The Two Sides of Pain Communication: Effects of Pain Expressiveness on Vicarious Brain Responses Revealed in Chronic Back Pain Patients

Graded brain fMRI response to somatic and visual acupuncture stimulation

Increased stimulation can enhance acupuncture clinical response; however, the impact of acupuncture stimulation as "dosage" has rarely been studied. Furthermore, acupuncture can include both somatic and visual components. We assessed both somatic and visual acupuncture dosage effects on sensory ratings and brain response. Twenty-four healthy participants received somatic (needle inserted, manually stimulated) and visual (needle video, no manual stimulation) acupuncture over the leg at three different dosage levels (control, low-dose, and high-dose) during functional magnetic resonance imaging (fMRI). Participants reported the perceived deqi sensation for each acupuncture dose level. Blood-oxygen-level dependent imaging data were analyzed by general linear model and multivariate pattern analysis. For both somatic and visual acupuncture, reported deqi sensation increased with increased dosage of acupuncture stimulation. Brain fMRI analysis demonstrated that higher dosage of somatic acupuncture produced greater brain responses in sensorimotor processing areas, including anterior and posterior insula and secondary somatosensory cortex. For visual acupuncture, higher dosage of stimulation produced greater brain responses in visual-processing areas, including the middle temporal visual areas (V5/MT+) and occipital cortex. Psychophysical and psychophysiological responses to both somatic and visual acupuncture were graded in response to higher doses. Our findings suggest that acupuncture response may be enhanced by the dosage of needling-specific and nonspecific components, represented by different neural mechanisms.

Ongoing first-hand pain facilitates somatosensory resonance but inhibits affective sharing in empathy for pain

Alterations of empathy for others' pain among patients with chronic pain remained inconsistent. Here, applying a capsaicin-based ongoing pain model on healthy participants, this study investigated how ongoing first-hand pain influences empathic reactions to vicarious pain stimuli. Healthy participants were randomly treated with topical capsaicin cream (capsaicin group) or hand cream (control group) on the left forearm. Video clips showing limbs in painful and non-painful situations were used to induce empathic responses. The capsaicin group showed greater empathic neural responses in the right primary somatosensory cortex (S1) than the control group but smaller responses in the left anterior insula (AI) accompanied with smaller empathic pain-intensity ratings. Notably, the intensity of ongoing pain negatively correlated with empathy-related neural responses in the left AI. Inter-subject phase synchronization analysis was used to assess stimulus-dependent dynamic functional connectivity within or between brain regions engaged in pain empathy. The capsaicin group showed greater empathy-related neural synchronization within S1 and between S1 and AI, but less synchronization within AI and between AI and MCC. Behaviorally, the differential inter-subject pain-intensity rating alignment between painful and non-painful videos was more positive for the capsaicin group than for the control group, and this effect was partially mediated by the inter-subject neural synchronization between S1 and AI. These results suggest that ongoing first-hand pain facilitates neural activation and synchronization within brain regions associated with empathy-related somatosensory resonance at the cost of inhibiting activation and synchronization within brain regions engaged in empathy-related affective sharing.

Impaired Empathic Abilities among Patients with Complex Regional Pain Syndrome (Type I)

OBJECTIVE

The aims of this study were to evaluate differences in empathic abilities between patients with complex regional pain syndrome (CRPS) Type I and healthy control subjects (HCs) and to assess correlations between empathic abilities and multidimensional aspects of pain.

METHODS

Empathic ability was measured in 32 patients with CRPS Type I and in 36 HCs using the Interpersonal Reactivity Index (IRI). A comprehensive assessment of pain was conducted in the patient group using the West Haven-Yale Multidimensional Pain Inventory (WHYMPI). Psychiatric symptoms were assessed using the Beck Depression and Anxiety Inventories (BDI and BAI), and quality of life was evaluated using the WHO Quality of Life (WHOQOL-BREF) questionnaire.

RESULTS

Patients with CRPS showed impaired cognitive and emotional empathic abilities compared with HCs. Significantly lower levels of perspective taking and empathic concern and higher levels of personal distress on the IRI were exhibited by the patient group. Perspective taking and personal distress were associated with affective distress and poor quality of life in social contexts (BDI, BAI, and WHOQOL). However, empathic concern was positively correlated with pain severity and social support from others (WHYMPI).

CONCLUSION

A tendency toward self-oriented distress in social cognition was exhibited among patients with CRPS Type I. Impaired empathic ability was shown to have potentially negative effects on subjective emotional outcomes and social performance in the lives of patients. Interventions to improve emotional awareness and theory of mind would be beneficial for enhancing social functioning in patients with CRPS Type I.

Mutual influences of pain and emotional face processing

The perception of unpleasant stimuli enhances whereas the perception of pleasant stimuli decreases pain perception. In contrast, the effects of pain on the processing of emotional stimuli are much less known. Especially given the recent interest in facial expressions of pain as a special category of emotional stimuli, a main topic in this research line is the mutual influence of pain and facial expression processing. Therefore, in this mini-review we selectively summarize research on the effects of emotional stimuli on pain, but more extensively turn to the opposite direction namely how pain influences concurrent processing of affective stimuli such as facial expressions. Based on the motivational priming theory one may hypothesize that the perception of pain enhances the processing of unpleasant stimuli and decreases the processing of pleasant stimuli. This review reveals that the literature is only partly consistent with this assumption: pain reduces the processing of pleasant pictures and happy facial expressions, but does not - or only partly - affect processing of unpleasant pictures. However, it was demonstrated that pain selectively enhances the processing of facial expressions if these are pain-related (i.e., facial expressions of pain). Extending a mere affective modulation theory, the latter results suggest pain-specific effects which may be explained by the perception-action model of empathy. Together, these results underscore the important mutual influence of pain and emotional face processing.