By studying the way certain species snooze, researchers are gaining new insight into the role sleep plays in animal behavior
- Michael Tennesen
- Aug 01, 2007
AS ANY NEW PARENT knows, the first months of an infant's life mean little sleep for mom and dad. But humans have it easy compared to orcas, or killer whales. University of California–Los Angeles neuroscientist Jerome Siegel and post-doctorate fellow Oleg Lyamin have found that for the first month after giving birth, killer whale moms and their calves do not experience normal sleep at all. Adult orcas normally snooze 5 to 8 hours a night, closing both eyes and floating motionlessly. But for the first 30 days after a youngster is born, neither calf nor mom shut their eyes, and neither stops moving for more than a few minutes at a time.
There are good reasons for this behavior. In the wild, new orca mothers must constantly look out for sharks while teaching calves to breathe. "These sleep patterns contrast with other mammals, which need extra sleep during infancy and gradually sleep less as they age, but dolphins and killer whales are never as active as in the first months of life," Siegel says.
According to Siegel, the results of his orca study fundamentally change our view of sleep. "It has often been said that sleep is necessary for primary development, particularly that of the brain," Siegel says. "But here we have a species that grows some of the largest brains in the animal kingdom, and yet it is doing this without sleep and without detrimental effects due to lack of sleep."
Siegel's lab has looked at a number of animal sleep habits and reports that not all species need 8 hours. Horses sleep 3 hours a day, giraffes 4.5, dolphins 10, ferrets 14.5, and bats 19. Sleep habits vary as well. Humans typically sleep at night, mice by day. Rabbits sleep in burrows, zebras in the open, and dolphins can sleep while moving.
Sleep is a dangerous undertaking for most animals, since they may be more susceptible to predators while sleeping. All mammals and birds appear to need sleep, but scientists are unsure if reptiles and fish do. "When you come downstairs at three in the morning, the goldfish isn't lying on the bottom of the bowl, it's swimming around," Siegel says. But other scientists believe fish do enter a restful dormant state that is at least akin to sleep.
Some animals die without proper sleep. Sleep deprivation in rodents and flies can cause death more quickly than food deprivation. Two weeks without sleep can kill a lab rat. Siegel thinks that the amount of sleep an animal needs is dictated less by biological functions than by the animal's environmental niche. The long night's rest typical of bats, for example, helps the animals to economize on energy. "If a bat eats insects for only three hours in the evening, then maybe the best thing is to go hang in a cave upside down for the rest of the day," Siegel says.
Humans are born relatively immobile and initially sleep 12 hours daily, which focuses the body's full attention on development and eventual mobility. For killer whale calves, which are mobile at birth, movement and wakefulness reduce danger from predators, help maintain body temperature until mass and blubber insulation develop and allow for frequent respiration.
Sleep is not the same for all creatures. Dolphins exhibit unihemispheric sleep, in which half the brain may rest while the other half stays vigilantly awake, and the animal carries on normal activities. Dolphins sleep literally with one eye closed—the eye on the opposite side of the body as the dozing brain hemisphere, since the right brain hemisphere works the left eye and vice versa. For unknown reasons, closed eyes seem to be a prerequisite for most forms of sleep. Like killer whales, dolphin calves show less than 1.5 percent of this kind of activity at birth but gradually increase to 16 percent by three months.
Neuroscientist Clifford Saper of the Harvard Medical School has studied a variety of species, including rats, mice, cats, monkeys and humans. He has located a small area at the base of the brain behind the eyes called the ventrolateral preoptic nucleus (VLPO) that sends chemical signals to other parts of the brain during sleep to slow those brain parts down. The VLPO takes in cues from a variety of brain functions and determines the best sleep budget for the animal. It is flexible, able to reverse the normal nocturnal habits of a rodent to make it active in the day if that is the only time food is available.
According to Saper, evidence suggests that for restoring tired muscles or any other body system, sleep is no more effective than a comparable period of wakeful resting—except for one critical organ, the brain. The human brain apparently cannot do without sleep. Studies show that prolonged wakefulness leads to degradation of memory, alertness, coordination and judgment.
Nevertheless, studies of insomniac species and their "natural models of sleep deprivation," as psychologist Verner Bingman of Ohio's Bowling Green State University calls them, may allow researchers to provide night-shift workers, military personnel, doctors and other assorted night owls with new methods for adapting to limited sleep without losing effectiveness. "We could live 20-hour lives instead of 12- or 14-hour lives," says Bingman, who is studying the behavior of Swainson's thrushes, which during migrations between Canada and Peru go from a normal night's sleep of 10 to 12 hours down to about 2.5 hours so they can migrate at night. To handle the energy output of the long migration they must nearly double the amount of fat in their bodies, switching from a diet of seeds to one of fruits and insects in order to build up fat and flight muscles. This dietary change means they must search for food during the day, which limits sack time. "All of a sudden they are subject to an enormous amount of sleep deprivation," Bingman says.
Bingman and doctoral student Thomas Fuchs have discovered that during morning and midday hours, the thrushes enter periods of drowsiness, during which they take as many as 50 micro naps per hour, most of them lasting about 10 to 20 seconds. When brain waves are measured, these napping behaviors look very much like normal sleep. Says Bingman, "The trick would be to develop techniques or drugs that could recreate a similar brain pattern in humans."
Similarly, orca sleeplessness in the initial stages of life, Siegel says, "raises the question of whether humans and other mammals have untapped physiological potential for coping without sleep."
Saper thinks we are dreaming if we think we're ever going to get by on as little sleep as newborn orcas or migrating thrushes. "If humans are deprived of sleep for long periods they lose motor, cognitive and memory function. The effect of 20 hours of wakefulness on driving is the equivalent of two shots of whiskey. This is unfortunately a major cause of death of young adults in the U.S., who have a very high crash rate between 3 and 6 a.m.," Saper says.
Even Bingman agrees that for now, the take-home message may be: "If you're functioning under sleep-deprived conditions, take naps, no matter how brief."
California-based writer Michael Tennesen is a frequent contributor to this magazine.