Lecture 9: Pain Flashcards
what is the purpose of pain
The purpose of pain it to signal potential damage to the body in order to react and prevent further damage
What is the difference in purpose and duration between actute and chronic pain
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
What are Nociceptors?
Nociceptors - Sensory neurons that respond to damaging/potentially damaging stimuli. Primarily free nerve endings specific for pain and temperature (no receptor cells)
What is the difference between A-delta fibres and c-fibres
A-delta fibres are used for reflexive pain responses
C - fibres are for slower, more burning types of pain
What are the locations of pain signals being sent to the brain?
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
What does Specificity Theory say about pain?
Specificity Theory: Causal relationship between pain stimulus and receptors (Stimulus Intensity = pain intensity)
What are the 3 problems with Specificity Theory
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
What does Pattern Theory say about pain?
Pattern Theory - Nociceptors generate summated signal in the spinal cord. Signal only transmitted if passes threshold
What is the problem with Pattern Theory?
oesn’t explain deferred pain (e.g. back pain on period), or pain without injury (and injury without pain)
What are the 3 potentional scenarios of Gate-Control Theory?
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
What is the Fear avoidance model? What are the 3 points about avoidance? How do we stop this cycle?
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
What is the Anterior Cingulate Cortex (ACC) and Insular Cortex (IC) associated with?
pain unpleasantness
What is the primary and secondary somatosensory cortex (S1 and S2) associated with
pain sensation, location, modality
What is the Pre-Frontal Cortex (PFC) assocaited with?
pain regulation (cortical antinociceptive system); descending pathway control
what are the 3 Limbic areas assocuated with?
Amygdala -> emotion, fear
Hippocampus -> memory
Hypothalamus -> modulation
Describe the Subjective Pain Experience in the brain experiment:
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
What is Phantom limb, how can we treat it?
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
Mirror Therapy
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
What is Congenital universal insensitivity to pain (CUIP)? What is the genetic cause?
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
What is Social pain
Being socially excluded feels awful but more than that, it actually hurts
What did Jaak Panksepp in the 1970s find?
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)
Describe the Swearing study by Stephens & Robertson, 2020
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
Eisenberger et al. (2003)
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
Social pain implications (Dewall et al.,2010): Experiment 1
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
