September 20, 2007
Missing sleep tonight may just boost your dreams tomorrow night.
By Christie Nicholson
About three years ago Eva Salem got into some trouble with a
crocodile. It snapped her hand in its jaws. In a panic, she managed to
knock out the crocodile and free herself. Then, she woke up.
"I imagine that's what it's like when you're on heroin. That's what my
dreams were like—vivid, crazy and active," she says. Salem, a new
mother, had been breast-feeding her daughter for five months before
the croc-attack dream, living on four hours of sleep a night. If she
did sleep a full night, her dreams boomeranged, becoming so vivid that
she felt like she wasn't sleeping at all.
Dreams are amazingly persistent. Miss a few from lack of sleep and the
brain keeps score, forcing payback soon after eyelids close. "Nature's
soft nurse," as Shakespeare called sleep, isn't so soft after all.
"When someone is sleep deprived we see greater sleep intensity,
meaning greater brain activity during sleep; dreaming is definitely
increased and likely more vivid," says neurologist Mark Mahowald of
the University of Minnesota and director of the Minnesota Regional
Sleep Disorders Center in Minneapolis.
The phenomenon is called REM rebound. REM refers to "rapid eye
movement," the darting of the eyes under closed lids. In this state we
dream the most and our brain activity eerily resembles that of waking
life. Yet, at the same time, our muscles go slack and we lie
paralyzed—a toe might wiggle, but essentially we can't move, as if our
brain is protecting our bodies from acting out the stories we dream.
Sleep is divided into REM and four stages of non-REM; each has a
distinct brain wave frequency. Stage one of non-REM is the nodding off
period where one is between sleeping and waking; it's sometimes
punctuated with a sensation of falling into a hole. In stage two the
brain slows with only a few bursts of activity. Then the brain
practically shuts off in stages three and four and shifts into
slow-wave sleep, where heart and breathing rates drop dramatically.
Only after 70 minutes of non-REM sleep do we experience our first
period of REM, and it lasts only five minutes. A total non-REM–REM
cycle is 90 minutes; this pattern repeats about five times over the
course of a night. As the night progresses, however, non-REM stages
shorten and the REM periods grow, giving us a 40-minute dreamscape
just before waking.
The only way scientists can study REM deprivation is by torturous
sleep deprivation. "We follow the [electroencephalogram] tracing and
then when we see [subjects] moving into REM, we wake them up," says
psychologist Tore Nielsen, director of the Dream and Nightmare Lab at
the Sacré-Coeur Hospital in Montreal. "As soon as you start to rob
them of REM, the pressure for them to go back into REM starts to
build." Sometimes Nielsen will have to wake them 40 times in one night
because they go directly into REM as soon as they are asleep.
Of course there is non-REM rebound as well, but the brain gives
priority to the slow-wave sleep and then to REM, suggesting that the
states are independent of each other.
In a 2005 study published in Sleep, Nielsen showed that losing 30
minutes of REM one night can lead to a 35 percent REM increase the
next night—subjects jumped from 74 minutes of REM to a rebound of 100
Nielsen also found that dream intensity increased with REM
deprivation. Subjects who were only getting about 25 minutes of REM
sleep rated the quality of their dreams between nine and eight on a
nine-point scale (one being dull, nine being dynamite).
Of course, REM deprivation, and the subsequent rebound, is common
outside the lab. Alcohol and nicotine both repress REM. And blood
pressure drugs as well as antidepressants are also well known REM
suppressants. (Take away the dreams and, curiously, the depression
lifts.) When patients stop the meds, and the vices, they're rewarded
with a scary rebound.
But the persistence of REM begs the question: Why is it so insistent?
When rats are robbed of REM for four weeks they die (although the
cause of death remains unknown). Amazingly, even though we spend about
27 years dreaming over the course of an average life, scientists still
can't agree on why it's important.
Psychiatrist Jerry Siegel, head of the Center for Sleep Research at
the University of California, Los Angeles, recently proved that REM is
nonexistent in some big-brained mammals, such as dolphins and whales.
"Dying from lack of REM is totally bogus," Siegel says. "It's never
been shown in any species other than a rat."
Some theories suggest that REM helps regulate body temperature and
neurotransmitter levels. And there is also evidence that dreaming
helps us assimilate memories. Fetuses and babies spend 75 percent of
their sleeping time in REM. Then again, platypuses experience more REM
than any other animal and researchers wonder why, because, as
Minnesota's Mahowald puts it, "Platypuses are stupid. What do they
have to consolidate?"
But, given that rats run through dream mazes that precisely match
their lab mazes, others feel that there must be some purpose or
meaningful information in dreams.
John Antrobus, a retired professor of psychology and sleep research at
the City College of New York says that dream content is tied to our
anxieties. But he never found the extreme vividness in REM rebound
that others assume is there, based on a higher level of brain activity
which likely means more action-packed dreams.
"The brain is an interpretive organ, and when regions are less
connected as they are in sleep, we get bizarre narratives," he says.
"But its purpose? For that we have to ask what is the purpose of
thought. We can't answer one without answering the other."
Taken from: Scientific America