Yesterday's post was an example of a dream setting. In the posts to come I'll talk more about sleep, what dreaming *is* from a brain activity standpoint, what dreams are made of (memories), the sense of time in a dream, and differences between the *mind* (psychology) and the brain (biology).
The recent movie "Inception" did a very good job of capturing the mystery of dreams, the surrealism of disconnected settings that blend seamlessly into each other, the *realism* of the settings, and the sense of timelessness.
Yesterday's post is an example of a seven-minute dream. Any of you who have the tendency to repeatedly hit the snooze button on your alarm clock have probably experienced it. The alarm goes off, you barely rouse yourself - just enough to reach out and hit the snooze button, then settle back into the pillows. You have a vivid dream, from which you are awakened by the alarm clock... again... your seven-minute snooze is over.
How can you have such a vivid dream in just seven minutes? And what is a dream, really?
To answer the first, we will need to talk about the sense of time in dreams, and that's really a long topic. For today I will focus on the second question, and it will give us some insight into the former.
Dreams are memories. Our memories. They needn't be personal. Snips of movies, commercials, descriptions by a friend, all are fodder for dreams. Sleep consists of many stages, typical scientific terms refer to 4 stages, from stage 1, light drowsiness in which you are vaguely aware of surroundings, to stage four, in which the body is so deeply unconscious that most muscles in the body are shut down. A person spends most of the night progressing from stage 2 to stage 4 sleep and back again. Persons with sleep apnea, asthma or who wake frequently in the night oscillate from Stage 1 to 4. Dreams occur during Stages 2 and 3 in what is called REM (rapid-eye-movement) or "paradoxical" sleep - so called because the brain (and eyes) are as active as during wakefulness even while the body stays completely asleep (even paralyzed).
A full sleep cycle can take as little as 45 minutes, or as much as two hours. During a cycle, the amount of time spent dreaming is quite short, about 10 minutes per cycle, although it is possible to cycle between REM and non REM sleep multiple times per cycle. "Inception" got a lot of things right regarding dreams, dream settings, and time within dreams, but sorry, this part they got wrong - people do not typically dream the entire time they are asleep, nor when they are sedated - at least not at the sedation level that would keep a person asleep for 7-10 hours. Sedation suppresses brain and body activity, similar to Stage 4, and usually also suppresses REM sleep. Sure there are drugs that promote sleep and dreaming, but they result in a very light sedation and have their effects mainly through pain relief and muscle relaxation.
But back to those seven-to-ten minutes of dreaming. How can a dream seem so complete, so detailed, and so *long* and occur within orders of magnitude less time than the events it portrays? Several reasons: First, dreams are strung together from memories – as stated about, memories of events during the day, the past, personal experience, stories read from books, movies, TV. Even if only vague impressions, the mind can make a dream from it.
Memories are stored in the brain as associations. Ever struggle to name a song? Remember part of a tune or a verse, but can't think of the title until you *sing* the verse through to the end and rewind to the beginning? That's association. Each verse, each phrase, is associated in memory, and you have to run through the chain of associations to get to the title. There are other types of associations: cooking smells may help recall a vivid memory of childhood, a sound can trigger a traumatic memory, a touch or color may bring back memories of a first date, first love, first kiss. Once a memory is recalled, it may lead in turn to another memory, and another, and another. Such associations are nearly instantaneous. A series of memories spanning minutes, days, months or years can be recalled in seconds.
Second reason why dreams seem complete and detailed is that filling in the gaps with details is what the brain does. Any student of music can tell you that they can *hear* instruments when reading music. [In fact, there is a fascinating study in which brain imaging which proves just that point: a conductor reading a score shows the same brain activity as if they were hearing the music.] Optical illusions work the same way – the eyes see only lines, shapes and shadows, and the brain fills in even when there are no details in the original image. Mathematical models that mimic the connections of neurons (brain cells) have demonstrated the ability to restore information even when up to half of it is missing or garbled.
Finally, dreams allow the brain to disconnect from the body. There is a location in the brain called the "Red Nucleus" that acts like a cut-off switch. During dreams, the nerve impulses to the muscles are stopped, and many signals from the rest of the body do not reach the brain (consciously). The brain acts as if all of the connections are intact, but the normal feedback delay is not present, and the whole process runs faster. Note that this can account for the "helpless" feeling in some dreams – running in slow motion, sitting in the back seat of a runaway car, unable to defend against an attacker. During these events, the Red Nucleus block of nerve signals is not complete. Commands to muscles are blocked, but the information that those muscles are not moving is getting to the brain.
So, dreams are memories. Memories can trigger recall of other memories at widely separate times. The brain (and mind) are good at taking incomplete information and filling in details – often with familiar situations and other memories. The brain does not have the normal feedback from the body to signal what is a real experience and what is not. Hence the seven-minute dream. In reality, the dream may have only lasted for about 2 minutes, but that is enough time to trigger a sequence of stored memory patterns in the brain, and for the mind to make up a script to go along with the sequences. Sort of like the ultimate moviemaker's storyboard.
Next: The science behind dreams.