Landmark Sleep Study Looks Beyond the Brain

September 12, 2009 08:00 AM
by Shannon Firth
Researchers at UCLA diverged from tradition, examining sleep as an adaptive strategy that has more than one distinct purpose, instead of studying the brain’s relation to sleep.

To Sleep or Not to Sleep

Scientists have been battling over theories of sleep for decades. Some experts believe sleep reinforces and “prunes” certain neural connections, others believe it helps the body recover from “oxidative stress” (when reactive molecules cause damage to cells), and still others say sleep helps us live longer.

None of these theories are well established, and many are mutually exclusive,” according to a recent statement from researchers at the University of California, Los Angeles, reported National Geographic.

Having observed the sleep habits of the platypus, the walrus, the echidna—which like the platypus is another egg-laying mammal—and several other animals, Jerome Siegel, a sleep researcher at UCLA, disagrees with the idea that sleep has a “vital universal function,” reported Live Science.

Put simply, Siegel argues that whatever happens while we sleep isn’t as important as the simple fact that we aren’t awake. According to National Geographic, Siegel sees sleep as part of a spectrum of other restful behaviors, with hibernation at one end and wakefulness at the other.

“I propose that sleep is best understood as a variant of dormant states seen throughout the plant and animal kingdoms and that it is itself highly adaptive because it optimizes the timing and duration of behaviour,” Siegel declared in his article, published in the journal Nature Reviews Neuroscience.

Siegel compared the big brown bat, which sleeps about 20 hours a day, to birds, which in migratory periods can fly without sleeping for days. In the past, scientists have seen sleep as a missed opportunity to mate, forage or hunt. According to Siegel’s theory, however, wakefulness can also be an expense of unnecessary energy or unnecessary risk. While certain birds’ survival depends on their migration and their continued wakeful state, sleep is advantageous for the big brown bat, which spends its scant waking hours chasing mosquitoes and moths when such insects are active. “If it spent more time awake, it would spend more energy but not be as successful at hunting,” Live Science quoted Siegel as saying.

Neuroscientist Amita Sehgal at the University of Pennsylvania disputes Siegel’s theory. She told Live Science, “[Sleep] is not something that is just passively there to keep animals out of trouble. Rest alone would do that.”

Background: On sleep and the brain

In 1994, the Weizmann Institute in Rehovot, Israel, reported a significant breakthrough in sleep research, recognizing that "procedural memory,” the type of memory that requires rehearsal in order to learn a new behavior, improved in subjects who had had the most REM sleep. Until then, scientists hadn’t differentiated between “declarative memory,” basic recall of facts, and procedural memory, in brain research.

Robert Stickgold, a cognitive neuroscientist at Harvard Medical School, expanded on this research, developing his own test of procedural memory. He measured right-handed subjects’ ability to perform a left-handed typing pattern 12-hours after learning it, reported Time.

Stickgold found that test subjects who were given a chance to sleep before being tested on the task out-performed the daytime learners who had not slept, showing a 15 to 20 percent increase in speed and a 30 to 40 percent increase in accuracy. In this study, the subjects who had had more non-REM sleep improved.

In 2007, researchers at the University of Arizona in Tucson traced the neuronal activity in the brains of rats as they ran through a maze and while they slept. Researchers found that the “neuronal activity sequences” they saw while rats ran were remarkably similar to the activity they saw during periods of sleep. Although the patterns occurred at roughly six and seven times the speed when the rats slept.

“One way you could strengthen memories is by playing them multiple times,” David Euston, an assistant research scientist at the U.A. College of Medicine’s Division of Neural Systems, Memory and Aging, told Scientific American.

Reinforcing connections between neurons might help the brain consolidate memories. “[A]s neuroscientists like to say, ‘neurons that fire together, wire together,’” Bruce McNaughton, a psychologist and physiologist also at the university, told Time.

Others are critical of the theory. Mayank Mehta, an assistant professor of neuroscience at Brown University, asks, “Is this consolidation or erasure?” Nikhil Swaminathan, a writer for Scientific American, explains that an activity appearing to be memory storage could actually be “akin to clearing a chalkboard.”

Christine Gorman, a writer for Time, wonders why we must be asleep for this breaking and strengthening of connections to happen. “[I]t’s like you’re leaving your house and the workmen come in to renovate. You don’t want to live in the house while the construction’s going on because it’s a mess,” Terry Sejnowski, a computational neurobiologist at the Salk Institute in La Jolla, Calif., told Time.

Related Topic: Sleep gene discovery

In 2008, Amita Sehgal Ph.D., professor of neuroscience and an investigator with the Howard Hughes Medical Institute, discovered that a mutation in a gene in fruit flies might explain why some people sleep less than others.

According to Science Daily, Sehgal and her colleagues believe this “sleep gene” contains the instructions for developing certain proteins that open and close ion channels. “When the channels are open, the brain is connected and working—the fly is awake. When closed, the channel shuts down and the fly sleeps,” Scientific American reported.  Flies who slept less, one to two hours, rather than the normal 12 hours, produced less of this protein. The sleep-deprived flies lived only half as long as their counterparts.

Reference: Sleep

If you’re having trouble sleeping, seek counsel! Using the Web Guide to Sleep, you’ll find advice on getting a good night’s sleep, information on what could be keeping you up at night, a host of theories about the function and meaning of dreams, resources to help you sleep better, and the latest professional research.

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