REM is such a huge topic to cover, I’m going to put down some key points and probably revisit them in detail in later entries.
Rapid eye movement (REM) sleep is the stage of sleep we generally associate with dreams, but as we’ve seen in the July 10th entry on slow-wave sleep, there are actually two dream stages. During REM, named for the random darting of the eyes, the body loses muscle tone and an EEG registers quick, low-voltage readings.
Scientists have some theories as to the function of REM sleep, and the most common being taught in psychology is that the brain is trying to process and store information that may not fit into a clear category, and so dreams are very surreal and disjointed because your mind is trying to give structure to the memories. It’s trying to make a story. According to some studies, REM establishes procedural memory, though there have been conflicting studies that would suggest that this is a function of slow-wave sleep (in reference to the repetitive dreams of games that seem to improve performance upon waking).
REM is important not only for humans, but all land mammals and also birds. Evolution has done us a favor by including a mechanism for tonic immobility during this important stage of sleep. At our most vulnerable, can you imagine how easily a predatory would pick us off if we all acted out our dreams? That’s not to say it never happens. Watch any dog dreaming and you’ll probably notice some foot movement; what I like to call “chasing rabbits.” When functioning ideally, this paralysis (REM atonia) is akin to feigning death. When not functioning ideally, it can result in sleep walking, or sleep paralysis if it continues to suppress movement as the person begins to regain awareness.
REM atonia is produced by the release of monoamines (norepinephrine, serotonin, and histamine). Norepinephrine is partially responsible for fight-or-flight response, activating parts of the brain such as the amygdala. This explains why REM dreams are often very emotional, and also why it is so dangerous to try to wake someone who is sleep walking. The synthesis of norepninephrine depends on the amino acid tyrosine (found in meat, nuts, eggs and cheese). Tyrosine can be synthesized by phenylalanine, but you’ve probably heard all sorts of warnings about that. You find it in many diet drinks containing aspartame. Some people are sensitive to phenylalanine and may suffer seizures, but the same natural sources of tyrosine also contain phenylalanine.
A typical night of sleep involves many cycles through the stages of sleep. A cycle is about 90 minutes, and with each consequent cycle the duration of REM increases while slow-wave tapers off. It is sometimes referred to as paradoxical sleep because brain waves are very similar to those of an awake, alert brain. While it has similar brain waves, the body does a poor job of regulating things like temperature and heart rate during this time. It is also the stage of sleep with increased blood flow to genital areas of both sexes (which could total anywhere from 1 to 3.5 hours during sleep).
As I’ve said, REM is such a huge topic, I will be revisiting more specific elements in future entries. Tomorrow, I will be discussing time-lapse video studies, with which I have had some limited personal success.