Pain Theories

Question 1

Briefly describe the intensity theory

Answer 1

• in existence since 400BC
• 1859: experiments to back the theory up

Theory:

• non-noxious or sub-threshold noxious stimuli summate in the spinal cord
• if enough stimuli and signals build up, pain will be experienced

Question 2

Briefly describe the pattern theory

Answer 2

• proposed in the 1920s

Theory:

• there are not separate neurons or pathways for noxious signals
• rather noxious and non-noxious signals have different time patterns, resulting in the creation of different sensations

Question 3

Briefly describe the specificity theory

Answer 3

• in existence for milennia
• popularized by Descarte in 1600s (bell image)

Theory:

• each modality has a separate neuron, separate signal and separate pathway
• existence of ‘pain fibres’

Question 4

Briefly describe the gate control theory

Answer 4

• proposed by Melzack and Wall in 1965

Theory:

• there are ‘gates’ (interneurons) in the dorsal horn that can either inhibit or facilitate the transmission of nociceptive signals
• input from nociceptive neurons (A delta and C fibres) ‘open’ the gate by inhibiting inhibitory interneurons
• input from non-nociceptive neurons (A alpha and beta) ‘closes’ the gate by activating inhibitory interneurons

Question 5

Describe the neuromatrix theory of pain

Answer 5

• proposed by Melzack in 1991

Theory:

• pain is a multidimensional experience with multiple inputs and outputs
• 3 inputs: cognitive evaluative, sensory discriminative and motivational affective
• 3 outputs: pain perception, actin programs, stress regulation programs

Question 6

What are the 3 outputs in the neuromatrix theory of pain?

Answer 6

Pain perception

• sensory
• affective
• cognitive

Action programs
- involuntary and voluntary action patterns

Stress regulation programs

• cortisol
• norepinephrine
• endorphin levels
• immune activity

Question 7

What are the 3 inputs in the neuromatrix model of pain?

Answer 7

Sensory discriminative

• felt sensation of pain (quality, sensation, spatial location)
• thalamus and primary somatosensory cortex

Motivational affective

• emotional component
• limbic system

Cognitive evaluative

• interpretation of pain
• pain beliefs
• higher processing centres

Question 8

What is the classical conditioning theory of motor control?

Answer 8

• people can learn to associate pain with movement via classical conditioning
• this can be protective in the short term when there is actual or potential tissue damage; but unhelpful in the long term when there is no threat of tissue damage

Question 9

What is the protective response theory of motor control?

Answer 9

• movement and motor control is altered as a response to pain and/or injury
• changes can include stiffness, altered biomechanics, altered loading
• changes can be protective in the short term but harmful in the long term (sub-optimal tissue loading can increase risk of future injury)

Question 10

What is the impaired movement theory of motor control?

Answer 10

• sub optimal loading can lead to pain and injury; and pain and injury can lead to sub optimal loading

Question 11

What is tissue creep?

Answer 11

The insidious onset lengthening or deformation of tissue under prolonged and inappropriate load (can be caused by sub-optimal loading and altered motor control in response to pain)