PERCEPTION OF PAIN, PHANTOM LIMBS

THE PERCEPTION OF PAIN

Pain is an unpleasant yet important function for survival: warning system (but not all pain is needed for survival).

There are two different pathways to the brain on which pain can travel - information brought from free nerve endings in the skin to the brain via two different systems:

1) fast pathways - registers localized pain (usually sharp pain) and sends the information to the cortex in a fraction of a second. EX. - cut your finger with a knife.

2) slow pathways - sends information through the limbic system which takes about 1-2 seconds longer than directly to the cortex (longer lasting, aching/burning).

Factors in Pain Perception - not an automatic result of stimulation:

1) expectations - research shown that our expectations about how much something will hurt can effect our perception.

Melzack - indicated that believing that something will be very painful helps us prepare for it.

For example - child birth: Lamaze method falsely leads us to believe it won't be painful. Maybe if we know it will be bad we can adequately prepare to handle it.

another example - placebo effect - if we believe pain has stopped, it may.

2) personality - people with negative types of personalities often have more pain. E

For example - a very uptight person may experience muscle pains, back pains, etc.

3) mood - bad moods, angry, unhappy, etc, can lead to the experience of increased pain.

For example - study manipulated moods of subjects then asked them to complete questionnaires of pain perception. Those in negative mood group reported significantly more pain than other subjects.

So, it seems that our brains can regulate, control, determine, and even produce pain.

THEORIES OF PAIN PERCEPTION

1) Gate Control Theory (Melzack & Walls, 1965) - incoming pain must pass through a "gate" located in the spinal cord which determines what information about pain will be sent to the brain. So, it can be opened to allow pain through or closed to prevent pain from being perceived.

The Gate - actually a neural network controlled by the brain. Located in an area of the spinal cord called the Substansia Gelatinosa. There are two types of nerve fibers in this area:

a) large - sends fast signals and can prevent pain by closing the gate.

b) small - sends slower signals which open the gate. So - when pain occurs it is because the large fibers are off and the small are on, opening the gate.

Since the gate is controlled by the brain, he factors discussed earlier (expectations, mood, personality) influence the functioning of the gate.

Contradiction to Gate Control Theory:

1) endorphins - the body's own pain killers (morphine-like). May explain acupuncture, acupressure, pain tolerance during last two weeks of pregnancy, etc.

BUT- endorphins may work with the gate control theory - maybe pain is perceived, endorphins are released, so the brain no longer needs the signals and closes the gate.

 PHANTOM LIMBS

ability to feel pain, pressure, temperature, and many other types of sensations including pain in a limb that does not exist (either amputated or born without).

the feelings and the pain are sometimes so life-like that person attempts to pick things up with phantom hand, step with phantom foot or leg, etc. Often person feels phantom moving in perfect coordination with the rest of the body - some report a missing arm extending outward at a 90 degree angle so they turn sideways when going through a doorway.

may occur right after amputation or not until years later.

often felt as part of the body (belonging to the rest of the body). EX. - with a missing leg, some report having a phantom foot but not the rest of the leg. Still, the foot feels as though it is part of the body.