Have you ever woken up from a dream that was so vivid and lifelike that  it actually seemed real? It's such a surreal experience that it may make  you wonder: What exactly is a dream, anyway? Scientists have long tried  to figure that out. The basic definition is that dreams are  subconscious imaginings that contain sounds, images, and other  sensations while you sleep.


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Dream States

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IF YOU HAVE SEEN the recent Hollywood blockbuster Inception, a movie that does to dreaming what The Matrix did for virtual reality, you may have been holding your breath as Ariadne, an architecture student, folded the streets of Paris over herself like a blanket. This stunning sequence, an homage to M. C. Escher, is testimony to the bizarre nature of dreams. Watching it made the neuroscientist in me reflect on what dreams are and how they relate to the brain.

The first question is easy to answer. Dreams are vivid, sensorimotor hallucinations with a narrative structure. We experience them consciously—seeing, hearing and touching within environments that appear completely real (though curiously, we do not smell in our dreams). Nor are we mere passive observers: we speak, fight, love and run.

Dream consciousness is not the same as wakeful consciousness. We are for the most part unable to introspect—to wonder about our uncanny ability to fly or to meet somebody long dead. Only rarely do we control our dreams; rather things happen, and we go along for the ride.


Everyone dreams, including dogs, cats and other mammals. But sleep lab data reveal that people consistently underreport how often and how much. The reason is that dreams are ephemeral. Memory for dreams is very limited and largely restricted to the period before awakening. The only way to remember a dream is to immediately recall it on waking and then write it down or describe it to another person. Only then does its content become encoded in memory.

Although we often have trouble remembering dreams, our dreaming selves have full access to our pasts. In dreams we recall earlier episodes from our lives, and we often experience intense feelings of sadness, fear, anxiety or joy. Perhaps it was this heightened emotionality that led Sigmund Freud to speculate that dreams serve as wish fulfillment. Regardless, the answer to my second question—how and why does the brain manufacture dreams?—remains a fundamental mystery. But psychologists and brain scientists have recently renewed their interest in this everyday surreal activity.

Perchance to Dream
In 1953 Nathaniel Kleitman of the University of Chicago and his graduate student Eugene Aserinsky discovered that slumber, which had been considered a single continuous period of downtime, contains recurring periods in which the sleeper’s eyes move about, heartbeat and breathing become irregular, most voluntary muscles are paralyzed and brain activity (as measured by electroencephalography) is heightened. These fast, low-voltage brain waves resemble the ones that occur during wakefulness. This state became known as rapid eye movement (REM) sleep, to distinguish it from deep sleep.

When people are woken from REM sleep, they usually report vivid dreams. Such reports do not occur when people are roused from non-REM sleep. Thus arose the close association between REM sleep and the oneiric state. For many years experts associated dream consciousness with the distinct physiology of the brain during REM sleep.

But in the past several decades that understanding has begun to slowly shift. When people who are woken from deep sleep are asked “What was passing through your mind just before you woke up?” rather than the more biased “Have you been dreaming?” a more nuanced picture emerges.


In the early phases of deep sleep, and during short daytime naps, which consist of pure non-REM sleep, people report vivid hallucinations that are shorter, more static and more thoughtlike than the dreams that occur during REM sleep. These visions are typically more like snapshots than narratives and do not include a self. Yet a minority of non-REM dream reports are indistinguishable from REM dreams. It is also notable that sleepwalking and nightmares occur in deep, not REM, sleep. Thus, scientists have had to revise the belief that the REM state is an external manifestation of the subjective dream state.

Further evidence comes from the study of brain-damaged patients by neuropsychoanalyst Mark Solms of the University of Cape Town in South Africa. When a part of the brain stem known as the pons is destroyed, people no longer experience REM sleep. But only one in 26 of such patients reports a loss of dreaming, and nobody has ever reported loss of dreaming from limited pons damage.

The regions critical for dreaming are not in the pons. They include the visual and audiovisual regions in and near the temporoparietal-occipital junction in the neocortex. Destruction of small portions of these areas leads to the loss of specific dreaming dimensions. For example, a stroke, tumor or other calamity in the cortical region necessary for color or motion perception will leach hue or movement from dreams.

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Moreover, medications that manipulate dopamine levels strongly affect dreaming while leaving the REM sleep cycle unaffected. L-dopa, the most popular medication for Parkinson’s disease, increases the frequency and vividness of dreams, whereas antipsychotic drugs that block dopamine reduce dreaming.

The dissociation of dreaming from REM sleep serves as a conceptual clearing of the deck for neuroscientists such as myself. Now we can focus on the neuronal causes of conscious mental activity, whether in a dreaming or wakeful state, without being confused by extraneous factors such as REM or non-REM sleep that, it turns out, do not pertain to subjective experience per se.


The Mind-Body Problem
Why am I so confident I experience anything while dreaming? Maybe I am unconscious while slumbering and confabulate my dreams when I awaken.

This is unlikely for many reasons. The bizarreness and vividness of dreams are distinct from normal experience and therefore unlikely to be “retrofitted.” Indeed, people with memory deficits do not report fewer dreams. Additionally, the length of dream reports correlates well with time elapsed in REM dreams.

More evidence comes from people with REM sleep behavior disorder, who lack the muscle paralysis, known as atonia, typical of REM sleep. They act out their dreams, sometimes even harming themselves or bed partners, and their actions match their dream reports. They might, for instance, move their legs while asleep and later report that they dreamed of walking.

Dreams are of great interest to the student of the mind-body problem, because they bear witness that the brain alone is sufficient to generate consciousness. We dream with eyes shut in the dark, disconnected from the outside world. The brain regions responsible for basic sensory perception are deactivated. Nor is behavior necessary, as we are motionless except for our breathing and eye movements. Thus, dreaming supports the old philosophical brain-in-the-vat idea that saw its modern renaissance in The Matrix.

Cognitive neuroscientists have recently learned to decode some simple mental states—in essence, a primitive form of mind reading. When scientists ask people to view one of two images—a portrait or a photograph of a house—or to imagine either a face or a house, they can tell from brain analyses which of the two the person is seeing or imagining.


Once such techniques become more sophisticated, they could be put to use in dream work, so that in addition to studying the physiology of the dreaming brain, investigators will be able to read out the content of the dream itself. Then neuroscience will be in a much better position to answer the age-old questions that have fascinated everyone from oracles and shamans to Freud and, more recently, science-fiction enthusiasts: Why do we dream, and what do dreams mean?

This article was originally published with the title "Consciousness Redux: Dream States" in SA Mind 21, 5, 16-17 (November 2010)


(Further Reading)

  • Dreaming and the Brain: Toward a Cognitive Neuroscience of Conscious States. J. Allan Hobson, Edward F. Pace-Schott and Robert Stickgold in Behavioral and Brain Sciences, Vol. 23, pages 793–842; 2000.
  • Dreaming and REM Sleep Are Controlled by Different Brain Mechanisms. Mark Solms in Behavioral and Brain Sciences, Vol. 23, pages 843–850; 2000.
  • Dreaming and the Brain: From Phenomenology to Neurophysiology. Yuval Nir and Giulio Tononi in Trends in Cognitive Sciences, Vol. 14, pages 88–100; 2010.


CHRISTOF KOCH is Lois and Victor Troendle Professor of Cognitive and Behavioral Biology at the California Institute of Technology. He serves on Scientific American Mind's board of advisers.



December 10, 2019 — Christopher Intagliata


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sleeping types

What happends when your sleeping

Demons, Falling from High, Dream Within a Dream: 5 Things That Happen When You're Sleeping

Here are the weirdest things that you may experience when you're sleeping, and their scientific explanations.

 You'd understand what I'm talking about when I say that it's the most relaxing time of the day. There's no better feeling than putting your head on your fluffy pillow, resting your eyes a little bit, checking your phone, watching something on Netflix, and relieving your tiredness. Sleep indeed is one of the most beautiful parts of living, and eating would be the runner-up.


However, even sleeping can be trouble for humans. Sometimes you don't want to go to sleep because you have the same nightmare every night, you have the boogeyman under your bed, or you have sleep apnea that sleeping makes you even more tired than working for hours.

But these aren't the only concerns we have about sleeping. There are more interesting things than having the same nightmare, more real things than the boogeyman and, well, more mysterious things than sleep apnea.

Here are the basic scientific explanations for the things we experience during sleep.

1. Sleep Paralysis

Have you ever had a moment where you can't move, speak or scream while you're falling asleep or waking up? Sometimes when you're experiencing this, you might see a shadow in the corner of your room, you feel someone's breath on your ear or someone's hands on your throat. If so, for sure you got scared, especially when it happened for the first time, but there's nothing to be scared of.

It actually has a simple, very simple explanation. If the sleep paralysis happens when you're waking up, it's called hypnopompic or postdormital sleep paralysis and if it happens when you're falling asleep, it's called hypnagogic or predormital sleep paralysis.

When you're falling asleep, your body slowly relaxes, you become less aware, and your body becomes less responsive to your brain signals. However, if you become aware or remain awake while you're falling asleep and while your body starts to relax, you'd realize that you can't speak or move.

It's different when you're waking up. Sleep has two stages; NREM sleep and REM sleep. NREM also has three different stages; the first stage is the transition from being awake to falling asleep. Heartbeats and breathing begin to slow. This stage lasts usually for 5-10 minutes and it constitutes 5% of sleep time.

The second stage lasts usually for 10 to 25 minutes, and it's considered a period of light sleep. Heart rate slows, muscles relax, eye movements stop. It constitutes 55% of total sleep time.

The third stage of the NREM sleep, "slow-wave," "delta," or "deep" sleep is the stage of sleep that lasts for 20 to 40 minutes and needed for an individual to feel refreshed in the morning. Heart rate and breathing become the lowest level, blood pressure falls and body temperature drops. It's the most difficult stage of sleep to wake up and represents 15% of total sleep time. 

Demons, Falling from High, Dream Within a Dream: 5 Things That Happen When You're Sleeping

After about 90 minutes into sleeping, a person enters REM sleep. This is the stage where a person's eyes move from side to side beneath closed eyelids. At this stage, most of the dreaming occurs. While heartbeats increase and blood pressure rise, arms and legs become unable to move, due to the reason of not acting out the dreams we have. Adults spend 20-25% of their total sleep time in REM sleep.

If you regain your consciousness and start to wake up before your REM sleep cycle finishes, you'll be unable to move or speak since your muscles are turned off to avoid acting out your dreams. 

As you can see, it's not something that you should be scared of, just stay calm when it happens, and it'll go away in seconds.

2. Hypnic Jerk

Sometimes when you're sleeping like an angel or like a gorgoneion, you wake up abruptly feeling like you're falling down. At the same time, you see yourself falling from a cliff, from the 17th floor or anywhere and you wake up jumping.

Hypnic jerks, also known as sleep starts, mostly happens when you're falling asleep and it's caused by a form of involuntary muscle twitch called myoclonus, hiccups are also a form of myoclonus.

There's no exact cause for hypnic jerks, but its possible causes include anxiety, caffeine, nicotine, stress, and sleep deprivation.

3. Sleepwalking

This is one of the scariest things that can happen when you're sleeping, except for the ghost of the old lady that used to live in your apartment and died horribly. Hehe, just kidding.

Sleepwalking basically is a behavior disorder occurs during sleep and performing walking or other behaviors while sleeping. Behaviors of people who sleepwalk may include, sitting up in their beds, walking around the house, leaving the house, driving, and sometimes even eating.

Demons, Falling from High, Dream Within a Dream: 5 Things That Happen When You're Sleeping

Sleepwalking usually occurs in the first hours of sleep. There's not an exact cause of sleepwalking but it's mostly seen in people with a sleepwalking behavior in the family history. Sleep deprivation, stress, anxiety, and certain types of medication can also cause sleepwalking.

4. Lucid Dreaming

During a lucid dream, the person is aware that s/he is dreaming. The dreamer may gain control of his or her dream, and lead the characters, environment, and the narrative in the way s/he wants.

Lucid dreaming has been studied from ancient times until today, and people have been fascinated by it. Lucid dreaming usually happens during REM sleep. Around 55% of people experience a lucid dream once or more in their lifetime while some other people train themselves to dream lucidly.

So, let's say a killer is chasing you in a dream and you're running away from him, and then you say to yourself "Wait for a second, why am I running from a killer in the middle of the night in an abandoned hospital? I didn't even come here, so, this is a dream. Let me just fly away from this jerk." This is exactly what happens when you're lucid dreaming.

5. False Awakening

Say, you're having a dream, a scary one. And you finally wake up, the monsters are gone. So you take a deep breath, go to the bathroom, wash your face, and what the ACTUAL HELL?! The monster is right behind you? What? Was it all real? Oh dear God, run! And everything starts from the beginning. Ah man, you have to run from the monster again. 

And then you wake up, this time for real. Or maybe not? Keep on trying until you wake up to real life. 

A false awakening is actually a thing that can happen to anyone. Sometimes it can be a dream within a dream, or maybe a dream within a dream within a dream, like a Russian nested doll. It can be caused by sleep apnea, insomnia, anxiety, mixed brain states or other causes. 

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This information was found on the Interesting Engineering website. Click the link below to find out more.

A very scary dream i had

Please contact me if you've had similar dreams

  I was outside under a parking lot awning next to a large building at night with 20 to 30 people. The sky's where dark and cloudy. It wasn't cold. All of a sudden I heard what sounded like a whining grinding gear sound above us. I stepped out from under the awning and looked up at the sky. I saw 4 black helicopters flying around two large white orbs going in and out of the clouds. I couldn't take my eyes off of it. All of a sudden I seen smaller crafts flying everywhere like bats all over the sky. The big light of the craft broke from the clouds coming down towards us. I backed up back under the awning with the rest of the people. And without lighting up the buildings near by or the street in front of us, the craft showed up 10 feet from the ground 20 feet in front of us. Nobody was talking or making any sound, just staring at this huge ship that looked like some star wars fighting jet. All of a sudden it started floating upwards to a point where we couldn't see it because of the roof we where under. Everyone was just staring out at the street. The gear whining sound was so loud it took over all sounds around us. All of a sudden a skinny whitish/blueish beam hit the street in front of us making an electrical snapping sound as it hit the concrete slowly moving towards us. I felt a strong pulling feeling on my body like gravity pulling my towards the beam. I turned around a grabbed a pipe the was holding up the roof above us when I noticed almost every body that was with me under that awning was on their backs and stomachs sliding towards the white crackling beam. When they slid out from under the roof they all started floating up in the air towards the craft. Everyone that was with me where now gone as I held on to that poll for my life. I heard the whining  gear sound slow down and the gravity feeling was now less but still slightly pulling on my body.  I let go of the poll and dropped  to my knees and with everything i got, i crawled away from the beam. I saw a doorway 10 feet away. I slowly crawled to it. There was large bolders in this room. It took every ounce of energy i had to pull myself over these bolders with gravity pulling me backwards to hide in the back of this room. I stopped and looked behind me and saw a short being standing there in a sparkling suit that seemed to be changing colors everytime he moved. He had some type of hood on with white shoulder length hair poking out. He had some sort of handheld device he was tapping on. I was so scared I couldn't talk well, and I mumbled..." i just want to learn more about you " and he/it responded to me without words..." then why don't you come with us " his face was not smiling but a  picture in my head of him WAS !

I felt like my body compressed into nothing and i woke up with my heart pounding. I kept thinking of this over and over so i could remember this and write it down as the scariest dream I've ever had. 

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From @ElectroDeeJ on Twitter

So here my short dream. I can remember I‘ve walked in the middle of the night alone on a street. Everything was quiet and calm, a clear sky, no clouds. Suddenly I‘ve a round shaped beam of light shot down to the ground out of nowhere. I was indeed captured in this light and I knew immediately what it was. Then I lifted off the ground and was pulled into the air. The ground below me became tinier and tinier and before I was at the end of this light beam I woke up and it scared the hell out of me. For god’s sake it was just a dream..... or wasn‘t it?

Suddenly a round shaped beam of light.....

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