Invitation to Psychology

212 Chapter 6 Sensation and Perception

signals through touch and internal sensations,

memories of these signals remain in the nervous

system, including memories of pain, paralysis, and

cramping that occurred prior to amputation. The

result is an inaccurate “body map” in the brain and

pain signals that cannot be shut off.

Vilayanur Ramachandran, the neurologist

who first proposed this explanation of phantom

pain, has developed an extraordinarily simple

but effective treatment for it. Ramachandran

wondered whether he could devise an illusion to

trick the brain of an amputee with phantom arm

pain into perceiving the missing limb as mov-

ing and pain-free. He placed a mirror upright

and perpendicular to the sufferer’s body, such

that the amputee’s intact arm was reflected in

the mirror. From the amputee’s perspective, the

result was an illusion of two functioning arms.

The amputee was then instructed to move both

arms in synchrony while looking into the mir-

ror. With this technique, which has now been

used with many people, the brain is fooled into

thinking its owner has two healthy arms or legs,

resynchronizes the signals—and phantom pain

diminishes or even vanishes (Ramachandran &

Altschuler, 2009). Neurologists have tested this

method with Iraq veterans and are finding it

to be more successful than control therapies in

which patients just mentally visualize having two

intact limbs (Anderson-Barnes et al., 2009; Chan

et al., 2007).

pain can help explain the many instances of severe,

chronic pain that occur without any sign of injury

or disease whatsoever.

Input from

spinal cord

Memories

Emotions

Expectations

Attention

Signals from

brain centers

Abnormal patterns

of activity in a

neural matrix

Pain

Because technology now allows scientists to

study pain at the molecular and cellular level, to-

day we know that the gate-control theory, though

still useful, is incomplete. Pain may also be caused

by changes to the sensitivity of neurons in the

central nervous system (CNS). For example, when

bursts of heat are repeatedly applied to an animal’s

paw, pain receptors in the paw and skin remain

sensitive for several hours. During that time, even

a light, harmless touch will activate the recep-

tors, and applying anesthetic at the site of injury

will not make the receptors return to normal.

Such changes can help explain how once-harmless

stimuli can end up causing pain (Latremoliere &

Woolf, 2009).

An extreme version of pain without injury oc-

curs in phantom pain, in which a person continues

to feel pain that seemingly comes from an arm

or leg that has been amputated, or from a bodily

organ that has been surgically removed. Phantom

limb pain afflicts up to 90 percent of amputees.

The person may feel the same aching, burning, or

sharp pain from sores, calf cramps, throbbing toes,

or even ingrown toenails that he or she endured

before the surgery. Even when the spinal cord has

been completely severed, amputees often continue

to report phantom pain from areas below the

break. There are no nerve impulses for the spinal-

cord gate to block or let through, yet the pain can

be constant and excruciating; some sufferers have

committed suicide.

A leading explanation of phantom pain is

that the brain has reorganized itself: An area in

the sensory cortex that formerly corresponded

to the missing body part has been “invaded” by

neurons from another area. Higher brain centers

then interpret messages from those neurons as

coming from the nonexistent body part (Cruz

et al., 2005; Ramachandran & Blakeslee, 1998).

Even though the missing limb can no longer send

phantom pain The
experience of pain in a
missing limb or other
body part.

After his right leg was destroyed in an explosion while

he was in Iraq, Army Sergeant Nicholas Paupore experi-

enced excruciating phantom limb pain. Even morphine

didn’t help. Then he underwent a simple daily proce-

dure. A mirror was placed at a strategic angle to reflect

his intact leg, tricking his brain into registering two

healthy legs that he could move freely. The pain sub-

sided almost immediately. A year after therapy, he had

only occasional, milder pain, and needed no medication.

In some patients, mirror therapy has eliminated phantom

pain entirely.