MADISON -- A newly published study by a University of Wisconsin research team points the way to solving two of life's seemingly eternal but unrelated mysteries: how birds that migrate thousands of miles every year accomplish the feat on very little sleep and what that ability means for humans who are seriously sleep-deprived or face significant sleep problems.
The study, published online in the July 13 issue of PloS (Public Library of Science) Biology, found that a group of sparrows studied in the laboratory dramatically reduced how long they slept during the time they would ordinarily be migrating. But they were nonetheless able to function and perform normally despite their sleep deprivation. During times when the birds were not migrating, however, sleep deprivation appeared to impair their performance - similar to what happens to sleep-deprived humans.
If researchers ascertain how the birds do so well on so little sleep during migration, the finding could benefit people who need to stay awake and function at a high level for long periods of time, as well as those who suffer from sleep disorders of various kinds. In addition, sleep in the migrating birds was similar to sleep changes that typically occur in humans with depression or bipolar disorder.
"We already know from human studies that people with severe depression and mania show characteristic changes in their sleep patterns, such as having insomnia and entering REM sleep (the dream stage) too quickly after falling asleep," says Ruth Benca, professor of psychiatry at UW Medical School and principal investigator of the study. "Finding this same pattern in the birds offers us an intriguing model for studying mechanisms for seasonal mood disorders, such as bipolar illness."
Benca and her colleagues studied captive white-crowned sparrows, songbirds that normally migrate at night between Alaska and Southern California twice a year. When in captivity in laboratory cages during periods when they would normally be migrating, the birds become active and restless at night, moving around and flapping their wings.
Brain sensors measure their sleep patterns continuously during migratory and non-migratory periods. During "migrating" times, they slept about one-third as much as usual and moved more quickly into REM sleep, marked by rapid eye movements. At night, when the birds were active, the brain recordings showed they were fully awake, and they did not appear to make up their lost nocturnal sleep with increased napping during the day.
Cognitive tests showed that, during the migration periods, the birds performed normally -- or even improved their ability to learn -- on little sleep; but during other times, sleep deprivation hurt their performance. The researchers theorize that migrating songbirds have developed the ability to apparently reduce their need for sleep temporarily, without suffering the consequences of sleep deprivation. While the researchers do not know how the birds do what they do, they are convinced that the birds' behavior sheds light on sleep processes in general and on some human disorders as well.
The Wisconsin researchers are also affiliated with the UW HealthEmotions Research Institute, created to study the scientific basis of emotion and health.
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