations. Dreams are brimming with sensory information, whether you’re running from “Slenderman,” shaking hands with a celebrity, or screaming because you forgot to wear pants to school.
Where does this sensory information come from? How does blindness affect your dreams?
What Are Dreams?
Dreams are a blend of thoughts and sensations that come together as neurons fire while sleeping. On average, humans spend two hours each night dreaming, with the most vivid dreams occurring during REM sleep, according to the National Institute of Neurological Disorders and Stroke.
Artistic depiction of a girl holding a skateboard in a dreamSource: Impressions | Penelope Peru Photography
Although the most vivid dreams occur during rapid eye movement sleep, they aren’t exclusive to the REM-stage, reports a study published in Nature Neuroscience two years ago.
Using an electroencephalography to monitor brain activity, the researchers were able to differentiate whether the participants were dreaming or not during both REM and NREM sleep. They were also able to correlate activity in various posterior cortical regions with the content of the participants’ dreams.
For context, the posterior parietal cortex is the region of our brain responsible for spatial representation and attention, which guides perception and planned movements, according to Science Direct.
The visual cortex is also in the posterior cortical region, which is responsible for processing visual stimuli, says a book by experts from Creighton University.
In short, dreaming activates the brain regions associated with visuospatial perception and visual stimuli. Additionally, dream content – thoughts, perceptions, faces, speech, and so forth – can be traced to activity in those respective areas of the brain.
Memory and emotional regulation play a critical role in the formation of our dreams, too, finds a 2017 study published in the Public Library of Science One.
For one week, researchers asked the participants to identify elements from their daily lives in their dreams and score their importance as well as their emotional intensity.
The participants rated most of these elements in their dreams as important, seeing less value in more mundane daily elements. They also rated both positive and negative dream representations of their living experiences as less emotionally intense than their original waking experiences.
Considering that our dreams are largely formed from our visual perceptions and memories, what might someone dream if they’re blind?
What Do The Blind Dream Of?
Tommy Edison, who has been blind since birth, describes how he dreamsSource: How Blind People Dream | The Tommy Edison Experience
Both those who were born blind (congenitally blind) and those who lost their sight later in life dream. In a 2014 study published in Sleep Medicine, researchers found those who are congenitally blind had dreams that relied more on their hearing or other senses, such as touch, taste, and scent. The congenitally blind participants were also more likely to report having nightmares.
Those who lost their sight later in life still had visual dreams, but the length of the visuals varied depending on how long they had been blind for. The visual content in their dreams may stem from their memories of being able to see or the structures that developed in the posterior cortical regions while they had sight.
Yet, other studies show the congenitally blind may have visual content in their dreams. A 2003 study published in Cognitive Brain Research asked congenitally blind participants to draw what they remember seeing from their dreams and compared them to the drawings from sighted participants.
The drawings were comparable, indicating that both groups had visual activity in their dreams.
Another 2003 Trends in Cognitive Sciences study demonstrated the activation of the cortical regions responsible for visual perception.
However, it’s important to take into consideration the structural differences in the visual cortex of those who are blind versus sighted.
While a sighted individual’s visual cortex responds to visual stimuli, research published in the Journal of Neuroscience found the visual cortex of blind individuals responded to their sense of touch while reading nouns in Braille. Their visual cortex also showed activity while hearing nouns.
Visual cortex activity also differed among individuals who had been blind since their early childhood in comparison to those who lost their sight later in life.
This study is a demonstration of how the brain reorganizes and restructures itself in the event of sensory deprivation. Although blind individuals can’t see, their other senses are feeding information to the visual cortex to compensate for the lack of visual stimuli.
In more recent years, researchers have used technology to take advantage of how the brain can restructure itself to adapt. For example, the BrainPort uses electrodes to simulate perception in blind individuals. While they can’t visualize what they’re looking at, the visual stimuli is redirected as a sensation on their tongue that allows them to perceive their surroundings.
Demonstration of the BrainPort in an individual who lost their sight for five yearsSource: How Is It Possible To USE YOUR TONGUE To See The World Again? | Upworthy
Considering that physical and auditory sensations activate the visual cortex in blind individuals, it calls into question whether the blind participants in the dream studies were “visualizing” the activity. Their visual cortex may have been active during their dreams because their other senses provide the information necessary for them to attain spatial awareness.
Perhaps the drawings weren’t of visuals in the blind participants dreams, rather, the “impressions” of visuals, as described during the video demonstration of the BrainPort.
Dreaming activates the regions of the brain responsible for processing visual stimuli and attaining spatial awareness. Dreams also rely on information from our memories and emotions.
Research shows that both congenitally blind and late blind individuals dream and may have visual content in their dreams based on the activity in posterior cortical regions that are comparable to sighted individuals.
However, it’s important to bare in mind that other senses feed information into the visual cortex of blind individuals to compensate for the lack of visual stimuli. This allows them to still navigate the world based on what they can hear and feel without being able to see what’s in front of them.
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