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Zack Lynch is author of The Neuro Revolution: How Brain Science Is Changing Our World (St. Martin's Press, July 2009).
He is the founder and executive director of the Neurotechnology Industry Organization (NIO) and co-founder of NeuroInsights. He serves on the advisory boards of the McGovern Institute for Brain Research at MIT, the Center for Neuroeconomic Studies, Science Progress, and SocialText, a social software company. Please send newsworthy items or feedback - to Zack Lynch.
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Brain Waves

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April 13, 2004

What Do Dreams Mean?

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Posted by Zack Lynch

Dennis Coates has an interesting post on why we dream (here). As he describes, "I’ve done a lot of reading about the brain and personality as a part of my research for MindFrames, and over the years I've revisited the scientific literature on dreaming a number of times."

My bottom line is that scientists still don't know why we dream. There have been a lot of theories, some of them over 100 years old, but none of them have been validated by research.

My preferred theory about why we dream, based on some of the new findings in sleep research, a separate area of inquiry. When asked why we sleep, researchers have much to say, but it’s mostly descriptive. They’ve identified three stages of sleep, in which EEGs show low-frequency brain waves, accompanied by reduced muscle tone, heart rate and breathing. These three stages are believed to be preparatory stages, after which the brain switches into a fourth, much deeper stage of sleep, which is marked by high-frequency brain waves, and practically no muscle tone. This is known as REM (rapid-eye-movement) sleep, which lasts 30-45 minutes and begins again in cycles of 90-120 minutes. Subjects report dreams five times as often in this fourth stage.

The most plausible explanation for why we sleep is that when the brain is active during waking hours, brain cell metabolism produces chemical byproducts. These need to be cleared out and replaced on a regular basis or they accumulate and get in the way of normal neurotransmitter activity, causing the sensation of being "mentally tired." Without mental rest (sleep), the brain would have difficulty functioning. This process is similar to what happens during "muscle fatigue." Prolonged use of a muscle area creates the waste byproducts of exercise metabolism, causing the sensation of need for physical rest, which gives the body time to remove these byproducts.

Moreover, the whole body requires rest in order to regenerate. The autonomic nervous system consists of two subsystems: sympathetic and parasympathetic. Both cannot be active at the same time; when one predominates, the other is switched off. When we’re active and coping with challenges and stressful situations, we're using our sympathetic nervous system. In this state, the human organism uses up energy. When we're calm and passive, the parasympathetic nervous system kicks in, so that the body can repair and restore itself. During rest, the immune system builds itself back up again. Without rest, we heal more slowly and are more vulnerable to disease. The importance of sleep, then, is that it forces this mental and physical inactivity upon us.

The above describes what happens, but it doesn’t explain why people dream. Freud believed that dreams were the experience of “the unconscious,” a repository for sexual and violent urges too raw to be dealt with consciously. Another long-standing theory is that dreams are how people sort through and integrate daily experience. I've also heard some say that dreams occur because the creative part of ourselves needs to be free to express itself, which it can't do adequately while we're awake. But these are all unproven speculations."

What do dreams mean to you?

Comments (21) + TrackBacks (0) | Category: Mental Health Issues


1. A.R. Yngve on April 16, 2004 6:31 PM writes...

It makes sense that the brain, like any other tissue, needs to rest and regenerate after a day's work. And the brain is "on" ALL DAY. It must be pretty exhausted when you finally fall asleep!

If the brain is like a computer, maybe dreams are simply when the brain processes loose bits of data that haven't been properly cataloged and indexed? A sort of "shuffling and stacking the cards" on a subconscious level, based on pure association (shape, color, properties)... which would explain how things morph into other things in dreams.

Also consider the likelihood that this "free-form shuffling" of data occurs while we're awake. It could be that the mind "dreams" 24 hours a day... but we're only aware of it during sleep, when the conscious parts of the mind are shut down.

Dreaming is always, waking is temporary... ;)

-A.R. Yngve

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2. Steven Zins on April 16, 2004 9:44 PM writes...

Given that why we sleep is to shut down brain-level thinking so that cell-level regeneration can occur. What then is dreaming? Well, assume that the brain has various structures (not to mention myriad processes) and the cell-level regeneration does not happen at the same time in all these structures. Therefore, at a given time, certain structures are functioning/thinking and others are non-functioning/regenerating. Everything else can follow from this. The main post, for example, associates REM sleep with "practically no muscle tone."; the muscle excitation structures are regenerating. Also, various frequencies are associated with various states, a state being a set of functioning structures; individual structures and sets of structures have specific excitation time constants associated with them. Etc.

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3. Peter Hankins on April 18, 2004 11:30 AM writes...

Very interesting. Surely sleep must have something to do with the pattern of day and night on this planet, not just the need to rest? I agree, though, with the conclusion that we dream because that’s all the brain can do without continuous input from the senses, which are turned off during sleep. Personally, I think the resemblance between reality and dreams is almost invariably overstated. I think dreams are always second-order stuff - you don't see things in dreams, you believe that you see things; you don't have experiences, you think you have had experiences. But perhaps my dreams are just less vivid than other people's?

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4. Gyan on April 21, 2004 6:55 AM writes...

The quoted commenter doesn't actually indicate his preferred theory of dreams.

To add to what Peter Hankins said, haven't there been experiments where the natural circadian rhythm loops in a 2-hour cycle as opposed to the 24-hour Earth cycle? From what I know, melatonin synthesis is controlled by activity of the suprachiasmatic nuclei, which in turn is stimulated by a branched output of the optic nerve.

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5. Gabe Gabriel on April 22, 2004 5:16 AM writes...

I tend to believe that all of the above comments about the dream state are correct.The dream state is a product of the mind and may be the most dynamic part of us all.It would seem to me that the dream state is our connection to the other dimensions in which we live but cannot currently see while waking,our link to the "who" and "what" we really are,and that state being the dominating alpha state of being for humans who for awhile must be encumbered by this flesh from our reality for only a short time.

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6. amanda on April 26, 2004 11:33 AM writes...

please analyze my dream! :

first i jumped in a swimming pool because something small fell in and then it fell in again but swam away from me. then all of a sudden i was at a building that from the outside looked like a church and the inside was a mall. i then realized my two friends kayla and kim were dead, but everyone could still see them. i don't know how they died but it felt kind of like a nightmare on elm street movie and the kind of horror movie about dead people that you can still see but eventually they disappear. well we were all in the mall not even thinking that anyone was dead and some guy that i knows came up to me and said something about my friends kayla, the dead girl he said. i got very angry and beat up that guy and then i looked around for kayla and ran to the bathroom. the last thing i remember is my two friends jerrica and shannon saying what's wrong and i was like "i can't see kayla anymore".

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7. Denny on April 27, 2004 12:12 PM writes...

Amanda: a possible interpretation. The pool represents the possibility of death, and your jumping in represents your willingness to confront death, to think about someone else's death, if not the idea of your own. The mall represents "the world of the living." Maybe someone you know died recently. Death may have been on your mind lately for some reason. In any case, it shocks you and puzzles you. The idea of losing someone through death angers you, it's very hard to accept. An unpleasant dream, but I would think a common kind of dream, given that we all sooner or later will be confronted with this kind of loss and have unresolved feelings about it.

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8. david mason on April 28, 2004 6:36 PM writes...

I keep dreaming that I am going to the toilet but the walls are low and I am trying to hide the fact that I am on the toilet.

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9. hayley gant on April 30, 2004 4:58 PM writes...

i had a dream the other day and it was that i had £500 and i lost £300 what dose this mean i'v got to give the council £300 and i'vput in for a lone can plz help and tell me what that dream means

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10. Barb on May 3, 2004 8:49 AM writes...

I had a dream last night that I was dying, and my mom was with me, but left the room when i was about to go. I was upset she couldnt be there, and i woke up. Then i had a dream that my best friends mom died, and I didn't go to the feuneral, and was soo upset that i wasnt there for her. I was sobbing when i woke up. What in the world does that mean? Is someone close to me going to die?

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11. Guest on May 5, 2004 1:43 AM writes...

I was talking with a fellow biologist the other day about some of the advancements in what we call “neurotechnology.” We discussed the advances made by MIT researchers who’ve worked on a technology to allow paraplegics to move the cursor of a mouse using brainwaves. Brainwaves are obviously forms of energy that leave our physical body and thus can be detected with electric devices. However, a question dawned on me, during our discussion. What it, we spend our days “receiving” the brainwaves of the individuals around us. Meaning, that when we are at the grocery store, the gym, classroom, work, or wherever we may be we are constantly picking up the brainwaves of the people in our close proximity. These brainwaves are transcribed in our subconscious and stored in memory. We don’t know enough about the human brain, nor the brain waves it creates to discount this theory of mine. Thus, when we sleep the memories, translated from the brainwaves we’ve collected throughout the day are ‘displayed’ in the form of a dream. So, perhaps our dreams are not our own, but the abstract property of other’s.

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12. Harish on May 14, 2004 1:46 PM writes...

Let the analysis be one to one

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13. A Mom on May 16, 2004 10:43 PM writes...

I have dreams almost every night. They're always in color and always clear. I almost always remember the whole dream, some details are unexplainable. Sometimes i don't recall having a dream when I wake up, but later in the day I will see or remember something that will trigger a whole dream and it's plot from the night before and it all comes back. COOL STUFF!

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14. Emily on May 17, 2004 8:53 PM writes...

My best guy friend died unexpectdly in Nov. of a heart condition. A few months later I had a dream of him coming back and telling me that he was always in love with me and hated seeing me hurt. Also how he missed me so much God have him 5 minutes to come talk to me. What could this mean? Could he actually be coming back to talk to me?

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15. marie on May 19, 2004 5:50 PM writes...

i keep havin this dream that im makeing out wit guys from my skool its so weird

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16. Mark on May 29, 2004 8:36 AM writes...

Hello, I keep dreaming that I am in horrible plane crashes. One was approximately 5 seconds after takeooff the 747 just nosed down but we landed safely on a crossroad. The other horrified me when we were preparing to land in hong kong when I was sitting next to my family members and the aircraft suddenly nosed down; about three seconds later I woke up.

The thing that worries me is that I am training to become an airline pilot, Just wondering if someone might be trying to say something before its too late?


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17. crumbley on May 31, 2004 2:12 PM writes...

i dreamed i was in class and the girl in front of me (that i like)turns around and smiles at me then i wake up

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18. Jessica on August 2, 2004 10:24 AM writes...

I just wanna tell u about a weird dream that I had some weeks ago.

In my dream I was lying in my bed awake, and it was dark all around me, but i felt that someone stod beside me and breathing in my face.
I was scared but I feelt that i had to do something, so I tried to grab the person with my right hand, and I grabed the persons througt/neck. At first nothing happend but the person became more scared then I was and he/she tried to get away, and started hitting me or something but I still couldent see anything, then I woke up, and I still had my right hand like I was holding that neck, I dont know why but I guess I through myself in the wall beacuse I got freaked, and then fell asleep again.

sorry but my English is not that good

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19. Niamh on August 10, 2004 11:53 AM writes...

My sister is in a coma and I had a dream that she was calling my name when I was at her bedside in the hospital, but then she woke up and gave me a hug!
What does this mean or is it only because I am wishing for her to wake up soon xxx

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20. danielle on October 14, 2004 2:43 PM writes...

my grandpa had just passed away before i had this dream but it was like i was in a dark room and all that i could see was a bright light and i was crying and all of a sudden my grandpa showed up in the light and was walking towards me but he didnt look normal and all of a sudden he came after me but in a ghost way and it scared me so bad i woke up crying.

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21. alejandra garcia on October 21, 2004 1:44 PM writes...

i always have this weird dreams were i see this river all the time and i also see a white house i feel like i've been to both of this places but i don't remember when or where i get really scared and i wonder what his dreams mean ????i also want to know what does it mean when u have a dream that someone is cheating on you

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