SLEEP DISORDERS
The vital importance of sleep has been known to man since antiquity. Indeed, as long ago as 400 BC Hippocrates remarked “both sleep and insomnolency, when immoderate, are bad” and in 350 BC Aristotle produced a work called “On Sleep and Sleeplessness”, in which he concluded that sleep was necessary for an animal’s “conservation”. Perhaps the most powerful proof of our need in sleep is the existence of a rare genetic disorder, called Fatal Familial Insomnia - is a disease characterized by the gradual loss of one’s ability to sleep and subsequent death from what could be described as total brain shutdown.
What is it?
Although the importance of sleep has been recognized for centuries and inability to sleep or excessive sleepiness have been viewed as abnormal, it was not until the last part of the XX century that scientists have gotten a better idea of what sleep actually is in terms of physiological processes that modulate sleep. We now know that sleep is not just a reversible state of sensory disengagement and poor responsiveness to environment; it is a complex change of electrical activity patterns in the brain that involve multiple areas in the brain stem and intricate communication paths of these nerve cells with the cortex.
On the basis of these activity patters, sleep has been divided into two separate states: the Rapid Eye Movement (REM) state, characterized by increase in brain’s electrical activity, loss of muscle tone and episodic burst of rapid movements of eyes, and the Non-Rapid Eye Movement (NREM) state. The latter is subdivided into 4 stages based upon differences in amplitude and duration of brain’s electrical activity as recorded in an Electroencephalogram (see “Seizures and Epilepsy” page for description). These 4 stages roughly correlate with the depth of sleep with stage 1 being more “superficial” sleep (when we fall asleep) and 4 being the most “deep” sleep. It is thought that dreaming occurs during the REM state – a state of an activated brain in a “paralyzed” body.
Interestingly enough, it is not always possible to predict with a 100% accuracy whether someone is actually asleep based upon instrumental data only – clinical experiments have shown that even those the brain’s electrical activity corresponds to stage 1 of NREM, the person (a volunteer in a sleep study) does not consider himself actually sleeping at that moment. Nevertheless, some generalizations about a normal sleep cycle can still be made. They are:
1. Sleep is entered into through NREM state.
2. NREM state alternates with REM state approximately every 1.5 hours.
3. Wakefulness within sleep accounts for approximately 5% of the night.
4. NREM state takes up 75-80% of sleep and REM state takes up the remaining 20-25%.
5. Stage 1 of NREM generally accounts for 2-5% of sleep.
6. Stage 2 of NREM generally accounts for 45-55% of sleep.
7. Stage 3 of NREM generally accounts for 3-8% of sleep.
8. Stage 4 of NREM generally accounts for 10-15% of sleep.
The distribution of these stages within sleep can be changed by various physiological factors.
Age remains the most consistent factor that can change our sleep patterns, as listed above 1-8. Newborns do not have the same pattern as adults and stage 3 and 4 do not even exist until about 6 months of age, because the brain is not capable of supporting a relatively high level of electrical activity. The transition from NREM state to REM is also shorter in newborns – about 50-60 minutes.
Youngsters have a different sleep pattern, and by “pattern” we do not refer to their habits of going to sleep, but to the characteristics of the brains’ electrical activity as represented on an electroencephalogram. At this age, stage 3 and 4 of NREM reach their peak, and that is why it is practically impossible to wake children up in during their first (after falling asleep) stages 3 and 4. In one study, a sound as strong as a noise produced by close-by a jet airplane failed to produce any signs of arousal in a group of children 10 years-old on average.
As we progress into the second decade of our life, we sleep “more superficially”, because electrical activity seen in stages 3 and 4 (so-called “slow wave sleep, associated with deeper sleep) decreases in intensity and duration. This change continues as we grow older and by age 60 slow-wave sleep may disappear, particularly in men.
The duration of REM sleep remains fairly constant throughout adult life, but decreases drastically when organic brain dysfunctions occur in the elderly. What is also interesting is that sleep patterns of the elderly can vary dramatically from person to person, and this fact precludes us from making meaningful generalizations about “normal” sleep patterns in later years of life.
These physical in nature changes that reflect physical changes in the way our brains produce and conduct certain electrical stimuli are responsible for more wake-up as we grow older, for more “superficial” sleep and for the perception that one just cannot fall asleep as easily as one could during teenage years.
Sleep history is another variable that may affect our sleep later in life. How frequently and for how long we sleep can affect how we will sleep later – deliberate sleep deprivation can changes the speed of onset and duration of sleep patterns, making subsequent sleep more “superficial” or more “deep” and can bring about other neurological abnormalities, such as hallucinations, sleep paralysis, can alter brain metabolism and thus affect cognition, emotions and mood.
Circadian rhythms, or day phases, may also change whether we can sleep, when we will sleep and how we will sleep. We are all familiar with this property of our brain to correlate sleep to the phase of day – it is exhibited as “jet lag”, for example. If one has to fly from the United States to Africa and finds himself startling wildlife with a thunderous snore, it does not happen because one is just bored; it happens because it is time to sleep according to the circadian rhythms that one brain has become accustomed.
Temperature of our immediate surroundings also can affect sleep, because our ability to regulate body temperature is very limited during REM state.
Medication we take can affect normal sleep patterns as well, and anti-depressants are just one group of medications that can change sleep patterns.
CLASSIFICATION OF SLEEP DISORDERS
The International Classification of Sleep Disorders has four major categories of sleep disorders:
1. Dyssomnias – disorders of initiating and maintaining sleep and the disorders of excessive sleepiness.
i. Intrinsic sleep disorders – ones that occur due to some physiological abnormality in the brain;
ii. Extrinsic sleep disorders – ones that occur due to factors located outside of the brain (poor sleep habits, altitude insomnia, sleep allergy
insomnia, stimulant-dependent insomnia and others);
iii. Circadian rhythm sleep disorders.
2. Parasomnias – disorders that do not primary cause a complaint of insomnia or excessive sleepiness. Insomnia is defined as difficulty to
initiate and maintain sleep, or sleep that does not “restore” or “refresh” one compared to one felt before sleep.
i. Arousal disorders (includes sleepwalking, for example)
ii. Sleep-wake transition disorders (includes sleeptalking, for example)
iii. Parasomnias usually associated with REM sleep (includes nightmares, impaired sleep-related penile erections, for example)
iv. Other (includes primary snoring and sudden infant death syndrome, for example)
3. Sleep Disorders Associated with Medical or Psychiatric Disorders
i. Associated with mental disorders
ii. Associated with neurological disorders
iii. Associated with other medical disorders
4. Proposed sleep disorders
IT IS CRITICAL THAT SLEEP PROBLEMS BE BROUGHT TO THE ATTENTION OF A NEUROLOGIST, AS IT IS VERY IMPORTANT TO COLLECT AN IN-DEPTH SLEEP HISTORY, PERFORM A THOROUGH NEUROLOGICAL EXAMINATION, DIAGNOSE THE PROBLEM, CHOOSE THE APPROPRIATE PLAN OF ADDITIONAL TESTING (IF NECESSARY) AND DEVELOP A PROPER TREATMENT REGIMEN.