Invitation to Psychology

Chapter 6 Sensation and Perception 213

areas of the brain, which is just what would have

happened had they taken a real pain killer.

Expectations about pain are affected not only

by placebos but also by your environment (does

it make you feel safe or apprehensive?), what

your doctor tells you, psychological states such as

anxiety or depression, and cultural beliefs about

The Pros and Cons of Punishment

expressing distress. These nonmedical influences

contribute to the rise and fall in pain epidemics,

such as mysterious outbreaks of back pain, whip-

lash, and repetitive-motion injuries (Gawande,

1998). People who suffer during such epidemics

are not faking it, and their pain is not “just in their

heads.” But it may be in their brains.

Watch the Video In the Real World: Managing

Pain at MyPsychLab

The environment Within Lo 6.25

We usually think of our senses as pipelines to

the world around us, but two senses keep us in-

formed about the movements of our own bodies.

Kinesthesis tells us where our bodily parts are

located and lets us know when they move. This

information is provided by pain and pressure re-

ceptors located in the muscles, joints, and tendons.

Without kinesthesis, you would have trouble with

any voluntary movement. Think of how hard

it is to walk when your leg has fallen asleep or

how awkward it feels to chew when a dentist has

numbed your jaw.

equilibrium, or the sense of balance, gives us

information about our bodies as a whole. Along

kinesthesis [KiN-es-

THee-sís] The sense of

body position and move-

ment of body parts; also

called kinesthesia.

equilibrium The sense

of balance.

The Psychology of Pain. Psychological as
well as physiological factors affect the severity of
chronic pain and a person’s reactions to it. When
people dwell on their pain and talk about it con-
stantly, or begin to define themselves as a sick,
suffering person, their pain typically intensifies
(Pincus & Morley, 2001). Conversely, when they
are distracted, they may not feel their pain as se-
verely as they usually would.
Expectations also exert a powerful influence.
In one study, volunteers were trained to expect
jolts of heat applied to their legs after a tone
sounded. The longer the delay between the tone
and the heat, the stronger the heat. Functional
MRI showed that the stronger the pain the vol-
unteers expected to feel, the greater the activity
in certain brain regions before actual delivery of
the pain—and most of these regions overlapped
with those that responded to the pain itself. But
eventually the delay stopped being predictable.
Sometimes a moderate jolt followed a long de-
lay, and sometimes a severe jolt followed a short
delay. When the volunteers expected a moder-
ate jolt and instead received a more painful one,
their self-reported pain fell by 28 percent, com-
pared with when they expected the most painful
heat and actually got it (Koyama et al., 2005; see
Figure 6.12). This decrease was equal to what they
would have experienced had they received a shot
of morphine!
Such findings suggest a mechanism for how
placebos reduce pain: When placebos affect ex-
pectations (“I’m going to get relief”), they also
affect the brain mechanisms underlying pain.
Volunteers in another study had an “analgesic
cream” (actually a placebo) rubbed on their skin
before getting a painful shock to the wrist; MRI
scans showed decreased activity in the pain matrix,
the pain-sensitive areas of their brains (Wager et
al., 2004). And when diabetes patients with painful
nerve damage were given either active medication
or an inactive placebo and rated their pain before
and after treatment, 62 percent of the improve-
ment in the medication group was attributable to
the placebo effect (Häuser et al., 2011).
Placebos may also promote the production of
endorphins, the body’s natural pain-relieving opi-
ates. Researchers gave volunteers a slow, harmless
injection of a pain-inducing solution in the jaw and
had them rate their pain level (Zubieta et al., 2005).
As the injection continued, the researchers told
some of the participants (falsely) that a pain-reliev-
ing serum had been added and again asked all of
the subjects to rank their discomfort. Throughout
the procedure, PET scans tracked the activity of
endorphins in the subjects’ brains. Those who got
the placebo produced endorphins in pain-control

2

4

Experienced pain intensity

Expected/got

intense heat

Expected/got

moderate heat

Expected

moderate/got

intense heat

0

6

Figure 6.12 expectations and Pain

When people expected moderate heat but got intense

heat (blue bar), their self-reported pain was lower than

it would have been had they expected the intense heat

(green bar).