Lecture 9: Pain

Question 1

what is the purpose of pain

Answer 1

The purpose of pain it to signal potential damage to the body in order to react and prevent further damage

Question 2

What is the difference in purpose and duration between actute and chronic pain

Answer 2

Acute Pain (< 6M) - immediate response from injury/disease (limited duration). Responsive to medical treatment

Chronic Pain (> 6M) - Tends to not be responsive to pharmacologic treatment

Question 3

What are Nociceptors?

Answer 3

Nociceptors - Sensory neurons that respond to damaging/potentially damaging stimuli. Primarily free nerve endings specific for pain and temperature (no receptor cells)

Question 4

What is the difference between A-delta fibres and c-fibres

Answer 4

A-delta fibres are used for reflexive pain responses
C - fibres are for slower, more burning types of pain

Question 5

What are the locations of pain signals being sent to the brain?

Answer 5

Pain is sent from sensroy neurons (A-delta or C fibres) to the ipsilateral side of the spinal cord (same side). Pain signal crosses to contralateral (opposite) side of spinal cord.
Transmission ascends spinal cord through brainstem (medualla, pons, midbrain) -> VPL nucleus of thalamus
Signal transmitted from the thalamus to the somatosensory areas of the cerebral cortex

A-delta/C fibres -> spinal cord -> meduall -> pons -> midbrain -> VPL nucleus of thalamus -> somatosensory cortex

Question 6

What does Specificity Theory say about pain?

Answer 6

Specificity Theory: Causal relationship between pain stimulus and receptors (Stimulus Intensity = pain intensity)

Question 7

What are the 3 problems with Specificity Theory

Answer 7

No specific cortical location for pain. Don’t know where its processed
Pain fibres for other purposes (pressure/temp)?
Doesn’t explain disproportionate pain reports

Question 8

What does Pattern Theory say about pain?

Answer 8

Pattern Theory - Nociceptors generate summated signal in the spinal cord. Signal only transmitted if passes threshold

Question 9

What is the problem with Pattern Theory?

Answer 9

oesn’t explain deferred pain (e.g. back pain on period), or pain without injury (and injury without pain)

Question 10

What are the 3 potentional scenarios of Gate-Control Theory?

Answer 10

When there is a lack of input from C-fibres, the inhibitory interneuron is active and suppresses the pain pathway, so the brain doesn’t receive a signal
When there is input from C-fibres, the inhibitory interneuron is inhibited and the pain pathway is active and sends the pain signal
When there is input from A-beta fibres and C-fibres, the inhibitory interneuron is active (from A-beta) and the pain pathway is active and a weaker pain signal sent to the brain

Question 11

What is the Fear avoidance model? What are the 3 points about avoidance? How do we stop this cycle?

Answer 11

Fear avoidance model: idea of fear of pain leads to avoidance behaviour

Avoidance is associated with catastrophizing patients. If pain is interpreted as threatening, fear evolves
* Avoidance behavior (stop exercising leads to further disability and reduced quality of life, mood disorders, further disability, vicious cycle
* Leads to the maintenance or even exacerbation of fear, hypervigilance to internal and external illness information, muscular reactivity
* Physical disuse in terms of deconditioning and guarded movement

Confrontation - Leads to reduction of fear over time

Question 12

What is the Anterior Cingulate Cortex (ACC) and Insular Cortex (IC) associated with?

Answer 12

pain unpleasantness

Question 13

What is the primary and secondary somatosensory cortex (S1 and S2) associated with

Answer 13

pain sensation, location, modality

Question 14

What is the Pre-Frontal Cortex (PFC) assocaited with?

Answer 14

pain regulation (cortical antinociceptive system); descending pathway control

Question 15

what are the 3 Limbic areas assocuated with?

Answer 15

Amygdala -> emotion, fear
Hippocampus -> memory
Hypothalamus -> modulation

Question 16

Describe the Subjective Pain Experience in the brain experiment:

Answer 16

Purpose:
* explore conscious sensory experience from a third- person observation
* identify neural correlates of individual subjective pain experience in relation to others receiving exact same stimulus

Method
* Rated temperature stimuli applied to their forearm and were split into groups based on pain sensitivity (Low = insensitive; High = sensitive)
* fMRI while having leg stimulated with heat

Results:
* Cortical regions related to sensation, attention, and affect were most associated with pain sensitive people vs pain insensitive (pFC, S1, and ACC)
* ACC Activation for 6/6 sensitive participants while No activation for all insensitive participants
* Activation in thalamus for all subjects - shows that the signals were transmitted to the brain
* Validates subjective pain report

Question 17

What is Phantom limb, how can we treat it?

Answer 17

Phantom limb - The sensation that an amputated or missing limb is still attached.
Possible mechanisms - Hyper-exciteability in peripheral nerves, or central nervous system
Possible treatment: Mirror threapy

Question 18

Mirror Therapy

Answer 18

Possible mechanism: mirror neurons
Found in animal studies which fire when animal performs or observes an action
Therefore is receiving tangential input of perception and tactile sensation
May block pain perception of phantom limb

Question 19

What is Congenital universal insensitivity to pain (CUIP)? What is the genetic cause?

Answer 19

Congenital universal insensitivity to pain (CUIP)
inability to perceive physical pain, but can tell the difference from different amounts of touch, temperature etc
Caused by the recessive gene, mutated SCN9 gene
SCN9 gene: responsible for instructions to make the alpha subunit part of the sodium channel (NaV1.7)
* Absence of functioning NaV1.7 channels impairs transmission of pain signals (stops electrical signals from being generated), causing those being insensitive to pain

Question 20

What is Social pain

Answer 20

Being socially excluded feels awful but more than that, it actually hurts

Question 21

What did Jaak Panksepp in the 1970s find?

Answer 21

Morphine calms the distress of social isolation in animals
* E.g., Herman & Panksepp (1978): injections of morphine stopped the distress vocalizations of maternally isolate guinea pigs

Panksepp conjectured that the social distress system piggybacked the more ancient physical pain system (PAG area of brain)
The endogenous brain opioid system may be one of the neurochemical regulators of the distress associated with social separation, as well as the pleasure associated w/ social connection (Eisenberger, 2012)

Question 22

Describe the Swearing study by Stephens & Robertson, 2020

Answer 22

N = 92; Repeated Measures Design
IVs: Type of swear words
* Conventional
* “New”
* Neutral

DVs:
* Ratings of emotion, humour, distraction
* cold pressure pain threshold
* cold pressor pain tolerance
* pain perception score
* change from resting heart rate

Results: participants that used conventional swear words had a increase in pain tolerance. Distraction words didn’t differ from each other. Suggests that the emotion attached to the swear word, changes the meaning and increases pain tolerance

Question 23

Eisenberger et al. (2003)

Answer 23

Participants played a game of Cyber-ball under 3 conditions, while imaging brain activity with fMRI:
* 1. Excluded due to technical difficulties
* 2. Included
* 3. Excluded due to rejection by other players
Found greater activity in the dACC and 2 regions of the right ventrolateral prefrontal cortex during exclusion than during inclusion

Question 24

Social pain implications (Dewall et al.,2010): Experiment 1

Answer 24

Design:
N=62
Randomly assigned participants to receive:
* Daily dose of Tylenol (1000mg) or
* Placebo over period of 21 days

Each evening, participants recorded questions regarding degree to which they felt emotionally hurt during the day

Results:
* Placebo group: no change in hurt feelings over 21 day period
* Tylenol group: significant decline in hurt feelings over the 21 day period

Question 25

Social pain implications (Dewall et al.,2010): Experiment 2

Answer 25

Design:
Randomly assigned to take:
* 1000mg Tylenol Morning
* 1000mg Tylenol at bed or
* Placebo of same dose (n=25)
* 3 weeks later – fMRI lab experiment, ball tossing game (social exclusion task)

Results: Compared to placebo group, participants who took acetaminophen showed less activity in dACC and anterior insula in response to cyberball exclusion

Question 26

Morphine has shown promise in preventing PTSD in people experiencing physical injury from a traumatic event. What brain area did this target, why does this matter?

Answer 26

Brain area of hippocampus or amygdala - interfere with memory consolidation