In-Depth Notes on Pain and Its Measurement
Definition of Pain
- Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
- It is a universal human experience and is also felt by many animals (e.g., birds and mammals).
Nociceptors
- Special receptors called nociceptors are crucial for the sensation of pain, localized in various tissues of the body.
- Pain can be evoked by:
- Hot stimuli
- Cold stimuli
- Mechanical stimuli (pressure, tension)
- Chemical stimuli (e.g., lack of oxygen, acids)
Nociception vs. Pain
- Nociception refers to the processing of pain information, exemplified by the withdrawal reflex after touching a hot surface.
- Key differences between pain and nociception:
- Pain has a top-down element (influence of expectations and meaning).
- Pain includes subjective suffering, requiring conscious awareness.
Top-Down Influences
- Factors such as expectation can modify the pain experience:
- Placebo analgesia can completely remove pain.
- Placebo hyperalgesia can induce pain without nociceptive input.
Pain Assessment
- Pain experience is multidimensional, involving:
- Sensory aspect (intensity)
- Affective-evaluative aspect (discomfort/unpleasantness)
- Visual analogue scales are often used for assessment (10 cm scale).
- Pain Threshold: Minimal intensity perceived as painful.
- Pain Tolerance: Level of discomfort causing avoidance reaction (e.g., participant stopping the experiment).
- Substantial individual differences exist regarding pain threshold and tolerance.
Physiological Changes
- Pain leads to sympathetic activation, observable via:
- Changes in heart rate (HR)
- Blood pressure (BP)
- Electodermal activity (EDA)
- Changes are usually proportional to pain intensity but vary between individuals.
Experimental Pain Types
- Four common types of pain in research:
- Cold Pressure Test:
- Participants submerge hand in icy water (4 °C).
- Pain threshold: Time when first pain is reported.
- Pain tolerance: Time when the participant removes their hand.
- Stimulation lasts a maximum of 3 minutes.
- Ischemic Pain Test:
- Applied on the striated muscles by restricting blood flow.
- Participants squeeze a hand exerciser; thresholds are noted post-exercise.
- Stimulation can last a maximum of 15 minutes.
- Thermal Pain Test:
- Utilizes a device that prevents skin damage by carefully controlling temperature.
- Pain threshold: Temperature perceived as slightly painful.
- Pain tolerance: Temperature evoking interruption of stimulation.
Safety in Experimental Pain
- All methods should ensure no harm to participants.
- Respect participant's discomfort and terminate stimulation if necessary.
Conclusion
- Generalization of experimental findings to spontaneous pain should be done cautiously due to differences in controllability and uncertainty
