Unique Autonomic Responses to Pain in Yoga Practitioners.

OBJECTIVE: Autonomic nervous system activity is associated with neurobehavioral aspects of pain. Yogis use breathing, relaxation, and mindfulness to tolerate pain, which could influence autonomic responses. To evaluate how the link between autonomic responses and pain is altered by other factors, we compared perceptual and autonomic responses to pain between yogis and controls. METHODS: Nineteen yogis and 15 controls rated warm and painfully hot stimuli (1-cm thermode on calf), with visual anticipatory cues indicating certainly painful, certainly nonpainful, or uncertainly either painful or nonpainful. Heart rate, skin conductance, respiration, and blood pressure were measured. RESULTS: At baseline, yogis breathed slower and deeper than did controls, with no differences in other autonomic measures. During the task, perceptual ratings did not differ between groups in either the certain or uncertain conditions. Nevertheless, yogis had higher phasic skin conductance responses in anticipation of and response to all stimuli, but particularly during painful heat in uncertain contexts (uncertain: 0.46 [0.34] µS; certain: 0.37 [0.28] µS; t(18) = 3.962, p = .001). Furthermore, controls showed a decrease in heart rate to warm (-2.51 [2.17] beats/min) versus painful stimuli (0.83 [1.63] beats/min; t(13) = 5.212, p < .001) and lower respiratory sinus arrhythmia during pain compared with warm trials, whereas yogis had similar reactions to painful and nonpainful stimuli. CONCLUSIONS: Autonomic responses to pain differed in yogis and healthy volunteers, despite similar pain ratings. Thus, autonomic reactivity to pain may be altered by environmental and psychological factors throughout an individual's life.

Multicenter assessment of quantitative sensory testing (QST) for the detection of neuropathic-like pain responses using the topical capsaicin model.

BACKGROUND: The use of quantitative sensory testing (QST) in multicenter studies has been quite limited, due in part to lack of standardized procedures among centers. AIM: The aim of this study was to assess the application of the capsaicin pain model as a surrogate experimental human model of neuropathic pain in different centers and verify the variation in reports of QST measures across centers. METHODS: A multicenter study conducted by the Quebec Pain Research Network in six laboratories allowed the evaluation of nine QST parameters in 60 healthy subjects treated with topical capsaicin to model unilateral pain and allodynia. The same measurements (without capsaicin) were taken in 20 patients with chronic neuropathic pain recruited from an independent pain clinic. RESULTS: Results revealed that six parameters detected a significant difference between the capsaicin-treated and the control skin areas: (1) cold detection threshold (CDT) and (2) cold pain threshold (CPT) are lower on the capsaicin-treated side, indicating a decreased in cold sensitivity; (3) heat pain threshold (HPT) was lower on the capsaicin-treated side in healthy subjects, suggesting an increased heat pain sensitivity; (4) dynamic mechanical allodynia (DMA); (5) mechanical pain after two stimulations (MPS2); and (6) mechanical pain summation after ten stimulations (MPS10), are increased on the capsaicin-treated side, suggesting an increased in mechanical pain (P < 0.002). CDT, CPT and HPT showed comparable effects across all six centers, with CPT and HPT demonstrating the best sensitivity. Data from the patients showed significant difference between affected and unaffected body side but only with CDT. CONCLUSION: These results provide further support for the application of QST in multicenter studies examining normal and pathological pain responses.

Contexte: L'utilisation de tests sensoriels quantitatifs (QST) dans les études multicentriques est limitée, en partie à cause de l'absence de procédures normalisées au sein des centres.But: évaluer l'application du modèle de la douleur traitée par capsaïcine en tant que modèle expérimental humain de substitution pour la douleur neuropathique dans différents centres et vérifier les variations dans les mesures des tests sensoriels quantitatifs entre les centres.Méthodes: Une étude multicentrique menée par le Réseau québécois de recherche sur la douleur dans six laboratoires a permis d'évaluer neuf paramètres de tests sensoriels quantitatifs chez 60 sujets en bonne santé traités par capsaïcine topique afin de modéliser la douleur unilatérale et l'allodynie. Les mêmes mesures (sans capsaïcine) ont été prises chez 20 patients atteints de douleur neuropathique chronique recrutés dans une clinique de la douleur indépendante.Résultats: Les résultats ont révélé une différence significative entre la zone de peau traitée à la capsaïcine et la zone contrôle pour six paramètres : 1) le seuil de détection du froid (CTF) et 2) le seuil de perception de la douleur causée par le froid (CPT) étaient plus bas sur le côté traité par capsaïcine chez les sujets en bonne santé, ce qui indique une diminution de la sensibilité au froid, 3) Le seuil de perception de la douleur causée par la chaleur (HPT) était plus bas sur le côté traité par capsaïcine chez les sujets en bonne santé, ce qui suggère une augmentation de la sensibilité à la douleur causée par la chaleur; 4) l'allodynie mécanique dynamique (DMA), 5) la douleur mécanique après deux stimulations (MPS2) et 6) la somme de la douleur mécanique après 10 stimulations (MPS10) ont augmenté sur le côté traité à la capsaïne, ce qui suggère une augmentation de la douleur mécanique (p < 0,002). Le CDT, le CPT et le HPT ont démontré des effets comparables dans les six centres, le CPT et le HPT démontrant la meilleure sensibilité. Les données des patients ont révélé une différence significative entre le côté affecté et le non côté non affecté, mais seulement dans le cas du CDT.Conclusion: Ces résultats soutiennent l'application de tests sensoriels quantitatifs dans les études multicentriques portant sur les réponses normales et pathologiques à la douleur.

Neuroprotective effects of yoga practice: age-, experience-, and frequency-dependent plasticity.

Yoga combines postures, breathing, and meditation. Despite reported health benefits, yoga's effects on the brain have received little study. We used magnetic resonance imaging to compare age-related gray matter (GM) decline in yogis and controls. We also examined the effect of increasing yoga experience and weekly practice on GM volume and assessed which aspects of weekly practice contributed most to brain size. Controls displayed the well documented age-related global brain GM decline while yogis did not, suggesting that yoga contributes to protect the brain against age-related decline. Years of yoga experience correlated mostly with GM volume differences in the left hemisphere (insula, frontal operculum, and orbitofrontal cortex) suggesting that yoga tunes the brain toward a parasympatically driven mode and positive states. The number of hours of weekly practice correlated with GM volume in the primary somatosensory cortex/superior parietal lobule (S1/SPL), precuneus/posterior cingulate cortex (PCC), hippocampus, and primary visual cortex (V1). Commonality analyses indicated that the combination of postures and meditation contributed the most to the size of the hippocampus, precuneus/PCC, and S1/SPL while the combination of meditation and breathing exercises contributed the most to V1 volume. Yoga's potential neuroprotective effects may provide a neural basis for some of its beneficial effects.

Insular cortex mediates increased pain tolerance in yoga practitioners.

Yoga, an increasingly popular discipline among Westerners, is frequently used to improve painful conditions. We investigated possible neuroanatomical underpinnings of the beneficial effects of yoga using sensory testing and magnetic resonance imaging techniques. North American yogis tolerated pain more than twice as long as individually matched controls and had more gray matter (GM) in multiple brain regions. Across subjects, insular GM uniquely correlated with pain tolerance. Insular GM volume in yogis positively correlated with yoga experience, suggesting a causal relationship between yoga and insular size. Yogis also had increased left intrainsular white matter integrity, consistent with a strengthened insular integration of nociceptive input and parasympathetic autonomic regulation. Yogis, as opposed to controls, used cognitive strategies involving parasympathetic activation and interoceptive awareness to tolerate pain, which could have led to use-dependent hypertrophy of insular cortex. Together, these findings suggest that regular and long-term yoga practice improves pain tolerance in typical North Americans by teaching different ways to deal with sensory inputs and the potential emotional reactions attached to those inputs leading to a change in insular brain anatomy and connectivity.

The ventral striatum is implicated in the analgesic effect of mood changes.

BACKGROUND: The ventral striatum, particularly the nucleus accumbens, is commonly associated with the processing of reward and positive stimuli, positive affect as well as antinociceptive processes. OBJECTIVES: The present study examined whether the ventral striatum is implicated in analgesia resulting from positive mood change induced by pleasant odours. METHODS: Functional magnetic resonance imaging studies were conducted in healthy individuals receiving painful heat stimuli in the presence of pleasant or unpleasant odours, which were used to induce positive and negative mood states. Ventral striatum activity was examined in the two mood states. RESULTS: For most subjects, pleasant odours improved mood and reduced pain unpleasantness perception relative to unpleasant odours. In the pleasant odour condition, the maximum activation of both the left and right ventral striatum was positively correlated with the amount of pain reduction. Furthermore, the left and right ventral striatum activations positively covaried with one another, and the right ventral striatum activation positively correlated with that in the periaqueductal grey matter. Both ventral striatum activations negatively covaried with the activation of the right mediodorsal thalamus, left dorsal anterior cingulate cortex, left medial prefrontal cortex and right ventrolateral prefrontal cortex. CONCLUSIONS: Because both the mediodorsal thalamus and anterior cingulate are involved in pain affect perception, and activation within the prefrontal areas and periaqueductal grey matter were previously shown to correlate with mood-related pain modulation, it is concluded that the ventral striatum is likely implicated in the analgesic effect of positive mood changes induced by pleasant odours on pain unpleasantness.

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.

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.

Effects of psychological state on pain perception in the dental environment.

Psychological factors have an important influence on pain perception. Both in the clinic and in experimental settings, distraction has been shown to reduce pain. Further, negative emotions increase pain, whereas positive emotions have the opposite effect. Other more complex psychological states alter the way we feel pain. For instance, empathy for another person who is suffering increases our own pain experience, and expectation of pain relief underlies much of the placebo effect. Neuroimaging studies show a physiological basis for psychological pain modulation, with activity in pain pathways altered by attentional state, positive and negative emotions, empathy and the administration of a placebo. The same psychological factors activate intrinsic modulatory systems in the brain, including those stimulated when opiates are given for pain relief. It is important for the dentist and patients to understand the influence of psychological state on pain transmission. Such an understanding will not only help patients learn how to participate in their own pain control, but will also help the clinician create a fostering environment.

The effects of the steroid androstadienone and pleasant odorants on the mood and pain perception of men and women.

BACKGROUND AND PURPOSE: We previously found that for both men and women odors influence mood, which in turn influences pain unpleasantness perception. Others showed that the steroid androstadienone modulates mood differently in men and women, improving mood in women and worsening it or leaving it unchanged in men. Based on its dissociable effect on mood, we hypothesized that women exposed to androstadienone would report lower pain unpleasantness than when exposed to the vehicle, while men would show no change or the reverse pattern. Because of the expected beneficial effect of pleasant odors on mood in both men and women, all subjects should report lower pain unpleasantness when exposed to the pleasant odor compared to the unscented air. METHODS: In one session subjects were exposed to: (1) androstadienone diluted in a vehicle while breathing unscented air and (2) androstadienone in vehicle while breathing a pleasant odorant. In another session they were exposed to: (1) vehicle and unscented air and (2) vehicle and a pleasant odorant. Phasic contact heat was used to induce pain. RESULTS AND CONCLUSIONS: Planned comparisons confirmed that, in the absence of pain, androstadienone improved mood only in women, while the pleasant odorants improved mood for all subjects. However, these positive mood changes did not persist with the introduction of pain. Consistent with the absence of positive mood changes, pain unpleasantness was not modulated. Unexpectedly, the presence of androstadienone increased perceived pain intensity especially in women, suggesting an effect of androstadienone on pain perception, independent of mood changes. Heightened attentional state may be responsible.

Unpleasant odors increase pain processing in a patient with neuropathic pain: psychophysical and fMRI investigation.

A 49-year old man with neuropathic pain in his right elbow, wrist and digits III-V of his hand reported that certain odors increased his pain by superimposing an electric shock-like pain to his already existing pain. Psychophysical testing revealed that the best predictor of pain exacerbation was odor unpleasantness. Functional magnetic resonance imaging (fMRI) showed increased activation following an unpleasant odor in pain related areas, including the thalamus, amygdala, insular and anterior cingulate cortices, with similar trends in primary somatosensory cortex hand/arm area. The increased pain and associated neural activations in response to unpleasant odors may be related to the phenomenon of synesthesia, to a rewiring of olfactory pathways onto pain pathways mimicking synesthesia or, to activation of the sympathetic nervous system.

Sparing of perceptual implicit memory despite suppression of the electrophysiological word repetition effect: a study with general anesthetic isoflurane.

OBJECTIVE: Much effort has been devoted to the search for the neurophysiological correlates of implicit memory. A commonly held view is that the early portion (250-500 ms) of the event-related potential (ERP) word repetition effect reflects processes important for perceptual implicit memory whereas the latter portion reflects processes implicated in explicit memory. It is, however, difficult to disentangle with certainty the relative contributions of each form of memory on ERPs since both forms co-exist in normal subjects. To dissociate ERP effect related to implicit and explicit memory, we used isoflurane sedation in normal subjects to suppress explicit remembering while sparing implicit memory. These ERPs were compared with those of non-medicated control subjects. METHODS: Thirteen subjects performed an incidental encoding task for words presented auditorily during the inhalation of a subanesthetic dose of isoflurane. After termination of isoflurane administration, we assessed free recall and recorded ERPs during a syllable completion task (implicit memory) and during a passive listening task (ERP repetition effect). Eleven non-medicated control subjects were tested in a similar manner. RESULTS: The controls showed robust early and late ERP repetition effect. The isoflurane group had implicit memory without free recall and showed no ERP repetition effect. CONCLUSIONS: These findings failed to show an association between any part of the repetition effect and perceptual implicit memory. The results are consistent with the view that processes linked to explicit memory contribute to the ERP repetition effect since there was a marked difference in free recall between the control and isoflurane groups. SIGNIFICANCE: The present study shows that the reversible alterations of memory by general anesthetics can be used to study the neurophysiological correlates of memory processes.

Effects of odors on pain perception: deciphering the roles of emotion and attention.

Emotions have been shown to alter pain perception, but the underlying mechanism is unclear since emotions also affect attention, which itself changes nociceptive transmission. We manipulated independently direction of attention and emotional state, using tasks involving heat pain and pleasant and unpleasant odors. Shifts in attention between the thermal and olfactory modalities did not alter mood or anxiety. Yet, when subjects focused attention on the pain, they perceived it as clearly more intense and somewhat more unpleasant than when they attended to the odor. In contrast, odor valence altered mood, anxiety level, and pain unpleasantness, but did not change the perception of pain intensity. Pain unpleasantness ratings correlated with mood, but not with odor valence, suggesting that emotional changes underlie the selective modulation of pain affect. These results show that emotion and attention differentially alter pain perception and thus invoke at least partially separable neural modulatory circuits.