CONSCIOUS CONTROL,
THINKING, MEMORY FUNCTION AND BIORHYTHMS OF ORGANISM’S ACTIVITY
Memory as psychical
function
Memory
function helps fixing of perceived information, keeping it in verbal form or as
traces of percept stimuli and recognizing of this information in proper time.
Genetic memory keeps information about body structure and forms of its behavior. Biological memory is presented in both philogenetic and ontogenetic forms. The immune memory and
psychical memory for instance, belong to ontogenetic memory.
General
characteristics of memory are duration, strength of keeping the information and
exactness of its recognizing. In man mechanisms of perception and keeping the
information are developed better, comparing to other mammalians.
According
to duration is concerned short-time and long-time memory; in relation to kind
of information – sensory and logic.
It’s discovered the
nervous substrate of long-term memory is mostly cerebral cortex. The most
important regions are temporal lobes, prefrontal area and hippocampus.
Experimental researches revealed that some thalamic nuclei and reticular
formation take part in memory function.
Reticular formation
gives ascending stimulatory influences to cerebral cortex, which help in
keeping awake condition of cortex and provides voluntary attention.
At the molecular
level, the habitation effect in the sensory terminal results from progressive
closure of calcium channels through the presynaptic
terminal membrane.
In case of
facilitation, the molecular mechanism is believed to be following. Facilitated
synapse releases serotonin that activates adenylyl cyclase in postsynaptic cell. Then cyclic AMP activates proteinkinase that then causes phosphorylation
of proteins. This blocks potassium channels for minutes or even weeks. Lack of
potassium causes prolonged action potential in the presynaptic
terminal that leads to activation of calcium pores, allowing tremendous
quantities of calcium ions to enter the sensory terminal. This causes greatly
increased transmitter release, thereby markedly facilitating synaptic
transmission.
Thus in a very
indirect way, the associative effect of stimulation the facilitator neuron at
the same time that the sensory neuron is stimulated causes prolonged increase
in excitatory sensitivity of the sensory terminal, and this establishes the
memory trace.
Eric
Kandel showed initially that weaker stimuli give rise
to a form of short term memory, which lasts from minutes to hours. The
mechanism for this "short term memory" is that particular ion channels
are affected in such a manner that more calcium ions will enter the nerve
terminal.
This
leads to an increased amount of transmitter release at the synapse, and thereby
to an amplification of the reflex. This change is due to a phosphorylation
of certain ion channel proteins, that is utilizing the molecular mechanism
described by Paul Greengard.
Sperling’s classic experiments on the
duration of visual sensory memory simulate Iconic Memory. You will see nine
random letters flashed in a 3 x 3 matrix, and will attempt to recall the
letters under three conditions: free-recall, cued-recall, and delayed
cued-recall. Your results will be compared to Sperling’s
finding of rapid decay of the visual “icon.”
A
more powerful and long lasting stimulus will result in a form of long term
memory that can remain for weeks. The stronger stimulus will give rise to
increased levels of the messenger molecule cAMP and
thereby protein kinase A. These signals will reach
the cell nucleus and cause a change in a number of proteins in the synapse. The
formation of certain proteins will increase, while others will decrease. The
final result is that the shape of the synapse can increase and thereby create a
long lasting increase of synaptic function.
In
contrast to short term memory, long term memory requires that new proteins are
formed. If this synthesis of new proteins is prevented, the long term memory
will be blocked but not the short term memory.
Thinking process as
psychical function
The prefrontal association area is essential to carrying out thought
processes in the mind. This presumably results from some of the same
capabilities of the prefrontal cortex that allow it to plan motor activities.
The prefrontal association area is frequently described as important for elaboration of thoughts to
store on a short-term basis “working memories” that are used to analyze each
new thought while it is entering the braine. The
somatic, visual, and auditory association areas all meet one another in the
posterior part of the superior temporal lobe. This area is especially highly
developed in the dominant side of the brain – the left side in almost all
right-handed people.
It plays the
greatest single role of any part of cerebral cortex in the higher comprehensive
levels of brain function that we call intelligence. This zone is also called
general interpretative area, the gnostic area, the
knowing area, tertiary association area. It is best known as Wernike’s area in honor of the
neurologist who first describes it.
Consciousness and
its mechanisms
Consciousness
is special form of perceiving surroundings and goal-orientated activity of
person with interrelation to surroundings. Only social life forms
consciousness. It involves life experience of entire society.
This
ability of prefrontal areas to keep track of many bits of information could
well explain abilities to prognosticate, do plan for the future, delay action
in response to incoming sensory signals, consider the consequences of motor
actions even before they are performed, solve complicated mathematical, legal,
or philosophical problems, correlate all avenues of information in diagnosing
rare diseases and control our activities in accord with moral laws.
Your immediate
awareness of thoughts, sensations, memories, and the world around you
represents the experience of consciousness (Hobson, 1999). That the experience of
consciousness can vary enormously from moment to moment is easy to illustrate.
Imagine that we could videotape three one-minute segments of your conscious
activities at different times while your psychology instructor lectures in class. What
might those three one-minute segments of consciousness reveal? Here are just a few
of the possibilities:
·
Focused concentration on your instructor’s words and
gestures
·
Drifting from one fleeting thought, memory, or image
to another
·
Awareness of physical sensations, such as the
beginnings of a headache or the sharp sting of a paper cut
·
Replaying an emotionally charged conversation and
thinking about what you wish you had said
·
Sexual fantasies
·
Mentally rehearsing what you’ll say and how you’ll act
when you meet a friend later in the day
·
Wishful, grandiose daydreams about the future
Most likely, the
three video clips would reveal very different scenes, dialogues, and content as
your consciousness changed from one minute to the next. Yet even though your conscious
experience is constantly changing, you don’t experience your personal consciousness as
disjointed. Rather, the subjective experience of consciousness has a sense
of continuity. One stream of conscious mental activity seems to blend into another,
effortlessly and seamlessly. This characteristic of consciousness led the
influential American psychologist William James (1892) to describe consciousness as a
“stream” or “river.” Although always changing, consciousness is perceived as unified
and unbroken, much
like a stream. Despite the changing focus of our awareness, our experience of consciousness as
unbroken helps provide us with a sense of personal identity that has continuity
from one day to the next. The nature of human consciousness was one of the first
topics to be tackled by
the fledgling science of psychology in the late 1800s. First psychologists
tried to determine the nature of the human mind through
introspection—verbal self-reports that tried to capture the “structure” of
conscious experiences. But because such self-reports were not objectively verifiable, many of
the leading psychologists at the turn of the twentieth century rejected the study of
consciousness. Instead, they emphasized the scientific study of overt behavior, which could be directly observed, measured, and verified.
Beginning in the
late 1950s, many psychologists once again turned their attention to the study of
consciousness. This shift occurred for two main reasons. First, it was
becoming clear that a complete understanding of behavior
would not be possible
unless psychologists considered the role of conscious mental processes in behavior. Second, although the experience of consciousness is
personal and subjective, psychologists had devised more objective ways to study
conscious experiences. For example, psychologists could often infer the conscious experience that
seemed to be occurring by carefully observing behavior.
Technological advances
in studying brain activity were also producing intriguing correlations between brain activity and
different states of consciousness.
Today, the
scientific study of consciousness is incredibly diverse. Working from a variety of
perspectives, psychologists and other neuroscientists are piecing together a picture
of consciousness that
takes into account the role of psychological, physiological, social, and
cultural
influences.
The Effects of Experience on Perceptual
Interpretations
Our educational,
cultural, and life experiences shape what we perceive. As a simple example,
consider airplane cockpits. If your knowledge of the instruments contained in an
airplane cockpit is limited, as is the case with your author Sandy, an airplane cockpit
looks like a confusing, meaningless jumble of dials. But your author Don, who is
a pilot, has a very different perception of an airplane cockpit. Rather than a blur
of dials, he sees altimeters, VORs, airspeed and RPM
indicators, and
other instruments, each with a specific function. Our different perceptions of an airplane
cockpit are shaped by our prior learning experiences. Learning experiences can vary
not just from person to person but also from culture to culture. The
important role that experiences unique to a particular culture can play in the
perception of illusions. Past experience often predisposes us to perceive a
situation in a particular way, even though other perceptions are possible.
Consider this experience, which one of our students shared in class. As he was driving
home late at night, he stopped at a convenience store to buy a pack of
cigarettes. Standing at the counter and rummaging through his wallet for some
cash, he requested “a pack of Nows.” When he looked up,
the young female clerk had put a copy of Penthouse on the counter. Obviously, the
clerk perceived what she had expected to hear. This example illustrates the
notion of perceptual set—the expectancies andpredispositions
that the observer brings to a perceptual situation.We’re
often mentally primed
to interpret a particular perception in a particular way. Our perceptual sets are, of
course, influenced by our prior learning experiences. One person’s mystery dial is
another person’s altimeter.
Perceptual sets can
exert a strong influence on the perceptual conclusions we reach. Our perceptual sets
usually lead us to reasonably accurate conclusions. If they didn’t, we would develop
new perceptual sets that were more accurate. But sometimes a perceptual set can
lead us astray. For example, when the partially decomposed body of a large,
hairy creature was discovered in upstate
Similar examples of
erroneous perceptual sets have occurred with supposed sightings of UFOs, the Loch
Ness monster, mermaids, and ghosts. In each case, observers interpreted ambiguous stimuli in
terms of the perceptual set they held in that situation and saw what their
expectations led them to see.
In this chapter,
we’ve seen the interaction of biological, behavioral,
and psychological
factors. As Paul’s and Warren’s stories illustrated, our experience of the world is
highly dependent on our physiology, specifically, our sense organs. Paul and Warren
both live in a world without odor or aroma—olfactory cues that are
important to many people, and as essential as sight to many other species.
The process of
sensation results in the transmission of neural messages to thebrain,
where the psychological process of perception occurs.We
actively construct perceptual
conclusions about this sensory information. In arriving at those perceptual conclusions, we are
guided by well-established perceptual principles, such as the cues that typically
indicate distance, movement, form, and so forth. But our perceptual
conclusions can also be influenced by a variety of psychological factors, including our
expectations, learning experiences, and experiences that are unique to our culture.
Biological and Environmental “Clocks” That Regulate
Consciousness
Throughout the
course of the day, there is a natural ebb and flow to consciousness. The most obvious
variation of consciousness that we experience is the daily sleep–wake cycle.
But conscious states also change in more subtle ways. For example, you’ve probably
noticed that your mental alertness varies throughout the day in a
relatively consistent way. Most people experience two distinct peaks of mental
alertness: one in the morning, usually around 9:00 or 10:00 A.M., and one in the
evening, around 8:00 or 9:00 P.M. In between these two peaks, you’ll probably
experience a slump in mental alertness at about 3:00 P.M. And, should you
manage to stay awake, your mental alertness will probably reach its lowest point at
about 3:00 A.M. One practical implication of this consistent daily pattern is
the increase in the number of traffic accidents at the times when mental alertness is
at its lowest points.
Mental
alertness and the sleep–wake cycle are just two examples of the daily highs and lows you
experience in a wide variety of bodily processes. These daily cycles are called
circadian rhythms. The word circadian combines the Latin words for “about”
and “day.” So, the term circadian rhythms refers to biological processes that
systematically vary over a period of about 24 hours.You
actually experience many different circadian rhythms that ebb and flow over the
course of any given 24-hour period. Researchers have discovered over 100 bodily
processes that rhythmically peak and dip each day, including blood pressure, the
secretion of different hormones, and pain sensitivity.
Normally, your
circadian rhythms are closely synchronized with one another. For example, the
circadian rhythm for the release of growth hormone is synchronized with the sleep–wake
circadian rhythm so that growth hormone is released only during sleep.
The Suprachiasmatic Nucleus - The Body’s Clock
Your many circadian
rhythms are controlled by a master biological clock—a tiny cluster of neurons
in the hypothalamus in the brain. Thiscluster of neurons is
called the suprachiasmatic nucleus, abbreviated SCN. The SCN is the
internal pacemaker that governs the timing of circadian rhythms,
including the sleep–wake cycle and the mental alertness cycle (Weaver, 1998). Keeping the
circadian rhythms synchronized with oneanother and on
a 24-hour schedule also involves environmental time cues. The most important
of these cues isbright light, especially sunlight. In
people, light detected by special photoreceptors in the eye is communicated via thevisual system to the SCN in the hypothalamus (Brainard
& others,
2001a, 2001b).
How
does sunlight help regulate the sleep–wake cycle and other circadian rhythms?
As the sun sets each day, the decrease in available light is detected by the SCN
through
its
connections with the visual system. In turn, the SCN triggers an increase in the
production of a hormone called melatonin.
Melatonin
is manufactured by the pineal gland, an endocrine gland located in the
brain.
Increased
blood levels of melatonin make you sleepy and reduce activity levels. At
night, blood levels of melatonin rise, peaking between 1:00 and 3:00 A.M. Shortly before sunrise, the
pineal gland all but stops producing melatonin, and you soon wake up. As the sun rises,
exposure
to
sunlight and other bright light suppresses melatonin levels, and they remain very
low throughout the day. In this way, sunlight entrains, or sets, the SCN so
that it keeps circadian cycles synchronized and operating on a 24-hour
schedule (Czeisler & Wright, 1999; Lavie, 2001).
Life Without a Sundial
Free-Running Circadian Rhythms Given that sunlight is responsible for setting your internal
clock, what would happen to the timing of your circadian rhythms if they were
allowed to “run free” in the absence of environmental time cues like sunlight and
clocks? To create free-running conditions, researchers typically use underground isolation units. In
some studies, they have
even constructed rooms in caves. Volunteers live in these underground
bunkers
for
weeks or months at a time, deprived of all environmental time cues (Webb, 1994).
Under free-running conditions, two distinct effects occur (Kronauer, 1994; Lewy & Sack, 1987). First,
in the absence of normal light, darkness, and other time cues, people tend to
drift to the natural rhythm of the suprachiasmatic
nucleus—roughly a 25-hour day, not a 24-hour day. Thus, people in a free-running
condition go to sleep about an hour later each day. Exactly why the human
sleep–wake cycle gravitates toward a 25-hour cycle—and under what conditions—is
an issue that continues to be actively researched and debated (
Second, under free-running conditions, circadian rhythms lose their
normal synchronization with one another (Aschoff,
1993, 1994). All circadian rhythms becomelonger, but
to different degrees. For example, normally the sleep–wake cycle, body temperature, and
the melatonin cycle are closely coordinated. At about 3:00 A.M., your body
temperature dips to its lowest point, just as melatonin is reaching its highest level and
you are at your sleepiest. But in the absence of environmental cues, the
sleep–wake, body temperature, and melatonin–circadian rhythms become desynchronized, so
that they are no longer properly coordinated with one another.
What happens when people leave the free-running condition and are once again exposed to
normal daylight and darkness cues? Within days, sunlight resets the biological
clock. Circadian rhythms become synchronized again and resume operating on a
24-hour rather than a 25-hour cycle (Lewy & Sack,
1987).
Circadian
Rhythms and the Blind Many blind people have free-running circadian cycles
because they are unable to detect the light that normally sets the SCN.
Like people deprived of
environmental time cues, blind people can experience free-running melatonin, body temperature,
and sleep–wake circadian cycles (Czeisler &
others, 1995; Klerman & others, 1998). Consequently,
many blind people suffer
from recurring bouts of insomnia and other sleep problems (Leger & others, 1999; Sack &
others, 1992).
Circadian Rhythms and Sunlight
Some Practical Implications
The close tie
between your internal biological clock and environmental time cues has some very
important practical applications. For example, imagine that you leave
Although numerous
physiological variables are involved in jet lag, the circadian cycle of the
hormone melatonin plays a key role. When it’s 10:00 A.M. in
You don’t need to
travel across multiple time zones to experience symptoms of jet lag. People
who work night shifts or rotating shifts often suffer from jet lag symptoms
because their circadian rhythms are out of sync with daylight and
darkness time cues (Monk, 1997). Like Nina in the Prologue, nurses, doctors, and
other medical personnel often have to work night shifts or rotating
shifts. So do people working in law enforcement and the military, broadcasting
and weather services, and other businesses that operate around the clock.
For night workers,
the problem of being out of sync with the environmental clock is compounded every
morning when they return home in the bright morning light. Exposure to bright
morning light is a potent stimulus that can reset the body clock to a day
schedule (Shanahan & Czeisler, 1991). Even
traces of sunlight through curtains can prevent a person’s body clock from
staying in sync with the night work schedule. Because sunlight time cues
exert such a powerful influence on circadian rhythms, many night-shift
workers never fully adjust to a nighttime work schedule.
The Dawn of Modern Sleep Research
The invention of
the electroencephalograph by German psychiatrist Hans Berger in the 1920s gave sleep
researchers an important tool for measuring the rhythmic electrical activity
of the brain (Stern, 2001). These rhythmical patterns of electrical activity are
referred to as brain waves. The electroencephalograph produces a graphic record
called an EEG, or electroencephalogram. By studying EEGs, sleep researchers have
firmly established that brain-wave activity systematically changes throughout
sleep.
Along with brain
activity, today’s sleep researchers monitor a variety of other physical functions
during sleep. Eye movements,muscle movements,
breathing rate, airflow,
pulse, blood pressure, amount of exhaled carbon dioxide, body temperature, and breathing
sounds are just some of the body’s functions that are measured in contemporary sleep research (Ancoli-Israel, 1997; Cooper & Bradbury, 1994). The next milestone
in sleep research occurred in the early 1950s. Eugene Aserinsky, a graduate
student at the
Monitoring Sleep
Using electrodes that are attached harmlessly to the face and scalp, the
electroencephalograph records the brain’s electrical activity throughout
the night. Although the
equipment may look cumbersome and uncomfortable, people generally sleep just fine with all
the wires attached.
The Onset of Sleep and Hypnagogic
Hallucinations
Awake and
reasonably alert as you prepare for bed, your brain generates small, fast brain waves,
called beta brain waves. After your head hits the pillow and you close your
eyes, your muscles relax.
Your brain’s electrical activity gradually gears down, generating slightly larger and
slower
alpha
brain waves. As drowsiness sets in, your thoughts may wander and become less
logical.
During this drowsy,
presleep phase, you may experience odd but vividly realistic
sensations. You
may hear your name called or a loud crash, feel as if you’re falling or
floating, smell something burning, or see kaleidoscopic patterns or an unfolding
landscape. These vivid sensory phenomena that occasionally occur during the transition from
wakefulness to light sleep are called hypnagogic
hallucinations (Mavromatis, 1987). Some hypnagogic
hallucinations can be so vivid or startling that they cause a sudden awakening.
Probably the most
common hypnagogic hallucination is the vivid
sensation of falling.
The sensation of falling is often accompanied by a myoclonic
jerk—an involuntary muscle
spasm of the whole body that jolts the person completely awake (Cooper, 1994).
Also known as sleep starts, these experiences can seem really weird (or
embarrassing) when they occur. But, you can rest assured, they are not abnormal. Almost
all of our students have reported occasionally experiencing the hypnagogic hallucination of
falling combined with a myoclonic jerk.
The First 90
Minutes of Sleep and Beyond The course of a normal night’s sleep follows a
relatively consistent cyclical pattern. As you drift off to sleep, you
enter NREM sleep and begin a progression through the four NREM sleep
stages. Each progressive NREM sleep stage is characterized by corresponding
decreases in brain and body activity. On average, the progression through the first four
stages of NREM sleep occupies the first 50 to 70 minutes of sleep (Cooper, 1994).
Stage 1 NREM
As
the alpha brain waves of drowsiness are replaced by even slower theta brain waves, you enter
the first stage of sleep. Lasting only a few minutes, stage 1 is a transitional
stage during which you gradually disengage from the sensations of the surrounding
world. Familiar sounds, such as the hum of the refrigerator or the sound of
traffic, gradually fade from conscious awareness. During stage 1 NREM, you can
quickly regain conscious alertness if needed. Although hypnagogic
experiences can occur in stage 1, less vivid mental imagery is common, such as imagining
yourself engaged in some everyday activity, much as Mike imagined himself unpacking
boxes at work. Although dreamlike, these images lack the unfolding, sometimes bizarre
details of a true dream.
Stage 2 NREM
Stage
2 represents the onset of true sleep. Stage 2 sleep is defined by the pearance of sleep spindles,
brief bursts of brain activity that last a second or two, and K complexes, single
but large high-voltage spikes of brain activity that periodically occur (see Figure
4.2). Other than these occasional sleep spindles, brain activity continues to slow
down considerably. Breathing becomes rhythmical. Slight muscle twitches may occur.
Theta waves are predominant in stage 2, but large, slow brain waves, called delta
brain waves, also begin to emerge. During the 15 to 20 minutes initially spent in
stage 2, delta brain-wave activity gradually increases.
Stage 3 and Stage 4 NREM
Stages
3 and 4 of NREM are physiologically very similar. Both stages are defined by the amount of
delta brain-wave activity. In combination, stages 3 and 4 are sometimes referred
to as slow-wave sleep. When delta brain waves represent more than 20 percent of total
brain activity, the sleeper is said to be in stage 3 NREM. When delta brain waves
exceed 50 percent of total brain activity, the sleeper is said to be in stage 4
NREM (Cooper, 1994).
During
the 20 to 40 minutes spent in the night’s first episode of stage 4 NREM, delta waves
eventually come to represent 100 percent of brain activity. At that point,
heart rate, blood pressure, and breathing rate drop to their lowest levels. Not
surprisingly, the sleeper in stage 4 NREM is virtually oblivious to the world. Noises as
loud as 90 decibels may fail to wake him (Empson,
1993). However, his
muscles are still capable of movement. For example, if sleepwalking occurs, it typically
happens during stage 4 NREM sleep.
It can easily take
15 minutes or longer to regain full waking consciousness from stage 4. It’s
even possible to answer a ringing phone, carry on a conversation for several
minutes, and hang up without ever leaving stage 4 sleep—and without remembering the
conversation the next day. When people are briefly awakened by sleep researchers
during stage 4 NREM and asked to perform some simple task, they often don’t
remember it the next morning (Dinges, 1990; Goodenough, 1991).
In both sexes, sexual arousal
may occur, which is not
necessarily related to dream content. This first REM episode tends to be brief, about 5 to
15 minutes. From the beginning
of stage 1 NREM sleep through the completion of the first episode of REM sleep, about 90
minutes have elapsed. Beyond the First 90 Minutes Throughout the rest of the
night, the sleeper cycles between NREM and REM sleep. Each cycle lasts about 90
minutes on average, but the duration of cycles may vary from 70 to 120
minutes. Usually, four
more 90-minute cycles of NREM and REM sleep occur during the night. Just
before and after REM periods,
the sleeper typically shifts position (Hobson, 1995). The progression of a typical
night’s
sleep
cycles.
Stages
3 and 4 NREM, slow-wave sleep usually occur only during the first two 90-minute cycles.
As the night progresses, REM sleep episodes become increasingly longer and less
time is
spent
in NREM. During the last two 90-minute sleep cycles before awakening, NREM sleep is
composed primarily of
stage 2 sleep and periods of REM sleep can last as long as 40 minutes. In a later section,
we’ll look at dreaming and REM sleep in more detail. Changes in Sleep Patterns over
the Lifespan Over
the course of our lives, the quantity and quality of our sleep change
considerably. REM sleep begins long before birth, as scientists have discovered by using
ultrasound to document fetal eye movements and by
studying
the
sleep of premature infants. Four months before birth, REM sleep seems to
constitute virtually
all of fetal life.
By one month before
birth, the fetus demonstrates distinct sleep–wake
cycles, spending around 12 hours each day in REM sleep (Mindell,
1997).
A newborn sleeps
about 16 hours a day, about 50 percent of which is REM sleep. By the end of the first
year of life, total sleep time drops to around 13 hours a day, about one-third
of which is REM sleep. In general, from birth onward, the average amount of
time spent sleeping each day gradually decreases (see Figure 4.4). The amount
of time devoted to REM sleep and slow-wave NREM sleep each night also gradually
decreases over the lifespan (Bliwise, 1997).Young
children can easily spend two hours or more each night in the deep sleep of
stages 3 and 4 NREM. By early adulthood, about an hour is spent in deep sleep each
night. And by late adulthood, only about 20 minutes of a night’s sleep is spent in
stages 3 and 4 NREM sleep (Williams & others, 1994). By the time people reach their
sixties, total sleep time averages about six hours per night and the quality of
sleep is much more shallow. That we have a biological need for sleep is clearly
demonstrated by sleep deprivation studies. After as little as one night’s sleep
deprivation, research subjects develop microsleeps, which are
episodes of sleep lasting only a few seconds that occur during wakefulness. People who
go without sleep for a day or more also experiencedisruptions
in mood, mental abilities, reaction time, perceptual skills, and complex motor skills (Gökcebay & others, 1994).
Getting less sleep
than you need (as many adults do) can also have negative effects. In one
study, young men whose sleep was restricted to four hours a night for as few as six
consecutive nights experienced harmful changes in metabolic and endocrine
functioning (Spiegel & others, 1999). As sleep researcher Eve Van Cauter (1999) explained,
“After only one week of sleep restriction, young, healthy males had glucose
levels that were no longer normal. That’s a rapid deterioration of the body’s
functions.” Sleep
researchers have also selectively deprived people of different components of
normal sleep. For example, to study the effects of REM deprivation, researchers wake sleepers
whenever the monitoring instruments indicate that they are entering REM sleep. After
several nights of being selectively deprived of REM sleep, the subjects are
allowed to sleep uninterrupted. What happens? The first time subjects are allowed to
sleep without interruption, they experience REM rebound—the amount of time
spent in REM sleep increases by as much as 50 percent (Ellman
& others, 1991).
Similarly, when people are selectively deprived of NREM stages 3 and 4, they
experience NREM rebound, spending more time in NREM sleep. The phenomena of
REM rebound and NREM rebound seem to indicate that the brain needs to make up for
missing components of sleep. Clearly, we need both to sleep and to
experience the full range of sleep stages. But what particular functions does
sleep serve? The
restorative theory of sleep suggests that sleep promotes physiological processes that
restore and rejuvenate the body and the mind (Gökcebay
& others, 1994).
According to this theory, NREM and REM sleep serve different purposes. NREM sleep is
thought to be important for restoring the body, whereas REM sleep is thought to
restore mental and brain functions (Maquet, 2001; Stickgold & others, 2001).
Evidence supporting
the role of NREM sleep in restoring the body comes from studies that have demonstrated
increased deep sleep following sleep deprivation, starvation, and strenuous
athletic activity. The secretion of growth hormone, testosterone, prolactin, and other
hormones increases during NREM sleep (Hirshkowitz & others,
1997).
The importance of
REM sleep in mental and brain functions is suggested by the abundance of REM sleep
in the developing fetus, in infants, and in young children and its
subsequent decrease throughout adulthood. Tentatively, this suggests that REM
sleep plays some role in stimulating the high rate of brain development that
occurs in the early stages of the lifespan. In contrast to the restorative
theory, the adaptive theory of sleep suggests that the sleep patterns
exhibited by different animals, including humans, are the result of evolutionary
adaptation (Webb, 1975). Also called the evolutionary theory of sleep, the basic
idea is that different sleep patterns evolved as a way of preventing a particular
species from interacting with the environment when doing so is most hazardous.
Animals
with
few natural predators, such as gorillas and lions, sleep as much as 15 hours a day. In
contrast, grazing animals, such as cattle and horses, tend to sleep in short
bursts that total only about 4 hours per day. Hibernation patterns of animals such as
bears and gophers also
coincide with periods during which environmental conditions pose the greatest threat
to survival. Although
there is evidence to support both the restorative and the adaptive theories of sleep,
many questions remain. The bottom line is that researchers still aren’t sure
exactly what physiological functions are served by sleep (Maquet, 2001). Sleep may
well fulfill multiple purposes.
Sleep disorders are
serious disturbances in the normal sleep pattern that interfere with daytime
functioning and cause subjective distress (American Psychiatric Association,
2000a). Virtually everyone is seriously troubled by the quality or quantity of their
sleep at some point. And, if you happen to be someone who regularly experiences
sleep-related problems, you’re not alone. According to the 2002 Sleep in America
Poll, seven out of ten American adults report frequent sleep problems, including
inadequate amounts of sleep.
Insomnia
By far the most
common sleep complaint among adults is insomnia (Dement & Pelayo, 1997). According
to the 2002 National Sleep Foundation survey, 58 percent of adults are
affected a few nights or more each week by at least one symptom of insomnia, such
as waking up and being unable to go back to sleep. Insomnia is not defined solely
on the basis of the amount of time a person sleeps, because people vary in
how much sleep they need to feel refreshed. Rather, people are said to experience
insomnia when they repeatedly complain about the quality or duration of
their sleep, have difficulty going to sleep or staying asleep, or wake before it is
time to get up. For
an estimated 12 million Americans, complaints of insomnia are related to a condition called
restless legs syndrome, abbreviated RLS. People with RLS complain of
unpleasant creeping, crawling, tingling, itching, or prickling sensations deep inside their
lower legs accompanied by an irresistible urge to move (National Institute of
Neurological Disorders and Stroke, 2001). These sensations are most prominent
in the evening and at night, especially when the individual lies down or sits
still for any length of time (Rothenberg, 1997). Moving the legs temporarily reduces
the unpleasant sensations but also interferes with the person’s ability to fall
asleep or stay asleep.
More commonly,
insomnia can often be traced to stressful life events, such as job or school
difficulties, troubled relationships, the death of a loved one, or financial problems.
Concerns about sleeping can add to whatever waking anxieties the person may
already be experiencing. This can create a vicious circle— worrying about the
inability to sleep makes troubled sleep even more likely, further
intensifying anxiety. Numerous studies have shown that behavior
therapy and different medications are effective in the short-term treatment of insomnia
(M. T. Smith & others, 2002). Behavioral
techniques often help people develop better sleep habits. For example, a
treatment called stimulus control conditions the person to associate the bed only with
sleepiness and sleep, rather than with watching television, talking on the
phone, or other nonsleep activities. Relaxation
training and meditation, which we will discuss later in the chapter, are also
commonly used to treat insomnia (Murtagh &
Greenwood, 1995).
Educating people on
sleep hygiene is often part of the successful treatment of insomnia. For
example, many people troubled by the inability to sleep use alcohol or over-the-counter
sleep medications to induce sleep. In the Prologue to this chapter, you saw how Mike
resorted to a stiff drink to help him relax and go back to sleep. Although
such remedies may temporarily help people fall asleep, both sleeping pills and alcohol
disrupt normal sleep cycles, including REM sleep (Roehrs
& Roth, 2001). Even
the sleep-inducing medications sometimes prescribed by physicians to treat insomnia
must be carefully managed to avoid drug dependence.
Sleep Apnea
The second most
common sleep disorder, sleep apnea, affects some 20
million
Americans
(Carskadon & Taylor, 1997). In sleep apnea, the sleeper repeatedly stops breathing during the
night. Carbon dioxide builds up in the blood, causing a momentary awakening, during
which the sleeper snorts or gulps in air. Breathing may stop for as little as 10
seconds or for so long that the sleeper’s skin turns blue before he or she wakes
up. During a single night, more than 300 sleep apnea attacks can occur.
Often the person has no recollection of the repeated awakenings but feels sleepy
throughout the following day (Orr, 1997). Sleep apnea
is more common in men over the age of 50, especially those who are overweight.
Special mouthpieces, weight loss, and surgical intervention have been effective in
treating sleep apnea. For people who suffer from
sleep apnea only when they sleep on their backs, treatment is
sometimes as simple as sewing a tennis ball to the back of their pajama
tops, which forces them to sleep on their sides (Saskin,
1997).
Sleepwalking and Night Terrors
Unlike insomnia,
sleepwalking and night terrors are much more common in children than in adults (Lask, 1995; Mindell, 1993). These
sleep disturbances occur during the deepest stages of NREM sleep, stages 3 and
4. As noted previously, young children spend considerably more time each night
in deep sleep than do adolescents or adults (Whyte
& Schaefer, 1995). Not surprisingly, most instances of bedwetting, or nocturnal
enuresis, also tend to occur when the child is in deep sleep (Barclay & Houts, 1995a).
About 25 percent of
all children have at least one episode of sleepwalking, also known as somnambulism.
Sleepwalking typically occurs during the first three hours after the child
has gone to sleep. The child gets out of bed and moves about in a slow, poorly
coordinated, automatic manner, usually with a blank, staring look on his face.
Surprisingly, the sleepwalking child is usually able to navigate around objects
without much difficulty. However, the child’s general lack of awareness of his
surroundings is evident. The sleepwalker may try to dress, eat, or go to the
bathroom in the wrong location (Ozbayrak & Berlin,
1995).
Night
terrors, or sleep terrors, also typically occur during stage 3 or 4 NREM sleep in the first
few hours of sleep. Physiologically, a night terror is much more intense than a
run-of-the-mill nightmare. The first sign of a night terror is sharply increased
physiological arousal—restlessness, sweating, and a racing heart. Typically, the child
experiencing night terrors abruptly sits up in bed and lets out a panic-stricken
scream or cry for help as she thrashes about in bed or even sleepwalks.
Terrified and
disoriented, the child may struggle with a parent who tries to calm her down. Night terrors tend
to be brief, usually lasting only a matter of seconds. Amazingly, the child almost immediately goes
back to quiet sleep and wakes in the morning with no recollection of the incident.
Unlike
the
unfolding dream story of a nightmare, night terrors are usually accompanied by a
single but terrifying sensation, such as being crushed or falling. Often,
the child imagines
that she is choking or that a frightening figure is present, such as a
threatening animal or monster (Kahn & others, 1991). Though dramatic, night
terrors are not regarded as a true sleep disorder or psychological problem unless
they occur frequently.
For the vast
majority of children who often experience night terrors, the problem usually
resolves itself by early adolescence (Lask, 1995).
REM Sleep Behavior Disorder
Another,more serious parasomnia is REM sleep behavior
disorder (Mahowald & Schenck, 1990). REM sleep behavior disorder typically affects men over the age of 60 and is
characterized by the brain’s failure to suppress voluntary muscle movements during REM sleep.
Consequently, the dreamer acts out his dreams, sometimes leaping out of bed, lashing
out at imagined intruders, or tackling a chest of drawers. Such behavior might seem comical
if the potential for serious injury to the sleeper or the sleeper’s bed
partner weren’t so great. Evidence suggests that the cause of REM sleep behavior disorder is deterioration or damage in the lower
brain centers that control physical and mental
arousal during sleep (Zoltoski & Gillin, 1994).
Narcolepsy
If you’ve ever
tried to stay awake for 36 hours or longer, you know how incredibly sleepy you can get.
That experience gives you an inkling of what life is like for people with
narcolepsy. The most common, and most troubling, symptom of narcolepsy is excessive
and recurring bouts of daytime sleepiness. People with narcolepsy experience an
overwhelming sleepiness, lapsing into brief periods of sleep throughout the day that
usually last an hour or less. These daytime sleep episodes occur regardless of
how much nighttime sleep the person has had. They also often occur at
inappropriate times, such as in the middle of a meeting. The onset of these
daytime sleep episodes is sometimes accompanied by frightening hypnagogic hallucinations,
such as the house or building being on fire. As the person awakens, he or she
may briefly experience the sensation of being unable to move, which is
termed sleep paralysis.
When these daytime
sleep episodes occur suddenly, they are termed “sleep attacks.” Along with
excessive daytime sleepiness, narcolepsy is often characterized by regular episodes
of cataplexy. Cataplexy is the sudden loss of voluntary muscle strength and
control, lasting from several seconds to several minutes. Cataplexy is usually
triggered by a sudden, intense emotion, such as laughter, anger, or
surprise. In mild episodes, the person’s head may droop or facial muscles sag
(Siegel, 2000). In more severe episodes, the person may completely lose muscle
control. As shown in the accompanying series of photos, the person’s knees
buckle and he collapses on the floor. The onset of narcolepsy typically occurs during
adolescence, and it is considered a chronic, lifelong condition. Although estimates
vary, approximately 250,000
Americans have narcolepsy, and it affects men and women equally (Carskadon & Taylor, 1997; Littner,
2001). Genetics seems to play an important role, as the disorder tends to
run in families (Mignot, 1998). Adding to the genetic evidence,
scientists have identified the genes that produce narcoleptic symptoms in mice
and dogs (Chemelli & others, 1999; Lin &
others, 1999).
Although the cause
of narcolepsy is still unknown, recent evidence suggests that people with
narcolepsy lack a hormone called hypocretin, which is manufactured in
the brain’s hypothalamus (Nishino & others, 2000). Hypocretin is involved in
regulating arousal, sleep, and eating behavior (Hungs & Mignot, 2001; Mignot, 2001). Many sleep researchers are hopeful that such
discoveries will lead to new treatments for this debilitating sleep disorder. Although narcolepsy
cannot be cured, a drug called modafinil (Provigil), reduces daytime sleepiness in people with narcolepsy
(Schwartz & others, 2000). Antidepressant medications can reduce episodes
of cataplexy, hypnagogic hallucinations, and sleep
paralysis. Stimulant drugs, such as Dexedrine and Ritalin, are also used to
minimize narcoleptic symptoms. Dreams have fascinated people since the beginning of
time. On average, about 25 percent of a night’s sleep, or almost two hours
every night, is spent dreaming. So, assuming you live to a ripe old age, you’ll devote
more than 50,000 hours, or about six years of your life, to dreaming.
Although dreams may
be the most spectacular brain productions during sleep, they are not the most common.
More prevalent is sleep thinking, which takes place during NREM sleep and
consists of vague, uncreative, bland, and thoughtlike ruminations about
real-life events (Hobson & Stickgold, 1995; Schatzman & Fenwick, 1994). For example, just before an important
exam, students may review terms and concepts during NREM sleep.
In contrast to
sleep thinking, a dream is an unfolding episode of mental images that is storylike, involving characters and events. According to
sleep researcher J.
Allan Hobson (1988), dreams have five basic characteristics:
·
Emotions can be intense.
·
Content and organization are usually illogical.
·
Sensations are sometimes bizarre.
·
Even bizarre details are uncritically accepted.
·
Dream images are difficult to remember.
Many people believe
that dreams occur only during REM sleep, but this is not the case. Dreams occur
during both NREM and REM sleep (Rosenlicht & Feinberg, 1997).
However, dreams during REM sleep are more frequent and of longer duration
than are dreams during NREM sleep (Foulkes, 1997).
When people are
awakened during REM sleep, they will report a dream up to 90 percent of the time—even
people who claim that they never dream. People usually have four or
five episodes of dreaming each night. Earlymorning dreams, which can
last as long as 40 minutes, are the dreams people are most likely to remember.
Contrary to popular belief, dreams happen in real time, not in split seconds. In fact,
dreamers tend to be quite accurate in estimating how long they’ve been dreaming (Empson, 1993).
The Brain During REM Sleep
What happens in the
brain during REM sleep? Earlier in the chapter, we noted that EEG
measurements show that the brain is highly active during REM sleep. In a recent series
of PET scans of sleeping subjects, neuroscientist Allen Braun and his colleagues
(1998) showed that the brain’s activity during REM sleep is distinctly
different from its activity during either wakefulness or slow-wave (NREM) sleep. Braun found that
both the primary visual cortex and the frontal lobes are essentially shut down during
REM sleep. The primary visual cortex is the area at the back of the brain
that first registers visual information transmitted by the retinas of
the eye. The frontal lobes are the brain areas responsible for higher-level
cognitive processes, including reasoning, planning, and integrating perceptual
information. Thus, during REM sleep, the sleeper is cut off from information about
the external world and from the brain centers most involved in
rational thought. Other
brain areas, however, are highly active during REM sleep. Activated areas include the amygdala and the hippocampus, structures of the limbic
system
that
are involved in emotion, motivation, and memory. Also highly active are other
parts of the brain’s visual system that are involved in generating visual
images.
These results
suggest that the dreamer’s uncritical acceptance of bizarre and chaotic dream
images and narrative can be explained in terms of the inactivityof
the frontal lobes—the very areas of the brain that are normally most active in
analyzing and interpreting new information. In the absence of meaningful stimuli
from the outside world, emotions and stored memories provide the raw data for
the vivid visual images conjured up by the sleeping brain. Brain Changes During REM Sleep
These PET scans reveal how brain activity during REM sleep differs from wakefulness
(scan a) and slow-wave sleep (scan b). The PET scans are color-coded:
Yellow-red indicates
areas of increased brain activity, and bluish-purple indicates areas of
decreased brain activity. Compared to wakefulness, scan (a) reveals that REM
sleep involves decreased activity in the frontal lobes, which are
involved in rational thinking, and the primary visual cortex, which processes external visual
stimuli. The yellow-red areas indicate increased activity in visual areas
associated with
visual imagery—the images occurring in a dream. Compared to slow-wave sleep,
the yellow-red areas in scan (b) indicate that REM sleep is characterized by a
sharp increase in areas of the limbic system that are associated with emotion, motivation, and
memory. The activation of these brain areas reflects the intense emotions that often characterize
dreams.
In
combination, these two PET scans document the high degree of mental imagery and
emotionality that
takes place in the dreaming brain. But the brain changes that occur during REM
sleep also show that the
dreamer is cut off from the reality-testing functions of the frontal lobes—a
fact that no doubt
contributes to the sometimes bizarre nature of dreams.
REM Sleep and Memory Consolidation
As you’ll see in
Chapter 6, memory consolidation refers to the gradual process of converting new
memories into a long-term, relatively permanent form. Research suggests that REM
sleep helps consolidate memories, especially procedural memories (Stickgold & others, 2001). Procedural memories are
essentially memories
for how to perform sequences of behaviors. For
example, when you
play a video game or the piano, you’re drawing on your procedural memories. Studies have shown
that REM sleep increases after learning a novel task and that deprivation of REM
sleep following training disrupts learning (Maquet, 2001). The
importance of REM sleep was demonstrated in one study in which volunteers were
trained on a simple but challenging perceptual task before going to sleep (Karni & others, 1994). Half the participants were
repeatedly awakened during
NREM sleep stages, while the other half were repeatedly awakened during REM sleep. The
volunteers who enjoyed uninterrupted REM (dreaming) sleep improved their
performance on the test the next day, but the participants whose REM sleep was
disrupted did not. While
REM sleep appears to play an important role in memory consolidation, exactly
how it does so is still unknown. Recent studies have shown that brain areas
activated during training on a particular task are actually reactivated during REM sleep
(Louie & Wilson, 2001; Maquet & others,
2000). Thus, REM
sleep may help stabilize the neural connections acquired through recent experience.
What Do We Dream About?
Although nearly
everyone can remember an unusually bizarre dream, most dreams are a reflection of
everyday life, including people we know and familiar settings (Domhoff,
1999; Weinstein & others, 1991). Recall Mike’s nightmare about his new boss,
which was described in the Prologue. The giant staircase and spiral escalators
were exaggerated versions of real architectural features of the atrium-style
lobby of the hotel where he works. Dream researcher Calvin Hall collected and analyzed
over 10,000 dreams from
hundreds of people. He found that a dream’s themes often reflect the daily
concerns of the dreamer (Hall & Van de Castle, 1966).Worries about
exams, money, health, troubled relationships, or jobs are all likely to be
reflected in our dreams—as was Mike’s anxiety about his new boss. Certain themes,
such as falling, being chased, or being attacked, are surprisingly common across
cultures. Although thousands of miles apart and immersed in two very different
cultures, American and Japanese college students share many dream themes.
Surveys of dream content in many cultures have shown that dreamers
around the world report more instances of negative events than of positive events (Domhoff, 1996). Instances of aggression are more common than are
instances of friendliness,
and dreamers are more likely to be victims of aggression than aggressors in
their dreams. There is more aggression in men’s dreams than in women’s
dreams, but women are more likely to dream that they are the victims of physical
aggression. Environmental
cues during dreaming can also influence dream content. In sleep labs,
researchers have played recordings of a rooster crowing, a bugle playing reveille, and a
dog barking. Researchers
have even sprayed water on sleeping subjects. Depending on the stimulus, up to
half the dreamers incorporated the external stimulation into their dream
content (Arkin & Antrobus, 1991).
Why Don’t We Remember Our Dreams?
Even the best dream
recallers forget the vast majority of their dreams—at
least 95 percent,
according to one estimate (Hobson, 1995). Why are dreams so much more difficult to
remember than waking experiences? Several theories have been proposed, each with
at least some evidence to support it. As we’ll discuss in more detail in Chapter 6, memory
requires information to be processed and stored in such a way that it can be
retrieved at a later time. One theory is that the fundamental changes in brain
chemistry and functioning that occur during sleep fail to support such
information processing and storage. For example, frontal lobe areas are
involved in the formation of new memories. But as you read earlier, PET scans of
sleeping volunteers have
shown that the frontal lobes are inactive during REM sleep (Braun & others,
1998). Research has also shown that the neurotransmitters needed to acquire
new memories—including serotonin, norepinephrine, and dopamine—are
greatly reduced during REM sleep (J. A. Hobson & others, 1998; Siegel,
2001).
Some
dreams are remembered, however, and several factors have been found to
influence dream recall. First, you’re much more likely to recall a dream if
you wake up during it (Schredl & Montasser, 1997).
When people are
intentionally awakened during REM sleep, they usually recall the dream content. There
are also individual differences in dream recall. Some people frequently
remember their dreams in vivid detail. Other people hardly ever remember their dreams.
Research has shown that people who are better at remembering visual details
while awake are also better at recalling their dreams (Schredl
& others, 1995). Second,
the more vivid, bizarre, or emotionally intense a dream is, the more likely it is to be
recalled the following morning. Vivid dreams are also more likely to be remembered
days or weeks after the dream has occurred (Goodenough, 1991). In many
respects, this is very similar to waking experiences. Whether you’re awake or
asleep, mundane and routine experiences are most likely to be forgotten. Third, distractions
on awakening interfere with our ability to recall dreams, as noted by
psychologist Mary Calkins (1893) over a century ago: To recall a dream requires
usually extreme and immediate attention to the content of the dream.
Sometimes the slight movement of reaching for paper and pencil or of lighting
one’s candle seems to dissipate the dream-memory, and one is left with the
tantalizing consciousness of having lived through an interesting dream-experience
of which one has not the faintest memory. Finally, it’s difficult to
remember any experience that occurs during sleep, not just dreams. Sleep
researchers have found that people who are briefly awakened during the night to
give reports or perform simple tasks frequently do not remember the incident the next
morning (Goodenough, 1991). It seems clear, then, that the
brain is largely programmed to forget not only the vast majority of dream experiences
but also other experiences that happen during sleep.
If I fall off a
cliff in my dreams and don’t wake up before I hit the bottom, will I die? The first obvious
problem with this bit of folklore is that if you did die before you woke up, how
would anyone know what
you’d been dreaming about? Beyond this basic contradiction, studies have shown that
about a third of dreamers
can recall a dream in which they died or were killed. Dream sensations such as falling,
soaring through the
air, and being paralyzed seem to be universal. Do animals dream? Virtually all mammals
experience sleep cycles
in which REM sleep alternates with slow-wave NREM sleep. Animals clearly demonstrate
perception and memory.
They also communicate using vocalizations, facial expressions, posture, and gestures to
show territoriality and
sexual receptiveness. Thus, it’s quite reasonable to conclude that the brain and other
physiological changes that occur during animal REM sleep are coupled with mental
images. One bit of anecdotal
evidence supporting this idea involved a gorilla that had been taught sign language to
communicate. The gorilla signed “sleep pictures,” presumably referring to REM
dream activity while
it slept. What
do blind people “see” when they dream? People who become totally blind before the age of five
typically do not have visual dreams as adults. Even so, their dreams are just as
complex and vivid as
sighted people’s dreams; they just involve other sensations—of sound,
taste,
smell,
and touch. Is
it possible to control your dreams? Yes, if you have lucid dreams. A lucid dream is one in
which you become aware that you are dreaming while you are still asleep. About half
of all people can recall at least one lucid dream, and some people frequently
have lucid dreams. The dreamer can often consciously guide the course of a lucid
dream, including backing it up and making it go in a different direction. Can you predict the
future with your
dreams?
History
is filled with stories of dream prophecies. Over the course of your life, you will have over
100,000 dreams. Simply
by chance, it’s not surprising that every now and then a dream contains elements that
coincide with future events. Are dreams in color or black and white? Up to 80 percent of our dreams contain color. When dreamers are
awakened and asked
to match dream colors to standard color charts, soft
pastel colors are frequently chosen.
Nightmares
An unpleasant
anxiety dream that occurs during REM sleep is called a nightmare. Nightmares often
produce spontaneous awakenings, during which the vivid and frightening dream
content is immediately recalled. The general theme of nightmares is of being
helpless or powerless in the face of great danger or destruction. Nightmares are
especially common in young children (Halliday, 1995).
For example, when our
daughter Laura was four years old, she told us about this vivid nightmare: There was a big
monster chasing me and Nubbin the Cat! And we jumped on a golden horse but the
monster kept chasing us! Then Nubbin jumped off and started to eat the
monster. And then Mommy came and saved me! And then Daddy took a sword and
killed the monster! And then me and Mommy and Nubbin rode the horse into
the clouds. Like Laura, young children often have nightmares in which they are
attacked
by an
animal or monster. In dealing with a child who has experienced a nightmare, simple reassurance
is a good first step, followed by an attempt to help the child understand the
difference between an imaginary dream and a real waking experience. In adults, an
occasional nightmare is a natural and relatively common experience (Wood & Bootzin, 1990). Nightmares are not considered indicative of
a psychological or
sleep disorder unless they frequently cause personal distress. Sigmund Freud:
Dreams as Fulfilled Wishes In the chapters on personality and psychotherapy.
Freud believed that sexual and aggressive instincts are the motivating forces
that dictate human behavior. Because these
instinctual urges
are so consciously unacceptable, sexual and aggressive thoughts, feelings, and wishes are
pushed into the unconscious, or repressed. However, Freud believed that these
repressed urges and wishes could surface in dreams. In his landmark work, The
Interpretation of Dreams (1900), Freud wrote that dreams are the “disguised fulfillments of repressed wishes” and provide “the royal road to a
knowledge of the unconscious mind.” Freud believed that dreams function as a sort
of psychological “safety valve” for the release of unconscious and unacceptable
urges.
Freud (1904)
believed that dreams have two components: the manifest content, or the dream images
themselves, and the latent content, the disguised psychological meaning of the
dream. For example, Freud (1911) believed that dream images of sticks,
swords, and other elongated objects were phallic symbols, representing the
penis. Dream images of cupboards, boxes, and ovens supposedly symbolized the
vagina.
In many types of
psychotherapy today, especially those that follow Freud’s ideas, dreams are
still seen as an important source of information about psychological conflicts. However,
Freud’s belief that dreams represent the fulfillment of repressed wishes
has not been substantiated by psychological research (Fisher & Greenberg,
1996; Schatzman & Fenwick, 1994). Furthermore,
research does not
support Freud’s belief that the dream images themselves—the manifest content of
dreams—are symbols that disguise the dream’s true psychological meaning (Domhoff, 1996).
The
Activation–Synthesis Model of Dreaming Armed with an array of evidence that dreaming involves
the activation of different brain areas during REM sleep, researcher J. Allan
Hobson and his colleague Robert McCarley first
proposed a new model of dreaming in 1977. Called the activation–synthesis model of
dreaming, this model maintains that dreaming is our subjective awareness of
the brain’s internally generated signals during sleep (Hobson, 1995; Hobson
& Stickgold, 1995). Since it was first proposed,
the model has evolved
as new findings have been reported (Hobson & others, 1998; Stickgold & others,
2001).
Specifically, the
activation–synthesis model maintains that the experience of dreaming sleep is
due to the automatic activation of brainstem circuits at the base of the brain. These
circuits arouse more sophisticated brain areas, including visual and auditory
pathways. As noted earlier, limbic system structures involved in emotion, such as
the amygdala and hippocampus, are also activated during REM sleep.
When we’re awake, these pathways and brain structures are involved in
registering stimuli from the external world. But rather than responding to stimulation from
the external environment, the dreaming brain is responding to its own internally
generated signals. In
the absence of external sensory input, the activated brain combines, or synthesizes, these
internally generated sensory signals and imposes meaning on them. The dream
story itself is derived from a hodgepodge of memories, emotions, and sensations that
are triggered by the brain’s activation and chemical changes during sleep.
According to this model, then, dreaming is essentially the brain’s
synthesizing and integrating memory fragments, emotions, and sensations
that are internally
triggered (Hobson & others, 1998).
The
activation–synthesis theory does not state that dreams are completely meaningless (Hobson
& Stickgold, 1995). But if there is a meaning to
dreams,
that
meaning lies in the deeply personal way in which the images are organized, or synthesized. In
other words, the meaning is to be found not by decoding the dream symbols, but
by analyzing the way the dreamer makes sense of the progression of chaotic dream
images.
Some Observations About the Meaning of Dreams
Subjectively, it
seems obvious that at least some of our dreams mirror our real life concerns,
frustrations, anxieties, and desires. Less subjectively, this observation is consistent with
sleep research on the content of dreams (Weinstein & others, 1991). Large-scale
analyses of dream reports demonstrate that dreams reflect the waking concerns and
preoccupations of the dreamer (Domhoff, 1993, 1996).
Thus, the topics you
think about during the day are most likely to influence the topics you dream about at
night (Nikles & others, 1998). Some dream
researchers believe that most dreams, however chaotic or disorganized, are
meaningfully related to the dreamers’ current concerns, problems, and waking lives
(Domhoff, 1998).
It may well be that
the more bizarre aspects of dream sequences—the sudden scene changes, intense
emotions, and vivid, unrealistic images—are due to physiological changes in the
brain during REM and NREM sleep. Dream researcher David Foulkes
(1993, 1997) argues that dreaming consciousness is no different from waking
consciousness in its attempt to make sense of the information that is available to it.
What differs is the source of the information. When we’re awake, we monitor the
external environment, making sense of the stimuli that impinge upon us from the
environment as well as our own thoughts, feelings, and fantasies. During sleep, we
try—as best we can—to make sense of the less orderly stimuli produced by the brain
itself.
If
nothing else, remember that the interpretation of dreams occurs when we’re awake. It seems
reasonable, then, to suggest that conscious speculations about the meaning of these
elusive nightly productions might reveal more about the psychological
characteristics of the interpreter than about the dream itself (Cartwright
& Kaszniak, 1991).
For many people the
word hypnosis conjures up the classic but sinister image of a hypnotist inducing
hypnosis by slowly swinging a pocket watch back and forth. But, as
psychologist John Kihlstrom (2001) explains, “The hypnotist does not
hypnotize the individual. Rather, the hypnotist serves as a sort of coach or
tutor whose job is to help the person become hypnotized.” After experiencing
hypnosis, some people are able to self-induce hypnosis. The word hypnosis is derived
from the Greek hypnos, meaning “sleep.” The idea
that the hypnotized person is in a sleep-like trance is still very popular among the
general public. However, the phrase hypnotic trance is misleading and
rarely used by researchers today (Wagstaff, 1999). When
hypnotized, people do not lose control of their behavior.
Instead,
they
typically remain aware of where they are, who they are, and what is
transpiring.
Rather than being a
sleeplike trance, hypnosis is characterized by highly focused
attention, increased responsiveness to suggestions, vivid images and
fantasies, and a willingness to accept distortions of logic or reality. During hypnosis,
the person temporarily suspends her sense of initiative and voluntarily accepts and
follows the hypnotist’s instructions (Hilgard, 1986a).
Although most
adults are moderately hypnotizable, people vary in their responsiveness to
hypnotic suggestions. About 15 percent of adults are highly susceptible to
hypnosis, and 10 percent are difficult or impossible to hypnotize (Hilgard, 1982; Register & Kihlstrom,
1986). Children tend to be more responsive to hypnosis than are adults,
and children as young as five years old can be hypnotized (Kohen & Olness, 1993).
Evidence suggests that the degree of susceptibility to hypnosis tends to run in
families. For example, identical twins are more similar in their susceptibility to hypnosis
than are fraternal twins (Nash, 2001).
The best candidates
for hypnosis are individuals who approach the experience with positive,
receptive attitudes. The expectation that you will be responsive to hypnosis also
plays an important role (Kirsch & others, 1995; Spanos
& others, 1993).
People who are highly susceptible to hypnosis have the ability to become deeply
absorbed in fantasy and imaginary experience. For instance, they easily become
absorbed in reading fiction, watching movies, and listening to music (Barnier & McConkey, 1999; Kihlstrom, 2001).
Effects of Hypnosis
Deeply hypnotized
subjects sometimes experience profound changes in their subjective experience of
consciousness. They may report feelings of detachment from their bodies,
profound relaxation, or sensations of timelessness. More commonly, hypnotized people
converse normally and remain fully aware of their surroundings. Often, they will
later report that carrying out the hypnotist’s suggestions seemed to happen by
itself. The action seems to take place outside the hypnotized person’s will or
volition.
Sensory and Perceptual Changes
Some of the most
dramatic effects that can be produced with hypnosis are alterations in sensation and
perception. Sensory changes that can be induced through hypnosis include temporary
blindness, deafness, or a complete loss of sensation in some part of the body (Hilgard, 1986a). For example, when the suggestion is made to a highly
responsive subject that her arm is numb and cannot feel pain, she will not
consciously experience the pain of a pinprick or of having her arm immersed in ice
water. This property of hypnosis has led to its use as a technique in pain control
(Montgomery & others, 2000). Painful dental and medical procedures, including surgery,
have been successfully performed with hypnosis as the only anesthesia
(Hilgard & others, 1994).
People can
experience hallucinations under hypnosis. If a highly responsive hypnotic subject is
told that a close friend is sitting in a chair on the other side of the room, she
will not only report seeing the friend in vivid detail but will walk over and “touch”
the other person. Under hypnosis, people can also not perceive something that is
there. For example, if
the suggestion is made that a jar of rotten eggs has no smell, a highly suggestible person will not
consciously perceive
any odor. Hypnosis can also influence behavior outside the
hypnotic state.
When a posthypnotic
suggestion is given, the person will carry
out that
specific
suggestion after the hypnotic session is over. For example, under hypnosis, a student
was given the posthypnotic
suggestion that the number
5 no longer existed. He was brought out of hypnosis and then asked to count his
fingers. He counted 11
fingers! Counting again, the baffled young man was at a loss to explain his results.
Hypnosis and Memory
Memory can be
significantly affected by hypnosis. In posthypnotic amnesia, a subject is unable
to recall specific information or events that occurred before or during hypnosis.
Posthypnotic amnesia is produced by a hypnotic suggestion that suppresses the
memory of specific information, such as the subject’s street address. The
effects of posthypnotic amnesia are usually temporary, disappearing either
spontaneously or when a posthypnotic signal is suggested by the hypnotist. When
the signal is given,
the information floods back into the subject’s mind. The opposite effect is called hypermnesia, which is enhancement of memory for past events
through
hypnotic
suggestion. Police investigators sometimes use hypnosis in an attempt to enhance the
memories of crime
victims and witnesses. Despite the common belief that you can “zoom in” on briefly seen
crime details under
hypnosis, such claims are extremely exaggerated (Smith, 1983). Compared
with regular police interview
methods, hypnosis does not significantly enhance memory or improve the accuracy of
memories (Nash, 2001; Register & Kihlstrom,
1987).
Many studies have
shown that efforts to enhance memories hypnotically can lead to distortions and
inaccuracies (Burgess & Kirsch, 1999). In fact, hypnosis can greatly
increase confidence in memories that are actually incorrect (Kihlstrom & Barnhardt, 1993).
False memories, also called pseudomemories, can be inadvertently
created when hypnosis is used to aid recall (Lynn & Nash, 1994; Yapko, 1994a).
The Limits of Hypnosis
Although the
effects of hypnosis can be dramatic, there are limits to the behaviors that can be influenced by hypnosis. First, contrary to
popular belief, you
cannot be hypnotized against your will. Second, hypnosis cannot make you perform behaviors that are contrary to your morals and values.
Thus, you're very
unlikely to commit criminal or immoral acts under the influence of hypnosis— unless, of course,
you find such actions acceptable (Hilgard, 1986b).
Third, hypnosis
cannot make you stronger
than your physical capabilities or bestow new talents. However, hypnosis can enhance physical
skills or athletic ability by increasing motivation and concentration (Morgan, 1993).
Table 4.4 provides additional examples of how hypnosis can be used to help people. Can hypnosis be
used to help you lose weight, stop smoking, or stop biting your nails? The
effectiveness of hypnosis in modifying habitual behaviors varies.
For example, research
provides little evidence to support the notion that hypnosis is more effective than other
methods in controlling smoking behavior (Green & Lynn,
2000). In study after
study, hypnosis has failed to produce long-term cessation of smoking (Spanos
& others, 1995b). In
contrast, hypnosis coupled with cognitive-behavior
therapy does enhance
the effectiveness of weight-loss programs (J. Green, 1999a; Kirsch, 1996).
Explaining Hypnosis
Consciousness
Divided?
How
can hypnosis be explained? Psychologist Ernest Hilgard
(1986a, 1991, 1992)
believed that the hypnotized person experiences dissociation—the splitting of
consciousness into two or more simultaneous streams of mental activity. According to Hilgard’s neodissociation theory
of hypnosis, a hypnotized person consciously experiences one stream of mental
activity that is responding
to the hypnotist’s suggestions. But a second, dissociated stream of mental activity is
also operating, processing information that is unavailable to the consciousness
of the hypnotized subject. Hilgard (1986a, 1992)
referred to this
second, dissociated stream of mental activity as the hidden observer. (The phrase hidden
observer does not mean that the hypnotized person has multiple personalities.) One of the great
debates in modern psychology comes down to this question: Are the changes in
perception, thinking, and behaviors that occur during
hypnosis the result
of a “special” or “altered” state of consciousness? Here, we’ll touch on some of the evidence for
three competing points
of view on this issue. The State View: Hypnosis Involves a Special State of
Consciousness Considered
the traditional viewpoint, the “state” explanation contends that hypnosis is a unique
state of consciousness, distinctly different from our normal wakingconsciousness
(Kosslyn & others, 2000).
The state view is
perhaps best represented by Hilgard’s neodissociation theory of hypnosis. According to this
view, consciousness is
split into two simultaneous streams of mental activity during hypnosis. One
stream of mental activity remains conscious, but a second streamof
mental activity—the one respondingto the hypnotist’s
suggestions—is “dissociated”from awareness. So
according to
the neodissociation explanation,the
hypnotized young woman shown on page 150, whose hand is immersed in ice water, reported
no pain because the painful
sensations were dissociated from awareness.
The Non-State View: Ordinary Social
Psychological Processes Can Explain Hypnosis
Some psychologists
flatly reject the notion that hypnotically induced changes involve a “special”
state of consciousness. According to the social-cognitive view of hypnosis, subjects
are responding to thesocial demands of the hypnosis
situation. They
act the way they think good hypnotic subjects are supposed to act, conforming to the
expectations of the hypnotist, their own expectations, and situational cues.
In this view, the “hypnotized” young woman on page 150 reported no pain because
that’s what she expected
to happen during the hypnosis session. To back up the social-cognitive theory of hypnosis,
Nicholas Spanos (1991, 1994, 1996) and his colleagues
have amassed an
impressive array of evidence showing that highly motivated people often perform just as well as
hypnotized subjects in demonstrating pain reduction, amnesia, age regression,
and hallucinations. Studies
of people who simply pretended to be hypnotized have shown similar results. On the
basis of such findings, non-state theorists contend that hypnosis can be
explained in terms of rather ordinary psychological processes,including
imagination, situational expectations,role enactment,
compliance, and conformity
(Wagstaff, 1999).
PET Scans During
Hypnosis: Does theBrain Respond Differently?In
trying to reconcile the state and nonstate
explanations of hypnosis, researcher Stephen Kosslyn and his
colleagues (2000)
conducted a brain-imaging study.
Highly hypnotizable
volunteers viewed two
images of rectangles, one in bright colors and one in shades
of gray, while lying in a PET scanner. During
the study, the
researchers measured activity in brain regions known to be involved in color perception. While
hypnotized, the participants
were instructed to perform three tasks: to see the images as they were; to mentally
“drain” color from the colored rectangles in
order to see them in
shades of gray; and to mentally “add” color to the gray rectangles. Essentially, these last two tasks were hypnosisinduced hallucinations. What did the PET scans reveal?
In contrast to what
might be expected if the participants were merely playing the role of
hypnotic subject, hypnosis produced distinct effects on brain activity.
When the hypnotized
participants were
instructed to perceive colored rectangles, color regions in the brain activated, regardless of
whether the participants were shown colored or gray rectangles. When participants were instructed to perceive gray rectangles, color regions in the
brain deactivated, regardless
of whether the participants were shown colored or gray rectangles.
In other words,
brain activity reflected the hypnosis-induced hallucinations— not the actual
images that were shown to the participants. These findings led Kosslyn (2001) to conclude
that “Hypnosis is
not simply ‘role playing,’ but does in fact reflect the existence of a distinct mental brain
state.”
The Imaginative Suggestibility View: Some People Are
Highly Suggestible Psychologists Irving Kirsch and Wayne
Braffman (2001) dismiss the
idea that hypnotic
subjects are merely acting. But they also contend that brain-imaging studies don’t
necessarily prove that hypnosis is a unique or distinct state. Rather, Kirsch and Braffman maintain that such studies emphasize individual
differences in
imaginative suggestibility—the degree to which a person is able to experience an imaginary state of
affairs as if it were real. In previous research, Braffman
and Kirsch (1999) found
that many participants were just as responsive to suggestions Brain Activation During Hypnosis The
rectangles shown here—one in bright colors and the
other in shades of gray—were used as stimuli to test
brain activity during hypnosis. When hypnotized participants were asked to
mentally add color to the gray
rectangles, activity in brain regions involved in color perception sharply
increased, as this PET scan shows. Conversely, when hypnotized participants
were instructed to
mentally drain color from the colored
rectangles, the brain’s color-perception regions
deactivated. In
other words, brain activity reflected the participants’ subjective experience
of the hypnosisinduced hallucinations—not the actual
stimuli that were shown. According to the researchers, such findings contradict
the notion that hypnosis is merely role playing (Kosslyn
& others, 2001).
Classical
Conditioning
Although learning by
association had been discussed for centuries, it remained for Ivan Pavlov to
capture the phenomenon in his classic experiments on conditioning.
Pavlov’s Experiments
Pavlov repeatedly
presented a neutral stimulus (such as a tone) just before an unconditioned
stimulus (UCS, food) that triggered an unconditioned response (UCR,
salivation). After several repetitions, the tone alone (now the conditioned
stimulus, CS) triggered a conditioned response (CR, salivation). Further
experiments on acquisition revealed that classical conditioning was usually
greatest when the CS was presented just before the UCS, thus preparing the
organism for what was coming. Other experiments explored the phenomena of
acquisition, extinction, spontaneous recovery, generalization, and
discrimination.
Pavlov’s work laid
a foundation for John B. Watson’s emerging belief that psychology, to be an
objective science, should study only overt behavior, without considering
unobservable mental activity. Watson called this position behaviorism.
Extending Pavlov’s Understanding
The behaviorists’
optimism that learning principles would generalize from one response to another
and from one species to another has been tempered. Conditioning principles, we
now know, are cognitively influenced and biologically constrained. In classical
conditioning, animals learn when to "expect" an unconditioned
stimulus. Moreover, animals are biologically predisposed to learn associations
between, say, a peculiar taste and a drink that will make them sick, which they
will then avoid. They don’t, however, learn to avoid a sickening drink
announced by a noise.
Pavlov’s Legacy
Pavlov taught us
that principles of learning apply across species that significant psychological
phenomena can be studied objectively, and that conditioning principles have
important practical applications.
Operant
Conditioning
Through operant
conditioning, organisms learn to produce behaviors that are followed by
reinforcing stimuli and to suppress behaviors that are followed by punishing
stimuli.
Skinner’s Experiments
Skinner showed that
when placed in an operant chamber, rats or pigeons can be shaped to display
successively closer approximations of a desired behavior. Researchers have also
studied the effects of primary and secondary reinforcers,
and of immediate and delayed reinforcers. Partial
reinforcement schedules (fixed-ratio, variable-ratio, fixed-interval, and
variable-interval) produce slower acquisition of the target behavior than does
continuous reinforcement, but they also create more resistance to extinction.
Punishment is most effective when it is strong, immediate, and consistent.
However, it can have undesirable side effects.
Extending Skinner’s Understanding
Skinner’s emphasis
on external control of behavior made him both influential and controversial.
Many psychologists criticized Skinner (as they did Pavlov) for underestimating
the importance of cognitive and biological constraints. For example, research
on latent learning and motivation, both intrinsic and extrinsic, further indicates
the importance of cognition in learning.
Skinner’s Legacy
Skinner’s ideas
that operant principles should be used to influence people were extremely
controversial. Critics felt he ignored personal freedoms and sought to control
people. Today, his techniques are applied in schools, sports, workplaces, and
homes. Shaping behavior by reinforcing successes is effective.
Learning by
Observation
Another important
type of learning, especially among humans, is what Albert Bandura
and others call observational learning. In experiments, children tend to
imitate what a model both does and says, whether the behavior is social or
antisocial. Such experiments have stimulated research on social modeling in the
home, within peer groups, and in the media. Children are especially likely to
imitate those they perceive to be like them, successful, or admirable.
The Phenomenon of
Memory
Information Processing
Memory is the
persistence of learning over time. Psychologists have proposed several
information-processing models of memory. We will use the influential
three-stage processing model, which suggests that we (1) register fleeting
sensory memories, some of which are (2) processed into on-screen short-term or
working memories, a tiny fraction of which are (3) encoded for long-term memory
and, possibly, later retrieval.
Encoding: Getting
Information In
How and What We Encode
Some types of
information, notably information concerning space, time, and frequency, we
encode mostly automatically. Other types of information, including much of our
processing of meaning, imagery, and organization, require effort. Mnemonic
devices depend on the memorability of visual images
and of information that is organized into chunks. Organizing information into
chunks and hierarchies also aids memory.
Storage: Retaining
Information
Sensory Memory
Information first
enters the memory system through the senses. We register and briefly store
visual images via iconic memory and sounds via echoic memory.
Short-Term and Long-Term Memory
Our short-term
memory span for information just presented is limited—a seconds-long retention
of up to about seven items, depending on the information and how it is
presented. Our capacity for storing information permanently in long-term memory
is essentially unlimited.
Storing Memories in the Brain
The search for the
physical basis of memory has recently focused on the synapses and their
neurotransmitters; on the long-term potentiation of
brain circuits, such as those running through the hippocampus; and on the
effects of stress hormones on memory. Studies of people with brain damage
reveal that we have two types of memory operating together—explicit
(declarative) memories processed by the hippocampus, and implicit (procedural)
memories processed by the cerebellum and the amygdala.
Retrieval: Getting
Information Out
Retrieval Cues
To be remembered,
information must be encoded, stored, and then retrieved. Memory is recall,
recognition, and relearning. With the aid of associations (cues) that prime the
memory, we retrieve the information we want to remember. Cues sometimes come
from returning to the original context. We use our senses as cues-a taste,
smell, or sight may evoke us to recall a memory. Mood affects memory, too.
While in a good or bad mood, we tend to retrieve memories congruent with that
mood.
Forgetting
Encoding Failure
One explanation of
forgetting is that we fail to encode information for entry into our memory
system. Without effortful processing, we never notice or process much of what
we sense. Age affects encoding efficiency, which explains age-related decline.
Storage Decay
Memories may also
fade after storage—often rapidly at first, and then leveling off. This is the
basis for one of psychology’s laws, the forgetting
curve.
Retrieval Failure
Forgetting also
results from retrieval failure. Retrieval-related forgetting may be caused by a
lack of retrieval cues, by proactive or retroactive interference, or even, said
Freud, by motivated forgetting.
Memory Construction
Misinformation and
Imagination Effects
Memories are not
stored as exact copies, and they certainly are not retrieved as such. Rather,
we construct our memories, using both stored and new information. Thus, when
child or adult eyewitnesses are subtly exposed to misinformation after an
event, they often believe they saw the misleading details as part of the event.
Source Amnesia
People also exhibit
source amnesia, by attributing something heard, read, or imagined to a wrong
source. Because false memories feel like true memories and are equally durable,
sincerity need not signify reality.
Discerning True and False Memories
Determining the
validity of a memory is difficult. A false memory may feel real and it may be
persistent. Interviewers may ask leading questions, contributing to the
misinformation effect. True memories tend to be more detailed than imagined
ones, which tend to be the gist of the meaning and feelings associated with an
event.
Children’s Eyewitness Recall
Children are
suggestible and, if asked leading questions, can report false events. On the
other hand, if children are interviewed using the cognitive interview technique
in developmentally-appropriate language, recalled memories can be accurate.
Repressed or Constructed Memories of Abuse?
Memory researchers
are especially suspicious of claims of long-repressed memories of sexual abuse,
UFO abduction, or other traumas "recovered" with the aid of a
therapist or suggestive book. More than we once supposed, incest and abuse
happen. But unless the victim was a child too young to remember any early
experiences, such traumas are usually remembered vividly, not banished into an
active but inaccessible unconscious.
Improving Memory
The psychology of
memory suggests concrete strategies for improving memory. These include spaced
study; active rehearsal; encoding of well-organized, vivid, meaningful
associations; mnemonic techniques; returning to contexts and moods that are
rich with associations; recording memories before misinformation can corrupt
them; minimizing interference; and self-testing and rehearsal.