Everyone I know has difficulty falling or staying asleep (called insomnia) from time to time. Lack of sleep causes sluggishness and poor concentration. It's bad enough to experience insomnia once in a while, but 10 percent of Americans have chronic insomnia, meaning their sleepless nights happen more often than not.
A complex group of brain circuits interacting with multiple brain chemicals controls sleep and wakefulness. Sleep is a very active brain process. Nerve cells (neurons) in the brain that promote sleep inhibit the neurons that promote wakefulness, and vice versa. This can be explained with the concept of the flip-flop switch from electrical engineering: because of the way the wakefulness and sleep circuits are connected, turning one on turns the other off, acting as a flip-flop switch. But in some sleep disorders, the switch does not flip easily, and the wakefulness circuits are difficult to turn off.
Sleep and wakefulness circuits are influenced by many external factors, such as sleep habits and pre-bedtime activities. Stimulating activities right before bedtime, such as video games and exercise, can interfere with sleep. Certain foods and medications contain compounds that prevent the sleep circuit from being turned on. These compounds block receptors on sleep-circuit neurons that flip the switch from wakefulness to sleep. For example, caffeine blocks receptors that are important for sleep, called adenosine receptors. Too much caffeine late in the day prevents the switch from flipping towards sleep.
Some neurologic conditions can also lead to sleep problems. Excessive daytime sleepiness—even in the presence of a good night's sleep—can be due to a problem with the wakefulness circuit. This is a common complaint in people with Parkinson's disease and narcolepsy, which is a primary sleep disorder with “sleep attacks” during the day, loss of all muscle tone when startled, very vivid dreams, and temporary paralysis upon awakening. However, excessive daytime sleepiness can occur in any disorder that affects the entire brain, such as diabetes, liver disease, and kidney disease.
In some cases, people may be unaware that they are not sleeping soundly. One cause of this is obstructive sleep apnea (OSA), which involves multiple episodes of upper airway obstruction causing snoring; periodic leg movements of sleep; and sleep walking or other behaviors performed during sleep.
Poor sleep can make some neurologic conditions worse. OSA, in addition to contributing to stroke and heart attack risk, is a common treatable cause of cognitive problems. In people with mild cognitive impairment or Alzheimer's disease, cognitive function can be made dramatically worse by OSA. Treatment for OSA can help improve cognitive function for these people.
Poor sleep can also cause problems in the absence of any neurologic condition. A recent study in the U.K. found that poor sleep habits (in particular, not having a regular bedtime) led to behavioral problems and poor school performance in elementary-aged children. These problems were reversed when a regular bedtime was introduced.
If you or someone you know has a persistent problem with falling asleep, staying asleep, or daytime sleepiness, talk with a doctor about possible underlying causes. If no clear cause is evident, many people can be helped by creating good sleep habits: maintain a regular bedtime; avoid caffeine, alcohol, and stimulating activities before bedtime; and ban TV and electronic devices from the bedroom. In some cases, short-term sleeping medication may be in order, but this is never a good idea over the long term because it is easy for people to become dependent on them.
Don't forget to read “Sleep Well” on page 34 of this issue. And if you have a good strategy for preventing sleepless nights, please share it with us!
Take good care,
Robin L. Brey, M.D.