Translating the experience of pain into words is challenging, as scientific evidence, literary sources, and personal experience attest. However, language remains the primary means of conveying our own experience of pain to others, including healthcare professionals. The International Association for the Study of Pain (IASP) recently revised the definition of pain as "an unpleasant sensory and emotional experience associated or similar to that associated with actual or potential tissue damage . " In an accompanying note, it is mentioned that “a person’s account of an experience as pain should be respected” , referring to the fact that the subjective nature of pain should not be interpreted as less valid or reliable.
Pain is defined and ultimately assessed through subjective reports: as Gracely (2016) put it: “Much can be inferred from objective measures of anatomy, physiology, and behavior, but verbal report remains the standard by which all other measures are compared . ” This led to the use, in medical research, of questionnaires that were intended to capture different aspects of the pain experience by asking patients to translate their pain into standardized pain descriptors (e.g., McGill Pain Questionnaire—MPQ; Melzack, 1975 ; Main, 2016).
Since pain communication depends significantly on language, it is important to establish how the mind and brain deal with the complex relationships between words and pain. Accumulating evidence suggests that actual physical pain (nociceptive pain) and pain conveyed by words (semantic pain) influence each other at behavioral and neural levels. This evidence clearly shows that the experience of physical pain impacts how we process pain-related words, and that the presentation of pain-related words impacts the experience of physical pain; Therefore, we can consider language as part of the broad set of endogenous modulators that ultimately modulate pain processing and perception. However, despite an increasing number of studies, the neural architecture underlying the bidirectional relationships between language and pain is still not fully understood.
The brain response to a nociceptive stimulus consists of the activation of a complex network of cortical and subcortical structures commonly known as the “pain matrix” . The pain matrix is believed to play a key role in elaborating two important aspects of the nociceptive experience: the sensory-discriminative aspect and the affective-motivational aspect; the affective-motivational aspect is processed by the anterior insula (AI) and the anterior middle cingulate cortex (aMCC), in turn, sometimes called the "medial component" of the pain matrix (because it projects through medial thalamic nuclei specific). Therefore, the thalamus is involved in both the sensory-discriminative and the affective-motivational components , with prominent functions played by different nuclei in one or the other.
A handful of neuroimaging studies in healthy participants have shown that, in the absence of noxious stimuli, brain areas involved in processing pain-related words partly overlap with those thought to be involved in experiencing physical pain, both the affective-motivational component of the pain matrix and also the sensory-discriminative one.
In many different languages, words describing physical pain are often also used to convey so-called social pain , that is, painful feelings associated with actual or potential social rejection, exclusion, or loss (e.g. betrayal). It can be described as a stab, a divorce as a scar, a defeat as something painful .
These ways of referring to social pain are not simply metaphorical extensions taken from otherwise unrelated experiences of physical pain: according to the literature, physical pain and social pain are more neurally intertwined than initially thought. This is not surprising, since social bonds are essential for survival in mammals, and their interruptions represent a threat potentially as relevant as a noxious stimulus.
Injury and neuroimaging studies have shown that physical and social pain partly share the same neural substrates , predominantly in the affective-motivational part of the pain matrix and/or with tasks and stimuli that elicit social pain more powerfully than with standard version of the Cyberball game (for example, by having participants, who recently experienced an unwanted breakup, view a photo of their ex-partner).
In the game Cyberball, participants are led to believe that they are playing online with other real people, when in reality they are playing against the computer. The game consists of throwing the ball to each other. The computer is programmed to initially include the participant in the game and then increase ball exchanges between the other simulated players to exclude the participant. Exclusion in the game Cyberball is considered a form of ostracism, which involves being ignored or excluded by others. It is considered a reliable paradigm for inducing negative feelings of distress, decreased satisfaction of the need to belong, and other psychological responses associated with social exclusion.
Since the affective-motivational component of pain is crucial for signaling an aversive state and for motivating behaviors aimed at reducing or escaping pain, activation of this component was interpreted as a hallmark of the neural overlap of physical and social pain. Some studies on social pain also reported activation of sensory-related brain regions, especially when the neural underpinnings of physical and social pain were tested in the same individuals. In these studies, social pain was predominantly elicited through participant exclusion from a virtual ball game, the Cyberball game.
However, it is still a matter of discussion whether and to what extent social pain operates in the same neural pain matrix as nociceptive stimuli. Although social pain can also be conveyed through words , it has predominantly been studied using either the game Cyberball or non-verbal stimuli reminiscent of socially painful experiences.
The objective of the present study is threefold: (i) to compare the brain areas involved in the experience of nociceptive pain and in the processing of semantic pain conveyed by physical and social words related to pain in the same individuals; (ii) clarify whether semantic pain processing conveyed by physical pain-related words or social pain-related words recruits common or different brain regions; and (iii) define whether the semantic activations of pain concern only the affective-motivational dimension of pain or also the sensory-discriminative dimension. Finding the involvement also of the sensory-discriminative dimension of pain would support the view that pain-related words resonate with past pain experiences, reactivating their memory, whether they are associated with physical or social events.
Methods:
Thirty-four healthy women underwent two fMRI sessions each.
- In the semantic session , participants were presented with positive words, negative non-pain words, words related to physical pain, and words related to social pain.
- In the nociceptive session , participants received mechanical cutaneous stimulations that could be painful or not.
During both sessions, participants were asked to rate the unpleasantness of each stimulus. Linguistic stimuli were also rated in terms of valence, arousal, pain-relatedness, and pain intensity immediately after the semantic session.
Results:
In the nociceptive session , the contrast between "nociceptive stimuli" and "non-nociceptive stimuli" revealed extensive activations in the somatosensory cortices SI, SII, insula, cingulate cortex, thalamus, and dorsolateral prefrontal cortex.
In the semantic session , words associated with social pain, compared to negative non-pain words, showed greater activity in most of the same areas , while words associated with physical pain, compared to Negative words not related to pain only activated the left supramarginal gyrus and partly the postcentral gyrus.
Discussion:
Our results confirm that semantic pain partly shares the neural substrates of nociceptive pain . Specifically, words related to social pain activate a broad network of regions, mostly overlapping with those related to the affective-motivational aspects of nociception, while words related to physical pain overlap with a small group that includes regions related to the sensory-discriminative aspects of nociception. However, most overlap regions are differentially activated under different conditions.
A strength of this study is that, to our knowledge, it is the first to compare nociceptive and semantic pain processing in the same individuals using both words associated with physical and social pain. Overall, the results of this study highlight the presence of extensive overlap in the areas involved in nociceptive and semantic pain processing.
Conclusion In summary, we have revealed that although the areas involved in nociceptive pain experience and semantic pain processing largely overlap, the degree of activity in the various overlapping areas depends on the type of pain conveyed by the words. While processing words that convey physical pain appears to activate the postcentral gyrus, a sensory discriminative area, processing words that convey social pain appears to activate areas associated with the affective-motivational component of pain processing. In most regions we analyzed, the signal increase during processing of words associated with social pain words is not significantly different from that caused by nociceptive stimuli. |
