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Friday, June 10, 2011

Dreams: Telling the story... [Full link to blog for email clients.][FT:C44]

So, what *really* is a dream, and what is the purpose of dreaming?

Simply stated, dreams are a necessary function of making *temporary* memories *permanent*.
It's long been known that dreams are composed of memories, and that memories can be triggered by specific electrical activity within the brain. Dr. Wilder Penfield was a Canadian neurosurgeon noted for mapping most of what we know as the "topography" of the brain. In the course of brain surgery to treat epilepsy, he would apply electrical stimulation to various brain areas to locate damaged brain cells. This was (and still is) performed with the patient awake to tell the surgeon what they see, feel, taste, etc. In this manner, as well as studying which functions are lost due to brain damage, neuroscientists know which brain areas are responsible for movement, sensation and various memories. In the 90's, Professors Wilson and McNaughton at the University of Arizona determined that brain cells activated in the rat brain while running a maze were activated in the exact same sequence and relationship while the animal slept immediately following the behavior. From studies since that time, we know that the reactivation of electrical patterns during sleep is essential to "consolidation" of memory from short term storage (essentially what you do when you repeat a phone number to remember it long enough to place a call) to long term storage.

Why is consolidation necessary?  Well, as we discussed a couple of blogs ago, short term/working memory is temporary. It will eventually be forgotten, and in fact, it is best if it is forgotten! It is, by definition, only for short periods or only for the duration of the "working" task at hand.  If we did not forget information, our memories would be cluttered with too much information.  Online the other day, I was asked how much memory (i.e. how many years) I thought a human could actually live before their memories collapsed.  Another correspondent quipped "Do you remember what you had for lunch this day last year?"  Well, of course the answer is no - unless it was a *truly* memorable event - first date or birthday, for example.  Our memories prune themselves, and unused memories are eventually diluted, the information may still be there, but the associations become parts of other memories. 

To get information into longer term memory, it has to be "consolidated".  The key feature is that repeating information strengthens the connections between brain cells that form the basis of the information "code" for memory. However, such strengthening requires time, and metabolic processes in the brain cells. This is one reason why an accident victim may not remember details of an accident (or up to hours before) – there may not have been enough time to *consolidate* the memory before the brain received a trauma that caused it to stop processing information. Sleep provides the time, the low body activity frees up the metabolic processes, and dreams provide the repetition to enable memory to be stored most efficiently.

The second method mentioned above is strong association: emotion, trauma, stress. This is a topic for another time, and as we move through The LabRat's Guide to the Brain, we'll touch on Post-Traumatic Stress, and abnormal memory.

With consolidated memory, the mind can build a sense of *time* with respect to events in the outside world. As with yesterday's post on time and dreams – time in the waking world is important, too.  A popular phrase in psychology from about 10 or more years ago is "time-binding." The label refers to that ability of humans to place memories of events in sequence and judge the amount of time that passes. Time-binding is less known by its *presence*, but by its *absence*. One of the tests given to children suspected of depression or attention deficit disorder is to have them place pieces of a story into sequential order and tell how much time they think elapses during the story. Failure to do so is a pretty good indicator that the child has a deficit in time-binding, and such deficits indicate an abnormal interaction with the outside world.

However, problems with time-binding are neither unusual, nor crippling. So why is time-binding an issue? Do we (humans) really need to know that only 2 minutes has elapsed while we wait at a traffic light? Or that James Garfield was president before Chester Arthur and after Rutherford B. Hayes?

Well, yes, we do. Temporal sequence is *important*! In the real world, everything is a sequence of events, and the consequences of those events only have a finite duration. Event A: A burner is lit on the stove; Event B: a hand is placed over the burner. If B precedes A, no problem – unless the hand remains after the burner is lit. If A precedes B, well, that could be a problem – it depends on how much time has elapsed. Time-binding is difficult for persons on mind-altering drugs, in clinical depression, schizophrenia, and many other disorders.

What does time-binding have to do with dreams?  


The key is sequence.  Ever have that dream where you're taking an exam but never went to class, left your book in your locker and can't remember the combination, and now you can't find the classroom, but vaguely remember that you shouldn't be doing this because you *graduated* 20 years ago? It's a perfect example of the types of problems that occur in novel with Point-of-View shifts and time-binding. The subconscious creates dreams by pulling events at random from memory, but those events don't stand alone, they are part of a sequence that includes other memories not incorporated in the dream. The mind tries to fill in the gaps in time-binding – sometimes failing, as in the case of the Exam Dream. In other cases it succeeds too well. Dreams can take on a reality, complete with false history, that is hard to distinguish from reality.

An important technique in writing is to allow a reader to visualize the passage of time in a story is successful time-binding:  Cause precedes effect, birth before death, and past precedes its future. In dreams, we don't actually have much sequence - a whole lot of memory is called up in *very* rapid succession, and it is up to the parts of the brain which *normally* deal with memory, sequence and cause-and-effect (the Limbic System) to put it all together...

...eventually creating...

...a dream.

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