Inside The Brain Of The REM Sleeper

Written by Carl DeGuzman, Spring 2010

Brain imaging technology has allowed us a glimpse into the fascinating world of what is happening inside our heads while we are in REM sleep. We can now see which parts of the brain are active during REM sleep and how that affects our sleep. Many of the findings explain the interesting phenomena that happen during REM sleep, particularly relating to the dreams that happen during this period.

Two parts of the region are of particular interest: the primary visual cortex and the extrastriate visual areas. Both are located in the back of the brain, and have to do with (you guessed it) vision-related things. The first region, the primary visual cortex, has the task of making sense of what we see in the outside world. It tells us what is happening around us by detecting patterns of light and interpreting them.

During REM sleep, it is mostly silent. This is not a big surprise, as most of the time while we sleep our eyes are obviously closed and cannot receive much visual stimuli. However, the extrastriate visual areas, which basically take the data from the primary visual cortex and tells us what is happening around us, are a lot more active in the brain than you would expect with no external stimuli. This can possibly help explain how we come up with such elaborate visual dreams, and along with other parts of the brain it helps to create a dream world complete with colors, textures, tastes, and smells.

Another part of the brain that shows intense activity during REM sleep is the limbic system, which is highly involved with emotions. Two areas of the limbic system in particular show a lot of activity, the hippocampus and the amygdala. The hippocampus is involved in turning short-term memories into long-term ones, which may help explain why many times we dream about things that were relevant to us recently. It also helps us in making associations, such as when we use a mnemonic device to memorize something. This feature may explain why we associate things that at first are seemingly unrelated, but if you look closer can in some way be explained. The amygdala on the other hand, is highly involved in fear and aggression. Obviously, this could explain the violent nature of some dreams, or one could even imagine an overactive amygdala leading to nightmares.

Interestingly, a part of the brain that is closely related to the limbic system, the frontal cortex, is relatively quiet during REM sleep. The frontal cortex, and in particular the prefrontal cortex, is involved in thought and judgment. In other words it helps reign in our animal instincts, as a professor of mine liked to say. This makes perfect sense, explaining why we sometimes dream of doing things that we know we would never do in real life, but seem perfectly normal while we are in the dream world.

Finally, what part of the brain is the trigger for REM sleep? Researchers have found that a region on the brainstem called the pons is necessary for REM sleep to happen. Various studies have shown that if you knock out part of one of the pons, known as the nucleus reticularis pontis oralis (or RPO for short), REM sleep cannot happen. Furthermore, two other nuclei in the pons that produce neurotransmitters related to keeping us awake must shut down before REM sleep can begin.

The brain stem is also the source of REM sleep paralysis, an important feature because if our body was as active as our brain during REM sleep, we would be able to act out our dreams which could lead to potentially harmful consequences. Unfortunately, this is actually possible, along with a number of other REM sleep disorders, which you can continue to read about here.

Carl used www.thebrain.mcgill.ca as a reference for this article.