Counter-stimulatory effects on pain perception and processing are significantly altered by attention: an fMRI study

Mechanical and thermal thresholds before and after application of a conditioning stimulus in healthy Göttingen Minipigs

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds' reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

The role of the male rat infralimbic cortex in distraction analgesia

Cognitive interventions, including distraction, have been successfully utilized in the manipulation of experimental pain and the treatment of clinical pain. Attentional diversions can reduce the experience of pain, a phenomenon known as distraction analgesia (DA). Prior research has suggested that variations in stimulus intensity may influence the magnitude of DA. However, the neural substrates of DA remain largely unknown. Converging evidence suggests that the infralimbic cortex (IL) in the brains of rats may contribute to the phenomenon of DA. The function of the rat IL in DA has never been directly investigated, therefore, this study sought to identify the role of the IL at two levels of noxious stimulus intensity among brain-intact and IL lesioned male rats within an established rat model of DA. A distractor object reduced formalin-induced nociceptive behavior in brain-intact rats, and this DA effect was detectable during low- (0.5% formalin) and high-intensity (1% formalin) stimulation. IL lesion resulted in a near-complete elimination of the DA effect and an overall reduction in formalin pain. These results provide the first known evidence that (i) the IL is involved in processing DA in rats, (ii) the IL contributes to formalin-induced nociceptive behavior irrespective of distraction, and (iii) a high-intensity stimulation was generally more susceptible to DA than low-intensity stimulation. These findings may further inform the mechanisms and future development of non-pharmacological strategies to reduce pain.

Targeting Neuroinflammation with Abscisic Acid Reduces Pain Sensitivity in Females and Hyperactivity in Males of an ADHD Mice Model

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental syndrome characterized by dopaminergic dysfunction. In this study, we aimed to demonstrate that there is a link between dopaminergic deficit and neuroinflammation that underlies ADHD symptoms. We used a validated ADHD mice model involving perinatal 6-OHDA lesions. The animals received abscisic acid (ABA), an anti-inflammatory phytohormone, at a concentration of 20 mg/L (drinking water) for one month. We tested a battery of behavior tests, learning and memory, anxiety, social interactions, and pain thresholds in female and male mice (control and lesioned, with or without ABA treatment). Postmortem, we analyzed microglia morphology and Ape1 expression in specific brain areas related to the descending pain inhibitory pathway. In females, the dopaminergic deficit increased pain sensitivity but not hyperactivity. In contrast, males displayed hyperactivity but showed no increased pain sensitivity. In females, pain sensitivity was associated with inflammatory microglia and lower Ape1 levels in the anterior cingulate cortex (ACC) and posterior insula cortex (IC). In addition, ABA treatment alleviated pain sensitivity concomitant with reduced inflammation and normalized APE1. In males, ABA reduced hyperactivity but had no significant effect on inflammation in these areas. This is the first study proving a sex-dependent association between dopamine dysfunction and inflammation in specific brain areas, hence leading to different behavioral outcomes in a mouse model of ADHD. These findings provide new clues for potential treatments for ADHD.

Within-day rhythms of pain and cognitive function in people with and without fibromyalgia: synchronous or syncopated?

ABSTRACT

Cognitive dysfunction is a common fibromyalgia (FM) symptom and can impact on the daily lives of those affected. We investigated whether within-day pain intensity ratings were associated with contemporaneous objective and subjective measures of cognitive function and whether within-day increases in pain intensity preceded increases in cognitive dysfunction or vice versa. Inclusion of a non-FM group allowed us to examine whether effects were specific to FM. Fifty people with FM and 50 non-FM controls provided 7 days of data. Cognitive tests (processing speed and working memory) and ecological momentary assessments (pain intensity and self-reported cognitive functioning) were conducted ×5/day. Three-level multilevel models examined contemporaneous and within-day 1-lag pain intensity-cognitive functioning associations. Interaction terms assessed possible moderating effects of FM status. Momentary increase in pain was associated with increased self-reported cognitive dysfunction, more strongly so for those with FM (B = 0.27, 95% confidence interval 0.22-0.32; non-FM B = 0.17, 95% confidence interval 0.10-0.23). For the FM group, higher pain was associated with longer processing speed; for the non-FM group, higher pain was associated with shorter processing speed. Pain increase did not precede change in subjective or objective cognitive function in the FM group, but reduction in working memory preceded increase in pain intensity. This finding warrants further research attention and, if replicated, could hold prognostic and/or therapeutic potential.

Physical Exercise with or without Whole-Body Vibration in Breast Cancer Patients Suffering from Aromatase Inhibitor—Induced Musculoskeletal Symptoms: A Pilot Randomized Clinical Study

In this study, we aimed to assess the safety and efficacy of physical exercise, with or without whole-body vibration (WBV), in patients with aromatase inhibitor-induced musculoskeletal symptoms (AIMSS). Eligible patients were adults (≥18 years) with a history of breast cancer and current AIMSS. Enrolled patients (n = 22) were randomly assigned 1:1 to receive physical exercise combined with WBV or sham WBV for 4 weeks. The primary endpoint was pain intensity measured by numerical pain rating scale (NPRS). The secondary endpoints were muscle strength, physical function, physical performance, and quality of life. The WBV group (mean age: 51.73 ± 10.73 years; body mass index (BMI): 25.56 ± 5.17 kg/m2) showed a statistically significant pain reduction (NPRS: 6.82 ± 1.17 vs. 5.73 ± 1.01; p = 0.031), whereas patients in the sham WBV group (mean age: 58.55 ± 9.71 years; BMI: 27.31 ± 3.84 kg/m2), did not reach statistical significance (NPRS: 6.91 ± 2.02 vs. 5.91 ± 2.51; p = 0.07). Concurrently, muscle strength, physical performance, and quality of life significantly improved in both groups, without significant differences between groups. No dropouts and no side effects were recorded. Both patients and the physical therapist reported a high level of satisfaction with the intervention. Our findings suggest that physical exercise and WBV combination might be a safe therapeutic option for improving the rehabilitative management of patients with AIMSS.

Brain circuits for pain and its treatment

[Figure: see text].

Exploring scraping therapy: Contemporary views on an ancient healing - A review

Gua sha is a traditional healing technique that aims to create petechiae on the skin for a believed therapeutic benefit. Natural healings are mostly based on repeated observations and anecdotal information. Hypothetical model for healing does not always fit the modern understanding. Yet, the mechanisms underlying Gua Sha have not been empirically established. Contemporary scientific research can now explain some events of traditional therapies that were once a mystery. It is assumed that Gua Sha therapy can serve as a mechanical signal to enhance the immune surveillance function of the skin during the natural resolving of the petechiae, through which scraping may result in therapeutic benefits. The current review, without judging the past hypothetical model, attempts to interpret the experience of the ancient healings in terms of contemporary views and concepts.

Nonpharmacologic Pain Management Among Hospitalized Inpatients: A Randomized Waitlist-Controlled Trial of Standard Virtual Reality (CGI VR) Versus Video Capture VR (360 degrees 3D/Stereoscopic Video Capture VR)

OBJECTIVES

Nonpharmacologic pain management strategies are needed because of the growing opioid epidemic. While studies have examined the efficacy of virtual reality (VR) for pain reduction, there is little research in adult inpatient settings, and no studies comparing the relative efficacy of standard animated computer-generated imagery (CGI) VR to Video Capture VR (360 degrees 3D/stereoscopic Video Capture VR). Here, we report on a randomized controlled trial of the relative efficacy of standard CGI VR versus Video Capture VR (matched for content) and also compared the overall efficacy of VR to a waitlist control group.

MATERIALS AND METHODS

Participants (N=103 hospitalized inpatients reporting pain) were randomized to 1 of 3 conditions: (1) waitlist control, (2) CGI VR, or (3) Video Capture VR. The VR and waitlist conditions were 10 minutes in length. Outcomes were assessed pretreatment, post-treatment, and after a brief follow-up.

RESULTS

Consistent with hypotheses, both VR conditions reduced pain significantly more relative to the waitlist control condition (d=1.60, P<0.001) and pain reductions were largely maintained at the brief follow-up assessment. Both VR conditions reduced pain by ∼50% and led to improvements in mood, anxiety, and relaxation. Contrary to prediction, the Video Capture VR condition was not significantly more effective at reducing pain relative to the CGI VR condition (d=0.25, P=0.216). However, as expected, patients randomized to the Video Capture VR rated their experience as more positive and realistic (d=0.78, P=0.002).

DISCUSSION

Video Capture VR was as effective as CGI VR for pain reduction and was rated as more realistic.

Posterior insular activity contributes to the late laser-evoked potential component in EEG recordings

OBJECTIVE

Nociceptive activity in some brain areas has concordantly been reported in EEG source models, such as the anterior/mid-cingulate cortex and the parasylvian area. Whereas the posterior insula has been constantly reported to be active in intracortical and fMRI studies, non-invasive EEG and MEG recordings mostly failed to detect activity in this region. This study aimed to determine an appropriate inverse modeling approach in EEG recordings to model posterior insular activity, assuming the late LEP (laser evoked potential) time window to yield a better separation from other ongoing cortical activity.

METHODS

In 12 healthy volunteers, nociceptive stimuli of three intensities were applied. LEP were recorded using 32-channel EEG recordings. Source analysis was performed in specific time windows defined in the grand-average dataset. Two distinct dipole-pairs located close to the operculo-insular area were compared.

RESULTS

Our results show that posterior insular activity yields a substantial contribution to the latest part (positive component) of the LEP.

CONCLUSIONS

Even though the initial insular activity onset is in the early LEP time window,modelingthe insular activity in the late LEP time window might result in better separation from other ongoing cortical activity.

SIGNIFICANCE

Modeling the late LEP activity might enable to distinguish posterior insular activity.

Behavioral, Physiological and EEG Activities Associated with Conditioned Fear as Sensors for Fear and Anxiety

Anxiety disorders impose substantial costs upon public health and productivity in the USA and worldwide. At present, these conditions are quantified by self-report questionnaires that only apply to behaviors that are accessible to consciousness, or by the timing of responses to fear- and anxiety-related words that are indirect since they do not produce fear, e.g., Dot Probe Test and emotional Stroop. We now review the conditioned responses (CRs) to fear produced by a neutral stimulus (conditioned stimulus CS+) when it cues a painful laser unconditioned stimulus (US). These CRs include autonomic (Skin Conductance Response) and ratings of the CS+ unpleasantness, ability to command attention, and the recognition of the association of CS+ with US (expectancy). These CRs are directly related to fear, and some measure behaviors that are minimally accessible to consciousness e.g., economic scales. Fear-related CRs include non-phase-locked phase changes in oscillatory EEG power defined by frequency and time post-stimulus over baseline, and changes in phase-locked visual and laser evoked responses both of which include late potentials reflecting attention or expectancy, like the P300, or contingent negative variation. Increases (ERS) and decreases (ERD) in oscillatory power post-stimulus may be generalizable given their consistency across healthy subjects. ERS and ERD are related to the ratings above as well as to anxious personalities and clinical anxiety and can resolve activity over short time intervals like those for some moods and emotions. These results could be incorporated into an objective instrumented test that measures EEG and CRs of autonomic activity and psychological ratings related to conditioned fear, some of which are subliminal. As in the case of instrumented tests of vigilance, these results could be useful for the direct, objective measurement of multiple aspects of the risk, diagnosis, and monitoring of therapies for anxiety disorders and anxious personalities.

The Rhythmic Finger Focus Hypnotic Technique: Multilevel Application of Ericksonian Utilization

This paper presents a hypnotic technique that starts with a suggested focus on one's fingertips, and movement of the hands in a self-determined rhythm. The technique involves the use of the utilization principle of Milton Erickson in multiple ways. This includes utilizing psychomotor agitation characteristic of psychophysiological arousal, directing it toward movement that generates the sensations upon which to focus. It utilizes the sensitivity of the fingertips, the high degree of representation of the hands in the somatosensory cortex, and the tendency of the brain to orient to novelty to help facilitate focused absorption. It generates counter stimulation for pain management, and emotionally self- soothing tactile sensations. The technique is further designed to activate and utilize prior sensorimotor learning and sensory experiences associated with the hands to access feelings of mastery, creativity, flow, self-efficacy, and other positive emotional experiences. It is hypothesized that multisystem coherence is generated through activating prior positive motor, behavioral and affective experiential learning. It is further hypothesized that the rhythmic movement and sensory input simultaneously generated by and processed in the right and left hemispheres, entrains the hemispheres toward greater sympathetic/parasympathetic balance.

Self-Focused Reasons for Having Sex: Associations Between Sexual Goals and Women's Pain and Sexual and Psychological Well-being for Couples Coping With Provoked Vestibulodynia

BACKGROUND

For couples coping with provoked vestibulodynia (PVD), interpersonal sexual goals are associated with sexual and psychological functioning as well as women's pain during intercourse, however, self-focused sexual goals (eg, having sex for personal pleasure, having sex to avoid feeling bad about oneself) have not been studied in this clinical population.

AIM

The purpose of this study was to examine the associations between self-focused approach and avoidance sexual goals and women's pain during intercourse and sexual satisfaction and depressive symptoms for both women and their partners.

METHODS

Women diagnosed with PVD (N = 69) and their partners completed measures of self-focused sexual goals, sexual satisfaction, and depressive symptoms. Women also reported on pain experienced during sexual intercourse.

OUTCOMES

Outcomes included the Global Measure of Sexual Satisfaction, the Beck Depression Inventory-II, and a Numerical Rating Scale of pain during sexual intercourse.

RESULTS

When women reported higher self-focused approach sexual goals, they also reported lower pain intensity. Women's higher self-focused avoidance sexual goals were associated with their own higher depressive symptoms, whereas men's higher self-focused approach goals were associated with their own higher depressive symptoms. When controlling for frequency of sexual intercourse, there were no significant associations between women or partners' sexual goals and sexual satisfaction.

CLINICAL IMPLICATIONS

Within a clinical context where many interpersonal pressures for sex exist, interventions should target self-focused sexual goals alongside interpersonal sexual goals to improve pain and psychological adjustment.

STRENGTHS & LIMITATIONS

This is the first study to examine self-focused sexual goals among women with PVD and their partners. This study is cross-sectional, and the direction of associations cannot be inferred. Couples were in mixed-sex relationships, and results may not generalize to same-sex couples.

CONCLUSION

Findings suggest that self-focused goals are relevant to the psychological adjustment of women with PVD and their male partners and for women's pain. Corsini-Munt S, Bergeron S, Rosen NO. Self-Focused Reasons for Having Sex: Associations Between Sexual Goals and Women's Pain and Sexual and Psychological Well-being for Couples Coping With Provoked Vestibulodynia. J Sex Med 2020;17:975-984.

Whole body vibration showed beneficial effect on pain, balance measures and quality of life in painful diabetic peripheral neuropathy: a randomized controlled trial

Purpose

The aim of the study was to determine the efficacy of whole body vibration (WBV) therapy on pain, neuropathy disability score, balance, proprioception and quality of life (QOL) in patients with painful diabetic peripheral neuropathy (PDPN).

Methods

Twenty-six (16 males and 10 females) patients with PDPN were selected on the basis of inclusion and exclusion criteria. Subjects were randomly allocated to an experimental group (n = 13, age = 60.69 ± 5.08) and a control group (n = 13, age = 59.54 ± 4.25). The experimental group was given WBV therapy for six weeks (3 days/week) in addition to standard medical care, dietary advice and lifestyle modifications. Control group was provided only standard medical care, dietary advice and lifestyle modifications. Outcome measures included numeric pain rating scale (NPRS), Leeds assessment of neuropathic symptoms and signs (LANSS), vibration perception threshold (VPT), neuropathy disability score (NDS), proprioception, single-leg stance test (SLST), timed up and go test (TUGT) and short form 36 questionnaire (SF-36).

Results

NPRS, LANSS, NDS, SLST and TUGT showed significant time effect (p ≤ 0.022) and time×group interaction (p ≤ 0.007), whereas group effect was found to be significant only in LANSS (p = 0.001). VPT showed significant group effect (p ≤ 0.045) and time×group interaction (p ≤ 0.007) at great toe, metatarsal head and total average score. SF-36 was found to be significant time effect (p ≤ 0.024) in all domains except limitations due to physical health (p = 0.461). SF-36 average score was found be significant for group effect (p = 0.002) and time×group interaction (p < 0.001).

Conclusion

WBV improves sensory sensations like pain and vibration perception, neuropathy disability score, balance measures and health-related QOL in PDPN.

Acute Effects of Whole-Body Vibration on the Pain Level, Flexibility, and Cardiovascular Responses in Individuals With Metabolic Syndrome

The aim of the study was to assess the acute effect of whole-body vibration (WBV) exercise, with low frequency (5 Hz), on the pain level (PL), trunk flexibility, and cardiovascular responses (blood pressure [BP] and heart rate [HR]) in individuals with metabolic syndrome (MetS). Forty-four individuals were included in the study (control: 15) or in (WBV exercise: 29) groups. They were submitted to 3 bouts (1 minute each) of WBV exercise (5 Hz and peak-to-peak displacements of 2.5, 5.0, and 7.5 mm, corresponding to peak accelerations of 0.12, 0.25, and 0.35 g, respectively, sitting in a chair with the feet on the platform with knees flexed, followed by 1 minute of interset rest. The Control Group performed the same protocol, but the platform was turned off. The PL was measured through the visual analog pain scale, and the flexibility was measured through the anterior trunk flexion test. Significant improvements on PL (P = .031) and flexibility (P = .004) were found only in the WBV exercise group. The BP and HR remained at physiological levels. In conclusion, the WBV exercise would lead to physiological response decreasing PL and increasing flexibility as well as maintaining the cardiovascular responses in individuals with MetS.

The Social Regulation of Pain: Autonomic and Neurophysiological Changes Associated With Perceived Threat

The analgesic effect of social support is proposed as a function of social support modulating perceived threat of painful stimuli. In the current study, we directly examined the social buffering effect in the context of the threat of pain. Eighteen healthy participants were subjected to the threat of pain while they held the hand of a close other, a stranger, or not at all. Neural and autonomic responses were recorded using electroencephalogram and heart rate, respectively. Close other hand-holding reduced pain perception. This was accompanied by decreased heart rate and frontal theta oscillation (4-8 Hz) during the threat phase preceding painful stimulation. Interestingly, decreased heart rate and frontal theta in the close other hand-holding condition were uniquely associated with greater pain reduction during subsequent nociceptive stimulation. Neural changes were source-localized to the insular cortex and the rostral-ventral portions of anterior cingulate cortex, regions involved in the processing of threat and pain. Together, our data build upon work to date linking social support to pain by showing autonomic and neurophysiological changes associated with pain reduction.

PERSPECTIVE

Social support may reduce pain through buffering the autonomic and neurophysiological response to the threatening quality of noxious stimuli. Results implicate that in clinical settings the caregiver could help people with chronic pain reappraise pain and related conditions as less stressful.

Oscillatory EEG activity induced by conditioning stimuli during fear conditioning reflects Salience and Valence of these stimuli more than Expectancy

Imaging studies have described hemodynamic activity during fear conditioning protocols with stimulus trains in which a visual conditioned stimulus (CS+) is paired with an aversive unconditioned stimulus (US, painful laser pulse) while another visual stimulus is unpaired (CS-). We now test the hypothesis that CS Event Related Spectral Perturbations (ERSPs) are related to ratings of CS Expectancy (likelihood of pairing with the US), Valence (unpleasantness) and Salience (ability to capture attention). ERSP windows in EEG were defined by both time after the CS and frequency, and showed increased oscillatory power (Event Related Synchronization, ERS) in the Delta/Theta Windows (0-8Hz) and the Gamma Window (30-55Hz). Decreased oscillatory power (Event Related Desynchronization - ERD) was found in Alpha (8-14Hz) and Beta Windows (14-30Hz). The Delta/Theta ERS showed a differential effect of CS+ versus CS- at Prefrontal, Frontal and Midline Channels, while Alpha and Beta ERD were greater at Parietal and Occipital Channels early in the stimulus train. The Gamma ERS Window increased from habituation to acquisition over a broad area from frontal and occipital electrodes. The CS Valence and Salience were greater for CS+ than CS-, and were correlated with each other and with the ERD at overlapping channels, particularly in the Alpha Window. Expectancy and CS Skin Conductance Response were greater for CS+ than CS- and were correlated with ERSP at fewer channels than Valence or Salience. These results suggest that Alpha ERSP activity during fear conditioning reflects Valence and Salience of the CSs more than conditioning per se.

Effect of negative emotions evoked by light, noise and taste on trigeminal thermal sensitivity

Background

Patients with migraine often have impaired somatosensory function and experience headache attacks triggered by exogenous stimulus, such as light, sound or taste. This study aimed to assess the influence of three controlled conditioning stimuli (visual, auditory and gustatory stimuli and combined stimuli) on affective state and thermal sensitivity in healthy human participants.

Methods

All participants attended four experimental sessions with visual, auditory and gustatory conditioning stimuli and combination of all stimuli, in a randomized sequence. In each session, the somatosensory sensitivity was tested in the perioral region with use of thermal stimuli with and without the conditioning stimuli. Positive and Negative Affect States (PANAS) were assessed before and after the tests. Subject based ratings of the conditioning and test stimuli in addition to skin temperature and heart rate as indicators of arousal responses were collected in real time during the tests.

Results

The three conditioning stimuli all induced significant increases in negative PANAS scores (paired t-test, P ≤0.016). Compared with baseline, the increases were in a near dose-dependent manner during visual and auditory conditioning stimulation. No significant effects of any single conditioning stimuli were observed on trigeminal thermal sensitivity (P ≥0.051) or arousal parameters (P ≥0.057). The effects of combined conditioning stimuli on subjective ratings (P ≤0.038) and negative affect (P = 0.011) were stronger than those of single stimuli.

Conclusions

All three conditioning stimuli provided a simple way to evoke a negative affective state without physical arousal or influence on trigeminal thermal sensitivity. Multisensory conditioning had stronger effects but also failed to modulate thermal sensitivity, suggesting that so-called exogenous trigger stimuli e.g. bright light, noise, unpleasant taste in patients with migraine may require a predisposed or sensitized nervous system.

Painful cutaneous laser stimuli induce event-related oscillatory EEG activities that are different from those induced by nonpainful electrical stimuli

The non-phase-locked EEG response to painful stimuli has usually been characterized as decreased oscillatory activity (event-related desynchronization, ERD) in the alpha band. Increased activity (event-related synchronization, ERS) in the gamma band has been reported more recently. We have now tested the hypothesis that the non-phase-locked responses to nonpainful electric cutaneous stimuli are different from those to painful cutaneous laser stimuli when the baseline salience of the two stimuli is the same and the salience during the protocol is modulated by count laser and count electric tasks. Both of these stimuli were presented in random order in a single train at intensities that produced the same baseline salience in the same somatic location. The response to the laser stimulus was characterized by five windows (designated windows I-V) in the time-frequency domain: early (200-400 ms) and late (600-1,400 ms) delta/theta ERS, 500-900 ms alpha ERD, 1,200-1,600 ms beta ERS (rebound), and 800-1,200 ms gamma ERS. Similar ERS/ERD windows of activity were found for the electric stimulus. Individual participants very commonly had activity in windows consistent with the overall analysis. Linear regression of ERS/ERD for parietal channels was most commonly found for sensory (pain or unpleasantness)- or attention (salience)-related measures. Overall, the main effect for modality was found in window I-delta/theta and window V-gamma, and the Modality with Task interaction was found in all five windows. All significant interaction terms included Modality as a factor. Therefore, Modality was the most common factor explaining our results, which is consistent with our hypothesis.

How does vibration reduce pain?

Cutaneous vibration is able to reduce both clinical and experimental pain, an effect called vibratory analgesia. The traditional explanation for this phenomenon is that it is mediated by lateral inhibition at the segmental (spinal cord) level, in pain-coding cells with center-surround receptive fields. We evaluated this hypothesis by testing for two signs of lateral inhibition-namely (1) an effect of the distance between the noxious and vibratory stimuli and (2) an inhibition-induced shift in the perceived location of the noxious stimulus. The experiment involved continuous ratings of the pain from pressure applied to the back of a finger, alone and in the presence of vibration delivered to sites on the palm of the hand both near to and far from the site of painful stimulation. Neither prediction of the segmental hypothesis was supported. There was also little evidence to support the view (widely held by subjects) that distraction is the primary mechanism of vibratory analgesia. The results are more consistent with a recently proposed theory of interactions between two cortical areas that are primarily involved in coding pain and touch, respectively.

EEG analysis reveals widespread directed functional interactions related to a painful cutaneous laser stimulus

During attention to a painful cutaneous laser stimulus, event-related causality (ERC) has been detected in recordings from subdural electrodes implanted directly over cortical modules for the treatment of epilepsy. However, these studies afforded limited sampling of modules and did not examine interactions with a nonpainful stimulus as a control. We now sample scalp EEG to test the hypothesis that attention to the laser stimulus is associated with poststimulus ERC interactions that are different from those with attention to a nonpainful stimulus. Subjects attended to (counted) either a painful laser stimulus (laser attention task) or a nonpainful electrical cutaneous stimulus that produced distraction from the laser (laser distraction task). Both of these stimuli were presented in random order in a single train. The intensities of both stimuli were adjusted to produce similar baseline salience and sensations in the same cutaneous territory. The results demonstrated that EEG channels with poststimulus ERC interactions were consistently different during the laser stimulus versus the electric stimulus. Poststimulus ERC interactions for the laser attention task were different from the laser distraction task. Furthermore, scalp EEG frontal channels play a driver role while parietal temporal channels play a receiver role during both tasks, although this does not prove that these channels are connected. Sites at which large numbers of ERC interactions were found for both laser attention and distraction tasks (critical sites) were located at Cz, Pz, and C3. Stimulation leading to disruption of sites of these pain-related interactions may produce analgesia for acute pain.

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.

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.

Gut memories: towards a cognitive neurobiology of irritable bowel syndrome

The brain and the gut are engaged in continual crosstalk along a number of pathways collectively termed the 'brain-gut axis'. Over recent years it has become increasingly clear that dysregulation of the axis at a number of levels can result in disorders such as irritable bowel syndrome (IBS). With recent advances in neuroimaging technologies, insights into the neurobiology of IBS are beginning to emerge. However the cognitive neurobiology of IBS has remained relatively unexplored to date. In this review we summarise the available data on cognitive function in IBS. Moreover, we specifically address three key pathophysiological factors, namely; stress, immune activation and chronic pain, together with other factors involved in the manifestation of IBS, and explore how each of these components may impact centrally, what neurobiological mechanisms might be involved, and consider the implications for cognitive functioning in IBS. We conclude that each factor addressed could significantly impinge on central nervous system function, supporting the view that future research efforts must be directed towards a detailed assessment of cognitive function in IBS.

The biological basis of headache

This article covers the remarkable recent decades as clinicians and scientists have grappled with understanding headache. It is a challenge to understand how a 'normal' brain can become dysfunctional, incapacitating an individual, and then become 'normal' again. Does the answer lie in the anatomy, electrical pathways, the chemistry or a combination? How do the pieces fit together? The components are analyzed in this article. Animal models have provided potential answers. However, these processes have never been proven in man. The dynamic imaging of pain and headache is rapidly evolving and providing new insights and directions of research.

Review of neuroimaging studies related to pain modulation

Background and purpose: A noxious stimulus does not necessarily cause pain. Nociceptive signals arising from a noxious stimulus are subject to modulation via endogenous inhibitory and facilitatory mechanisms as they travel from the periphery to the dorsal horn or brainstem and on to higher brain sites. Research on the neural structures underlying endogenous pain modulation has largely been restricted to animal research due to the invasiveness of such studies (e.g., spinal cord transection, brain lesioning, brain site stimulation). Neuroimaging techniques (e.g., magnetoencephalography (MEG), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI)) provide non-invasive means to study neural structures in humans. The aim is to provide a narrative review of neuroimaging studies related to human pain control mechanisms.

Methods: The approach taken is to summarise specific pain modulation mechanisms within the somatosensory (diffuse noxious inhibitory controls, acupuncture, movement), affective (depression, anxiety, catastrophizing, stress) and cognitive (anticipation/placebo, attention/distraction, hypnosis)domains with emphasis on the contribution of neuroimaging studies.

Results and conclusions: Findings from imaging studies are complex reflecting activation or deactivation in numerous brain areas. Despite this, neuroimaging techniques have clarified supraspinal sites involved in a number of pain control mechanisms. The periaqueductal grey (PAG) is one area that has consistently been shown to be activated across the majority of pain mechanisms. Activity in the rostral ventromedial medulla known to relay descending modulation from the PAG, has also been observed both during acupuncture analgesia and anxiety-induced hyperalgesia. Other brain areas that appear to be involved in a number of mechanisms are the anterior cingulate cortex, prefrontal cortex, orbitofrontal cortex and nucleus accumbens, but their exact role is less clear.

Implications: Neuroimaging studies have provided essential information about the pain modulatory pathways under normal conditions, but much is still to be determined. Understanding the mechanisms of pain control is important for understanding the mechanisms that contribute to failed pain control in chronic pain. Applying fMRI outside the brain, such as in the trigeminal nucleus caudalis of the spinotrigeminal pathway and in the dorsal horn of the spinal cord, and coupling brain activity with activity at these sites may help improve our understanding of the function of brain sites and shed light on functional connectivity in the pain pathway.

© 2011 Scandinavian Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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.

Effects of somatosensory stimulation and attention on human somatosensory cortex: an fMRI study

It is well known that primary and non-primary areas of human somatosensory cortex are involved in the processing of adequate deviant/rare stimuli and omission of frequent stimuli. However, the relative weight and interaction of these variables is poorly known. This functional magnetic resonance imaging (fMRI) study tested the hypothesis that somatosensory stimulus processing and attention especially interact in non-primary somatosensory areas including secondary somatosensory cortex (SII) and insula. To test this hypothesis, responses of somatosensory cortex were mapped during four conditions of an oddball paradigm: DELIVERED COUNT and IGNORE (count or ignore deviant/rare electrical stimuli, respectively); OMITTED COUNT and IGNORE (count or ignore the rare omission of frequent electrical stimuli, respectively). The deviant/rare and frequent electrical stimuli were delivered to median and ulnar nerve, respectively. It was observed that contralateral (left) primary somatosensory responses were not markedly modulated by the mentioned deviant/rare events. Furthermore, contralateral SII and insula responded to all but not OMITTED IGNORE (purely attentive) condition, whereas ipsilateral (right) SII responded to all conditions. Finally, ipsilateral insula responded to the COUNT (attentive) conditions, regardless of the physical presence of the deviant/rare stimuli. The results suggest that in somatosensory modality, bilateral SII and left (contralateral) insula reflect complex integrative processes of stimulus elaboration and attention, whereas right (ipsilateral) insula mainly sub-serves active attention to deviance within a sequence of somatosensory stimuli.

Differential effects on pain intensity and unpleasantness of two meditation practices

Pain is an unpleasant sensory and emotional experience that can be regulated by many different cognitive mechanisms. We compared the regulatory qualities of two different meditation practices during noxious thermal stimuli: Focused Attention, directed at a fixation cross away from the stimulation, which could regulate negative affect through a sensory gating mechanism; and Open Monitoring, which could regulate negative affect through a mechanism of nonjudgmental, nonreactive awareness of sensory experience. Here, we report behavioral data from a comparison between novice and long-term meditation practitioners (long-term meditators, LTMs) using these techniques. LTMs, compared to novices, had a significant reduction of self-reported unpleasantness, but not intensity, of painful stimuli while practicing Open Monitoring. No significant effects were found for FA. This finding illuminates the possible regulatory mechanism of meditation-based clinical interventions like Mindfulness-Based Stress Reduction (MBSR). Implications are discussed in the broader context of training-induced changes in trait emotion regulation.

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.

Central processing of noxious somatic stimuli in patients with irritable bowel syndrome compared with healthy controls

OBJECTIVE

To compare a central analgesic mechanism known as diffuse noxious inhibitory controls (DNIC) using somatic test stimuli and somatic conditioning stimuli, (CS) in irritable bowel syndrome (IBS) patients and healthy controls.

METHODS

Participants were 48 premenopausal females (27 with IBS), mean age of 29 years. The phasic heat test stimulus (peak temperature, 50 degrees C) was applied to the left palm. The DNIC effect, which measured reductions in average pain ratings (APR) during counter irritation (submersion of the participant's right hand in painful 12 degrees C circulating water) compared with baseline, was compared between groups. In addition, a second, counterbalanced, CS protocol (right hand submerged in nonpainful 32 degrees C circulating water) was performed. Differences in APR between the 2 counterirritation protocols were compared between groups to control for nonspecific effects known to influence DNIC. Psychologic measures and cardiovascular reactivity were also assessed.

RESULTS

IBS patients demonstrated smaller DNIC than controls (P=0.011, repeated measures analysis of variance), and greater state-anxiety, depression, catastrophizing, and anger-out expression (P<0.05). Group differences in DNIC were enhanced after controlling for nonspecific effects occurring during the nonpainful CS, and for psychologic measures (P=0.001, repeated measures analysis of covariance). There were no group differences in age, cardiovascular reactivity, APR, or pain ratings for the 12 degrees C CS.

DISCUSSION

These data demonstrate deficient DNIC in IBS. This is the first study to adequately control for alternative explanations of pain reduction during counterirritation. Only by controlling for nonspecific effects can evidence of deficient DNIC be attributed to dysregulation in endogenous analgesic mechanisms.

Catastrophizing delays the analgesic effect of distraction

Behavioral analgesic techniques such as distraction reduce pain in both clinical and experimental settings. Individuals differ in the magnitude of distraction-induced analgesia, and additional study is needed to identify the factors that influence the pain relieving effects of distraction. Catastrophizing, a set of negative emotional and cognitive processes, is widely recognized to be associated with increased reports of pain. We sought to evaluate the relationship between catastrophizing and distraction analgesia. Healthy participants completed three sessions in a randomized order. In one session (Pain Alone), pain was induced by topical application of a 10% capsaicin cream and simultaneous administration of a tonic heat stimulus. In another session (Pain+Distraction), identical capsaicin+heat application procedures were followed, but subjects played video games that required a high level of attention. During both sessions, verbal ratings of pain were obtained and participants rated their degree of catastrophizing. During the other session (Distraction Alone) subjects played the video games in the absence of any pain stimulus. Pain was rated significantly lower during the distraction session compared to the "Pain Alone" session. In addition, high catastrophizers rated pain significantly higher regardless of whether the subjects were distracted. Catastrophizing did not influence the overall degree of distraction analgesia; however, early in the session high catastrophizers had little distraction analgesia, though later in the session low and high catastrophizers rated pain similarly. These results suggest that both distraction and catastrophizing have substantial effects on experimental pain in normal subjects and these variables interact as a function of time.

Temperature perception on the hand during static versus dynamic contact with a surface

Innocuous cooling or heating of the forearm can evoke nociceptive sensations, such as burning, stinging, and pricking (low-threshold thermal nociception, LTN), that are inhibited by dynamic contact. In the present study, I investigated whether LTN can also be perceived on the hand, and if so, whether it is normally suppressed by active touching. Innocuous cold (28 degrees , 25 degrees , and 18 degrees C) and warm (38 degrees , 40 degrees , and 43 degrees C) temperatures were delivered to the distal metacarpal pads and intermediate and distal phalanges of the fingers via a handgrip thermode that subjects either statically held or actively grasped. The same temperatures were delivered to the forearm via another thermode that either rested on the arm or was touched to the arm. Subjects rated the intensity of thermal (warmth, cold) and nociceptive (e.g., burning) sensations and indicated the qualities of sensation experienced. The results showed that LTN can be perceived on the hand, although less frequently and less intensely than on the forearm. Dynamic contact inhibited nociceptive and thermal sensations on the hand, although less strongly than on the forearm. These findings indicate that temperature perception on the hand is attenuated and its quality is changed when thermal stimulation is accompanied by dynamic tactile stimulation, as it is during haptic exploration.

Brain imaging approaches to the study of functional GI disorders: a Rome working team report

Progresses in the understanding of human brain-gut interactions in health and disease have been limited by the lack of non-invasive techniques to study brain activity. The advent of neuroimaging techniques has made it possible not only to study the structure and function of the brain, but also to characterize signaling system underlying brain function. This article gives a brief overview of relevant functional neuroanatomy, and of the most commonly used brain imaging techniques. It summarizes published functional brain imaging studies using acute visceral stimulation of the oesophagus, stomach and colon in healthy control subjects and patients with functional GI disorders, and briefly discusses pertinent findings from these studies. The article concludes with a critical assessment of published studies, and with recommendations for improved study paradigms and analysis strategies.

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.

fMRI of supraspinal areas after morphine and one week pancreatic inflammation in rats

Abdominal pain is a major reason patients seek medical attention yet relatively little is known about neuronal pathways relaying visceral pain. We have previously characterized pathways transmitting information to the brain about visceral pain. Visceral pain arises from second order neurons in lamina X surrounding the spinal cord central canal. Some of the brain regions of interest receiving axonal terminations directly from lamina X were examined in the present study using enhanced functional magnetic resonance imaging (fMRI) before and one week after induction of a rat pancreatitis model with persistent inflammation and behavioral signs of increased nociception. Analysis of imaging data demonstrates an increase in MRI signal for all the regions of interest selected including the rostral ventromedial medulla, dorsal raphe, periaqueductal grey, medial thalamus, and central amygdala as predicted by the anatomical data, as well as increases in the lateral thalamus, cingulate/retrosplenial and parietal cortex. Occipital cortex was not activated above threshold in any condition and served as a negative control. Morphine attenuated the MRI signal, and the morphine effect was antagonized by naloxone in lower brainstem sites. These data confirm activation of these specific regions of interest known as integration sites for nociceptive information important in behavioral, affective, emotional and autonomic responses to ongoing noxious visceral activation.

Treatment of chronic back pain by sensory discrimination training. A Phase I RCT of a novel device (FairMed) vs. TENS

BACKGROUND

The causes of chronic low back pain (CLBP) remain obscure and effective treatment of symptoms remains elusive. A mechanism of relieving chronic pain based on the consequences of conflicting unpleasant sensory inputs to the central nervous system has been hypothesised. As a result a device was generated to deliver sensory discrimination training (FairMed), and this randomised controlled trial compared therapeutic effects with a comparable treatment modality, TENS.

METHODS

60 patients with CLBP were recruited from physiotherapy referrals to a single-blinded, randomised controlled, non-inferiority trial. They were randomised to receive either FairMed or TENS and asked to use the allocated device for 30 minutes, twice a day, for 3 weeks. The primary outcome variable measured at 0 and 3 weeks was pain intensity measured using a visual analogue scale averaged over 7 days. Secondary outcome measures were Oswestry Disability Index, 3 timed physical tests, 4 questionnaires assessing different aspects of emotional coping and a global measure of patient rating of change. Data were analysed for the difference in change of scores between groups using one-way ANOVA.

RESULTS

Baseline characteristics of the two groups were comparable. The primary outcome, change in pain intensity (VAS) at 3 weeks showed a mean difference between groups of -0.1, (non significant p = 0.82). The mean difference in change in ODI scores was 0.4; (non significant p = 0.85). Differences in change of physical functioning showed that no significant difference in change of scores for any of these test (p = 0.58 - 0.90). Changes in scores of aspects of emotional coping also demonstrated no significant difference in change scores between the groups (p = 0.14 - 0.94).

CONCLUSION

FairMed was not inferior to TENS treatment. The findings have implications for further research on current chronic pain theories and treatments. Further work to explore these mechanisms is important to expand our understanding of chronic pain and the role of neuro-modulation.

Brain imaging of visceral functions in healthy volunteers and IBS patients

From experience, most people know about a link between psychological processes and gastrointestinal sensory and motor functions. Cognitive processes (e.g., attention) as well as affective processes (e.g., fear) play a role in gastrointestinal sensations in healthy controls and patients with irritable bowel syndrome (IBS) alike. However, the exact nature of this relationship has not been completely understood yet. Brain imaging techniques allow for the study of brain-gut interactions in vivo. Accordingly, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been widely used to study neural mechanisms underlying visceral sensations. This article will summarize the results of functional brain imaging studies in healthy controls and selected studies assessing the influence of psychological processes on gastrointestinal functions. Subsequently, this article will deal with those brain areas activated by visceral stimulation in IBS patients. Special attention will be paid to recently published studies concerning psychological factors and novel research questions.

Human secondary somatosensory cortex is involved in the processing of somatosensory rare stimuli: an fMRI study

In the human somatosensory system, the contralateral primary somatosensory cortex (SI) is presumed to process and encode type and intensity of the sensory inputs, whereas the bilateral secondary somatosensory cortex (SII) is believed to perform higher order functions including sensorimotor integration, integration of information from the two body halves, attention, learning and memory. In this fMRI study we investigated the effect of attention on the activation of SI and SII, as induced by nonpainful and painful rare deviant electric stimuli during somatosensory oddball tasks. The working hypothesis is of stronger effects of attention on SII with respect to SI. Four runs were acquired according to an oddball scheme. Frequent nonpainful electrical stimuli were delivered to the ulnar nerve at motor threshold, whereas rare/deviant stimuli were delivered to median nerve in four conditions (one condition per run): nonpainful, painful, counting nonpainful, and counting painful. Results showed a statistically significant fMRI activation in bilateral SII but not in contralateral SI when the rare/deviant median nerve stimuli were delivered at nonpainful and painful levels as well as at the two levels of attention considered (i.e., associated with counting and non-counting tasks). Furthermore, fMRI activation in SII did not differ across the different levels of stimulus intensity (nonpainful, painful) and attention (non-counting, counting). These results corroborate the notion that SII is the target of independent pathways for the processing and integration of nonpainful and painful somatosensory stimuli salient for further high-order elaborations.

Attention and reality constraints on the neural processes of empathy for pain

Recent brain imaging studies have shown that the neural substrates underlying the ability to infer and share the feeling of pain of other individuals overlap with the pain matrix that mediates the process of one's own pain. While there has been evidence that the neural activity mediating pain experience is influenced by top-down attention, it remains unclear whether the neural substrates of empathy for pain are modulated by top-down controlled mechanisms. The current work investigated whether the neural correlates of empathic processes of pain are altered by task demand and prior knowledge of stimulus reality. Subjects were scanned using functional magnetic resonance imaging (fMRI) while watching pictures or cartoons of hands that were in painful or neutral situations. Subjects were asked either to evaluate pain intensity supposedly felt by the model or to count the number of hands in the stimulus displays. Relative to counting neutral stimuli, rating pain intensity of painful pictures and cartoons induced increased activation in ACC/paracingulate and the right middle frontal gyrus. Rating pain intensity also activated the inferior frontal cortex bilaterally and the right insula/putamen for pictures but activated the left parietal cortex, the postcentral gyrus, and the occipito-temporal cortex for cartoons. However, the neural activities related to pain rating were eliminated when subjects counted the number of hands in the painful stimuli. In addition, the ACC activity associated with empathy for pain was stronger for the pictures than for the cartoons. Our findings indicate that the involvement of the neural substrates underlying pain-related empathy is constrained by top-down attention and contextual reality of stimuli.