THE PSYCHOLOGY OF SLEEP AND DREAM

Dreaming can happen. View Source during any stage of sleep, but dreams are the most prolific and intense during the rapid eye movement (REM) stage. During the REM sleep stage, brain activity ramps up considerably compared to the non-REM stages, which helps explain the distinct types of dreaming.

First of all, no one is sure why we dream. During the past century, however, scientists have made significant progress in understanding the factors that influence sleep and dreaming. Evidently, our nights are influenced by what we're doing during the day. We spend our days gathering information, some of it we would like to keep, most of it we need to discard. If we do not clear out our mental storage space regularly we risk saturating our brain with too much useless trivia. In order to fully process this information, we need to shut our brain down; disconnect it entirely from the outside world. The challenge is that we only have one brain to work with.

About two millions years ago (that's the current guess) brains became sufficiently complex that they were able to solve the problem of memory processing by dividing the night into two types of sleep, one is now called slow wave sleep (SWS) and one is called rapid eye-movement (REM) sleep. We can, and do, dream in either phase of sleep but the characteristics of our dream differ greatly; the curious and unique features of SWS and REM have taught us a lot about why we sleep or dream at all.

During the day, many of the things we learn are stored in a structure called the hippocampus. Then, while we are in SWS the hippocampus is busy showing movies to our frontal cortex. What's odd about these movies is that they are very compressed packets of information; events are transpiring at over ten times normal speed in these packets. During SWS, our dreams are often more static, involve older memories or are quite emotionally charged. If you've ever dreamed of being buried alive, or of having a beast sitting on your chest, you were likely in SWS at the time. For most people, nightmares, bedwetting, sleep-walking and night terrors occur during SWS.

Then, as we transition into REM our hippocampus is shut down to allow our frontal cortex to process the newly deposited information. Surprisingly, the presentation of events to be processed occurs in almost real time. We experience this processing during REM as a narrative dream that feels "real." What's happening in the cortex? For one, REM sleep facilitates the use of prior information for creative problem solving, thus our cortex is busy filtering out the useless memories in favor of useful ones. Often, stronger emotional content helps to consolidate long-lasting memories.

Overall, recent studies suggest that we require a balance of both phases of sleep, SWS and REM, in order to consolidate memories for future use. Thus, it is not the quantity of sleep that is important; rather, the quality of sleep is more important for making new memories. Unfortunately, lots of things interfere with the quality of a night's sleep.