What causes insomnia?

—H. York, England

Henry Olders, assistant professor of psychiatry at McGill University, explains:

PEOPLE CAN EXPERIENCE sleep difficulties for a variety of reasons, including medications, alcohol, caffeine, stress and pain. When the underlying cause is removed, these bouts usually get better on their own. For many people, however, sleep problems turn into insomnia, the chronic inability to either fall asleep or keep sleeping.

Whereas many insomniacs believe that they lack sufficient sleep, evidence is mounting that they are in fact getting at least as much as they require and possibly more. Insomniacs tend to go to bed early, stay there late and sleep during the day—all of which contribute to the problem.

Why would someone spend more time asleep than he or she needs? Opinions about sleep seem to be important. Individuals who experience insomnia are more likely to be concerned about not sleeping and to think about problems, events of the day and noises in the environment while preparing to sleep. They also underestimate the amount of time they actually sleep. Simply put, if you believe you need eight hours of sleep a night, you will arrange your retiring and rising times so that you spend eight hours in bed. If you require only six hours of sleep, however, you will spend two hours tossing and turning.

How much sleep do you need? And how can you tell if you are getting the right amount? Although eight hours a night is a figure repeated so often that it has almost become an article of faith, the reality is that sleep need is highly individual. Large-scale epidemiological studies have shown that sleeping seven hours a night is associated with the lowest mortality risk (for factors including heart disease, cancer and accidental death) compared with longer or shorter periods of shut-eye. In addition, as we age, we probably need less sleep. Many people believe that if they have a good night's sleep they will wake up without an alarm, feeling rested and refreshed. Yet circadian rhythm studies show that people are usually drowsy early in the morning, even after a full night's sleep. If you are truly sleep-deprived, you will have trouble remaining awake during the day. (Brief, 10-minute naps can be rejuvenating.)

To help treat insomnia, practice good “sleep hygiene.” Measures include adjusting the levels of noise, light and temperature so that you are comfortable; not reading or watching TV in bed; avoiding excess food, alcohol, nicotine, caffeine and other stimulants; completing exercise at least three hours before lights out; and determining your optimum bedtime. The longer you are awake, the more slow-wave (delta) sleep you will have; slow-wave sleep is what leads to feeling rested and refreshed. Limiting the time you spend in bed may also help. Together these nonpharmacological approaches are more effective and longer-lasting than medications for insomnia are.

Are humans the only primates that cry?

—C. Henderson, Winter Park, Colo.

Kim A. Bard, a reader in comparative developmental psychology at the University of Portsmouth in England, responds:

THE ANSWER to this question depends on how you define “crying.” If crying is defined as tears coming from the eyes, then the answer is yes: tears appear to be unique to humans among the primates. If you define crying as a vocalization that occurs under conditions of distress or what humans might describe as sadness, then you can find crying in almost all primates.

In contrast, others argue that all mammals have feelings, because emotions are the product of deep-brain functioning with a long evolutionary history. Some reserve such emotional terms for humans alone and will not use such words for other primates. Others take a conservative stance and say that it is too difficult to tell whether or not nonhuman primates have feelings. Rather than broadly describing some primate vocalizations as crying, scientists prefer specific names for certain conditions. For example, a young primate that is not in contact with its mother produces a separation call. Investigators will also describe what the vocalization sounds like, as with the “smooth early high” coos of squirrel monkeys. Or researchers will describe what the animal is trying to communicate, such as when infants try to satisfy their basic needs for food, social contact or relief from pain.

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