Sleep is a complex mental process that is critical for human life. It’s importance to healthy functioning is dramatized by one simple fact-we take our conscious vigilance off-line for a significant portion of each day. Historically, this would not have made survival sense. Recent research has clarified that sleep is absolutely necessary for brain and body restoration and homeostasis. Without sleep rats will die within 16 to 21 days. Learning and memory stops and organ systems break down. It is during sleep that the brain support cells, glia cells, help to clear metabolic waste that may build up as toxins. Sleep deprivation may prevent the brain from clearing these toxins. Over time they are thought to contribute to neurodegenerative diseases. Even short periods of sleep deprivation in humans remarkably decreases immune function, glucose metabolism, bone health, hormonal regulation, and learning and memory capacities. Sleep provides time our for body and brain reconditioning and to renew chemical energy that is available for learning and adaptation while we are awake. For complex evolutionary reasons, humans need sleep and need it regularly.
Long term learning is contingent upon night time sleep. It appears that it is necessary to suspend incoming information (in sleep) in order to effectively sift through new experience and to store and integrate the significant information into memory stockpiles-and to forget new experience that is not important. During daytime learning new experience is stabilized into short term memory, the hippocampus, to be consolidated and integrated into long term memory cortical areas at night.
Understanding Functions of Sleep Cycles
Brain researchers have been able to image increased activity during sleep in the very areas of the brain that have been active during the prior waking period. For instance, if you have practiced a new measure of music during the day, the pattern etched in the active neurons while practicing will be replayed during sleep. This motif will then be embedded into long term memory and consolidated with earlier parts of the music that already exist in memory repertoire.
Sleep occurs in 2 primary stages. It always begins in what is called nonRem (non-rapid eye movement) sleep. About every 90minutes the sleep cycle ends with the conclusion of the second stage, which is REM (rapid eye movement-dream) sleep. NonRem sleep is longer and more intense earlier in the night with REM sleep phases increasing as the night progresses. NonRem sleep is more robust if we have been awake for a long period of time. And remember, it reflects the reactivation of the very cellular connections established while learning new information during the prior waking period.
NonREM Sleep Functions
NonREM sleep is now thought to be a phase during which nonessential information is erased, freeing up synapses so that future connections may be available to store information that is of greater significance for recollection. As mentioned this nonREM sleep phase enhances and stabilizes important information acquired during the previous awake period. It facilitates the etching of newly imprinted cellular connections, representing recently learned experience, into long-term cellular pathways in the cortical memory regions of the brain. The hippocampus is the fast learning, temporary memory repository. But there is parallel learning occurring in the cortex during initial encounters with new experience also. The cortex, in contrast to the hippocampus, is a slower, long term memory reservoir. The fast learning system, the hippocampus, is thought to mentor the slower learning cortex during nonREM sleep, priming only the newly etched pathways that are worthy of recollection.
NonRem sleep also has a crucial chemical restoration function. While other body parts can use protein and fats for fuel, the brain only uses carbohydrates. It is our body’s most energy intense system, using up about thirty percent of daily fuel. When adenosine triphosphate (ATP), our primary energy transporter molecule in the blood, is depleted with activity in the brain during the day, glia cells step in to support the immediate brain energy needs. These support glia cells relinquish chemicals that are converted to ATP, rapidly making more energy available to the brain.
As energy is utilized in ATP, a byproduct adenosine builds up. One of the functions of this chemical is to influence the area of the brain that controls a “sleep switch” releasing an inhibitory system, to induce sleep. While sleeping, adenosine levels fall and the level of ATP, our energy delivery molecule, rises. As we begin to understand the important role of adenosine in sleep regulation, we may find ourselves questioning the excessive use of caffeine, an adenosine inhibitor. Caffeine can build up during the day and block the incredibly significant adenosine regulation of our sleep cycle and related restoration and memory storage processes.
REM Sleep-Dreaming for Integration and Insight
REM sleep periods increase as the sleep night progresses. The final approximately 90 minute sleep cycle in an 8 hour nighttime rest is dominated by REM sleep. It is REM sleep that promotes integration and insight capabilities. It is believed that REM sleep assimilates newly coded information into already existing memory stores. Memory in sleep is a two step operation involving the differing functions of nonREM and REM sleep cycles. Because the brain is unconscious during sleep, not taking in new sensory experience, there is no interference with new information coming into sensory systems that may alter what is being integrated into existing memory. Importantly, insight and creativity are part and parcel of REM sleep.
Sleep is a continuum of brain states. Darkness is sleep inducing. Melatonin, a sleep promoting neurochemical, increases in the dark. Light activates wakefulness. We seem to be wired for daytime, light/activity and nighttime, dark/rest. Insomnia is often caused by a number of dysregulated living patterns, some of them disrupting circadian rhythms. For instance, it only takes a few pulses of bright light at night to put the brain back into alert mode. This is one reason sleep professionals are suggesting that electronic devices are put away well before bedtime. It seems that regular wake/light, sleep/dark and even regular feeding habits are significant for good sleep. The brain needs to have a period of quiet, low light time to cycle effectively into sleep states. Agitation during the day impacts the brain’s ability to segue into restful sleep at night.
Loss of sleep can be physically, emotionally and cognitively debilitating. Sleep experts tell us that adults need 7 to 8 hours nightly, teens 8 to 9, and children 10 to 11 hours. Countless studies have tested sleep deprived people and animals, finding that they do not retain learned information and that intellectual ability, reaction time, emotional equilibrium, and physical and immune system restoration have been dramatically dissipated. Sleep loss is cumulative such that immune functions and reaction times may take many nights to recover, even from a single night’s sleep loss. One may use caffeine to function during several nights of shortened sleep, but sleep debt is cumulative with small sleep debts accruing into large ones that you may have to pay back- or pay an immune system, body/reaction, cognitive/memory price.
Sleep loss is strongly associated with depression and anxiety. Almost all psychiatric disorders are exacerbated by poor sleep. Sleep cycle synchrony is disturbed in emotional dysregulation. For instance there is early REM onset in depressed patients. Fifty percent of schizophrenic patients have very little deep, nonREM sleep.
Many disease symptoms appear within the day/night rhythms. The incidence of heart attack peaks at around nine in the morning. Seizures most often occur late afternoon, early evening. Disruption of sleep/wake cycles decreases survival for many disease states notoriously including dementia.
Recently many surgeons have begun to urge patients to “load up” on sleep before surgery. It has been demonstrated that post-surgery pain is decreased by pre-surgery sleep. Your immune function will also benefit from the pre-surgery sleep. Chronic pain often disrupts sleep, but sleep helps to decrease pain levels.
One recent government study reported that one in twenty drivers recalled nodding off while driving in the past year. Millions of Americans are sleep deprived on a regular basis. Many studies of medical students have shown that there is a sharp increase of patient related errors with sleep deprivation. Some 50 percent of all big truck accidents are related to sleep loss. People are poor judges of when they are too exhausted to drive or do other important, risky tasks.
Assessing Sleep Aids
Antidepressant medications, all of them, profoundly decrease nonREM sleep. Don’t forget, this is the stage where the significant newly acquired information is stabilized into memory. Antidepressants target and increase the very neurochemicals that activate us in the waking day. The activation of (monoamine) chemicals is dramatically decreased during sleep, especially in nonREM sleep. When they are elevated by antidepressants, it is more difficult for sleep restoration and normal sleep cycles to occur. Regular good sleep is necessary for the successful treatment of depression. Adequate sleep boosts the impact of cognitive behavioral therapy and antidepressant medication (even though this medication itself disrupts sleep stages-an unfortunate oxymoron). Benzodiazepines, Valium/Xanax type medications, and alcohol tend to disrupt REM cycles.
Several studies have sounded the alarm that there may be increased mortality with the chronic use of sleep medications. This does not mean that there is not an important place for antidepressant and sleep medications. It does mean that we must use them judiciously, working quickly to re-stabilize sleep/wake living patterns, and to discontinue sleep promoting agents as soon as possible.
Children and Sleep
A child’s brain at birth does not have fully developed stages of sleep. In fact, a baby’s first sleep patterns appear almost random. It typically takes about three months for a baby’s sleep to be entrained to light/dark, day/night, sleep cycles. A baby needs time for development and routine daylight exposure along with dark sleep experience, and regular feeding schedules to establish good sleep patterns. Interestingly, the involvement of the father seems to facilitate sleep in very young children. But, it is several years of brain development and predictable, routine nurturing before a baby evolves into adult sleep patterns.
The younger the child, the more difficult loss of sleep becomes. Persistent sleep deprivation during the critical years of childhood development renders lasting changes in the child’s brain organization. Even missing one nap for a toddler is very disruptive. The pressure for homeostatic body restoration and the mnemonic integration of new experience is intense during childhood. For children, learning during this critical early developmental life phase, establishes patterns of living that are essential for future survival and adaptation. Almost always after sleep loss, a child will go to sleep faster and sleep longer in the next sleep session. Adolescents, who typically have a period of sleep phase delay, i.e. want to stay up later and sleep in later, are easily dysregulated also. Like all of us, their homeostatic restoration of cognition and emotional reactivity is disrupted without adequate sleep.
Sleep for Success
Sleep makes us smarter. If you intensely study something new, your recall will be much better after a night’s sleep. A nap shortly after a period of learning will immediately increase recollection and will boost your ability to remember after the following night’s rest. Sometimes it takes several nights or longer for newly learned information to be fully integrated into the facile recollection of long term memory.
Routine nightly sleep seems to be brain enhancing. Sleep is impacted by many factors, but good sleep habits that are established patterns of daily living promote health, well-being, intelligence and creativity. Routine morning light exposure, exercise, careful life modulation, avoidance of emotional rumination, positive social support and a generally peaceful, quiet lifestyle promote sleep. A prominent sleep researcher has pointed out that health involves 3 main factors: nutrition, physical fitness and sleep. Our understanding of sleep activity is far from complete, but gaining clarity leaves us deeply inspired with its significance and complexity.
Dr. Linda Klaitz, Medical Psychologist