Modulation of pain processing in hyperalgesia by cognitive demand

Reward and motivation in pain and pain relief

Pain is fundamentally unpleasant, a feature that protects the organism by promoting motivation and learning. Relief of aversive states, including pain, is rewarding. The aversiveness of pain, as well as the reward from relief of pain, is encoded by brain reward/motivational mesocorticolimbic circuitry. In this Review, we describe current knowledge of the impact of acute and chronic pain on reward/motivation circuits gained from preclinical models and from human neuroimaging. We highlight emerging clinical evidence suggesting that anatomical and functional changes in these circuits contribute to the transition from acute to chronic pain. We propose that assessing activity in these conserved circuits can offer new outcome measures for preclinical evaluation of analgesic efficacy to improve translation and speed drug discovery. We further suggest that targeting reward/motivation circuits may provide a path for normalizing the consequences of chronic pain to the brain, surpassing symptomatic management to promote recovery from chronic pain.

Disrupted functional connectivity of the periaqueductal gray in chronic low back pain

Chronic low back pain is a common neurological disorder. The periaqueductal gray (PAG) plays a key role in the descending modulation of pain. In this study, we investigated brain resting state PAG functional connectivity (FC) differences between patients with chronic low back pain (cLBP) in low pain or high pain condition and matched healthy controls (HCs). PAG seed based functional connectivity (FC) analysis of the functional MR imaging data was performed to investigate the difference among the connectivity maps in the cLBP in the low or high pain condition and HC groups as well as within the cLBP at differing endogenous back pain intensities. Results showed that FC between the PAG and the ventral medial prefrontal cortex (vmPFC)/rostral anterior cingulate cortex (rACC) increased in cLBP patients compared to matched controls. In addition, we also found significant negative correlations between pain ratings and PAG–vmPFC/rACC FC in cLBP patients after pain-inducing maneuver. The duration of cLBP was negatively correlated with PAG–insula and PAG–amygdala FC before pain-inducing maneuver in the patient group. These findings are in line with the impairments of the descending pain modulation reported in patients with cLBP. Our results provide evidence showing that cLBP patients have abnormal FC in PAG centered pain modulation network during rest.

Our results provide evidence showing that cLBP patients have abnormal FC in PAG centered pain modulation network during rest, which might have important treatment implications.

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cLBP patients exhibited enhanced PAG–mPFC coupling.

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cLBP duration was correlated with PAG–mPFC coupling.

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Pain intensity was correlated with PAG–insula and PAG–amygdala coupling.

The effect of acupuncture needle combination on central pain processing--an fMRI study

Background

Empirical acupuncture treatment paradigm for acute pain utilizing Tendinomuscular Meridians (TMM) calls for the stimulation of Ting Points (TPs) and Gathering point(GP). This study aims to compare the supraspinal neuronal mechanisms associated with both TPs and GP needling (EA3), and TPs needling alone (EA2) with fMRI.

Results

A significant (P < 0.01) difference between pre-scan (heat Pain) HP, and post-EA HP VAS scores in both paradigms was noted (n = 11). The post-EA HP VAS score was significantly (P < 0.05) lower with EA3 comparing to EA2 Within-group random effect analysis indicated that EA3+HP>EA3 (condition EA3+HP subtracted by condition EA3) appeared to exert a significant degree of activity suppression in the affective supraspinal regions including the IPL, anterior cingulate cortex (ACC) and the insular cortex (IN). This level of suppression was not observed in the EA2+HP>EA2 (condition EA2+HP subtracted by condition EA2) within-group random effect analysis Between-group random effect analysis indicated that EA3 induced a significantly (P < 0.01, cluster size threshold 150) higher degree of deactivation than EA2 in several pain related supraspinal regions including the right prefrontal cortex, rostral anterior cingulate (rACC), medial cingulate cortex, left inferior frontal lobe and posterior cerebellum. The 2-factor ANOVA in those regions indicated both rACC and posterior cerebellum had a significant (P < 0.01) needle effect, and the right prefrontal area showed a significant (P < 0.01) HP effect. However, a significant interaction between the two factors was only found in the right prefrontal lobe. Granger causality analysis showed EA3 induced a much higher degree of inference among HP related supraspinal somatosensory, affective and modulatory components than EA2. Deactivation pattern at the medullary-pontine area casted a direct inference on the deactivation pattern of secondary somatosensory cortices which also affected the deactivation of the IN.

Conclusions

While both EA2 and EA3 induced a significant degree of deactivation in the human brain regions related to pain processing, the addition of GP stimulation further exerts an inhibitory effect on the ascending spinoreticular pain pathway. Therefore, different needling position as mandated in different empirical acupuncture treatment paradigms may play a different role in modulating pain related neuronal functions.

Fluctuating experimental pain sensitivities across the menstrual cycle are contingent on women's romantic relationship status

We explored the social-signaling hypothesis that variability in exogenous pain sensitivities across the menstrual cycle is moderated by women's current romantic relationship status and hence the availability of a solicitous social partner for expressing pain behaviors in regular, isochronal ways. In two studies, we used the menstrual calendars of healthy women to provide a detailed approximation of the women's probability of conception based on their current cycle-day, along with relationship status, and cold pressor pain and ischemic pain sensitivities, respectively. In the first study (n = 135; 18-46 yrs., Mage = 23 yrs., 50% natural cycling), we found that naturally-cycling, pair-bonded women showed a positive correlation between the probability of conception and ischemic pain intensity (r = .45), associations not found for single women or hormonal contraceptive-users. A second study (n = 107; 19-29 yrs., Mage = 20 yrs., 56% natural cycling) showed a similar association between greater conception risk and higher cold-pressor pain intensity in naturally-cycling, pair-bonded women only (r = .63). The findings show that variability in exogenous pain sensitivities across different fertility phases of the menstrual cycle is contingent on basic elements of women's social environment and inversely correspond to variability in naturally occurring, perimenstrual symptoms. These findings have wide-ranging implications for: a) standardizing pain measurement protocols; b) understanding basic biopsychosocial pain-related processes; c) addressing clinical pain experiences in women; and d) understanding how pain influences, and is influenced by, social relationships.

Supraspinal characterization of the thermal grill illusion with fMRI

Background

Simultaneous presentation of non-noxious warm (40°C) and cold (20°C) stimuli in an interlacing fashion results in a transient hot burning noxious sensation (matched at 46°C) known as the thermal grill (TG) illusion. Functional magnetic resonance imaging and psychophysical assessments were utilized to compare the supraspinal events related to the spatial summation effect of three TG presentations: 20°C/20°C (G2020), 20°C/40°C (G2040) and 40°C/40°C (G4040) with corresponding matched thermode stimuli: 20°C (P20), 46°C (P46) and 40°C (P40) and hot pain (HP) stimuli.

Results

For G2040, the hot burning sensation was only noted during the initial off-line assessment. In comparison to P40, G4040 resulted in an equally enhanced response from all supraspinal regions associated with both pain sensory/discriminatory and noxious modulatory response. In comparison to P20, G2020 presentation resulted in a much earlier diminished/sedative response leading to a statistically significantly (P < 0.01) higher degree of deactivation in modulatory supraspinal areas activated by G4040. Granger Causality Analysis showed that while thalamic activation in HP may cast activation inference in all hot pain related somatosensory, affective and modulatory areas, similar activation in G2040 and G2020 resulted in deactivation inference in the corresponding areas.

Conclusions

In short, the transient TG sensation is caused by a dissociated state derived from non-noxious warm and cold spatial summation interaction. The observed central dissociated state may share some parallels in certain chronic neuropathic pain states.

Does cognitive functioning predict chronic pain? Results from a prospective surgical cohort

It is well established that chronic pain impairs cognition, particularly memory, attention and mental flexibility. Overlaps have been found between the brain regions involved in pain modulation and cognition, including in particular the prefrontal cortex and the anterior cingulate cortex, which are involved in executive function, attention and memory. However, whether cognitive function may predict chronic pain has not been investigated. We addressed this question in surgical patients, because such patients can be followed prospectively and may have no pain before surgery. In this prospective longitudinal study, we investigated the links between executive function, visual memory and attention, as assessed by clinical measurements and the development of chronic pain, its severity and neuropathic symptoms (based on the 'Douleur Neuropathique 4' questionnaire), 6 and 12 months after surgery (total knee arthroplasty for osteoarthritis or breast surgery for cancer). Neuropsychological tests included the Trail-Making Test A and B, and the Rey-Osterrieth Complex Figure copy and immediate recall, which assess cognitive flexibility, visuospatial processing and visual memory. Anxiety, depression and coping strategies were also evaluated. In total, we investigated 189 patients before surgery: 96% were re-evaluated at 6 months, and 88% at 12 months. Multivariate logistic regression (stepwise selection) for the total group of patients indicated that the presence of clinical meaningful pain at 6 and 12 months (pain intensity ≥ 3/10) was predicted by poorer cognitive performance in the Trail Making Test B (P = 0.0009 and 0.02 for pain at 6 and 12 months, respectively), Rey-Osterrieth Complex Figure copy (P = 0.015 and 0.006 for pain at 6 and 12 months, respectively) and recall (P = 0.016 for pain at 12 months), independently of affective variables. Linear regression analyses indicated that impaired scores on these tests predicted pain intensity (P < 0.01) and neuropathic symptoms in patients with pain (P < 0.05), although the strength of the association was less robust for neuropathic symptoms. These results were not affected by the type of surgery or presurgical pain, similar findings being obtained specifically for patients who initially had no pain. In conclusion, these findings support, for the first time, the notion that premorbid limited cognitive flexibility and memory capacities may be linked to the mechanisms of pain chronicity and probably also to its neuropathic quality. This may imply that patients with deficits in executive functioning or memory because of cerebral conditions have a greater risk of pain chronicity after a painful event.

Cognitive-behavioral therapy increases prefrontal cortex gray matter in patients with chronic pain

Several studies have reported reduced cerebral gray matter (GM) volume or density in chronic pain conditions, but there is limited research on the plasticity of the human cortex in response to psychological interventions. We investigated GM changes after cognitive-behavioral therapy (CBT) in patients with chronic pain. We used voxel-based morphometry to compare anatomic magnetic resonance imaging scans of 13 patients with mixed chronic pain types before and after an 11-week CBT treatment and to 13 healthy control participants. CBT led to significant improvements in clinical measures. Patients did not differ from healthy controls in GM anywhere in the brain. After treatment, patients had increased GM in the bilateral dorsolateral prefrontal, posterior parietal, subgenual anterior cingulate/orbitofrontal, and sensorimotor cortices, as well as hippocampus, and reduced GM in supplementary motor area. In most of these areas showing GM increases, GM became significantly higher than in controls. Decreased pain catastrophizing was associated with increased GM in the left dorsolateral prefrontal and ventrolateral prefrontal cortices, right posterior parietal cortex, somatosensory cortex, and pregenual anterior cingulate cortex. Although future studies with additional control groups will be needed to determine the specific roles of CBT on GM and brain function, we propose that increased GM in the prefrontal and posterior parietal cortices reflects greater top-down control over pain and cognitive reappraisal of pain, and that changes in somatosensory cortices reflect alterations in the perception of noxious signals.

PERSPECTIVE

An 11-week CBT intervention for coping with chronic pain resulted in increased GM volume in prefrontal and somatosensory brain regions, as well as increased dorsolateral prefrontal volume associated with reduced pain catastrophizing. These results add to mounting evidence that CBT can be a valuable treatment option for chronic pain.

Cerebral activation during von Frey filament stimulation in subjects with endothelin-1-induced mechanical hyperalgesia: a functional MRI study

Endothelin-1 (ET-1) is an endogenously expressed potent peptide vasoconstrictor. There is growing evidence that ET-1 plays a role in the pain signaling system and triggers overt nociception in humans. The underlying neuronal pathways are still a matter of great debate. In the present study, we applied an intradermal ET-1 sensitization model to induce mechanical hyperalgesia in healthy subjects. Functional magnetic resonance imaging (fMRI) was used to tease out the cortical regions associated with the processing of ET-1-induced punctate hyperalgesia, as compared to a nonnoxious mechanical stimulation of the contralateral arm. Von Frey hair testing revealed the presence of increased responsiveness to punctate stimulation in all subjects. Activational patterns between nonpainful control stimulation and hyperalgesic stimulation were compared. Two major observations were made: (1) all cortical areas that showed activation during the control stimulation were also present during hyperalgesic stimulation, but in addition, some areas showed bilateral activation only during hyperalgesic stimulation, and (2) some brain areas showed significantly higher signal changes during hyperalgesic stimulation. Our findings suggest that injection of ET-1 leads to a state of punctate hyperalgesia, which in turn causes the activation of multiple brain regions. This indicates that ET-1 activates an extended neuronal pathway.

Identifying neural patterns of functional dyspepsia using multivariate pattern analysis: a resting-state FMRI study

BACKGROUND

Previous imaging studies on functional dyspepsia (FD) have focused on abnormal brain functions during special tasks, while few studies concentrated on the resting-state abnormalities of FD patients, which might be potentially valuable to provide us with direct information about the neural basis of FD. The main purpose of the current study was thereby to characterize the distinct patterns of resting-state function between FD patients and healthy controls (HCs).

METHODOLOGY/PRINCIPAL FINDINGS

Thirty FD patients and thirty HCs were enrolled and experienced 5-mintue resting-state scanning. Based on the support vector machine (SVM), we applied multivariate pattern analysis (MVPA) to investigate the differences of resting-state function mapped by regional homogeneity (ReHo). A classifier was designed by using the principal component analysis and the linear SVM. Permutation test was then employed to identify the significant contribution to the final discrimination. The results displayed that the mean classifier accuracy was 86.67%, and highly discriminative brain regions mainly included the prefrontal cortex (PFC), orbitofrontal cortex (OFC), supplementary motor area (SMA), temporal pole (TP), insula, anterior/middle cingulate cortex (ACC/MCC), thalamus, hippocampus (HIPP)/parahippocamus (ParaHIPP) and cerebellum. Correlation analysis revealed significant correlations between ReHo values in certain regions of interest (ROI) and the FD symptom severity and/or duration, including the positive correlations between the dmPFC, pACC and the symptom severity; whereas, the positive correlations between the MCC, OFC, insula, TP and FD duration.

CONCLUSIONS

These findings indicated that significantly distinct patterns existed between FD patients and HCs during the resting-state, which could expand our understanding of the neural basis of FD. Meanwhile, our results possibly showed potential feasibility of functional magnetic resonance imaging diagnostic assay for FD.

Temporal sequencing of brain activations during naturally occurring thermoregulatory events

Thermoregulatory events are associated with activity in the constituents of the spinothalamic tract. Whereas studies have assessed activity within constituents of this pathway, in vivo functional magnetic resonance imaging (fMRI) studies have not determined if neuronal activity in the constituents of the tract is temporally ordered. Ordered activity would be expected in naturally occurring thermal events, such as menopausal hot flashes (HFs), which occur in physiological sequence. The origins of HFs may lie in brainstem structures where neuronal activity may occur earlier than in interoceptive centers, such as the insula and the prefrontal cortex. To study such time ordering, we conducted blood oxygen level-dependent-based fMRI in a group of postmenopausal women to measure neuronal activity in the brainstem, insula, and prefrontal cortex around the onset of an HF (detected using synchronously acquired skin conductance responses). Rise in brainstem activity occurred before the detectable onset of an HF. Activity in the insular and prefrontal trailed that in the brainstem, appearing following the onset of the HF. Additional activations associated with HF's were observed in the anterior cingulate cortex and the basal ganglia. Pre-HF brainstem responses may reflect the functional origins of internal thermoregulatory events. By comparison insular, prefrontal and striatal activity may be associated with the phenomenological correlates of HFs.

Alterations of the default mode network in functional dyspepsia patients: a resting-state fmri study

BACKGROUND

Increasing brain imaging studies have emphasized the role of regional brain activity abnormalities in functional dyspepsia (FD) during the resting state. The goal of this study was to investigate the default mode network (DMN) in FD patients and healthy controls (HCs).

METHODS

Resting-state functional magnetic resonance imaging (fMRI) scanning was carried out on 49 patients and 39 HCs. Independent component analysis (ICA) was used to isolate the DMN in each subject. Group topography of the DMN was compared to study significant alteration in FD. A correlation analysis was then performed in the FD group to investigate the effects of symptom severity and the psychological factors on the DMN.

KEY RESULTS

Significant spatial differences with the DMN in FD patients, compared with HCs, were mainly found in the dorsomedial prefrontal cortex (dmPFC), ventromedial prefrontal cortex (vmPFC), orbitofrontal cortex (OFC), pregenual anterior cingulate cortex (pACC), thalamus, parahippocampal gyrus, precuneus, parietal cortex, and temporal pole. Meanwhile, Nepean Dyspepsia Index (NDI) scores were positively correlated with the pACC, and was negative correlated with the OFC. However, both the Self-Rating Anxiety Scale (SAS) and Self-Rating Depression Scale (SDS) scores were not correlated with any regions of interest showing differences between the FD patients and the HCs.

CONCLUSIONS & INFERENCES

These findings suggested that the DMN might indeed undergo dysfunctional changes due to the abnormal persistent activity in FD patients. To a certain extent, the changes in the DMN were related to the FD-related symptom severity.

Cognitive and emotional control of pain and its disruption in chronic pain

Chronic pain is one of the most prevalent health problems in our modern world, with millions of people debilitated by conditions such as back pain, headache and arthritis. To address this growing problem, many people are turning to mind-body therapies, including meditation, yoga and cognitive behavioural therapy. This article will review the neural mechanisms underlying the modulation of pain by cognitive and emotional states - important components of mind-body therapies. It will also examine the accumulating evidence that chronic pain itself alters brain circuitry, including that involved in endogenous pain control, suggesting that controlling pain becomes increasingly difficult as pain becomes chronic.

Pain, decisions, and actions: a motivational perspective

Because pain signals potential harm to the organism, it immediately attracts attention and motivates decisions and action. However, pain is also subject to motivations—an aspect that has led to considerable changes in our understanding of (chronic) pain over the recent years. The relationship between pain and motivational states is therefore clearly bidirectional. This review provides an overview on behavioral and neuroimaging studies investigating motivational aspects of pain. We highlight recent insights into the modulation of pain through fear and social factors, summarize findings on the role of pain in fear conditioning, avoidance learning and goal conflicts and discuss evidence on pain-related cognitive interference and motivational aspects of pain relief.

The effect of threat on attentional interruption by pain

Pain is known to interrupt attention. This interruption is highly sensitive to the extent of involvement of both attentional control and the level of threat associated with the sensation. However, few studies have examined these factors together. This study aimed to examine the interruptive effect of pain on higher-order attentional tasks under conditions of low and high threat. Fifty participants completed an n-back task, an attentional switching task, and a divided attention task, once in pain and once without pain. Twenty-five participants were given standard task instructions (control condition), and the remainder were given additional verbal information designed to increase threat (threat condition). Pain interrupted participant performance on both the n-back and attentional switching task, but not on the divided attention task. The addition of the threat manipulation did not seem to significantly alter the effect of pain on these attentional tasks. However, independent of pain, threat did moderate performance on the divided attention task. These findings support the robustness of the effect of pain on performance on higher-order attention tasks. Future research is needed to examine what factors alter the cognitive interruption caused by pain.

Effects of music engagement on responses to painful stimulation

OBJECTIVES

We propose a theoretical framework for the behavioral modulation of pain based on constructivism, positing that task engagement, such as listening for errors in a musical passage, can establish a construction of reality that effectively replaces pain as a competing construction. Graded engagement produces graded reductions in pain as indicated by reduced psychophysiological arousal and subjective pain report.

METHODS

Fifty-three healthy volunteers having normal hearing participated in 4 music listening conditions consisting of passive listening (no task) or performing an error detection task varying in signal complexity and task difficulty. During all conditions, participants received normally painful fingertip shocks varying in intensity while stimulus-evoked potentials (SEP), pupil dilation responses (PDR), and retrospective pain reports were obtained.

RESULTS

SEP and PDR increased with increasing stimulus intensity. Task performance decreased with increasing task difficulty. Mixed model analyses, adjusted for habituation/sensitization and repeated measures within person, revealed significant quadratic trends for SEP and pain report (Pchange<0.001) with large reductions from no task to easy task and smaller graded reductions corresponding to increasing task difficulty/complexity. PDR decreased linearly (Pchange<0.001) with graded task condition. We infer that these graded reductions in indicators of central and peripheral arousal and in reported pain correspond to graded increases in engagement in the music listening task.

DISCUSSION

Engaging activities may prevent pain by creating competing constructions of reality that draw on the same processing resources as pain. Better understanding of these processes will advance the development of more effective pain modulation through improved manipulation of engagement strategies.

The use of functional neuroimaging to evaluate psychological and other non-pharmacological treatments for clinical pain

A large number of studies have provided evidence for the efficacy of psychological and other non-pharmacological interventions in the treatment of chronic pain. While these methods are increasingly used to treat pain, remarkably few studies focused on the exploration of their neural correlates. The aim of this article was to review the findings from neuroimaging studies that evaluated the neural response to distraction-based techniques, cognitive behavioral therapy (CBT), clinical hypnosis, mental imagery, physical therapy/exercise, biofeedback, and mirror therapy. To date, the results from studies that used neuroimaging to evaluate these methods have not been conclusive and the experimental methods have been suboptimal for assessing clinical pain. Still, several different psychological and non-pharmacological treatment modalities were associated with increased pain-related activations of executive cognitive brain regions, such as the ventral- and dorsolateral prefrontal cortex. There was also evidence for decreased pain-related activations in afferent pain regions and limbic structures. If future studies will address the technical and methodological challenges of today's experiments, neuroimaging might have the potential of segregating the neural mechanisms of different treatment interventions and elucidate predictive and mediating factors for successful treatment outcomes. Evaluations of treatment-related brain changes (functional and structural) might also allow for sub-grouping of patients and help to develop individualized treatments.

On the psychology of cough

Neurobiological research is increasingly documenting the role of higher brain areas in cough, but little systematic behavioral research on the role of psychological factors exists. In this article we discuss the role of perceptual, attentional, cognitive, and emotional factors, learning mechanisms, self-regulation, and the role of social context. We also describe how interactions among these mechanisms can help to shed light on idiopathic cough and on placebo/nocebo effects on cough. This functional-behavioral perspective may lay the groundwork for a structured research program on the role of psychological factors in cough.

The analgesic effect of electroacupuncture on acute thermal pain perception--a central neural correlate study with fMRI

BACKGROUND

Electrical acupuncture (EA) has been utilized in acute pain management. However, the neuronal mechanisms that lead to the analgesic effect are still not well defined. The current study assessed the intensity [optimal EA (OI-EA) vs. minimal EA (MI-EA)] effect of non-noxious EA on supraspinal regions related to noxious heat pain (HP) stimulation utilizing an EA treatment protocol for acute pain and functional magnetic resonance imaging (fMRI) with correlation in behavioral changes. Subjects underwent five fMRI scanning paradigms: one with heat pain (HP), two with OI-EA and MI-EA, and two with OI-EA and HP, and MI-EA and HP.

RESULTS

While HP resulted in activations (excitatory effect) in supraspinal areas known for pain processing and perception, EA paradigms primarily resulted in deactivations (suppressive effect) in most of these corresponding areas. In addition, OI-EA resulted in a more robust supraspinal sedative effect in comparison to MI-EA. As a result, OI-EA is more effective than MI-EA in suppressing the excitatory effect of HP in supraspinal areas related to both pain processing and perception.

CONCLUSION

Intensities of EA plays an important role in modulating central pain perception.

Affective brain regions are activated during the processing of pain-related words in migraine patients

Several brain areas that constitute the neural matrix of pain can be activated by noxious stimuli and by pain-relevant cues, such as pictures, facial expressions, and pain-related words. Although chronic pain patients are frequently exposed to pain-related words, it remains unclear whether their pain matrix is specifically activated during the processing of such stimuli in comparison to healthy subjects. To answer this question, we compared the neural activations induced by verbal pain descriptors in a sample of migraine patients with activations in healthy controls using functional magnetic resonance imaging. Participants viewed pain-related adjectives and negative, non-pain-related adjectives that were matched for valence and arousal and were instructed to either generate mental images (imagination condition) or to count the number of vowels (distraction condition). In migraine patients, pain-related adjectives as compared with negative adjectives elicited increased activations in the left orbitofrontal cortex and anterior insula during imagination and in the right secondary somatosensory cortex and posterior insula during distraction. More pronounced pain-related activation was observed in affective pain-related regions in the patient as compared with the control group during imagination. During distraction, no differential engagement of single brain structures in response to pain-related words could be observed between groups. Overall, our findings indicate that there is an involvement of brain regions associated with the affective and sensory-discriminative dimension of pain in the processing of pain-related words in migraine patients, and that the recruitment of those regions associated with pain-related affect is enhanced in patients with chronic pain experiences.

Brain activity associated with pain, hyperalgesia and allodynia: an ALE meta-analysis

The use of functional brain imaging techniques offers the possibility of uncovering the cerebral processing of the human pain experience. In recent years, many imaging studies have focused on defining a network of brain structures involved in the processing of normal pain. Additionally, it has been shown that stimulus-evoked pain, which is a frequent symptom of neuropathic pain, causes distinct patterns of brain activation. In the present study, we quantitatively analyzed the data of previous functional imaging studies. Studies were thus collected by means of a MEDLINE query. A meta-analysis using the activation-likelihood estimation method was conducted to quantify the acquired results. We then used this data to summarize and compare the cerebral activations of (i) normal and stimulus-evoked pain, (ii) thermal and mechanical pain, (iii) different types of stimulus-evoked pain (hyperalgesia, allodynia), and (iv) clinical neuropathic and experimental pain. The results suggest the existence of distinct, although overlapping, neuronal networks related to these different types of pain.

Chronic low-back pain modulation is enhanced by hypnotic analgesic suggestion by recruiting an emotional network: a PET imaging study

This study aimed to characterize the neural networks involved in patients with chronic low-back pain during hypnoanalgesia. PET was performed in 2 states of consciousness, normal alertness and hypnosis. Two groups of patients received direct or indirect analgesic suggestion. The normal alertness state showed activations in a cognitive-sensory pain modulation network, including frontotemporal cortex, insula, somatosensory cortex, and cerebellum. The hypnotic state activated an emotional pain modulation network, including frontotemporal cortex, insula, caudate, accumbens, lenticular nuclei, and anterior cingulate cortex (ACC). Direct suggestion activated cognitive processes via frontal, prefrontal, and orbitofrontal cortices, while indirect suggestion activated a widespread and more emotional network including frontal cortex, anterior insula, inferior parietal lobule, lenticular nucleus, and ACC. Confirmed by visual analog scale data, these results suggest that chronic pain modulation is greater with hypnosis, which enhances both activated networks.

The relationship between amygdala activation and passive exposure time to an aversive cue during a continuous performance task

The allocation of attention modulates negative emotional processing in the amygdala. However, the role of passive exposure time to emotional signals in the modulation of amygdala activity during active task performance has not been examined. In two functional Magnetic Resonance Imaging (fMRI) experiments conducted in two different groups of healthy human subjects, we examined activation in the amygdala due to cued anticipation of painful stimuli while subjects performed a simple continuous performance task (CPT) with either a fixed or a parametrically varied trial duration. In the first experiment (N = 16), engagement in the CPT during a task with fixed trial duration produced the expected attenuation of amygdala activation, but close analysis suggested that the attenuation occurred during the period of active engagement in CPT, and that amygdala activity increased proportionately during the remainder of each trial, when subjects were passively exposed to the pain cue. In the second experiment (N = 12), the duration of each trial was parametrically varied, and we found that amygdala activation was linearly related to the time of passive exposure to the anticipatory cue. We suggest that amygdala activation during negative anticipatory processing depends directly on the passive exposure time to the negative cue.

Pain imaging in health and disease--how far have we come?

Since modern brain imaging of pain began 20 years ago, networks in the brain related to pain processing and those related to different types of pain modulation, including placebo, have been identified. Functional and anatomical connectivity of these circuits has begun to be analyzed. Imaging in patients suggests that chronic pain is associated with altered function and structural abnormalities in pain modulatory circuits. Moreover, biochemical alterations associated with chronic pain are being identified that provide information on cellular correlates as well as potential mechanisms of structural changes. Data from these brain imaging studies reinforce the idea that chronic pain leads to brain changes that could have functional significance.

Expectations modulate long-term heat pain habituation

Habituation to pain was shown to be a complex mechanism involving the pain encoding regions and the antinociceptive system in the brain. Pain perception can be modulated by cognitive factors; however it is unclear whether cognitive factors also influence habituation to pain. We used an established experimental design with repetitive moderate painful heat stimulation over eight consecutive days. Thirty-seven healthy subjects were recruited and assigned to four different groups: The first group (n=10) was instructed that pain perception over time will habituate; the second group (n=9) that pain will increase; the third group (n=8) was instructed that pain will remain stable over the 8 days of pain stimulation and the fourth group (n=10) was not given any specific information and served as a control group. We found that the control group habituated as described before. However, it was abolished in the second (sensitize) and third (stable) group, but was very strongly demonstrated in the first (habituation) group. In this group, habituation tended to be increased as compared to the control group. In conclusion, our findings highlight the importance of context information in pain studies and contribute to our knowledge about pain processing and behaviour.

The cerebellum and pain: passive integrator or active participator?

The cerebellum is classically considered to be a brain region involved in motor processing, but it has also been implicated in non-motor, and even cognitive, functions. Though previous research suggests that the cerebellum responds to noxious stimuli, its specific role during pain is unclear. Pain is a multidimensional experience that encompasses sensory discriminative, affective motivational, and cognitive evaluative components. Cerebellar involvement during the processing of pain could thus potentially reflect a number of different functional processes. This review will summarize the animal and human research to date that indicates that (1) primary afferents conduct nociceptive (noxious) input to the cerebellum, (2) electrical and pharmacological stimulation of the cerebellum can modulate nociceptive processing, and (3) cerebellar activity occurs during the presence of acute and chronic pain. Possible functional roles for the cerebellum relating to pain will be considered, including perspectives relating to emotion, cognition, and motor control in response to pain.

Insular cortex activity is associated with effects of negative expectation on nociceptive long-term habituation

It is generally accepted that acute painful experience is influenced by context information shaping expectation and modulating attention, arousal, stress, and mood. However, little is known about the nature, duration, and extent of this effect, particularly regarding the negative expectation. We used a standardized longitudinal pain paradigm and painful heat test stimuli in healthy participants over a time course of 8 consecutive days, inducing nociceptive habituation over time. Thirty-eight healthy volunteers were randomly assigned to two different groups. One group received the information that the investigators expected the pain intensity to increase over time (context group). The other group was not given any information (control group). All participants rated the pain intensity of the daily standardized pain paradigm on a visual analog scale. In agreement with previous studies the pain ratings in the control group habituated over time. However, the context group reported no change of pain ratings over time. Functional imaging data showed a difference between the two groups in the right parietal operculum. These data suggest that a negative context not only has an effect on immediate pain but can modulate perception of pain in the future even without experience/conditioning. Neuronally, this process is mediated by the right opercular region.

Deviations in the endocrine system and brain of patients with fibromyalgia: cause or consequence of pain and associated features?

The brain and endocrine system are crucial interfaces responding to pathological and psychological processes. This review discusses whether endocrine deviations and structural and functional changes in the brain are a cause or consequence of fibromyalgia. Studies in patients with fibromyalgia virtually uniformly observed subtle alterations in hypothalamic pituitary adrenal functioning, hyporeactive autonomic nervous system responsiveness to stressors, and structural and functional changes in the brain. Our model proposes that predisposing factors, such as genetic vulnerability and trauma, have led to an alteration of the nociceptive system including several neuroendocrine changes. The resulting pain and associated symptoms, such as sleep disturbance, low fitness, fatigue, stress, and distress, are a cause of new neuroendocrine changes. The model predicts that favorable neuroendocrine changes are to be expected after successful pharmacological or non-pharmacological interventions that target pain and associated symptoms.

Supraspinal pain processing: distinct roles of emotion and attention

Attentional and emotional states alter the way we perceive pain. Recent findings suggest that the mechanisms underlying these two forms of pain modulation are at least partially separable. This concept is supported by the observation that attention and emotions differentially alter the sensory and affective dimensions of pain perception and apparently implicate different brain circuits. In this review, we will examine those recent findings within the broader cognitive neuroscience conceptualization of human attention and emotion and the corresponding functional neuroanatomy.

Performance-dependent inhibition of pain by an executive working memory task

It is widely assumed that distraction reduces pain. Similarly, it is assumed that pain distracts from concurrent, unrelated cognitive processing, reducing performance on difficult tasks. Taken together, these assumptions suggest pain processing and cognitive function engage an overlapping set of domain-general, capacity-limited mental resources. However, experimental tests of this proposal have yielded mixed results, leading to alternative proposals that challenge the common model of a bidirectional relationship between concurrent pain and task performance. We tested these contrasting positions using a novel concurrent pain and executive working memory paradigm. Both task difficulty and nociceptive stimulus intensity were individually calibrated for each participant. Participants reported less pain during the working memory task than a visually matched control condition. Conversely, increasing levels of heat incrementally reduced task performance. Path analyses showed that variations in pain completely mediated this effect, and that even within a given heat level, trial-by-trial fluctuations in pain predicted decrements in performance. In sum, these findings argue that overlapping cognitive resources play a role in both pain processing and executive working memory. Future studies could use this paradigm to understand more precisely which components of executive function or other cognitive resources contribute to the experience of pain.

The neural bases of distraction and reappraisal

Distraction and reappraisal are two commonly used forms of cognitive emotion regulation. Functional neuroimaging studies have shown that each one depends upon interactions between pFC, interpreted as implementing cognitive control, and limbic regions, interpreted as mediating emotional responses. However, no study has directly compared distraction with reappraisal, and it remains unclear whether they draw upon different neural mechanisms and have different emotional consequences. The present fMRI study compared distraction and reappraisal and found both similarities and differences between the two forms of emotion regulation. Both resulted in decreased negative affect, decreased activation in the amygdala, and increased activation in prefrontal and cingulate regions. Relative to distraction, reappraisal led to greater decreases in negative affect and to greater increases in a network of regions associated with processing affective meaning (medial prefrontal and anterior temporal cortices). Relative to reappraisal, distraction led to greater decreases in amygdala activation and to greater increases in activation in prefrontal and parietal regions. Taken together, these data suggest that distraction and reappraisal differentially engage neural systems involved in attentional deployment and cognitive reframing and have different emotional consequences.

The influence of negative emotions on pain: behavioral effects and neural mechanisms

The idea that pain can lead to feelings of frustration, worry, anxiety and depression seems obvious, particularly if it is of a chronic nature. However, there is also evidence for the reverse causal relationship in which negative mood and emotion can lead to pain or exacerbate it. Here, we review findings from studies on the modulation of pain by experimentally induced mood changes and clinical mood disorders. We discuss possible neural mechanisms underlying this modulatory influence focusing on the periaqueductal grey (PAG), amygdala, anterior cingulate cortex (ACC) and anterior insula as key players in both, pain and affective processing.

Painful dilemmas: the ethics of animal-based pain research

While it has the potential to deliver important human benefits, animal-based pain research raises ethical questions, because it involves inducing pain in sentient beings. Ethical decision-making, connected with this variety of research, requires informed harm-benefit analysis, and the aim of this paper is to provide information for such an analysis. We present an overview of the different models and their consequences for animal welfare, showing that, of the many animal models available, most have a considerable welfare impact on the animal. While the usual approach to pain control through administration of analgesic substances is usually unsuitable in pain research, refinement remains an option, both within the experimental protocol and in general husbandry and handling. Drawing on the overview, we develop a discussion of the ethical acceptability of animal-based pain research against the background of the kinds of harm done to the animals involved, the potential for refinement, and the expected benefits of the research.

Mood influences supraspinal pain processing separately from attention

Studies show that inducing a positive mood or diverting attention from pain decreases pain perception. Nevertheless, induction manipulations, such as viewing interesting movies or performing mathematical tasks, often influence both emotional and attentional states. Imaging studies have examined the neural basis of psychological pain modulation, but none has explicitly separated the effects of emotion and attention. Using odors to modulate mood and shift attention from pain, we previously showed that the perceptual consequences of changing mood differed from those of altering attention, with mood primarily altering pain unpleasantness and attention preferentially altering pain intensity. These findings suggest that brain circuits involved in pain modulation provoked by mood or attention are partially separable. Here we used functional magnetic resonance imaging to directly compare the neurocircuitry involved in mood- and attention-related pain modulation. We manipulated independently mood state and attention direction, using tasks involving heat pain and pleasant and unpleasant odors. Pleasant odors, independent of attentional focus, induced positive mood changes and decreased pain unpleasantness and pain-related activity within the anterior cingulate (ACC), medial thalamus, and primary and secondary somatosensory cortices. The effects of attentional state were less robust, with only the activity in anterior insular cortex (aIC) showing possible attentional modulation. Lateral inferior frontal cortex [LinfF; Brodmann's area (BA) 45/47] activity correlated with mood-related modulation, whereas superior posterior parietal (SPP; BA7) and entorhinal activity correlated with attention-related modulation. ACC activity covaried with LinfF and periacqueductal gray activity, whereas aIC activity covaried with SPP activity. These findings suggest that separate neuromodulatory circuits underlie emotional and attentional modulation of pain.

Neurocognitive aspects of pain perception

The perception of pain is sensitive to various mental processes such as the feelings and beliefs that someone has about pain. It is therefore not exclusively driven by the noxious input. Attentional modulation involving the descending pain modulatory system has been examined extensively in neuroimaging studies. However, the investigation of neural mechanisms underlying more complex cognitive modulation is an emerging field in pain research. Recent findings indicate an engagement of the ventrolateral prefrontal cortex during more complex modulation, leading to a change or reappraisal of the emotional significance of pain. Taking placebo-induced analgesia as an example, we discuss the contribution of attention, expectation and reappraisal as three basic mechanisms that are important for the cognitive modulation of pain.

Is There a Role for Acupuncture in Endometriosis Pain, Or ‘endometrialgia’?

Endometriosis is a common cause of pelvic pain in women, many of whom suffer a progression of symptoms over their menstrual life. Symptoms may include combinations of abnormal visceral sensations and emotional distress. Endometriosis pain, or ‘endometrialgia’ often has a negative influence on the ability to work, on family relationships and sense of worth.

Endometrialgia is often considered to be a homogeneous sensory entity, mediated by a specialised high threshold sensory system, which extends from the periphery through the spinal cord, brain stem and thalamus to the cerebral cortex. However, multiple mechanisms have been detected in the nervous system responsible for the pain including peripheral sensitisation, phenotypic switches, central sensitisation, ectopic excitability, structural reorganisation, decreased inhibition and increased facilitation, all of which may contribute to the pain.

Although the causes of endometrialgia can differ (eg inflammatory, neuropathic and functional), they share some characteristics. Endometrialgia may be evoked by a low intensity, normally innocuous stimulus (allodynia), or it may be an exaggerated and prolonged response to a noxious stimulus (hyperalgesia). The pain may also be spontaneous in the absence of any apparent peripheral stimulus.

Oestrogens and prostaglandins probably play key modulatory roles in endometriosis and endometrialgia. Consequently many of the current medical treatments for the condition include oral drugs, like non-steroid anti-inflammatory drugs, contraceptives, progestogens, androgenic agents, gonadotrophin releasing hormone analogues, as well as laparoscopic surgical excision of the endometriosis lesions. However, management of pain in women with endometriosis is currently inadequate for many. Possibly acupuncture and cognitive therapy may be used as an adjunct.