In Dreams

October 23rd, 2007at 11:50pm Posted by Eli

There were a pair of fascinating articles about dreams in today’s NYT Science News – one about regular dreams, and one about nightmares.

The common theme is that dreams are our brains’ way of Working Through Stuff. And between the two articles, it appears that that’s happening in two different ways. Part of it is simply processing the events of the day, a kind of triage process that sorts through the experiences and thoughts of the day and moves the relevant stuff from the sphere of immediate experience and short-term memory into the sphere of long-term memory, knowledge, and skills. Kind of like transferring photos from your digital camera to your hard drive, or more generically, from a capture device to a storage device. And as all of this material flashes through your sleeping brain, some of it bleeds through and turns into dreams.

The other part of it, which is more prone to generating nightmares, is the unconscious brain’s attempt to grapple with unresolved issues. My gut feeling on this is that it’s a mechanism that we’ve outgrown. I think we’re supposed to somehow work through and resolve these issues in our sleep so we can focus on what we need to do during the day (look for the passage about “fear extinction memories” in the nightmares article), but our lives have simply become too complex to be sorted out while we sleep. But the brain thrashes through it all the same, and it probably even gets mixed together with the stream of data getting copied into main memory, recombining in new and different ways.

I also really liked this description of what happens physiologically when we’re in REM sleep, and how it affects the nightmare experience:

When slipping into REM sleep, Dr. Levin said, “the whole brain changes.” “Neurochemically, it’s like the Fourth of July,” as cortical precincts shift colors in scanning images to indicate arousal or quiescence, he said, adding, “The limbic system becomes incredibly active, much more so than when you’re awake, which is why you’re emotionally on edge in dreams.”

Blazing with particularly patriotic fervor in the limbic system are the amygdala and anterior cingulate cortex, constituting what Steven H. Woodward, a psychologist at the V.A. hospital in Menlo Park, Calif., terms the brain’s “axis of fear.” At the same time, the prefrontal cortex, seat of rational thought and critical reasoning, is on lunch break, Dr. Levin said, “which is why you can have a dream where something has 4 heads and 12 legs, and you think, ‘No problem, what’s next?’”

Also relatively tranquilized is the primary visual cortex, recipient of visual signals from the outside world. The secondary visual cortex, however, which helps process and interpret those signals, remains alert. It is here that the fabulous imagery of dreams probably arises, said Tore Nielsen of the University of Montreal, as the secondary visual cortex strives to decipher the signals ricocheting through it, many of them internally generated, and to splice them into some approximation of a coherent whole.

Other sensory and motor systems remain active in REM, including those that would normally control the arms and legs, which is why motion figures prominently in many dreams. But if you often feel frustrated, as though you can never get to where you’re going, well, you can’t.

As it happens, one vigilant player in dreaming is a small region of the brainstem that paralyzes most of the body, preventing you from physically acting out your dream. People with neurogenerative diseases that disable this brainstem disabler can end up injuring themselves during extreme dream-driven actions. Most cases of sleepwalking occur in non-REM sleep, when the body is not paralyzed.

Fascinating stuff.

Entry Filed under: Coolness,Science


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