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10/11/2006
Sleepy Time
Last week I had a frustrating dream about rushing to an
appointment of some sort and finding no elevator in the location
it had been earlier. In almost all of my dreams, I’m being
frustrated, usually missing a train, a bus or a plane. Recently, my
wife attended a lecture on the meaning of dreams that she found
very interesting. I hoped to glean some information from her
about my own dreams but when I questioned her she admitted
that she was falling asleep during most of the lecture! I can’t
fault her inasmuch as I on occasion doze off even while watching
a favorite TV program. The nature and purpose of sleep is still a
mystery despite its being the subject of numerous studies and
conjectures.
One thing we do know is that sleep is essential for us humans
and other animals. Last Sunday’s New York Times Book
Review section had a review by Natalie Angier of “The Family
That Couldn’t Sleep” by D.T. Max. The book deals with an
Italian family that for 200 years or more has endured a hereditary
disease known as fatal familial insomnia. According to a Merck
Manual Web site, the disease generally shows up anywhere in
age from the 30s to 60s. Gradually, over a period of years, the
ability to sleep is lost and the victim dies.
I also found a long article on the Web site of the National Center
on Sleep Disorders Research of the National Institutes of Health
(NIH). The article, a teacher’s guide, contains a plethora of
information on sleep, sleep disorders and biological rhythms.
Did you know that the brown bat sleeps on average 19.9 hours a
day while the giraffe only sleeps 1.9 hours? Humans sleep, or
should sleep, about 8 hours a day. Some fall asleep at the wrong
time; 100,000 accidents a year are blamed on falling asleep at the
wheel. Having nodded off myself on the New Jersey Turnpike a
few years ago, I was surprised that, in one large study of drowsy-
driver accidents, half involved drivers 25 years old or younger.
Why do we sleep? I would have thought the answer is that we
need to sleep to save energy. If we played or worked day and
night, wouldn’t we wear ourselves out? On the other hand,
couldn’t the same thing be accomplished just by resting with our
eyes open? Some suggest that sleep evolved to protect us from
predators, assuming we found a safe place to sleep. Various
other hypotheses have been put forward but it seems that none
are totally satisfactory.
Some studies have shown that memory improves after sleep. A
favorite view among scientists has been that during sleep the
brain reorganizes memories or strengthens those memories that
become long-term memories. Our memories are stored in the
brain by the patterns and strengths of connections among the
billions of neurons that make up the brain. “Strengthening” of
one of these connections, or synapses, involves various chemical
reactions that in effect bulk up the synapses. In a brief article in
the September Discover magazine, Anne Wootton discusses the
work of psychiatrist and neuroscientist Giulio Tononi and his
colleagues at the University of Wisconsin. Tononi proposes a
contrary view of what goes on during sleep.
Tononi’s view of the brain’s actions during sleep resembles
emptying the recycle bin on your computer. During sleep,
billions of the brain’s neurons participate in simultaneous 1-
second bursts of electrical energy. This happens about a
thousand times a night. After the bursts, there’s silence – no
electrical activity. This lack of electrical activity does not
happen during one’s waking hours. Tononi’s proposal is that,
instead of strengthening the synapses, the brain weakens them.
If this is true, it does make a lot of sense. Think of all the useless
information we gather during the day. For example, I enter our
medical expenses into a spreadsheet. I memorize the figures for
the second or so it takes to enter the expense. I don’t want my
brain to be cluttered with those numbers. Better I should
preserve things such as my wife’s birth date in those synapses.
If Tononi is correct, the stronger synapses will survive while the
weaker ones will disappear or weaken during the night’s sleep.
These bursts occur during non-REM sleep. Remember, there are
two classes of sleep, one characterized by rapid eye movement
(REM) during which most dreaming occurs. The deeper sleep
occurs in the non-rapid eye movement (non-REM) period when
it is much harder to arouse the sleeper. It sort of makes sense
that the brain would pick the non-REM sleep period to prune
useless memories since there’s not much dreaming or other
mental activity going on. Tononi’s idea seems reasonable in that
the brain needs the space to store new important memories.
Tononi, Chiara Cerelli, Barry Ganetsky and their colleagues at
the Center for Sleep and Consciousness at the University of
Wisconsin have not only shown that fruit flies sleep but that their
sleep characteristics are quite similar to those of us humans.
They’ve even put electrodes in the flies’ brains and measured
brain waves as in our electroencephalograms (EEGs). An
interview by Jill Neimark of Tononi in the August 2005 issue of
Discover and the Wisconsin Web site cite some of the results of
their fruit fly studies.
How do they know a fruit fly is sleeping, you might ask. The
flies are immobile and hard to arouse for long periods. They
don’t respond to light puffs of air, vibration or heat and their
brain waves change, as do ours, during sleep. Young flies sleep
longer than older flies. When I have a bad night and don’t sleep
well, the next night I usually sleep very soundly. Same with
flies. Most people need 7 or 8 hours sleep a night but some rare
individuals function well with only 3 or 4 hours. Same with
flies.
The Wisconsin group looked at about 10,000 different mutant
lines of fruit flies and found that some mutant flies sleep only a
third as much as other fruit flies. Team member Daniel Bushey
analyzed the DNA of these flies and found that one amino acid
was changed in a particular gene called Shaker. It’s called
Shaker because the gene causes shaking of the flies’ legs when
they come out of anesthesia. More importantly, Shaker also
controls how potassium flows through cell membranes. The
mutation in the short sleepers blocks this flow of potassium.
You might think all this stuff about short- and long-sleeping flies
is of no practical interest. However, I note that the work was
funded by DARPA, the Defense Advanced Research Projects
Agency of the Department of Defense. Sleep is pretty important
in the military. I’m not sure of the details but I do recall reading
not too long ago about controversy concerning the use of drugs
to keep certain military personnel awake significantly longer
than normal. Pilots come to mind as individuals who would be
well advised to stay awake during long missions.
Tononi’s mission is to understand consciousness; he thinks sleep
is the most obvious and dramatic modification of consciousness.
Where does consciousness go during sleep? He points out you
can remove the roughly 50 billion neurons in Joe’s cerebellum,
an ancient part of the brain, and he’ll still be Joe. He won’t get
around very well and probably won’t be able to use his hands
much but his personality will be there. However, remove the 30
billion neurons from the cerebral cortex and Joe’s gone, no more
consciousness. There’s a lot more to learn.
All this is taxing my own brain. I’m going to take a nap!
Allen F. Bortrum
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