Last updated: Wed, Feb 26, 2025
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The effect of what are termed "psychological factors" in the brain's processing of pain. This includes factors such as attention, "emotional state," and expectation or anticipation.
QUESTION: Does expectation always increase perception, or can it also decrease??? QUESTION: look at some actual reported results.... WRT "Effects of Expectation/Anticipation"
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This section is based largely on the chapter by Apkarian, A. V., Bushnell, M. C., and Schweinhardt, P., "Representation of Pain in the Brain", which is Chapter 7 in McMahon, S. B., Koltzenberg, M., Tracy, I., and Turk, D. C., "Wall and Melzack's Textbook of Pain", Elsevier Saunders, 2013. That chapter contains a section titled "Mechanisms Underlying Psychological Modulation of Pain." This current section takes its title from that section.
In A Brief Critique of the Pain Matrix Analysis I will present a critique of some of the concepts which one encounters in that chapter by Apkarian et al. The authors seem to conceptualize attention, emotion, and "psychology" in general as states of the brain which influence pain processing but which are in some important way separate from the states of brain which are pain processing. In A Rational Model of Emotion and Pain, I conceptualize attention and emotion as an integral part of brain processing. I regard this difference in models as basic to a clear understanding of pain experience, and hence enclose some of their terms in quotation marks here.
Early medically harmful studies on primate subjects revealed that the response of individual neurons to controlled painful stimulation is changed based upon the attention of the subject to or distraction from the painful stimulus. Imaging studies have allowed a variety of studies to assess the effects of attention on pain response among humans. Human studies generally show that attention directed to a painful stimulus increases its perceived intensity.
Brain imaging studies on humans have shown that distracting the subject from the painful stimulus modifies the pain reponse in the thalamus, S1, ACC, and IC. Activity in the PAG, and in parts of the ACC and PFC, is increased under distraction. EEG and MEG studies have indicated that modulation of pain processing has early effects on activity in S2 and IC, and later on the ACC.
Changes to pain perception caused by attention/distraction seem to be caused by two factors. One of these is changed processing in the cortex. The other involves activation of descending pain modulation (The Descending Tracts and Descending Pain Modulation).1
Since a human's "emotional state" is both hard to define and hard to measure, experimenters have studied the effect of emotional state on pain processing by using standardized stimuli. Experimenters have available, for instance, photographs of faces that have a graded amount of pleasantness/unpleasantness as evaluated by numbers of humans, including across cultures. Imaging and EEG/MEG studies can then measure brain activations when subjects are exposed to controlled painful stimuli, and compare activations after subjects are exposed to pleasant or neutral pictures versus after exposure to unpleasant pictures. Music and odors can also be graded as to their pleasantness or unpleasantness and used to set subjects' "emotional state."
Subjects generally report a given painful stimulus as more unpleasant when they are in an unpleasant emotional state, and less unpleasant when they are in a pleasant emotional state. The pleasant/unpleasant dimension of pain is the dimension that is most affected by emotional state. Location, quality, and intensity are less affected by emotional state.
Emotional state most affects activation of brain areas that are involved in evaluating the pleasantness/unpleasantness of the pain sensation, especially the ACC and IC.2
Studies have also shown that the anticipation or expectation of pain can activate pain-involved areas of the brain in the absense of a painful stimulus. When pain is expected, areas of the brain that are involved in descending modulation (the PAG, the PFC, and the ventral striatum) are activated prior to occurrence of the painful stimulus.3
Studies on chronic pain patients and depressed individuals have shown that they have enhanced brain activity in response to pain that is anticipated. These same groups are believed to have higher response to painful stimuli in general.4.