Scenes of Sleep — Elephants, Giraffes, and Narcoleptic Dogs
By one estimate, researchers have studied the sleeping cycles and habits of over 150 different animal species, looking at both aberrant and normal sleep patterns.

Narcolepsy
Interest in how the circadian system interacts with the sleep cycle has also led investigators to study narcolepsy, a condition characterized by excessive daytime sleepiness. Initial studies indicated that while the circadian pacemakers appeared to function normally, the mechanisms responsible for promoting alertness might be deficient. This has just led to the finding that a neuropeptide called orexin or hypocretin is markedly deficient in patients with narcolepsy.

A Woman Who Watches Elephants Sleep.
Irene Tobler is a professor in the pharmacology department of the University of Zurich, in Switzerland. She has a longstanding interest in brain function and sleep regulation. In an effort to understand the nature of sleep regulation, she has focused on normal and aberrant sleep behaviors in mammals ranging from elephants and giraffes to hamsters. Her first published research was a study on the effect of shortened light-dark cycles on hamster sleep patterns.

To Sleep or Not To Sleep. This chart shows the relationship between the human biological clock, which promotes wakefulness, and the urge to sleep during a single 24-hour period.

An Alternative to Counting Sheep.
While the electric light and jet travel have increased our sleep problems, insomnia is seemingly age-old, as are remedies purporting to treat it. These three packages of a remedy known as Nervine were all marketed in the 20th century. Warner's Safe Nervine and Pastor Koenig's Nervine relied on alcohol for their sedative effects. Although used early in this century to help induce sleep, alcohol fell into disfavor. While it may act as a nighttime sedative (calming agent), it can disrupt sleep patterns, induce nightmares, and cause early morning awakening. Alcohol is one of several agents being studied to see how it specifically affects the workings of the biological clock.

Snooze Times. The number of hours that animals sleep varies greatly by species — but that is only half the story. Sleep patterns and postures vary enormously as well. Rats sleep intermittently. Dolphins sleep with only half of their brains at a time. Cattle can sleep standing up, and often with their eyes open. Bats sleep upside down.

Do All Animals Sleep? The answer depends, in large part, on how sleep is defined. Animals with primitive nervous systems likely sleep, but their brains do not generate the sort of electrophysiological patterns of brain activity that researchers often use to "measure" sleep. Recent studies suggest that rest in Drosophila has the characteristics of mammalian sleep, for example, and that fruit flies may therefore serve as a model system for the genetic study and analysis of sleep.

1. Golden-headed lion tamarin with infant
2. Horse
3. Pig
4. Madagascar hedgehog
5. Green anole lizard
6. Servall cat

Keeping an Eye Out — The Sleeping Habits of Birds. Recent research has shown that birds are capable of sleeping with one eye open. This ability is quite likely an evolutionary adaptation that allows them to watch for approaching predators. In cases where large groups of birds are sleeping, the birds on the outside edge of the group seem to be the ones keeping watch. These birds are thought to be sleeping with only one hemisphere of their brains at a time, as dolphins do.