When I bought my ticket to Friday’s World Science Festival (WSF) event, The Mind After Midnight: Where Do You Go When You Sleep?, I didn’t think one of my main takeaways would be “birds are even cooler than I thought they were.” It’s not enough that they can fly, but did you know that some birds, such as the Bar-Tailed Godwit, can fly for several days without resting? And, that many birds (and some marine animals, for that matter) can sleep with one eye open?
According to Niels Rattenborg, group leader at the Max Planck Institute for Ornithology and one of the three scientists presenting at the WSF event, the first phenomenon is still in the process of being studied, although Dr. Rattenborg’s lab has issued a hypothesis that “some forms of sleep could well be compatible with flying.”
The Max Planck Web site notes,
Like mammals, birds exhibit two forms of sleep: slow-wave sleep and REM sleep (rapid eye movement). While slow-wave sleep can occur alternately in each of the brain's two halves, REM sleep always takes place in both sides of the brain simultaneously. During unihemispheric slow-wave sleep, the eye connected to the awake side of the brain remains open. This condition might allow birds to continue visually navigating while asleep. If it is not necessary for the birds to watch their environment continuously, a version of slow-wave sleep involving both halves of the brain should also be possible. The reduction in muscular tone that accompanies REM sleep makes it unlikely that birds experience REM sleep in flight.
In addition to potential navigation, Dr. Rattenborg and his colleagues have proven that some birds sleep with one eye open to detect predators. He described one experiment in which he literally put his ducks in a row and found that the two birds on either end kept the eye facing away from the group open while they were sleeping. He explained that the brain connected to the open eye can function in a half awake or drowsy state.
While humans obviously don’t have this ability, Rattenborg did note that parts of the human brain can sleep more deeply. For example, if one arm experiences a more rigorous workout, the brain area connected to that limb will experience a deeper sleep, he said.
Completely switching gears from birds to humans, another key takeaway at the WSF event was that sleeping can be dangerous for some people. Dr. Schenck spoke about extreme parasomnia cases such as sleep aggression, sleep terrors, and sleepwalking. He showed several videos of people exhibiting these types of behavior and told the much-publicized story of Ken Parks, a Canadian man who murdered his mother-in-law and attacked his father in law while asleep (he was tried and acquitted).
Parasomnias of this nature occur because the mammalian paralysis in REM sleep is not working, resulting in people acting out their dreams. Many diagnosed people have been successfully treated with the drug clonazepam, Schenck said.
And while the studies on parasomnia in and of themselves are quite fascinating, an eye-opening discovery has been the relationship between REM sleep behavior disorder (the category of parasomnia in which muscle paralysis does not work) and Parkinson’s disease (PD). According to Schenck, 81 percent of REM sleep behavior disorder cases convert to PD. He views this as an exciting opportunity for early intervention for PD, and explained that it is an area being researched by a collaborative international effort.
–Ann L. Whitman