Neurophysiology of Nociception: Perception

Question 1

What does perception refer to?

Answer 1

the final output of the nociceptive stimulus being transmitted through the pathways of the nervous system and the interpretation of the higher cortical regions

Question 2

What are so diverse behaviors or reactions that occur with perception of pain?

Answer 2

• Protection withdrawal reflexes (i.e. flexor reflex)
• Grimacing, shouting, crying, or even fainting
• Some responses to ANS

Question 3

What are some ANS responses to pain?

Answer 3

• Diaphoresis
• Increased muscle tone
• Increased respiration rate
• Increased heart rate
• Pupil dilation

Question 4

Pain is a complex sensory and emotional experience which involves the activation of what?

Answer 4

the higher centers of the CNS

Question 5

What are the 4 principle cortical regions that appear to play a role in the processing of nociceptive information?

Answer 5

1. Primary somatosensory cortex (S1) in the postcentral gyrus of the parietal lobe
2. Secondary somatosensory cortex (S2) in parietal lobe
3. Anterior part of the cingulate gyrus/cortex (ACC)
4. Insula/insular cortex (IC)

Question 6

What are S1 & S2 implicated in?

Answer 6

the sensory-discriminative component of pain

Question 7

What are the ACC & IC linked to?

Answer 7

the affective-emotional component of pain

Question 8

Where does the spinothalamic tract from the thalamus send projections?

Answer 8

to S1 and S2

Question 9

What happens when damage occurs to S1 & S2?

Answer 9

a loss of the ability to localize and perceive the intensity of nociceptive stimulation

Question 10

Plasticity to the somatosensory regions example?

Answer 10

in patients who have undergone a hemispherectomy, stimulation of the leg contralateral to the removed hemisphere produces activation of the ipsilateral S1 cortex (as opposed to the contralateral activation seen in healthy subjects)

Question 11

A number of studies have implicated the anterior region of the cingulate cortex (ACC) plays a part in what?

Answer 11

nociception processing

Question 12

Injury or surgical lesions to the ACC have shown?

Answer 12

to produce an inhibitory effect for pain perception

Question 13

What does injury to the insular cortex (IC) show?

Answer 13

an absence of emotional responses to nociceptive stimuli

Question 14

ACC has connections to?

Answer 14

the limbic system and appears to play a dominant role in the affective-emotional component of pain

Question 15

What does visceral pain associated with irritable bowel syndrome (IBS) show strong activation of?

Answer 15

ACC

Question 16

What other cortical areas does the IC send projections to?

Answer 16

• S1, S2, and the cingulate cortices

- also contacts limbic structures: amygdala an perirhinal cortex of the hippocampus

Question 17

What does stimulation of the IC produce?

Answer 17

intense emotional sensations of fear

Question 18

With interpretation of pain there is often a discrepancy between what?

Answer 18

objective reality of nociceptive stimulus and the subjective response to it

Question 19

Example of interpretation of pain discrepancies?

Answer 19

in WWII battlefield soldiers suffering from severe battle wounds often reported experiencing minimal or no pain
- evidence of Top down/psychological effects on pain interpretation

Question 20

What is the “placebo effect”?

Answer 20

the psychological response following the administration of a pharmacologically inert “treatment”

Question 21

Who discovered the placebo effect?

Answer 21

Henry Beecher while woking as a medic in WWII

Question 22

How did Beecher utilize the placebo affect?

Answer 22

after running out of morphine in WWII, he replaced it with simple saline solution but continued telling the wounded soldiers it was morphine
- almost half of the soldiers reported that the solution actually reduced or eliminated their pain