Experiments have shown that there is a strip of neurons which when
activated turn off the ability to move your muscles, and in cats when
they cut this strip of neurons the cat sleep walks. This might allow
for the strange part of dreaming since we lose connetion with the
constraints of the body and we can fly around.
Memories can access and influence experience, we probably practice the
things we have learned over the last couple of weeks, trying to
integrate it into and along with our more long term memory. We have
about 20 minutes of dreaming every hour and a-half, REM, or rapid eye
movement periods. Deep sleep inbetween where we are more or less dead
to the world and vulnerable.
......In a sparse distributed network - memory is a type of
perception.....The act of remembering and the act of perceiving both
detect a pattern in a vary large choice of possible patterns....When
we remember we recreate the act of the original perception - that is
we relocate the pattern by a process similar to the one we used to
perceive the pattern originally.
Kevin Kelly......oUt Of cOnTrOl......page 18---
http://www.kk.org/outofcontrol/ch2-d.html
Why Do We Sleep? Why Do We Dream?
Going Inside
by John McCrone
http://www.amazon.co.uk/Going-Inside-John-McCrone/dp/0571201016
- Does sleep have a purpose? Do you really know what its like to
dream? The answers may surprise you. Feature by John McCrone from
Frontiers, March 1999. -
FIRST, WHAT'S THE EVOLUTIONARY PURPOSE OF SLEEP
Every night we shut our eyes, slip the moorings of consciousness and
enter the confused limbo of sleep and dreams. But why? Couldn't
evolution have allowed us to take a nightly rest without this
apparently dangerous loss of awareness? Or do we need to sleep because
the brain has to have its time in dreams?
Despite nearly 2,000 sleep clinics around the world investigating this
vital subject, scientists still seem, ahem, a little in the dark about
the answer. But first a few of the facts that are certain. Sleep is a
universal among animals. Even cockroaches have moments of quiescence.
Their antennae will droop and they will become insensitive to gentle
stimuli. Fish and reptiles also have their drowsy periods while birds
and mammals have proper sleep cycles.
And don't be fooled into thinking that humans are the great slugabeds.
Humans average seven and a half hours sleep a night. True, large
ungulates make do with less. Giraffes sleep as little as two hours a
night while elephants and cattle sleep about four. But for the rest of
the mammalian kingdom, sleep can seem to be what they do best. Cats
and lions will happily nap for 18 hours a day; sloths, armadillos, owl
monkeys and opossums will snooze away just about as many; while bats
can go 20 hours - they might come out at night, but not for very long
it seems.
And once scientists began tapping electrodes to the heads of sleeping
animals and humans, they found that all higher mammals and birds share
a similar sleep cycle. Recordings of the brain's EEG rhythms - the
crackle of neural activity - show that sleep has a distinct pattern
with phases that in humans follows a 90 minute period. First we
descend through four increasingly deep stages of slow wave sleep - so
named because the EEG rhythm changes from a busy jagged buzz to a slow
relaxed throb. At its deepest, it becomes very difficult to rouse a
person from slow wave sleep. The sleeper may take fully a minute to
become orientated. This is also the time when people are liable to
sleep walk (see box) or, in children, wet the bed. Then after an hour
and a half of this slow wave slumber, the sleeper's brain will rise
back through the levels before eventually convulsing with its first
period of REM - a sleep stage as dramatic as it is misunderstood.
In REM (which stands for rapid eye movement) the eyes leap about in
their sockets as if chasing some phantom vision. Electrodes show that
the brain is highly aroused as if back in a waking state. The body
also seems a bit out of control with the heart pumping, temperature
control gone awry, and blood pressure all over the place. But despite
this metabolic furore, outwardly the sleeper appears at his or her
most inert as REM also brings on complete motor paralysis. A
neurochemical block is put on messages entering and leaving the
brainstem, preventing any movement apart from a few twitches.
When sleep researchers first discovered REM sleep in the 1950s, they
found that subjects awoken during this stage invariably reported
having vivid dreams. Putting two and two together, REM sleep became
dreaming sleep - an idea that has stuck in the public mind. But in
fact it has since been shown that dreaming of a sort goes on all night
long. Subjects roused from slow wave sleep can usually tell of vague
ruminations or mundane fantasies.
David Foulkes, a psychologist at Emory University in Atlanta, Georgia,
says these slow wave dreams seem identical to the kind of drifty
daydream thinking we have during idle moments of waking. The only
difference is that in our sleep, our mental experiences create no
permanent record. Each thought is forgotten almost as soon as it
occurs. Foulkes says the dreams of REM sleep are certainly brighter,
more emotional, and more bizarre. But these differences are mostly
ones of internal arousal level than of mechanism. So whatever the
reason for our having dreams, it cannot explain the different stages
of the sleep cycle. REM sleep simply increases the intensity and
detectability of something we were already doing.
Our first REM period of the night actually lasts only a few minutes.
But as the night goes on, the REM phases grow longer until much of our
time in the last few hours before waking are spent in REM. With such a
strikingly set pattern of sleep in both higher animals and humans, it
is natural to feel that it must serve some equally defined purpose.
And yet the best current explanations for the sleep cycle are
surprisingly prosaic.
Certainly, there is much support for the idea that sleep is
restorative. In the depths of stage four slow wave sleep, when brain
and body activity is turned down about as low as it can go, there are
surges in various growth hormones. Some researchers have claimed that
the adolescent body can grow as much as a centimetre at this time of
night, as if the body is taking advantage of a time when it can devote
itself entirely to building and repair. And feeling good in the
morning is linked to the quality of our slow wave sleep - if we toss
and turn without properly hitting stage four, then we wake feeling
rough. But sleep is not completely mandatory because humans have
lasted a couple of weeks awake and despite being dog tired, could
still rouse themselves to beat sleep researchers in games of pinball.
And while laboratory rats will die after some weeks of sleep
deprivation, it seems to be a collapse of the immune system that
actually kills them.
Another favoured theory is that sleep is a good way of saving energy.
This certainly seems true in small animals - bats and hummingbirds go
into a hibernation-like torpor when they sleep - but the metabolic
savings are not actually that great in larger animals. Even deep stage
four sleep sees a drop of just 20 percent while the rest of sleep
hardly differs from just lying still all night and resting.
Then there is the ever-popular idea that sleep - especially the wild
activity of REM - might play a special role in the fixing of memories
accumulated during the day. Dreams often seem like a confused riffling
through the memory banks or - shades of Freud - the surfacing of
repressed thoughts. However careful work by Avi Karni of the Weizmann
Institute in Israel seems finally to have put paid to this theory. It
is already known that it does indeed take time for the brain to
consolidate a memory trace. Growth changes are needed to strengthen
the connections between brain cells and so turn a jangling pattern of
neural activity into some more permanent record of an event. By
testing subjects at intervals after learning a task, Karni showed that
this hardening process goes on in the background all during the day
but seems to be interrupted during the metabolic drop of slow wave
sleep. So slow wave sleep actually appears to suspend the fixing of
memories. Then in REM sleep, the fixing resumed - but Karni argues
this is only because REM is near enough a waking mental state in terms
of arousal levels. There is nothing special about REM itself.
Summing up the various findings, Jim Horne of Loughborough
University's sleep lab says slow wave sleep seems the key. It is a
necessary downtime for certain kinds of renewal. But this job only
takes the first few hours of the night and the question is why we then
stay asleep in dreams? His answer is that it is simply safer. Leaving
an animal exposed all night with a fully alert and worrying mind would
only lead to trouble. Much better to keep it in a state of
unremembering, dimly sensing, dream rumination. In this view, REM
sleep would merely act as a way of regularly bringing the mind back
close to the surface without actually awakening it. Horne says that
while it may not always feel like it, we can tumble out of the REM
sleep phase and go straight into action. So it turns out then that our
slumbers are mostly just nature's way of keeping us all out of
crepusculan mischief. Now there's a thought to sleep on.
SO WHAT ARE DREAMS REALLY LIKE?
Yes, yes, I know other people's dreams are boring. But let me tell you
about one of mine - the one where I discovered I even dream of smells
and tastes!
It was one of those usual Technicolor, jump-cut, jobs. There I was
racing along in a Flintstones's cartoon car, when the next instant I
was soaring high like a bird over the ocean. Passing a cruise ship, I
swept down to the bridge where I saw a bearded figure standing alone
eating a bag of greasy chips. I immediately knew this person was me,
that I was a spy and that I was in command of an empty ship. However
there was no time to linger. Next I was sweeping down the length of
the vessel - yet now it was a grey painted frigate. The intricate
ironwork of a radar mast caught my eye and I had a momentary close-up
of a few struts. Then when I pulled back, I found the scene had
changed completely and I was now seated at a desk with the parts of a
model ship strewn about. My final thought as I awoke was how difficult
it was going to be to glue all the fiddly bits of the mast together.
It was not the contents of the dream that got me. Instead, I felt that
for the first time - after some months of trying - I had glimpsed the
mechanics of the dreaming process. I had seen the kind of features
reported by famous Victorian documenters of dreams like Hervey de
Saint-Denys, and also what a modern neuroscientific understanding of
the brain might lead us to expect.
The first point was that my dream seemed to consist of a series of
supernaturally sharp, yet oddly frozen, pictures. We tend to take our
dreams at face value, remembering them as if they were a smoothly
projected slice of life. But looking closely I could see that each
frame seemed quite disconnected from the next like a succession of
tableaux. And while there was always a powerful sense of movement in
these images, it came from the way my mind's eye seemed to sweep
across and around. Despite the feeling that there were tossing waves
or billowing smoke from a funnel, nothing really moved.
The second big feature of my dream was that the scene might change
utterly from one frame to the next, yet the thinking, commenting, part
of my mind did not appear to notice. Clearly, there was a vague theme
about ships connecting all the images, but each scene was of a
completely different type of ship. Nor was I fussed about the way in
one frame I might be the soaring viewer of the scene, then the
following I was the bearded figure or a modeller at a desk.
Thinking back on the dream, I realised that I had not even been right
about that. The bearded figure had actually looked nothing like me,
but was the German actor from a U-boat film I had recently seen. And
while I had thought the modeller was me in my bedroom as a teenager,
it was really nothing like my old bedroom - or, indeed, me. As turns
out to be the rule in dreams, everything was cheerfully misidentified
or assumed.
Finally there was the puzzle of why it had taken so much effort to
notice these things. For example, only the day before I had been
wondering why my dreams had most kinds of sensations but not tastes or
smells. Then I realised that when I had seen the soggy bag of chips in
the bearded figure's hand, there had been a sudden intense experience
of their savour. I had to think hard to catch such details.
So what does science have to say about dreams? The vividness of our
dreams means it is difficult not to believe they must serve some
purpose. Why put on a nightly display of weirdness and leaping emotion
unless it signified something - perhaps a Freudian battle with the
unconscious or a ritual cleansing of the memory banks? Yet sleep
researchers like John Antrobus of the City University of New York have
mostly come to just the opposite conclusion. They say the sleeping
brain dreams simply because it has no proper way of switching itself
off.
Unlike a computer, the brain cannot pull out the plug and shut down
its circuits for the night. Living cells have complex metabolisms to
support and all 100 billion neurons of the brain must discharge at
least once or twice each second just to maintain their electro-
chemical tone. And as Antrobus says: "If you can't switch the brain
off, then you can't really stop it thinking or trying to make sense of
the state it then finds itself in." So even in the depths of slow wave
sleep, there is some meandering mental activity. And in the bright
pseudo-arousal of REM, this activity can take on a waking intensity.
But why do dreams take the form that they do? For Antrobus, the key is
that when we fall asleep, we enter a state of deep sensory
deprivation. The brainstem - the first thickening of the spinal cord
where it enters the brain - puts a neurochemical block on all but the
most urgent traffic entering or leaving the brain, so cutting us off
from our senses and also preventing movement (a motor damping that
turns into total paralysis during REM). In fact, sometimes we can
actually catch this sensory curtain falling. Many a drowsy commuter
has probably had the experience of nuchal atonia - a sudden slump of
the head and eerie silence as they are cut off from the external
world.
This crude brainstem gating serves the purpose of holding us in a
state of physical quiescence. But it does not mean our brains are then
empty of thoughts or even perceptions. Antrobus says it surprises
people that a sensation-starved brain will immediately begin
manufacturing substitute experiences. It would seem that producing
mental imagery should involve some sort of selective effort. But
instead the brain is built to generate a constant flow of images.
During waking life, we need to go into each moment armed with a set of
perceptual expectations. As we reach for a door knob, we must already
be making mental predictions about what the handle will feel like in
our hands. Or if we hear a siren coming down the street, we need to be
prepared soon to see the flashing blue lights of a police car or
ambulance. There is so much information to deal with during every
instant of life that we have anticipate as much of it as possible to
be able to assimilate the world smoothly - and also to recognise when
some event is actually surprising, such as finding a door handle is
made of squishy jelly or the siren is mounted on a milk cart.
This built-in ability to anticipate sensations is believed to be why
we have mental imagery in the first place. As Ulric Neisser, a
psychologist at Cornell University in New York state, points out, a
mental image is an expectation without the answering sensation. We ask
ourselves to think what it would be like to see something - an
elephant in a balloon perhaps - without actually going on to see it.
Furthermore, experiments show that it takes about half a second to
generate a full blown mental image - and it fades just as fast. Also,
while most people can conjure up a momentarily convincing image of
some object or situation, it tends to be rather static. The picture is
like a sudden view - or succession of views - rather than an animated
film. In other words, our waking mental images are remarkably similar
to those we have in dreams, except that in sleep the visions appear to
erupt unbidden rather than coming as part of an organised train of
thought.
So shut off the brain from real sensation and it cannot help but throw
up a series of fleeting anticipatory states in a restless perceptual
search. Exactly the same happens in real sensory deprivation
experiments where subjects are left a few hours floating in a muffled,
darkened tank of salty water. It is not long before they report
disorientated thoughts and weird visions. But a hallucinatory parade
of images is only part of the story of the dreaming state. There is
also the question of the dazed misidentifications and almost immediate
forgetting of our dream experiences.
Antrobus says the latest evidence suggests that as well as the brain
putting a block on outside traffic, it also appears to become
internally decoupled. The brain is made up of many processing areas -
perhaps hundreds - each responsible for some small aspect of mental
experience. There are speech centres, planning centres, memory-fixing
centres, and even separate centres for a sharp sense of colour or
sense of direction. Normally, all these areas of activity are tightly
bound into an integrated whole - neuroscientists believe that some
form of synchronised firing may tie the many bits of the brain into a
common rhythm. It appears that in sleep, this co-ordination unravels,
leaving each module of processing only weakly in touch with the
activity of all the others.
The result is confused thinking about the relentless parade of images.
The frontal areas of the brain that do the planning and the commenting
on experience will be trying to make sense of what they see, but
because they are only loosely in touch with the sensory evidence, they
will make mistaken assumptions about identity and fail to notice the
crazy shift in scenery every half second or so.
This lack of integration would also mean there was no coherent story
feeding into the parts of the brain responsible for capturing a record
of mental life. So to remember the content of a dream, we would have
to wake up and relive its last few moments. Then unless we had learnt
how our dreams should appear, we would tend to gloss over their
disjointedness, smoothing our memory into something that looked more
like the steady logical flow of normal waking consciousness.
So that is what dreams are made of. What's that? You don't believe me?
Well put a pen and notebook by your bedside tonight, set your alarm
clock for a little earlier than usual, and we can compare notes in the
morning. We will see if you too can taste those chips.
SLEEP-WALKING AND SLEEP PATHOLOGIES
We all know about sleep-walking. But can you rape and even murder in
your sleep? In 1994, a Sunderland prison officer was cleared of
breaking into the home of his neighbour at 5am and attempting to rape
her because experts said he suffered from a serious sleep disorder. In
1992, a London policeman was similarly found not guilty after nearly
strangling his uncle with a rope in the course of a nightmare.
Researchers can tell you hundreds of other equally extraordinary tales
of what people do in their sleep such as the woman who packed her dogs
into the car and drove 20 miles before waking up, the dieter who
raided the fridge at night to gorge on raw meat and vegetables, and
the holidaymaker who walked straight off the balcony of her hotel,
fell 15 feet, smashed her hip, but did not wake up until she reached
the hospital.
That the sleeping mind is capable of confused and largely automatic
behaviour is no surprise if the brain never really shuts down, just
becomes dazed and unremembering. However researchers have found there
is a clear difference between ordinary sleep walking and a more
specific REM sleep syndrome.
The less alarming activity takes place in the depths of slow wave
sleep. We come awake enough to act on automatic pilot - to get up and
do something routine like go to the toilet, or perhaps take the car
for a midnight spin - but not awake enough to recall doing so. However
murders and other violent acts must occur in the high arousal of REM
sleep. The explanation seems to be that sufferers lose their usual REM
paralysis that prevents them acting out their dreaming behaviour. In
such cases, doctors often find evidence of a degenerative disorder
like multiple sclerosis affecting the brainstem.
SIX OF THE WACKIER REASONS THAT HAVE BEEN GIVEN FOR DREAMS
We dream to rinse our eyeballs: David Maurice of Columbia University
in New York suggests the violent eye-movements of REM sleep are to
shake-up the aqueous humor inside, so allowing fresh oxygen to
circulate.
We dream to practice our response to danger: Antti Revonsuo of the
University of Turku, Finland, says dreams evolved in our cavemen
ancestors as a safe virtual reality playground in which to get used to
handling threatening situations.
We dream to get in touch with our internal organs: Steven Maier of the
University of Colorado in Denver believes that dreaming sleep is
essential to give the brain a sensitive time to listen to what our
immune system has to report about the state of our body. Some of what
is learnt may be symbolised as dream imagery.
We dream to exercise rarely used brain circuits: Jim Krueger of the
University of Tennessee in Memphis thinks that the wild activity of
REM might tone critical, but rarely employed, brain pathways - for
example, the brainstem feedback mechanism which causes us to breathe
more deeply when exposed to high levels of carbon dioxide.
We dream to stockpile key neurotransmitters: J Allan Hobson of the
Harvard Medical School in Boston wonders whether REM sleep builds up
levels of important brain transmitters just prior to waking. He notes
that the consumption of both noradrenaline and serotonin, two of the
most important messenger molecules, drops to almost zero in REM.
We dream to reinforce our genetic individuality: Michel Jouvet of the
University of Lyon, France, argues that REM sleep allows time for our
brain to run through its genetic program and so prevent the day's
experiences from causing us to deviate too far from our meant to be,
DNA-encoded, personality profile.
Going Inside
by John McCrone
http://www.amazon.co.uk/Going-Inside-John-McCrone/dp/0571201016
