Sleep, Dreams and REM Sleep Behavior Disorder
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The discovery of rapid eye movement (REM) sleep suggested that sleep was not, as it was thought to be, a dormant state but rather a mentally dynamic one. Your brain is, in fact, very active in this state, almost to the level at which it is when a person is awake. Yet during this active stage in which most dreams occur, the movements of the rest of the body are completely stilled. To imagine this paralysis during dreams not occurring is a frightful image, since in many cases dreams are violent and active. When the neurotransmitters that control the movement of the body do not work properly the person develops REM sleep behavioral disorder (RBD).
While we are sleeping the sensory world is essentially revolving around us without our knowledge. Our senses of hearing, touch, taste, sight, and smell no longer function as they do when we are awake. Except for the threshold for each of these senses that each of us has while we sleep, our inner systems are working essentially free of input from the outside world. And yet people are able to have vivid dreams. The cortex can only pass into sleep mode with the help of the are of the brain called the thalamus. The thalamus is one of the two structures that make up the diencephalon, the lower part of the fore brain. Its main function in mammals is as the relay station of sensory information its way to the cortical center. Specific regions of the thalamus, as well as different nuclei process different sensory information on its way to the cortex.
In normal sleeping patterns a person usually passes through five phases of sleep, the fifth being REM. The sleeping human passes cyclically through these five phases throughout a night's rest. These phases can be defined in electrical activity of the brain; much like the activity of the heart is often defined. The technique of measuring the electrical activity of the brain is call Electro-encephalogram, or EEG. When the electrical events of a person's brain are graphed on a electrical magnitude versus time axis the graph of a person who is in different stages of being asleep or awake appear to have different levels of electrical activity occurring in the brain. (See (14))
During the cycle of the phases each lasts for a different period of time during the time we are sleeping.
The first stage is the lightest stage of sleep and is characterized by drifting in and out of sleep and slow muscle and eye activity. When people are awakened during this phase they usually have fragmented visual memory of what they were experiencing while asleep. The second stage is the one in which the most time is spent, close to fifty percent, during this stage three electrical activity, measured by electrodes, slows down except for infrequent bouts of rapid waves called sleep spindles. Stage three and four are considered stages of deep sleep, delta wave appear during phase three and are produced almost exclusively during phase four. Delta waves are extremely slow brain waves. Though there is no consistent eye movement or muscle activity during these two periods, they are the phases of sleep when some children experience bedwetting, night terrors, or sleepwalking ((12)).
The next phase is REM sleep, after reaching stage four the pattern of progressively slower, larger brain wave and deeper sleep, reverses and sleep becomes lighter until the REM sleep state is reached. REM is the most active part of sleep, in which the rain waves, when viewed using EEG have a pattern the most similar to those of person who is awake. REM sleep and dreaming, which occurs mainly during REM, are triggered by the pons, a bridge that connects the brainstem with the cerebellum, and neighboring structures of the brainstem (See illustration ((10))). A pathway originates in a group of acetylcholinergic neurons located in these rostral pons. These neurons project to the sensory areas of the thalamus and to the reticular nucleus. In the sensory areas of the thalamus control whether the gate that allows information from the outside world pass into the brain is open or closed. The acetylcholine produced by the pons' neurons sensitizes these neurons of the thalamus to sensory input by slightly depolarizing, and hence changing the level of potassium. By contrast the reticular nucleus is inhibited by the acetylcholine, as a result the thalamus lets sensory information through , and the cortex is highly active. This process is very similar to what occurs when a person is awake. In the other stage of sleep in which the brain is less active the system works in the opposite manner. The acetylcholine system is inactive, the reticular nucleus is uninhibited and can thus inhibit the thalamus, as a result the cortical neurons move in a slow rhythm , very different from the active state they are in while the creature is awake, or in REM sleep.
The majority of the Dreaming that occurs during a sleep cycle occurs during the REM or paradoxical sleep state. As described above the brain literally awakens internally during REM sleep. In a person with normal sleep behavior the REM sleep stage is one of near paralysis for the entire body other than the muscles of the eye and the middle ear. This occurs because of descending inhibition, in which a group of cells in the medulla that descend down the spinal cord and inhibit motor activity. RBD, rapid eye movement sleep behavior disorder, is characterized by the afflicted person acting out their dreams, which are usually violent in nature. The violent nature of these dream enactments is very distinct from the person's normal waking personality. This suggests that RBD is not only a motor control disorder, but a dream disorder as well. When the person awakens they can remember their dream vividly but cannot recall their physical actions during the dreams. Most of the incidents that occur within the dream are similar in affect to those that the individual was enacting, in one instance an adult male nearly strangled his wife while dreaming that he was saving her from drowning ((13)).
The majority of patients afflicted with RBD though there are cases of females and children having this disorder. About 25% of diagnosed patients tested reported limb twitching, talking, yelling, jerking and a progressive decline in motor control during sleep ((9)). These symptoms starkly contrast to the typical atonia, lack of normal muscle tension, which is associated with the REM phase of sleep. In very few isolated cases have any family history of RBD been found. In approximately half of the cases chronic RBD is associated with several different neuropathologies including: vascular insult, tumors, degenerative disorders, etc. In instances where RBD is not a consequence of some other affliction it may be a warning sign of Parkinson's disease.
RBD and other similar dissociative disorders bring up interesting questions about the self. In one respect an individual self is more active during these phases of sleep since there actions and functions are more similar to those that occur when that individual is awake, and supposedly has full use of the self. Yet during these sleep stages the individual loses awareness and control of there physical and mental self. The dreams that they experience, as seen in cases studies, are rarely attributed to what occur in their daily life, and thus are the vivid images are not provided for by their memory bank. Furthermore they have little control over their physical presence, which is controlled by the dream sequence and have no recollections of the actions that took place after they are awakened. These two opposing standpoints leave the question: is the self retained when awareness of the individuals own actions is lost?
1) The Study of Neurophysiological Mechanisms of Dreaming. By M. Jouvet and D. Jouvet
2) Paradoxical Sleep- A Study of its Nature and Mechanisms. By M. Jouvet
3) Paradoxical Sleep Mechanisms. By M. Jouvet.
4) Why Do We Dream? By Jarrett Carberry.
5) Sleep and Language
6) Why Don't We Act On Our Dreams. By Silvia Helena Cardoso, PhD.
7) The Science of Sleep and Dreams
8) States of Consciousness: Concepts and Definitions
9)REM Sleep Behavior Disorder: A Neurologic Dissociative Sleep Disorder. By Niels C. Rattenborg.
10) Brain Briefings: REM Sleep.
11) Cortical Arousal During REM Sleep, LDEs and OBEs.
12) Brain Basics: Understanding Sleep.
13) Slumber Interrupters
14)Sleep stages in EEG