- a more elaborate behavioural response,
which may include expressing the pain verbally, moaning, shouting, crying, or
complaining. This response may also include typical facial expressions, rubbing
the affected area to
reduce the pain, adopting a body posture that reduces the intensity of the
pain, reducing movement and activity in general, and so on.
The description that 19th-century Scottish explorer
David Livingstone gives of his being attacked by a lion provides eloquent
evidence that pain is not always proportional to the seriousness of the injury:
horribly close to my ear, he shook me as a terrier dog does a rat. The shock produced
… a sort of dreaminess, in which there was no sense of pain nor feeling
of terror, though quite conscious of all that was happening. It was like what
patients … under the influence of chloroform describe, who see all the
operation, but feel not the knife… The shake annihilated fear, and allowed
no sense of horror in looking round at the beast. This peculiar state is probably
produced in all animals killed by the carnivora…”.
Livingstone, Missionary Travels and Researches in South Africa, 1857
A very small number of people are born with a
complete inability to sense pain. They don’t try to protect themselves when
they get hurt (which happens frequently), and they generally die fairly young.
These people are said to have a congenital insensitivity to pain or
Because of this condition, these
people are in constant danger and must rely on learned rules of behaviour to try
to avoid being injured. But rules such as “try not to bump too hard into
stationary objects” and “keep away from things that are hot”
are still just intellectual constructs with none of the edifying power of pain
to repel one’s body from sources of danger. And these rules are even harder
to apply when these people are still children; as a result, such children often
succumb to injuries or internal bleeding that go unnoticed—a simple attack
of appendicitis, for example, can prove fatal.
When these children do survive,
they often suffer injuries to their mouth (because they bite their tongue without
feeling it) or to their eyes (because they fail to remove foreign particles soon
enough). They also commonly experience problems with their joints, as well as
multiple broken bones. Even during sleep, the lack of nociception can lead to
injuries caused by staying in uncomfortable positions for too long.
good example of this condition is the case of a Canadian woman who was born with
an indifference to pain stimuli but with no other sensory deficits, and who was
highly intelligent. Even though she learned early in life to avoid any situations
that might hurt her, she developed a progressive degeneration of her joints and
vertebrae, which rapidly led to a major deformation of her skeleton and an infection
that ended her life at age 28.
The existence of such individuals also confirms
that pain is different from the other senses, and that it does not result from
an excess of any one of them, because the people in question do not have any somatic
sensory disorders other than their nociception deficit.
This deficit may
have many different causes. Some people with this condition appear to have excessively
high levels of endorphins.
The administration of endorphin-blocking substances reduces the intensity of the
stimulus needed for such individuals to experience pain.
This deficit occurs
most often in homogeneous societies where recessive genes, such as the one for
congenital analgesia, can be expressed more readily. For example, in the village
of Gällivare, in northern Sweden, some 40 cases have been reported.
VARIOUS TYPES OF PAIN
Pain is an unpleasant subjective experience.
It is also the main reason that people go to see their doctor. That is not surprising,
because one of the main functions of pain is to tell us when something is wrong
and threatens our physical well-being.
It might seem reasonable to suppose
that sensations of pain are simply due to excessive stimulation of the same receptors
that give us other information about the state of our bodies and the state of
the world. But that is not really the case. Alerting the brain to the dangers
that a painful stimulus represents is quite different from informing it of the
presence of an innocuous tactile stimulus. That is why the perception of pain,
or nociception, depends on pain-specific
pain-specific neural pathways.
baume d’acier (The Balm of Steel), Louis Léopold Boilly, circa
and pathways detect conditions that are potentially harmful to our bodies and
arouse in us the particular conscious
sensation that we call pain.
and pain are thus two different things. Nociception
is the sensory process that produces the nerve signals that trigger pain. Pain
itself is an aching, throbbing, or excruciating subjective sensation coming from
a specific part of the body.
situations, nociception and pain can even occur in each other’s absence.
For example, sometimes an individual’s nociceptors
may be highly activated without any experience of pain—think of the
times that you have cut yourself without even realizing it, because you were so
focused on whatever task you were doing. Similarly, people can be severely injured
but feel no pain, because of intense stress or emotions that they are experiencing
at the same time (see the story of David Livingstone and the lion, in the second
sidebar on this page).
can also experience very intense pain without any major activation of their nociceptors—the
mysterious phenomenon known as neuropathic
Nor is pain always directly
proportional to the seriousness of an illness. Some cancers cause very little
pain until they reach an advanced stage, while other, relatively benign problems
such as kidney stones can be extremely painful.
pain is such a complex, subjective phenomenon, it escapes any highly formalized
definition. The International Association for the Study of Pain (IASP) has nevertheless
attempted one, describing pain as “an unpleasant sensory and emotional experience
associated with actual or potential tissue damage, or described in terms of such
damage”. This definition, as vague as can be, tends to support another one
offered by a doctor who said that ultimately, pain is “anything identified
as such by the patient”.
the IASP’s definition of pain does draw attention to the fact that pain
has two components: one sensory, the other emotional.
sensory component is one that pain shares with the other, conventional
sensory modalities (vision,
hearing, touch, taste, and smell). It is the discriminative component that enables
any sensory modality to identify the location and intensity of a stimulus. In
the case of pain, this component involves the primary
and secondary cortexes.
component of pain, variously described as emotional, affective, or motivational,
involves the anterior
cingulate cortex and the insula. It is this component that makes us subjectively
experience discomfort and that drives us to do something to make it stop, or to
reduce it, or to
flee from it.
Obviously, nobody likes
to be hurt. But pain is nevertheless a valuable thing. Some rare individuals are
born with a total inability to experience pain (see sidebar), and they live with
the constant risk of getting themselves killed because they never realize when
they are hurting themselves. Such individuals have a considerably shorter than
normal life expectancy.
Pain thus plays
a protective role that can be broken down into the following four functions.
Pain acts as a protective alarm system that alerts you to threats to your body’s
integrity and motivates you to do something to prevent serious injury. For example,
if you accidentally touch a hot element on an electric stovetop, a protective
makes you pull your hand away immediately to avoid getting burned.
When you injure part of your body—when you sprain an ankle, for example—pain
can cause you to immobilize it to avoid making the injury any worse.
Painful experiences also teach you to avoid dangerous situations in future, or
to avoid repeating risky behaviours that have caused you injuries in the past.
- Lastly, pain facilitates healing, because
when you are in pain, you tend to stay still and to rest.
if evolution has made pain a kind of signal that we cannot ignore, the purpose
was not to torment us needlessly. Paradoxical as it may seem at first, the purpose
was to ensure our well being and, in many instances, to save our lives. Thus,
things are perfect just the way they are—except when pain is disassociated
from its purpose and becomes
a chronic disease.
The intensity of pain is not always correlated
with the severity of the injury. A given pain stimulus will not always produce
the same reaction in two different people, and the same person may even react
very differently to the same pain stimulus from one day, month, or year to the
next. The reason that our subjective experience of pain varies so greatly is that
so many different sets of factors influence the way that we perceive it.
One such set consists of biological or genetic
factors, such as a person’s sex, or the levels
of certain hormones in his or her body, or his or her ability to respond to stress.
For example, the thresholds at which women begin to feel pain have been
shown to vary with their menstrual cycle. Several studies have also shown that
women’s pain tolerance levels are lower than men’s. Published studies
provide anatomical data to support this finding: the density of nerve fibres is
almost two times higher in women’s skin than in men’s. Hence it is
no surprise that women feel pain more quickly than men do.
the male hormone testosterone helps to mask the discomfort associated with pain.
Many researchers believe that from an evolutionary
perspective, selection would have favoured those males who had higher
testosterone levels and hence could tolerate pain from their injuries longer when
fighting other males in competition for females.
But things aren’t
all that simple. In a study published in the April 2004 edition of the journal
Pain, researchers from McGill University showed that sustained low-level
pain might produce more anxiety in men than in women, even if women feel pain
more intensely than men.
* * *
The perception of pain
is also influenced by cultural
factors. For example, if people have philosophical or religious beliefs
that pain represents a test, a punishment, a necessary evil, or something unavoidable,
those beliefs will definitely affect the way that those people experience pain.
Thus, people who are raised in families or cultures where they are taught to endure
pain stoically will show less discomfort than people who focus their attention
on their pain. For example, cases have been documented in East Africa where people
underwent brain surgery without anesthesia, in the middle of the bush, without
showing any signs of pain.
Another extreme example of cultural factors’
influencing the perception of pain comes from the Tamil community of Malaysia,
which celebrates the festival of Thaipusam every year. As part of the celebrations,
some participants compete in acts of self-mutilation, during which their faces
betray no signs of pain.
* * *
The subjective perception
of pain is also greatly influenced by a multitude of cognitive or psychological
factors. Some of these factors, such as stress and depression,
increase our perception of pain, while others, such as a calm, optimistic attitude,
Distress and anxiety
are two of the cognitive factors that most often amplify pain. In a 1985 study,
British psychologist Gerry Kent noted that people who regarded themselves as anxious
were the ones who reported the highest levels of pain immediately following a
visit to the dentist. Three months later, these people evaluated the level of
pain that they had experienced during that visit as four times higher than than
they had initially. In contrast, the subjects who considered themselves less anxious
reported levels half as high as they had initially.
Other studies have
shown that another factor that can greatly increase pain is simply how much attention
is paid to it by the individuals experiencing it, or by the people close to them.
For example, if the parents of children with a disease that makes their skin itch
express sympathy when their children scratch the itch (even though they have been
told not to), those children will scratch themselves more than children whose
parents do not pay such attention. Similarly, in experiments where men were interviewed
about their sensations of pain, those men who knew that their sympathetic wives
were listening behind a two-way mirror evaluated their pain as more intense than
those men who did not have this sympathetic ear.
Among those cognitive
factors that can reduce our perception of pain, simple distraction has proven
its effectiveness many times over. Experiments have shown that simply listening
to sounds while receiving a painful stimulus reduces the subjective perception
of pain. This finding has also been confirmed by brain-imaging studies showing
that the areas of the brain that are involved in processing pain become less active
when sounds are played.
In ordinary life, too, there are myriad examples
of distractions’ attenuating pain. Haven’t you ever cut yourself and
not even noticed, because you were so wrapped up in the task you were working
on? And yet, if someone else cut you the same way while you had to watch, you
would feel a sharp pain and probably cry out.
There are also many examples
where athletes have sustained heavy blows in the course of a game and continued
playing until the end, only then to discover that they had broken a finger or
are many other reported cases of soldiers who have been seriously injured on the
battlefield but experienced minimal pain. The positive emotions associated with
the knowledge that for them, the war was over, must surely have had something
to do with these spectacular examples of the descending
control of pain.
This phenomenon has been investigated
more systematically in studies comparing civilians and military personnel who
had received similar injuries. The civilians demanded medication more often and
complained much more intensely than the military personnel. One can also speculate
that for for the civilians, such injuries represented not a welcome respite from
adversity, but a prolonged inability to work, loss of income, loss of mobility,
and so on.
The meaning that people ascribe to their pain can thus also
influence its perceived intensity. If someone is stuck at home with a painful
illness or injury but sees it in a positive light—for example, as a chance
to think about the meaning of life, or to get some writing done, or to spend time
with his or her children—that will have beneficial effects on his or her
perception of the pain’s intensity.
muscle spasm is another aspect of the healing process that can
cause pain. Unlike a cramp, which is a painful, involuntary
muscle contraction of short duration, a muscle spasm is a cramp that can
last for days and days, or even years.
Muscle spasms originate in a protective
mechanism: after someone sustains a blow or suffers a fall, or injures themselves
by failing to warm up properly before engaging in some physical activity that
they are unused to, one of their muscles may contract to immobilize the injured
part of the body and thus act as a natural splint or cast. But if the contraction
persists, it can become harmful instead of helpful. When a muscle fails to relax
normally, the results are poor blood circulation and painful congestion. These
in turn make the muscle contract even more tightly and painfully, and the vicious
cycle of muscle spasm is then established.
A stiff neck is
a classic example of a muscle spasm. This spasm in the broad muscles of the neck
usually affects one side more than the other, forcing the person to keep his or
her head facing in one particular direction. Most muscle spasms occur in the back,
between the base of the neck and the lumbar region.
”Physician communication with patients
is the closest thing to magic. It gets communicated in incredibly subtle ways—a
flash in the eye, a smile, a spring in the step.” - Daniel Moerman
A pure placebo is a pharmacologically
inert substance prescribed in a therapeutic context— generally, lactose
in a gel capsule, for oral administration, or normal saline solution, for injection.
By extension, the term “placebo” is also used in expressions such
as “placebo surgery” (which consists solely of making incisions in
the skin) and “placebo therapies” (such as simulated acupuncture treatments).
An impure placebo is a medication that is marketed for
a given condition but is being used for another for which its therapeutic effectiveness
has not been demonstrated—in other words, a drug that is intended for a
specific condition but is diverted to another use. Vitamin C, for instance, is
unquestionably effective for treating scurvy (which results from a deficiency
of this vitamin), but has no proven effects on flu, fatigue, or colds, much less
any proven ability to prevent cancer, even though people sometimes take it for
is a procedure used in clinical drug trials to overcome the influence that doctors
might have on their patients —sometimes even unconsciously—if the
doctors knew whether the substance that they were giving them was actually an
active medication or only a placebo. A double-blind can be achieved in a variety
of ways, such as by having someone other than the doctors determine which subjects
receive what and by keeping this information hidden from the doctors for the duration
of the protocol.
In this way, not only do the patients not know what they
are receiving, but the doctors do not know what they are giving, so that they
cannot influence their patients in any way. The information on who receives the
placebo also remains hidden throughout all the procedures for measuring physiological
effects, and is disclosed only at the end of the trial, when the results are analyzed.
For ethical reasons, patients who participate in double-blind drug trials are
told in advance that they may receive a placebo instead of a medication.
In clinical drug trials, the undesirable side
effects of the medication being tested may sometimes give the researchers some
indications as to which patients have received the actual medication rather than
the placebo. These indications can thus invalidate the double-blind control (see
To avoid this kind of bias, researchers sometimes use
what is known as an active placebo:a substance
that produces the same undesirable effects as the medication being tested, but
without containing the same active molecule. It thus becomes much harder to detect
which patients have received the placebo.
Atropine is an example of a substance
that is used as an active placebo. It is a molecule that binds to muscarinic
acetylcholine receptors, causing symptoms such as dry mouth, constipation,
and elevated body temperature.
example, the harmful effects on health of a mental state such as chronic
stress—feeling oppressed by external events without being able to fight
or flee them—are now well known. But that is not the only way in which
our thoughts can have very tangible effects on our bodies. The placebo
effect is another. But contrary to stress, this is a case where our thoughts
affect our bodies positively.
“placebo” (from the Latin for “I shall please”) was first
used in protocols for testing new medications. In such pharmacological trials,
the researchers always compare two groups of patients to see whether the medication
being tested is effective. One group receives this medication, while the other
receives a pill that seems identical in all respects but does not contain the
active molecule that the medication does. This inert tablet (often a simple sugar
pill) is called the placebo and is given to this group of patients to “please”
them, that is, to make them think that they too are receiving a real medication.
If a comparison of the measurements that
are are then taken on the two groups of patients shows a significant difference
in favour of the group that received the medication, then it is deemed to have
had a real physiological effect. This kind of testing, with a placebo control
group, is the only way to see beyond certain random variations that are inevitable
within each group and that might be misinterpreted as specific effects of the
medication if it were simply tested on a single group of patients.
when researchers began applying such protocols, they observed a phenomenon that
was surprising, to say the least: sometimes, the substance that they had considered
inert alleviated the same kinds of symptoms as the medication itself was expected
to. In other words, the patients who thought that they had taken the medication
but had actually taken nothing but a sugar pill got better! This strange result
is now known as the placebo effect, and it is especially effective for alleviating
symptoms of pain.
The placebo effect
is thus based on a kind of deception, or rather, self-deception,
because it depends entirely on the patient’s own conviction that the treatment
that he or she is receiving will be effective. This form of self-deception shows
just how much power people’s minds can have over their bodies.
placebo effect may even begin the moment that a patient walks into the doctor’s
office, because it is now known that among all
of the factors that contribute to the placebo effect, the relationship of
trust established between the patient and the health-care practitioner is one
of the most powerful.
researchers have long regarded the placebo effect as a nuisance, because it can
always potentially falsify the results of trials of new drugs. To counter this
effect, the first strategy that researchers tried was to introduce the double-blind
procedure into drug trials (see sidebar). Only later did researchers realize all
the implications and potential of this effect, which is seen not only in sick
people but in healthy people as well (see box below).
The above diagram explains why the
placebo effect is often described as a kind of “bonus medication”.
It occurs in about one out of every three patients in addition to the specific
effects of the active ingredient of a medication and can thereby considerably
enhance its effectiveness. Thus the placebo effect plays an active role in the
therapeutic results achieved by every physician every day.
The proportion of patients who show a
placebo effect varies greatly with the nature of the illness being treated.
This proportion ranges from virtually 0 to 100%, with about 33% often cited as
For example, in one study of a tranquilizer,
10 to 20% of the patients who had received only a placebo experienced negative
side effects. (Such “nocebo
effects” are the reverse of the placebo effect but arise from the same
belief that one has received an actual medication.) In another study, of a new
chemotherapy drug, 30% of the individuals who received the placebo lost their
But the percentage response to a placebo often exceeds one-third.
For example, in one study, an analgesic effect was observed in 39% of the people
who had received a placebo after having their wisdom teeth extracted. In another
study, such an effect was seen in 56% of the people who had had a potentially
painful amount of heat applied to the skin of their left hand. In people with
the placebo response rate is about 30%, but it can be as high as 70% in people
whose depression is slight. Lastly, in a study of how the analgesic effects of
a placebo pill varied according to what the subjects were told that it cost, 61%
of the subjects who were told a lower price said that the pill reduced their pain,
while among the subjects who were given a higher price, the figure was 85%. These
results clearly show the sensitivity
of the placebo effect to certain factors.
As regards the percentage
of the effects of active medications that a placebo generally achieves,
the average figure is about 55% for the effects of analgesics such as aspirin
In treatment for depression, numerous studies on tricyclic
antidepressants have shown that the placebo was about 59% as effective as
the actual medication. The percentages when placebos are used in place of insomnia
medications also range from 55 to 60%.
One last example with the
two types of statistics: in a study on the analgesic effect of morphine, 75% of
the patients who received morphine reported experiencing a 50% reduction in their
pain, whereas 36% of those who had received a placebo said that they had experienced
a reduction in pain that they too estimated at 50%.
These results demonstrate
an important fact: not everyone responds to the placebo effect, but not everyone
responds to the active medication either! The human body is a very complex thing.
In a 1972 study that has since become a classic,
medical researcher Barry Blackwell showed that the placebo effect can
be clearly observed in healthy subjects—in this case, in 56 medical
students who agreed to participate in what they were told was an experiment on
the effects of taking a single dose of a stimulant or a sedative drug.
students were divided into four groups. The first group were asked to take one
blue sedative pill, the second two blue sedative pills, the third one pink stimulant
pill, and the fourth two pink stimulant pills. What the students did not know
was that all of these pills were actually placebos that contained nothing but
Of the students who had been told that they were receiving
sedatives, more than two-thirds reported feeling sleepy, and the students who
had taken two of these blue “sedative” pills felt sleepier than those
who had taken only one. Likewise, a large proportion of the students who had been
told that they were receiving stimulants reported feeling less tired.
about a third of the 56 participants complained of side effects such as headaches
and dizziness. And here too, the
effect felt was proportional to the dose of placebo received: in other words,
more severe side effects were reported by the students who had received two pills.
Only 3 of the 56 students said that they had experienced no noticeable effects
after taking the pills.