Jet lag disturbs sleep by
upsetting internal clocks in 2 neural centers
Thursday, April 16,
2009
Jet lag is the bane of many travelers, and similar fatigue can
plague people who work in rotating shifts. Scientists know the
problem results from disruption to the body's normal rhythms and
are getting closer to a better understanding that might lead to
more effective treatment.
New University of Washington research shows the disruption occurs
in two separate but linked groups of neurons in a structure called
the suprachiasmatic nucleus, below the hypothalamus at the base of
the brain. One group is synchronized with deep sleep that results
from physical fatigue and the other controls the dream state of
rapid eye movement, or REM, sleep.
The ventral, or bottom, neurons receive light information directly
from the eyes and govern rhythms in tune with periods of light and
dark. The dorsal, or top, neurons do not receive direct light
information and so govern rhythms as a more independent internal,
or circadian, biological clock.
It turns out that some of the body's rhythms are "more loyal" to
the ventral neurons and others are much more in tune with the
dorsal neurons, said Horacio de la Iglesia, a UW associate
professor of biology.
Normally the two neuron groups are synchronized with each other,
but disruptions such as jet travel across time zones or shift work
can throw the cycles out of kilter. Deep sleep is most closely tied
to light-dark cycles and typically adjusts to a new schedule in a
couple of days, but REM sleep is more tied to the light-insensitive
dorsal neurons and can be out of sync for a week or more.
"When we impose a 22-hour light-dark cycle on animals, the ventral
center can catch up but the dorsal doesn't adapt and defaults to
its own inner cycle," de la Iglesia said.
In the laboratory rats he uses for his research, that normal cycle
is 25 hours. When the artificial 22-hour light-dark schedule was
imposed, he found that the rats' deep sleep, largely governed by
light but also a response to fatigue, quickly adapted to the
22-hour cycle, while their REM sleep continued to follow a 25-hour
cycle. As a result, REM sleep did not occur in a normal progression
following deep sleep.
"We found that after exposing rats to a shift of the light-dark
timing that simulates a trip from Paris to New York, REM sleep
needed 6 to 8 days to catch up with non-REM, or deep, sleep, the
sleep you usually experience in the first part of the night," de la
Iglesia said.
The two types of sleep overlap immediately after the simulated jet
lag occurs, he noted, and there is a greater likelihood of the
animals entering REM sleep earlier than they should. That likely
explains why it can take several days for travelers and shift
workers to adapt to their new schedules, he said.
"It also could explain why jet lag is associated with lower
learning performance. We think the disruption of the normal
circadian sequence of sleep states is very detrimental to
learning," he said.
"One of the problems is that you are doing things at times that
your body isn't prepared to do them. One group of neurons tells
your body it is Paris time and another says that it is New York
time. You are internally desynchronized," said de la Iglesia.
He is lead author of a paper describing the work published online
April 16 by Current Biology. Co-authors are Michael Lee and Beryl
Swanson of the UW. The work was funded by the National Institutes
of Health and the Mary Gates Endowment for Students at the
UW.
Previous research has indicated that treatments such as physical
activity can help the body resynchronize its rhythms following jet
lag. The new work, de la Iglesia believes, could be useful in
fine-tuning pharmaceutical and other therapies.
"We can go back to the treatments that are believed to be effective
and see where they might be acting in the circuitry of these neuron
centers, then refine them to be more effective," he said.
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University of Washington
Thanks to University of Washington
for this article.