Once we thought sleep was an unconscious state of mental rest. Now we know that it is an active process preparing our minds and bodies for the next day of life. Sleep restores mental and physical health and is intimately related to memory and learning. It also reactivates patterns of neural activity that occurred during the previous days experience. Key patterns of connections between firing brain cells are strengthened. In this way new memories (laid down as patterns of sequentially firing cells) begin to be etched in brain pathways for future memory recollection.
While sleeping, the brain analyzes the previous dayís life experience that has been saved in short term memory so that what is important to recall can be gradually stored into long-term memory. Experience is reviewed in such a way that new or subtle connections may be found that were not discerned while awake. Many of us have recalled becoming aware of something that has happened during the dayís events but became clearer in the nightís mentation. Rapid Eye Movement Sleep (REM), sometimes called dream sleep, is a sleep stage that is especially associated with memory consolidation in the brain. This stage actively inscribes neuronal connections coding events that have been noted by the brain into long-term memory.
In order for the brain to lay down memories of our experience it seems we need to be asleep. Especially in REM sleep, the brain utilizes some of the same networks activated when awake. It may be that the relatively unconscious state of sleep is necessary for the brain to cut off incoming signals in order to analyze experience and sort important information into memory. It is easy to see that understanding sleep may help us to understand memory. People who sleep after new learning experiences have better recall than those who do not sleep. Recollection of newly learned material is clearly enhanced by sleep, and it is now thought that a minimum of six hours of sleep is necessary for improved memory to occur.
The quality of our awake time is dramatically affected by the quantity and quality of our sleep. We cannot feel peaceful if we are not biochemically regulated, and sleep plays a major role in that process. Sleep loss may lead to increased emotional fragility, reckless behavior, poor concentration, irritability and impatience. Negative emotions are intensified and positive ones diminished. Sleep researchers have documented a progressive decline in mood with accumulated sleep loss. People who slept four to six hours nightly for several nights became less able with each passing day to focus, concentrate and control negative mood states. An interesting factor in these studies is that there seems to be no subjective awareness of cognitive loss for sleep deprived individuals. Never the less, testing and brain scans reveal dramatic decreases in cognitive abilities. In addition, MRI (Magnetic Resonance Imaging) reveals a sixty percent increase in emotional center reactivity with healthy subjects who were sleep deprived for a single night. It has recently been found that sleep significantly helps to maintain the connections from the brain center that exerts thoughtful control to the emotional reactivity center. This connective pathway is critical to oneís ability to respond appropriately to the next dayís emotional challenges. Who among us doesnít know that children and adults get cranky and canít think clearly without adequate sleep? Now sleep research is documenting just how and why this happens.
A number of key factors promote a good nightís rest. Daily bright light, preferably sunlight, for at least an hour a day is essential to good sleep. Our bodies take in daylight through many light receptors, but some receptors through our eyes connect to the place in our brain that governs our circadian rhythms and influences our sleep/wake cycles. Bright light increases the strength of our rest/activity cycle and decreases nighttime awakenings. Morning light is associated with setting our internal clock for an early to bed and early to rise schedule. Afternoon light tends to predispose us for a later bedtime and a later awakening. Genetic components and life stage factors also determine oneís preference for early or late bedtimes, but an hour of daily light exposure improves body rhythm synchrony for all of us. No documentation exists about the daily bright light exposure of the average American, but working people may be drastically limited to bright daylight, especially during the winter.
A dark room also assists the slumber process. Our bodyís level of melatonin increases in the dark, and melatonin promotes sleep. Body temperature seems to decrease in sleep but, daytime heat is associated with sleepiness. Vigorous daily exercise and bright light tend to increase stages three and four of the sleep cycle. These significant stages, which importantly include REM and so called deep sleep, tend to decrease in later life. The sequencing of REM episodes throughout the night is related to maintaining emotional equilibrium. Good sleep hygiene is a vital life habit.
Integrating our present sleep research knowledge base into cultural life patterns is important for optimal life development. For instance, our present school schedules transgress the normal internal clock of adolescence. Middle school and high school students naturally have a delayed phase sleep cycle during the teen years. This means that they are more likely to go to bed later at night and attempt to sleep later in the mornings. Early school start times may be biologically hard for these youngsters, as their internal clocks are not scheduled for awake time until later in the morning.
In the past we often thought that if we were asleep then physical restoration was occurring. Now we are beginning to understand that the natural progression and occurrence of sleep stages are essential to physical renewal and memory. Like nearly all body systems, the sleep/wake cycle needs regularity and balance. Consumption of alcohol and many medications disrupt sleep and sleep stage progression. Effexor, a commonly prescribed antidepressant, is strongly associated with REM behavior disorder and with sleep movement disorders like Restless Leg Syndrome. (Some sleep movement disorders are related to an iron deficiency.) The Serotonin agents, Prozac and family, are also known to disrupt the natural sleep stages. The old Tricyclic antidepressants like Trazodone, which are sometimes still prescribed at small doses to induce sleep, disrupt sleep cycle synchrony also. Caffeine is also an offender. These are merely some among a hundred disorders of sleep that impair the quality of life.
Quite recently sleep researchers have found that an upsetting, chaotic and/or abusive childhood predicts later adult life insomnia. This insomnia is thought to be related to lasting feelings of insecurity. A childhood of turbulent family life often causes anxiety and worry that continue into adulthood. Anxiety and worry are antithetical to sleep. Chaotic families often set up habits of poor sleep hygiene. Rather than teaching children to establish good sleep habits and to set up life conditions that promote sleep, stability and peacefulness, these families may be in wearisome circumstances or promote lifestyles that adversely affect good sleep. For example, a knowledgeable focus on bedrooms that are dark and relatively cool is important for good sleep. Furthermore, disorganization or chronic conflict may reign in too many households.
Poverty is associated with a decrease in the average amount of daily sleep and sleep efficiency. Educators have found that poor children of every ethnic group have less stable sleep patterns than their more affluent schoolmates. People that are anxious to make financial ends meet may view sleep as a luxury rather than a necessity. Worry and stress may further disrupt sleep habits. The world energy crisis may be a hardship on sleep in the future. If people are financially unable to cool or heat their homes sleep will be badly impacted.
One study indicates that chronic sleep disruption may reduce lifespan some fifteen years - the same loss of life estimated from smoking two packs of cigarettes daily. In old age, chronic sleep disruption may be a harbinger for nursing home institutionalization. Sleep efficiency seems to change in old age. Most elderly take a longer time to go to sleep, experience more awakenings and have less REM and deep sleep. As a consequence, older adults often spend more time in bed and are beset with fatigue and daytime sleepiness. Cataracts decrease the light that is received in the brainís circadian center and thus frequently disrupts internal rhythms. The average nursing home patient gets only ten minutes of bright light daily. For the healthy old sleep becomes even more consequential, and of course sleep interfaces with light, exercise, social support and positive thinking habits to promote a general sense of peacefulness.
Scientists have discovered that lack of good sleep can even influence certain diseases that were once thought to be linked to other causes. Some sleep dysregulation, like REM Behavior Disorder, are predictive of later neurodegenerative disease, including Parkinsonís disease. Most of us know that dementia is a neurodegenerative disease, but many do not know that it is associated with a breakdown in the integrity of the neurologically based sleep mechanisms. In fact, sleep fragmentation and disruption are common characteristics of dementia. Thirty-three to fifty-three percent of patients with Alzheimerís disease have sleep apnea - a sleep respiratory disturbance that causes stress reactions throughout the body during the night. Even a mild apnea may result in cardiac damage. Sleep apnea is also associated with trouble in concentration, attention and memory, and can induce irritability and difficulty with clear thinking.
Because of genetic and imaging research, we understand now that sleep is a very important part of setting up habits that support our best selves throughout life. If it is true that sleep is preparing us for the level and quality of consciousness and memory for the next day, then improving our sleep habits will surely improve our lives.
- Dr. Linda Klaitz, Medical Psychologist