Sleep is but a dream to the 3 million
Canadians who suffer from insomnia. But the Sandman
could be on his way, thanks to a group of scientists
studying a little-understood sleep function called slow
wave activity (SWA). They've figured out a way to induce
SWA — which occurs in the third and fourth stages
of sleep, the non-REM phase, and is believed to be responsible
for the restorative power of sleep — using transcranial
magnetic stimulation (TMS).
"Insomnia patients have difficulty
in reaching stable periods of sleep stage 4," says Dr
Marcello Massimini, a psychiatrist at the University
of Milan and one of the authors of the study in the
May 4 issue of PNAS. "They lack periods with
large numbers of slow waves. As a result, insomnia has
daytime consequences such as tiredness, lack of energy,
difficulty in concentrating and irritability. "
The
known unknowns
While still largely a mystery, there are a few established
facts about the land of slumber. For one, the longer
you stay awake, the more slow waves are produced and
the larger they are. What's more, slow waves increase
locally in the brain after learning a task associated
with that brain part. "Evidence suggests that slow waves
are strictly linked to learning and plasticity," says
Dr Massimini. "The more slow waves our brain produces
during the night, the better we perform at various motor
and cognitive tasks."
Study subjects were asked to sleep
on a special reclining chair with their heads partially
restrained to maintain the position of the non-invasive
stimulator on the selected brain target. "The setting
we used is not a familiar and cosy bedroom," laughs
Dr Massimini. "In fact, it looks more like the control
room of a nuclear power plant." Once the subjects fell
into a light sleep, the researchers started the stimulations
by TMS at less than 1 Hz for 10 minutes at a time. The
changes in the brain were monitored with an EEG, with
slow waves appearing as the subjects were put into a
deeper sleep.
The current study was mainly aimed
at inducing SWA, says Dr Massimini, rather than looking
at fatigue outcomes. But he says some patients did report
they felt much less tired than usual after the treatment.
"Being able to increase the amount
of slow waves, globally and locally, in a controlled
manner may have important medical applications that
go beyond the field of sleep disorders," adds Dr Massimini.
"In the future, one could think about an effective tool
to modulate cortical excitability in selected brain
regions for the rehabilitation of brain-injured patients."
A
real snoozer
Study co-author Dr Giulio Tononi, a psychiatrist at
University of Wisconsin-Madison, has a hunch about what
happens in dreamland. "You strengthen synapses in the
brain from things you learn during wakefulness," he
explains. "Stronger connections consume more energy
and sooner or later will impair the ability to learn
further. That's why you need sleep," he adds. "Sleep
downscales the connections gradually and by morning,
the amount of synapses is back to baseline and you're
ready to learn new things." He believes slow waves have
a hand in the downscaling of these connections.
In addition to regenerative power
and memory consolidation, sleep has a hand in regulating
the immune system. Some researchers believe that ongoing
sleep deprivation can bring on heart disease, diabetes
and depression.
On the other hand, some people
appear to function very well on very little sleep. "There's
report of some people who have three hours of sleep
at night and are in perfectly good health," reveals
Dr Tononi. "When they looked at their sleep patterns,
they found that these people have only stage 4 sleep,
which has lots of slow waves and hardly anything else."
The findings, he adds, suggest that some people, for
genetic reasons, have more efficient sleep. If the same
can be induced in insomniacs as a treatment, then they
may at least get the full benefits of a good night's
sleep, minus the hours.
The risk that some might use the
treatment to sleep less and be more productive doesn't
worry him. "Between the use of stimulants such as coffee
to keep you awake and enhancing sleep to make it more
efficient, I definitely prefer the last," says Dr Tononi.
"At least you get the benefits, unlike with stimulants."
A
night in shining armour
There's one pretty big obstacle to overcome before TMS
can be offered as a treatment in a clinical setting:
it's just not practical to sleep with a TMS apparatus
lashed to one's head. Dr Massimini sees another drawback.
"The machine cannot induce sleep in a subject who is
awake, it can only make sleep deeper."
Both doctors agree that there are
still many basic unanswered questions about sleep. "We
need to know what sleep is for," says Dr Tononi. "What's
the point to try and improve sleep if you don't know
what it's doing?"
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