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READING
PASSAGE 3
You should spend about 20 minutes on Questions 27–40,
which are based on Reading 3 on pages 10 and 11.
The
science of sleep
Emma Bailey explores the curious world of deep (or NREM)
sleep and light (or REM) sleep
Sleep is not an optional activity and is more essential
to our survival than food. By the time they die, most people will have spent
more than 25 years asleep. As Paul Martin, author of Counting Sheep: The
Science and Pleasures of sleep and Dreams, puts it: When you die, a bigger
slice of your existence will have passed in this state than in raising
children, playing games, listening to music, or any other activity that humanity
values highly. Why is it necessary to spend quite so long in this unconscious
state? Unlike breathing or eating, the biological benefits of sleep are not
immediately obvious.
It is a behaviour that can be found remarkably far back
down the evolutionary ladder. In all creatures, sleep generally involves a
cessation of physical activity and reduction of sensory awareness for regular
periods. Like us, other animals are kept awake by stimulants such as caffeine
and sleep more as babies.
Sleep is therefore a mainstay of animal existence and has been honed by
millions of years of evolution. Yet until 1952, scientists assumed it was a
passive state in which brain activity ceased. But then an extraordinary discovery
was made. Sleep research pioneer Nathaniel Kleitman, of the University of
Chicago noticed it was marked by periods of rapid eye movement, now known as
REM sleep, and that REM sleep was accompanied by a frenzy of brain activity
akin to that seen during periods of consciousness.
We now know that brain activity differs in both duration
while we sleep Over a 60-minute period it goes through four distinct stages of
NON-REM(NREM) sleep, and one episode of REM sleep. It has been discovered that
most dreaming occurs during REM sleep, and that deep sleep occurs during the
NREM stages. In fact, the two types of sleep are as different as sleeping is
from wakefulness. Interestingly, while all mammals, birds and more recent
reptiles have both types of sleep, primitive reptiles experience just NREM
sleep. This implies that REM sleep evolved more recently, possibly around the
time of the reptilian ancestors of all mammals, 250 million years ago.
For centuries it was assumed that sleep served simply as
a mechanism for allowing the body to recuperate. Recently, it has been shown
that NREM sleep does indeed increase after vigorous exercise. However, people
who lie in bed all day also enter NREM sleep, so it can’t only be due to this.
Jerome M Siegel of the University of California believes that NREM sleep
provides an opportunity to repair the body cells damaged during wakefulness. As
he explains, ‘The decrease both in metabolic rate and in brain temperature
occurring during NREM sleep seems to provide an opportunity to repair this
damage.’
However, Professor Jim Horne of the University of
Loughborough disagrees: There is little evidence that any organ apart from the
brain goes through repair during sleep. All the evidence shows that these other
organs recover just as well during restful wakefulness. The brain, Horne points
out, never shuts down during wakefulness. Even if we are resting, it remains in
a state of readiness. Scans have shown that it is only during NREM sleep that
the brain gets any rest. Recognising that when NREM sleep evolved millions of
years ago, animals didn’t have highly developed brains, he concludes, ‘The
functions of NREM sleep have probably changed with evolution, maybe beginning
as an energy conserver and culminating, in humans, as a facilitator for the
recovery of high-level brain function.’
While NREM most probably involves rest and recovery, REM sleep and dreams is
a much more contentious area of research. According to Dr Claudio deprived of
REM sleep, memory consolidation is compromised. We need it to reprocess what
has happened during the previous period of wakefulness in order to store information
that is useful.
Certainly, there are studies that suggest a strong link between REM sleep and
memory. After being taught a new skill, people exhibit a rise in REM sleep. If
they are deprived of REM sleep, they are less able to remember the skill.
Experiments have shown that REM sleep must equal 1–2 hours of an experience if
it is to be remembered.
There are other views about the function of REM sleep.
The pioneering sleep researcher Michel Jouvet believes that the intense
activity seen in the brain during REM sleep is essential to neuronal
development before birth. There is little to activate the developing brain
during the long, dark months in the uterus, so Jouvet hypothesises that the
brain generates its own stimuli in the form of REM sleep and dreams to aid its
own development.
In short, the function of REM sleep and dreaming is still
something of a mystery. The hope is that, as scanning techniques become more
refined, the brain regions underlying the two types of sleep will be better
understood. However, we’re not likely to get a straightforward answer. As Horne
says: ‘Already over 100 neurochemicals and brain regions connected with
sleep have been found, and more and more are being discovered. So clearly
there’s no single sleep centre.’ One thing is certain, we’ll never be without
sleep. It’s highly improbable that any new drug could enable us to avoid it and
remain healthy for any length of time.
Questions 27–32
Look at the following statements (Questions 27–32) and
the list of people below.
Match each statement with the correct person, A–F
Write the correct letter, A–F in boxes 27–32 on your
answer sheet.
27 All of the body is able to recover during one type of
sleep.
28 The brain benefits from one type of sleep during an
early stage of life.
29 Humans spend more time asleep than engaged in any
other activity.
30 It is likely that the purpose of one type of sleep has
altered over time.
31 Brain activity during one type of sleep is similar to
that when people are awake.
32 One type of sleep enables an individual to learn from
past experience.
List of People
A Paul Martin
B Nathaniel Kleitman
C Jerome M Siegel
D Jim Horne
E Claudio Stampi
F Michel Jouvet
Questions 33–39
Complete the notes
below.
Choose NO MORE THAN TWO WORDS from the passage for each
answer. Write your answers in box as 33–39 on your answer sheet.
People
– sleep is vital for human survival
– biological advantages of sleep not clear–this makes it
different from either 33. __________ or __________
Animals
– aspects of sleep that most creatures share:
• lack of physical movement
• reduced sensory awareness
• sleep longer when they are 34. __________
Research
– scientists once believed that 35. __________
stopped during sleep–now know it takes place but not in uniform way
Types of sleep–REM and NREM
– primitive reptiles do not experience REM sleep
– now possible to prove that amount of NREM sleep rises with 36. __________
– the metabolic rate and the 37. __________ of the brain fall during
NREM sleep
The Future
– mysteries of REM sleep may become clearer as the 38.
__________ improve
– unlikely that a 39. __________ will ever replace the need for sleep
Question 40
Choose the correct letter A, B, C or D
Write the correct letter in box 40 on your
answer sheet.
The writer’s main aim in this passage is to
A compare animal and human brain activity during
sleep.
B suggest why some people need more sleep than others.
C account for the fact that some dreams are easily forgotten.
D describe the differences between two types of sleep.
C
-
F
-
A
-
D
-
B
-
E
Questions 33–39
-
breathing, eating
-
babies
-
brain activity
-
vigorous exercise
-
temperature
-
scanning techniques
-
drug
Question 40:
40. D
PASSWORD: REALEXAMPDF
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