SLEEP [ back to Glossary Index ]
Sleep is a biological necessity not just for survival, but for normal, healthy mental and physical functioning. Persons deprived of any sleep for too long lose body heat, lose weight, lose vigor and eventually die. The 3 major brain states are waking, sleep and REM sleep. These states occur predictably on a 24 hour cycle of light and dark known as the circadian rhythm which emanates from a "master circadian clock" in the suprachiasmatic nucleus of the hypothalamus.  The clock is kept running by molecular signals from proteins which include albumin D-binding protein (DBP). Traumatic damage to the suprachiasmatic nucleus abolishes the circadian sleep-wake rhythm.

A person is said to be awake when he alert, aware of his environment, able to move freely about and able to respond to stimuli. Sleep comes when growing darkness and the body's circadian rhythm signal the brain systems responsible for mental alertness (the locus coeruleus in the brain stem and the hypothalamus) to slow their secretion of norepinephrine and cortisol. Brain metabolism slows. The slowing of norepinephrine secretion triggers a slowing of serotonin secretion accompanied by relaxation of muscles, slowing of heartbeat and lowering of blood pressure. The reticular inhibiting system switches on. There is some evidence, although quite conflicting, that pineal gland secretion of melatonin, helps trigger the initial phase of sleep. As mental activity slows and the muscles relax, the person becomes drowsy, heavy lidded and less responsive. After a while his eyes close, he ceases all perception of external stimuli. and characteristic slow frequency brain waves appear, followed by sleep spindles emitted by the thalamus.

The first phase of sleep, non-REM sleep, rests the mind, recharges the immune system and allows for tissue repair. During the night the sleeper will undergo repeated transitions in and out of REM sleep, and will be in REM sleep for about 25% of his entire period of sleep. REM sleep is when we dream, and when beneath closed eyelids our eyeballs engage in rapid jerking back and forth motions. It is called paradoxical sleep because paradoxically the voluntary skeletal muscles become completely paralyzed and without tone, while the mind increases its activity to a greater pitch than during day time. Although voluntary muscle activity ceases, this is the stage of sleep marked by penile erection in the male. During REM sleep there is an increase is release of Ach (acetylcholine) which is associated with increased mental function and memory consolidation. Is there a connection between the insomnia and poor memory of the elderly Alzheimer's patient and depleted Ach? During REM sleep the threshold for being awoken by loud noise or shaking goes up. It is much harder to wake a dreaming person than a person in non-REM sleep. During REM sleep the human organism is highly vulnerable to attack, because of absent muscle tone, and increased waking threshold. Hence human beings cannot fall asleep until they feel secure and safe from threat. Evolutionary biologists have observed that only warm blooded creatures like humans, dogs and cats, have REM sleep. No reptiles, amphibians or fish do.

REM sleep is produced and maintained by the PGO system (a combination of impulses from the pons, lateral geniculate nucelus and occipital cortex). During REM experience ourselves as really  eating, drinking, seeing, talking, walking, running or fighting, because the brain centers which handle such activities have been activated by the PGO but our body remains motionless because of muscular paralysis. Dr. Allen Braun of NIH has confirmed with PET scans of sleepers' brains that the frontal lobes are inactive during REM. This bypass of rationality and objectivity is what enables dreamers to fly, to travel back and forth through time, to use super strength, etc. The powerful sense of reality we have during our dream fantasies comes from intense activation of the limbic system, the emotional part of the brain. REM occurs in cycles, because so much glucose and oxygen are burned up during dreaming, that down periods or needed to replenish energy stores of glycogen in the glial or supply cells. Shutting down all peripheral muscular activity, slowing and resting the heart, dilating blood vessels which cools body temperature and lowers blood pressure, all serve to conserve energy for dreaming.

Why do we dream? No one knows for certain, but the current consensus is that dreaming allows for consolidation and long term storage of newly learned material, integration of such material into our existing thought process and rehearsal of new behavioral sequences. Research in sleep labs shows that repeatedly waking people up to deprive them of REM sleep, interferes with memory consolidation and cognitive functioning. Sleep research into how TBI generates sleep disorders is fairly new, but it is known for certain that TBI can cause a variety of sleep disorders including excessive sleepiness, insomnia, fragmented non-REM sleep (with repeated wakenings) and reduced quantities of REM sleep. Such sleep disorders are likely to have a negative impact on many aspects of day time functioning, especially energy level, alertness, attentiveness, endurance and cognitive function.