Psychophysics of Pain: Some Insights for Understanding Pain

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Psychophysics of PainSome Insights for
Understanding Pain

• Daniel Algom
• Department of Psychology

In honor of Professor Harvey Babkoff
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The Puzzle of Pain Is It a Puzzle?

• The puzzle Pain is associated with a host of
  emotional motivational and cultural factors.
• The puzzle A stimulus causing intolerable pain
  on one occasion might go hardly noticed on
  another.
• The puzzle Pain can be crippling following
  noxious stimuli, but may fail to occur after
  extensive tissue injury.

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The Puzzle of Pain

• The puzzle Pain may persist after all the
  injured tissue has been healed or removed.
• The puzzle Morphine is more effective in
  reducing clinical pain than reducing pain in the
  laboratory, but the opposite holds with respect
  to placebo.

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What is Pain?

• Given the current preoccupation with the
  physiological, biological, and neural substrates
  associated with pain, it cannot be overemphasized
  that pain is a perceptual experience, not a
  neural reaction.
• The verbal report is the sole genuine expression
  of human pain.

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Livingston, 1953, pp. 68-69

• what counts most with my patient and what counts
  with me as his physician is the amount of pain he
  feels. When a patient needs a surgical operation
  and asks me to perform it, he does not ask how
  deeply the knife will cut, nor would he be
  concerned if I were to tell him that pain signals
  would continue to traverse his nervous system
  after he had gone to sleep. What he asks is, How
  much it will hurt me? He is really asking, how
  much of the inevitable tissue injury he will
  consciously experience as pain

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Drawbacks of the Puzzle

• Tendency to focus on the unique, bizarre and
  paradoxical phenomena.
• Paucity of research/discussion on the measurement
  of the magnitude of pain.
• Limited role to psychophysics of pain. It has
  been dubbed farcical in its wild variability,
  denying a relation between stimulus intensity and
  pain intensity.
• Wall, 1979

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In Fact

• Pain sensitivity is more uniform than that of the
  common senses.
• There is a lawful dependence of pain sensation on
  stimulus intensity.
• In everyday life, pain intensity is proportional
  to the force of the blow, to the heat of the
  iron, to the pressure of the sound, or the depth
  of the wound.

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Livingston, 1943, 1953

• In the majority of instances, pain is
  proportional to the injury (1953, pp. 64).
• We wonder why some insignificant-looking scar
  should give severe pain, or why serious injury is
  not noticed in the excitement of the automobile
  accident

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Therefore

• It is the lawfulness of the stimulus-response
  relationship that enables the puzzle of pain to
  emerge in the first place.
• In the absence of a proportional pain sensation
  there would not have been a puzzle to ponder.
• The exceptions subsumed under he puzzle are
  important, but they are exceptions nonetheless.
  

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Hardy, Wolff Goodell (1940-1955)

• The Dolorimeter Applying the heat of a 500
  1000 watt lamp on a small area of the skin.
• Absolute threshold (N 150, Age 14-74) 220
  millicalories per second per square centimeter.
• All observations within 5 of this value.

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Pain Perception vs. Reaction

• Sensitivity vs Mood Pain threshold measured
  daily over the period of several months while
  recording mood and emotion.
• Mood exhibited wide variation, but the threshold
  remained constant.
• Sensitivity vs Fatigue Pain threshold measured
  after sleep deprivation of 24 hours and/or at
  2-hour intervals.
• Subjective well-being, alertness, and fatigue
  varied considerably but the threshold remained
  constant.

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Pain Perception vs. Reaction

• Independence of threshold and GSR Over a two
  months period both were measured on a daily
  basis.
• GSR reflecting alarm, anxiety, or stress
  changed considerably, but the threshold remained
  constant.

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Pain Perception vs. Reaction

• Distraction and suggestion can alter (elevate)
  pain threshold.
• Reading an adventure story.
• Repeating digits forward or backward.
• Clanging a loud bell concurrently with pain.
• Autosuggestion - having the person convince
  herself than she could not feel pain.
• Each of these manipulations acted to raise
  threshold (approximately by 15).

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Suprathreshold Pain - The Dol Scale
Number of JNDs
Stimulus Intensity (mcal/sec/cm2)
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The Dol Scale Arithmetic Properties

• The method of fractionation The scale erected on
  the basis of judgments of fraction agreed with
  the Dol Scale.
• The Dol Scale has ratio properties. A 4-dol pain
  feels twice intense as a 2-dol pain.
• The sum of 2 JNDs ( 1 dol) represented the same
  difference in all parts of the Dol Scale.
• Pain in dols is associative.

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The Dol Scale Arithmetic Properties

• The numbers on the Dol Scale, representing the
  intensity of pain,
• are capable of being added and divided according
  to the ordinary rules of arithmetic, and it is
  possible to define two dols as both the sum of a
  two 1-dol stimuli and as one-fifths of the
  ceiling pain.
• It is proper also to speak of one pain as being
  either twice as strong as another or as
  equivalent in intensity to the sum of two smaller
  pains.
• Hardy, Wolff Goodell (1948)

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Cross Modality Matching of Pain (Hardy, Wolff
Goodell, 1952)
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Contemporary Pain Psychophysics

• Integrating multiple pains
• (Algom, Raphaeli Cohen-Raz, 1986, 1987)

Estimated pain
Shock intensity (mA)
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Integrating Auditory, Visual, and Electric Pain.
(Algom Meidler, 1990)
Electric Intensity1(mA)
Electric Intensity2(mA)
Estimated pain
Visual intensity (Candlepower)
Visual intensity
Auditory Intensity (SPL)
Auditory Intensity
Electric Intensity5 (mA)
Electric Intensity3 (mA)
Electric Intensity4 (mA)
Estimated pain
Visual intensity
Visual intensity
Visual intensity
Auditory Intensity
Auditory Intensity
Auditory Intensity
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Memory and Perception for Labor Pain (Algom
Lubel, 1994)
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Integration of Perceptual, Remembered and Mental
Pain.(Algom Lindenberg, 1991)
Mental
Remembered
Perceived
Pain Estimates
Shock intensity (mA)
Shock intensity (mA)
Shock intensity (mA)
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Thank you!