What is REM sleep?
In 1953 two researchers in Chicago, Dr. Nathaniel Kleitman and his young assistant Dr. Aserinsky, made a crucial discovery about sleep. They noticed that there was a form of sleep during which the eyeballs move rapidly, whereas the rest of the body was pretty much paralyzed. Intriguingly, the electrical brain activity of this period of sleep was also observed to be very similar to that seen during wakefulness. Two names for this stage of sleep subsequently emerged – Rapid eye movement sleep (or REM sleep) to referring to the eye movements, and Paradoxical sleep, referring to the paradoxically enhanced brain activity being very similar to that in the waking brain.
Research emerged showing that REM sleep was related to dream content: people woken up during this phase of sleep are more likely to report dream fragments relative to every other stage of sleep. The content of dreams during REM sleep also tend to be more bizarre, vivid and emotionally charged. Brain imaging studies have since provided further insight into the physiological basis of dreams. Parts of the brain involved in the processing of emotional information are very active, as are areas known to be involved in visual imagery. While these parts of the brain are intensely active, other parts of the brain, typically those involved in self-awareness and executing control, actually show reduced activity. This may help us understand why dreams often have very little logical order and that we are usually unable to control what happens during our dreams. Finally, the eye movements that occur during REM sleep have also been shown to closely follow the dreamed action. For example, if a person is climbing a ladder in their dream, often the recorded eye movements will follow the dreamed movement (i.e. change in gaze upwards as the individual begins to climb up several rungs).
The muscle paralysis (or muscle atonia) that takes place during REM sleep prevents us from acting-out our dreams. A neurological condition called REM-sleep Behavior Disorder (or RBD) is characterized by a failure of this muscle atonia (or muscle paralysis), leading patients to literally act out their dreams. Acting-out dreams may lead to self-injury or injury to a proximal bed-partner. When woken from the dream, patients with RBD will tend to have good recall of the recent dream content (this is in contrast to those who sleep-walk, where there is usually poorer recall of thought content prior to awakening). Studies have discovered a link showing that a sizeable number of those with RBD may go on to develop Parkinson's disease or dementia in the future.