Pain processing during three levels of noxious stimulation produces differential patterns of central activity

Social Decision-Making: Insights from Game Theory and Neuroscience

By combining the models and tasks of Game Theory with modern psychological and neuroscientific methods, the neuroeconomic approach to the study of social decision-making has the potential to extend our knowledge of brain mechanisms involved in social decisions and to advance theoretical models of how we make decisions in a rich, interactive environment. Research has already begun to illustrate how social exchange can act directly on the brain's reward system, how affective factors play an important role in bargaining and competitive games, and how the ability to assess another's intentions is related to strategic play. These findings provide a fruitful starting point for improved models of social decision-making, informed by the formal mathematical approach of economics and constrained by known neural mechanisms.

Dopamine receptors in the anterior insular cortex modulate long-term nociception in the rat

The rostral agranular insular cortex (RAIC) receives dopaminergic projections from the mesolimbic system, which has been involved in the modulation of nociceptive processes. In this study we determined the contribution of dopamine D(1) and D(2) receptors in the RAIC regarding nociception processing in a neuropathic pain model, as well as inflammatory articular nociception measured as pain-induced functional impairment in the rat (PIFIR). Microinjection of vehicle or substances into the RAIC was performed after the induction of nociception. The groups were treated with: a dopamine D(1) receptor antagonist (SCH-23390), a dopamine D(1) receptor agonist (SKF-38393), a dopamine D(2) receptor agonist (TNPA) and a dopamine D(2) receptor antagonist (spiperone). Chronic nociception, induced by denervation, was measured by the autotomy score in which onset and incidence were also determined. The SCH-23390 and TNPA groups showed a decrease in the autotomy score and a delay on the onset as compared to control, whereas the PIFIR groups did not show statistical differences. This work shows the differential role of dopamine receptors within the RAIC in which the activation of D(2) or the blockade of D(1) receptors elicit antinociception.

Phosphorylation of c-Jun N-terminal kinase isoforms and their different roles in spinal cord dorsal horn and primary somatosensory cortex

The present study was undertaken to investigate whether isoforms of c-Jun N-terminal kinase (JNK 46 kDa and 54 kDa), one component of the mitogen-activated protein kinase (MAPK) family, might show region-related differential activation patterns in both naïve and pain-experiencing rats. In naïve rats, no significant difference was observed in total expression level of the two JNK isoforms between spinal cord and primary somatosensory cortex (S1 area). However, phosphorylated JNK 46 kDa was normally expressed in the S1 area, but not in the spinal cord, while neither of the two structures contained phosphorylated JNK 54 kDa. Subcutaneous bee venom (BV)-induced persistent pain stimulation resulted in a significant increase in the phosphorylation of both JNK isoforms in each area for a long period (lasting at least 48 h). Nevertheless, JNK 46 kDa exhibited a much higher activation than JNK 54 kDa in the spinal cord, whereas the same noxious stimulation elicited evident activation of JNK 54 kDa in the S1 area, leaving JNK 46 kDa less affected. Intraplantar injection of sterile saline solution, causing acute and transient pain, produced almost the same changes in activation profile of the two JNK isoforms as found in the BV-treated rats. These results implicate that individual members of the JNK family may be associated with specific regions of nociceptive processing. Also, the two JNK isoforms are supposed to function differently according to their locations within the rat central nervous system.

Region- or state-related differences in expression and activation of extracellular signal-regulated kinases (ERKs) in naïve and pain-experiencing rats

BACKGROUND

Extracellular signal-regulated kinase (ERK), one member of the mitogen-activated protein kinase (MAPK) family, has been suggested to regulate a diverse array of cellular functions, including cell growth, differentiation, survival, as well as neuronal plasticity. Recent evidence indicates a role for ERKs in nociceptive processing in both dorsal root ganglion and spinal cord. However, little literature has been reported to examine the differential distribution and activation of ERK isoforms, ERK1 and ERK2, at different levels of pain-related pathways under both normal and pain states. In the present study, quantitative blot immunolabeling technique was used to determine the spatial and temporal expression of ERK1 and ERK2, as well as their activated forms, in the spinal cord, primary somatosensory cortex (SI area of cortex), and hippocampus under normal, transient pain and persistent pain states.

RESULTS

In naïve rats, we detected regional differences in total expression of ERK1 and ERK2 across different areas. In the spinal cord, ERK1 was expressed more abundantly than ERK2, while in the SI area of cortex and hippocampus, there was a larger amount of ERK2 than ERK1. Moreover, phosphorylated ERK2 (pERK2), not phosphorylated ERK1 (pERK1), was normally expressed with a high level in the SI area and hippocampus, but both pERK1 and pERK2 were barely detectable in normal spinal cord. Intraplantar saline or bee venom injection, mimicking transient or persistent pain respectively, can equally initiate an intense and long-lasting activation of ERKs in all three areas examined. However, isoform-dependent differences existed among these areas, that is, pERK2 exhibited stronger response than pERK1 in the spinal cord, whereas ERK1 was more remarkably activated than ERK2 in the S1 area and hippocampus.

CONCLUSION

Taken these results together, we conclude that: (1) under normal state, while ERK immunoreactivity is broadly distributed in the rat central nervous system in general, the relative abundance of ERK1 and ERK2 differs greatly among specific regions; (2) under pain state, either ERK1 or ERK2 can be effectively phosphorylated with a long-term duration by both transient and persistent pain, but their response patterns differ from each other across distinct regions; (3) The long-lasting ERKs activation induced by bee venom injection is highly correlated with our previous behavioral, electrophysiological, morphological and pharmacological observations, lending further support to the functional importance of ERKs-mediated signaling pathways in the processing of negative consequences of pain associated with sensory, emotional and cognitive dimensions.

Activity in the human amygdala corresponds to early, rather than late period autonomic responses to a signal for shock

Laboratory animal and human subject studies report that the amygdala is a critical brain structure that supports the acquisition and expression of conditional fear. Recent functional neuroimaging studies in humans have reported that activity in this region is closely related to the behavioral expression of conditional skin conductance responses (SCR). However, SCR waveforms following conditional stimulus (CS) presentation contain both early period and late period responses that may differ with respect to underlying central processes. It is not known whether amygdala activity corresponds to the expression of early conditional responses (CRs) that occur shortly following CS onset or late CRs that closely precede UCS onset. The present study used event-related functional magnetic resonance imaging and concurrent skin conductance measurements to determine whether amygdala activity is more closely related to the expression of early or late period CRs. Increased amygdala activity was detected during the formation of early, but not late period CRs. Additionally, this pattern of amygdala activity did not dissipate, but persisted into late stages of the experiment. These findings are consistent with the idea that amygdala responding is critically involved in the generation of CRs formed shortly following CS onset.

Different transfer of nociceptive sensitivity from rats with postnatal hippocampal lesions to control rats

Hippocampal lesions in newborn rats alter the development of mechanisms involved in the processing of nociception. The hippocampal lesion was induced by the bilateral infusion, into the lateral cerebral ventricles, of 0.25 microL of saline containing either 0.25 micromol quinolinic acid (QUIN) and/or 0.25 micromol N-acetyl-L-aspartyl-L-glutamate (NAAG) on postnatal day 12. The same amount of sterile saline was injected into the sham-operated animals (group SHAM). It was expected that the QUIN- and NAAG-lesioned rats would exhibit some differences in thermal pain perception; however, we wanted to know if the control rats would exhibit, at least in part, similar changes in pain perception as their chemically lesioned siblings with which they were housed. Young adult NAAG-injured rats exhibited increased withdrawal latencies in the tail-flick and plantar tests, whereas young adult QUIN-injured animals exhibited only marginally decreased latencies. Nociceptive responses in the SHAM rats paralleled the littermates that had been neonatally treated with QUIN or NAAG, i.e. the responses in the SHAM(QUIN) group decreased, whereas the responses in the SHAM(NAAG) group increased. No significant changes in nociception were observed in intact animals, regardless of which group they were housed with. Our results show that social factors, which were originally demonstrated only for the pain behavior, may also influence basal nociceptive sensitivity in rats. We concluded that the "sham operation" may have had a long-term, nonspecific impact on nociceptive behavior by inducing behavioral mimicry of other animals.

Imaging visceral pain

The application of functional imaging to study visceral sensation has generated considerable interest regarding insight into the function of the brain-gut axis. Brain activation in normal control subjects during visceral sensation includes the perigenual cingulate cortex, which is involved in affective processing and has direct connections to autonomic centers. In contrast, somatic pain rarely activates the perigenual cingulate. This difference in brain activation is highly interpretable because visceral stimuli are experienced as more unpleasant than somatic stimuli. Clinical studies are suggestive of functional changes that may be a consequence or cause of conditions such as irritable bowel syndrome, but the findings are not consistent and are not as obviously interpretable as the differences observed when contrasting visceral and somatic stimulation. Although this is partly because brain imaging is still a relatively new technique, it also reflects weaknesses inherent to the understanding of chronic visceral pain as a biopsychosocial phenomenon. The biopsychosocial concept is very broad and rarely provides for precise predictions or mechanisms that can be directly tested using brain imaging. Future use of brain imaging to examine chronic visceral pain and other pain disorders will be more likely to succeed by describing clear theoretical and clinical endpoints.

Imaging of pain: recent developments

Brain imaging of pain has made remarkable strides in the past year and a half. The basic regional activation pattern after acute nociceptive stimulation is now fairly well clarified. The extension of imaging studies from normal subjects to include cohorts of pathological pain patients is occurring. The techniques of positron emission tomography, functional magnetic resonance imaging and single photon emission computed tomography have all been applied to the study of human pain processing and the assessment of physiological interventions or psychological manipulations. Studies using labelled ligands to trace receptor alterations have also been conducted. Although more work could be done on the pharmacology and physiology of anesthesiology, the resulting set of observations provides a deeper understanding of the basic human neurophysiology of pain and a potential neural framework for better pain management.

Striatal dopamine D2 receptors attenuate neuropathic hypersensitivity in the rat

Earlier studies indicate that striatal dopamine D(2) receptors are involved in pain regulation in non-neuropathic conditions. We assessed whether striatal dopamine D(2) receptors contribute to pain regulation also in neuropathic conditions. The spared nerve injury model of neuropathy was induced by unilateral ligation of the tibial and common peroneal nerves in the rat. In awake nerve-injured animals, pain-related withdrawal responses to calibrated monofilaments or noxious heating were attenuated following striatal administration of a dopamine D(2) receptor agonist quinpirole. Pain-related responses were attenuated only in the nerve-injured limb ipsilateral to the injection and in the midline (tail). In unoperated controls, striatal administration of quinpirole at an antihypersensitive dose did not influence withdrawal responses to mechanical stimulation. Attenuation of pain-related responses induced by striatal administration of quinpirole was reversed by intrathecal administration of a dopamine D(2) receptor antagonist (eticlopride) or a non-selective 5-HT receptor antagonist (methysergide), but not by an alpha(2)-adrenoceptor antagonist (atipamezole). In the rostroventromedial medulla of lightly anesthetized neuropathic animals, striatal administration of quinpirole significantly decreased the activity of presumably pronociceptive cells that are activated by noxious stimulation. The innocuous H-reflex in lightly anesthetized control animals was not suppressed by striatal administration of quinpirole at an antihypersensitive dose. The results indicate that striatal dopamine D(2) receptors attenuate neuropathic hypersensitivity. The antihypersensitive effect induced by striatal dopamine D(2) receptors in peripheral neuropathy involves suppression of impulse discharge of presumably pronociceptive neurons in the rostroventromedial medulla, and a descending influence acting on spinal 5-HT and dopamine D(2) receptors.

Hypnosis and surgery: past, present, and future

Hypnosis has been defined as the induction of a subjective state in which alterations of perception or memory can be elicited by suggestion. Ever since the first public demonstrations of "animal magnetism" by Mesmer in the 18th century, the use of this psychological tool has fascinated the medical community and public alike. The application of hypnosis to alter pain perception and memory dates back centuries. Yet little progress has been made to fully comprehend or appreciate its potential compared to the pharmacologic advances in anesthesiology. Recently, hypnosis has aroused interest, as hypnosis seems to complement and possibly enhance conscious sedation. Contemporary clinical investigators claim that the combination of analgesia and hypnosis is superior to conventional pharmacologic anesthesia for minor surgical cases, with patients and surgeons responding favorably. Simultaneously, basic research of pain pathways involving the nociceptive flexion reflex and positron emission tomography has yielded objective data regarding the physiologic correlates of hypnosis. In this article I review the history, basic scientific and clinical studies, and modern practical considerations of one of the oldest therapeutical tools: the power of suggestion.

Neural correlates of perceptual difference between itching and pain: a human fMRI study

It has been wondered why we can discriminate between itching and pain as different sensations. Several researchers have investigated neural mechanisms underlying their perceptual differences, and found that some C fibers and spinothalamic tract neurons had different sensitivity between itching and pain. These findings suggest that such differences in ascending pathways are partly associated with perceptual difference between itching and pain. However, it was still unclear how our brains distinguish itching from pain. Thus, by functional magnetic resonance imaging (fMRI) time series analysis, we investigated the neural substrates of perceptual differences between itching and pain. The anterior cingulate cortex, the anterior insula, the basal ganglia and the pre-supplementary motor area were commonly activated by itching and pain. Neural activity in the posterior cingulate cortex (PCC) and the posterior insula associated with itching was significantly higher than that associated with pain and significantly proportional to itching sensation. Pain, but not itching, induced an activation of the thalamus for several minutes, and neural activity of this brain region significantly correlated to pain sensation. These findings demonstrate that the difference in the sensitivity of PCC, the posterior insula and the thalamus between itching and pain would be responsible for the perceptual difference between these sensations. The previous itching studies did not observe an activation of the secondary somatosensory cortex (S2) by itching. However, we observed that an activation of S2 by pain was not significantly different from that by itching, indicating that S2 was associated with not only pain but also itching.

Ideas about pain, a historical view

The expression 'painful' can be used to describe both an embarrassing moment and a cut on the finger. An explanation for this dichotomy can be found in the convoluted history of ideas about pain. Whether pain is an independent sensation and the product of dedicated neural mechanisms continues to be a topic of debate. This overview concentrates on the issue of specificity together with other notable information regarding pain that has emerged since 1800.

Capsaicin-induced thermal hyperalgesia and sensitization in the human trigeminal nociceptive pathway: an fMRI study

The aim of this study was to differentiate the processing of nociceptive information, matched for pain intensity, from capsaicin-induced hyperalgesic vs. control skin at multiple levels in the trigeminal nociceptive pathway. Using an event-related fMRI approach, 12 male subjects underwent three functional scans beginning 1 h after topical application of capsaicin to a defined location on the maxillary skin, when pain from capsaicin application had completely subsided. Brush and two levels of painful heat (low-Thermal-1 and high-Thermal-2) were applied to the site of capsaicin application and to the mirror image region on the opposite side. Temperatures for each side were set to evoke perceptually matched pain (mean temperatures [capsaicin/control]: Thermal-1=38.4/42.8 degrees C; Thermal-2=44.9/47.8 degrees C). We found differences in activation patterns following stimuli to treated and untreated sides in sensory circuits across all stimulus conditions. Across the trigeminal nociceptive pathway, Thermal-2 stimulation of hyperalgesic skin evoked greater activation in trigeminal ganglion and nucleus, thalamus, and somatosensory cortex than the control side. Thus, trigeminal nociceptive regions showed increased activation in the context of perceptually equal pain levels. Beyond these regions, contrast analyses of capsaicin vs. control skin stimulation indicated significant changes in bilateral dorsolateral prefrontal cortex and amygdala. The involvement of these emotion-related regions suggests that they may be highly sensitive to context, such as prior experience (application of capsaicin) and the specific pain mechanism (hyperalgesic vs. normal skin).

Dipole source localisation using independent component analysis: single trial localisation of laser evoked pain

The accuracy of the inverse solution that finds the spatial location of the generating sources from averaged scalp-recorded event related potentials (ERPs) relies on assumptions about the ERP signals and the sources. We provide evidence that using independent component analysis (ICA) as a signal decomposition filter prior to applying the inverse solution reveals sources that cannot be detected by conventional source localisation methods. Five clusters of sources emerged: a single source cluster in caudal cingulate and bilateral sources in secondary somatosensory cortex (SII), inferior parietal cortex, premotor cortex and insular cortex. The locations of the source dipoles were consistent with findings using fMRI and PET but have not all been previously detected in a single electrophysiological study. In addition, the time-course of the activation of these dipoles was estimated. The results suggest that using ICA to localise single trial data is a powerful tool for exploring the spatiotemporal dynamics of rapid and complex brain processes.

Mécanismes cérébraux impliqués dans l’interaction entre la douleur et les émotions

INTRODUCTION

Pain is an unpleasant and intrusive sensation, warning of actual or potential tissue damage. Over the last fifteen years, functional cerebral imaging research has demonstrated the involvement of many cerebral structures in the experience of pain.

BACKGROUND

Intimately linked to the notion of suffering, the affective dimension of pain relies on neurophysiological systems partly distinct anatomically from those involved more specifically in its sensory dimension. Some pathways convey nociceptive information to the somatosensory cortex and the insula, contributing to the sensory aspects of pain (e.g.: sensory intensity), and secondarily, to its affective dimension. Other pathways project directly to the anterior cingulate cortex, the insula, the amygdala and to the prefrontal cortices, which are structures involved in the affective dimension of pain (unpleasantness of pain and regulation of autonomic and behavioral responses). Interestingly, these latter regions are an integral part of the cerebral emotional networks.

PERSPECTIVES AND CONCLUSION

This close anatomical relationship between pain and emotions circuits could explain the powerful emotional impact of pain as well as the reciprocal modulatory effect of emotions on pain observed in clinical and experimental studies. More specifically, this modulatory effect might reflect interactions between emotional and nociceptive systems in the prefrontal and cingulate cortices, ventral striatum, amygdala and hippocampal regions. Taken together, these observations further attest to the emotional nature of pain experience.

Hypothalamus and amygdala response to acupuncture stimuli in Carpal Tunnel Syndrome

Brain processing of acupuncture stimuli in chronic neuropathic pain patients may underlie its beneficial effects. We used fMRI to evaluate verum and sham acupuncture stimulation at acupoint LI-4 in Carpal Tunnel Syndrome (CTS) patients and healthy controls (HC). CTS patients were retested after 5 weeks of acupuncture therapy. Thus, we investigated both the short-term brain response to acupuncture stimulation, as well as the influence of longer-term acupuncture therapy effects on this short-term response. CTS patients responded to verum acupuncture with greater activation in the hypothalamus and deactivation in the amygdala as compared to HC, controlling for the non-specific effects of sham acupuncture. A similar difference was found between CTS patients at baseline and after acupuncture therapy. For baseline CTS patients responding to verum acupuncture, functional connectivity was found between the hypothalamus and amygdala--the less deactivation in the amygdala, the greater the activation in the hypothalamus, and vice versa. Furthermore, hypothalamic response correlated positively with the degree of maladaptive cortical plasticity in CTS patients (inter-digit separation distance). This is the first evidence suggesting that chronic pain patients respond to acupuncture differently than HC, through a coordinated limbic network including the hypothalamus and amygdala.

Chronic pain and the emotional brain: specific brain activity associated with spontaneous fluctuations of intensity of chronic back pain

Living with unrelenting pain (chronic pain) is maladaptive and is thought to be associated with physiological and psychological modifications, yet there is a lack of knowledge regarding brain elements involved in such conditions. Here, we identify brain regions involved in spontaneous pain of chronic back pain (CBP) in two separate groups of patients (n = 13 and n = 11), and contrast brain activity between spontaneous pain and thermal pain (CBP and healthy subjects, n = 11 each). Continuous ratings of fluctuations of spontaneous pain during functional magnetic resonance imaging were separated into two components: high sustained pain and increasing pain. Sustained high pain of CBP resulted in increased activity in the medial prefrontal cortex (mPFC; including rostral anterior cingulate). This mPFC activity was strongly related to intensity of CBP, and the region is known to be involved in negative emotions, response conflict, and detection of unfavorable outcomes, especially in relation to the self. In contrast, the increasing phase of CBP transiently activated brain regions commonly observed for acute pain, best exemplified by the insula, which tightly reflected duration of CBP. When spontaneous pain of CBP was contrasted to thermal stimulation, we observe a double-dissociation between mPFC and insula with the former correlating only to intensity of spontaneous pain and the latter correlating only to pain intensity for thermal stimulation. These findings suggest that subjective spontaneous pain of CBP involves specific spatiotemporal neuronal mechanisms, distinct from those observed for acute experimental pain, implicating a salient role for emotional brain concerning the self.

Brain activity for spontaneous pain of postherpetic neuralgia and its modulation by lidocaine patch therapy

Postherpetic neuralgia (PHN) is a debilitating chronic pain condition, yet there is a lack of knowledge regarding underlying brain activity. Here we identify brain regions involved in spontaneous pain of PHN (n=11) and determine its modulation with Lidoderm therapy (patches of 5% lidocaine applied to the PHN affected body part). Continuous ratings of fluctuations of spontaneous pain during fMRI were contrasted to ratings of fluctuations of a bar observed during scanning, at three sessions: (1) pre-treatment baseline, (2) after 6h of Lidoderm treatment, and (3) after 2 weeks of Lidoderm use. Overall brain activity for spontaneous pain of PHN involved affective and sensory-discriminative areas: thalamus, primary and secondary somatosensory, insula and anterior cingulate cortices, as well as areas involved in emotion, hedonics, reward, and punishment: ventral striatum, amygdala, orbital frontal cortex, and ventral tegmental area. Generally, these activations decreased at sessions 2 and 3, except right anterior insular activity which increased with treatment. The sensory and affective activations only responded to the short-term treatment (6h of Lidoderm); while the ventral striatum and amygdala (reward-related regions) decreased mainly with longer-term treatment (2 weeks of Lidoderm). Pain properties: average magnitude of spontaneous pain, and responses on Neuropathic Pain Scale (NPS), decreased with treatment. The ventral striatal and amygdala activity best reflected changes in NPS, which was modulated only with longer-term treatment. The results show a specific brain activity pattern for PHN spontaneous pain, and implicate areas involved in emotions and reward as best reflecting changes in pain with treatment.

Could neuroimaging help us to interpret the clinical effects of acupuncture?

One of the problems in assessing acupuncture efficacy has been the lack of a standardised placebo/control. Despite the lack of 'proof', acupuncture is widely used; hence it would seem that a large proportion of the public are not too concerned with the question of efficacy. Patients and researchers approach the issue of whether acupuncture "works" in an entirely different way. It may be that the management of chronic pain as a whole is largely context driven and non-specific. Therefore, research should focus on areas such as pragmatic/comparative trials and the non-specific effects of treatment. Improving our understanding of the neural mechanisms and substrates of acupuncture, placebo and non-specific effects might enable us to better define a "true placebo" and improve trial design. Imaging studies, however, need to be much more pragmatic. Because of the large overlap in areas of brain activated through acupuncture, pain, placebo and non-specific factors, separating these out in an attempt to pinpoint the mechanisms behind acupuncture will be difficult. Ultimately we need a balance between efficacy, comparative and mechanistic trials using imaging work to inform the whole picture. A broader view of research is therefore necessary to yield meaningful answers and we need to look at the whole package that acupuncture delivers.

Pharmacological FMRI in the development of new analgesic compounds

Chronic pain is a major problem for the individual and for society. Despite a range of drugs being available to treat chronic pain, only inadequate pain relief can be achieved for many patients. There is therefore a need for the development of new analgesic compounds. The assessment of pain depends to date entirely on the subjective report of the patient, in contrast to many other clinical conditions where biomarkers that help determine the severity and stage of the disease enable the physician to monitor the course of the disease and treatment effects longitudinally. In this article, we illustrate that magnetic resonance-based imaging techniques have the potential to provide sensitive and specific biomarkers of the pain experience, as well as clarifying disease mechanisms. Functional magnetic resonance imaging (FMRI) is particularly suited to investigating the effects of pharmacological agents on pain processing within the human central nervous system. Combination of FMRI and drug administration is termed pharmacological FMRI (phFMRI). In addition to outlining several methodological considerations that have to be taken into account when performing phFMRI, we discuss phFMRI studies that have already used this technique to study the effects of analgesic compounds. These studies provide promising data for the use of phFMRI as sensitive tool in assessing a potential drug effect. Such pharmacodynamic readouts obtained early in the process of drug development would not only save the pharmaceutical industry substantial amounts of money, but would also avoid the unnecessary exposure of patients to molecules with limited or no therapeutic value. We are therefore optimistic that phFMRI will be used as a tool with high sensitivity and specificity for evaluating analgesic agents in early drug development and clinical studies.

Imaging valuation models in human choice

To make a decision, a system must assign value to each of its available choices. In the human brain, one approach to studying valuation has used rewarding stimuli to map out brain responses by varying the dimension or importance of the rewards. However, theoretical models have taught us that value computations are complex, and so reward probes alone can give only partial information about neural responses related to valuation. In recent years, computationally principled models of value learning have been used in conjunction with noninvasive neuroimaging to tease out neural valuation responses related to reward-learning and decision-making. We restrict our review to the role of these models in a new generation of experiments that seeks to build on a now-large body of diverse reward-related brain responses. We show that the models and the measurements based on them point the way forward in two important directions: the valuation of time and the valuation of fictive experience.

Effect of patellar taping on vasti onset timing, knee kinematics, and kinetics in asymptomatic individuals with a delayed onset of vastus medialis oblique

This randomized within-subject study investigated the effects of patellar tape on the onset of electromyographic (EMG) activity of vastus medialis obliquus (VMO) relative to vastus lateralis (VL), knee kinematics, and kinetics in 12 currently asymptomatic individuals with a VMO timing deficit and a history of patellofemoral pain. Participants were required to complete stair stepping and normal-pace and fast-pace walking tasks under three experimental conditions; no tape, control tape and therapeutic tape. EMG onsets of VMO and VL were measured by surface electrodes, stance phase knee flexion by the PEAK movement analysis system and vertical ground reaction force by a force plate. A two-way repeated measures analysis of variance showed that neither therapeutic tape nor control tape had any effect on the EMG VMO-VL onset timing difference. Therapeutic tape, but not control tape, led to significant increases in stance phase knee flexion. The first peak vertical ground reaction force was lowered by both control and therapeutic tape but only during fast walking. The results suggest that tape induced effects on neuromotor control of the vasti seen in other studies are related to reductions in pain rather than the presence of a baseline timing deficit. However, this cannot explain the improvements in stance phase knee flexion observed with tape.

Interactions of Pain Intensity and Cognitive Load: The Brain Stays on Task

Pain naturally draws one's attention. However, humans are capable of engaging in cognitive tasks while in pain, although it is not known how the brain represents these processes concurrently. There is some evidence for a cortical interaction between pain- and cognitive-related brain activity, but the outcome of this interaction may depend on the relative load imposed by the pain versus the task. Therefore, we used 3 levels of cognitive load (multisource interference task) and 2 levels of pain intensity (median nerve stimulation) to examine how functional magnetic resonance imaging activity in regions identified as pain-related or cognitive-related responds to different combinations of pain intensity and cognitive load. Overall, most pain-related or cognitive-related brain areas showed robust responses with little modulation. However, during the more intense pain, activity in primary sensorimotor cortex, secondary somatosensory cortex/posterior insula, anterior insula, paracentral lobule, caudal anterior cingulate cortex, cerebellum, and supplementary motor area was modestly attenuated by the easy task and in some cases the difficult task. Conversely, cognitive-related activity was not modulated by pain, except when cognitive load was minimal during the control task. These findings support the notion that brain networks supporting pain perception and cognition can be simultaneously active.

Distraction affects frontal alpha rhythms related to expectancy of pain: An EEG study

Previous electroencephalographic (EEG) evidence has shown event-related desynchronization (ERD) of alpha rhythms before predictable painful stimuli, as a possible neural concomitant of attentional preparatory processes (Babiloni, C., Brancucci, A., Babiloni, F., Capotosto, P., Carducci, F., Cincotti, F., Arendt-Nielsen, L., Chen, A.C., Rossini, P.M., 2003. Anticipatory cortical responses during the expectancy of a predictable painful stimulation. A high-resolution electroencephalography study. Eur. J. Neurosci. 18 (6) 1692-700). This study tested the hypothesis that alpha ERD before predictable painful stimuli is reduced as an effect of distraction. A visual warning stimulus preceded a laser painful stimulation, which was strictly followed by visual imperative stimuli. In the Pain (control) condition, no task was required after the imperative stimuli. In the Pain + Movement condition, subjects had to perform a movement of the right index finger. In the Pain + Cognition condition, they had to mentally perform an arithmetical task. EEG data were recorded in 10 subjects from 30 electrodes. Artifact-free recordings were spatially enhanced by surface Laplacian transformation. Alpha ERD was computed at three alpha sub-bands according to subjects' individual alpha frequency peak (i.e., about 6-8 Hz, 8-10 Hz, 10-12 Hz). Compared to the control condition, the subjects reported a significantly lower stimulus intensity perception and unpleasantness in the Pain + Movement and Pain + Cognition conditions. In addition, there was a cancellation of the alpha 3 ERD (i.e., about 10-12 Hz) in Pain + Cognition condition and even a generation of a statistically significant alpha 3 ERS in Pain + Movement condition. These effects were maximum over fronto-central midline. These results suggest that distraction during the expectancy of pain is related to a reduced neural desynchronization of fronto-central midline alpha rhythms (i.e., reduced cortical activation) towards an overt hyper-synchronization (cortical idling).

Functional neuroanatomy of the hypnotic state

The neural mechanisms underlying hypnosis and especially the modulation of pain perception by hypnosis remain obscure. Using PET we first described the distribution of regional cerebral blood flow during the hypnotic state. Hypnosis relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in "normal alertness". The hypnotic state was related to the activation of a widespread set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal and anterior cingulate cortices. This pattern of activation shares some similarities with mental imagery, from which it mainly differs by the relative deactivation of precuneus. Second, we looked at the anti-nociceptive effects of hypnosis. Compared to the resting state, hypnosis reduced pain perception by approximately 50%. The hypnosis-induced reduction of affective and sensory responses to noxious thermal stimulation were modulated by the activity in the midcingulate cortex (area 24a'). Finally, we assessed changes in cerebral functional connectivity related to hypnosis. Compared to normal alertness (i.e., rest and mental imagery), the hypnotic state, significantly enhanced the functional modulation between midcingulate cortex and a large neural network involved in sensory, affective, cognitive and behavioral aspects of nociception. These findings show that not only pharmacological but also psychological strategies for pain control can modulate the cerebral network involved in noxious perception.

An fMRI study of cerebral processing of brush-evoked allodynia in neuropathic pain patients

Previous human imaging studies have revealed a network of brain regions involved in the processing of allodynic pain; this includes prefrontal areas, insula, cingulate cortex, primary and secondary somatosensory cortices and parietal association areas. In this study, the neural correlates of the perceived intensity of allodynic pain in neuropathic pain patients were investigated. In eight patients, dynamic mechanical allodynia was provoked and brain responses recorded using functional magnetic resonance imaging (fMRI). Voxels in which the magnitude of fMRI signal correlated linearly with the ratings of allodynic pain across the group were determined in a whole brain analysis using a general linear model. To ensure that activation reflected only allodynic pain ratings, a nuisance variable containing ratings of ongoing pain was included in the analysis. We found that the magnitude of activation in the caudal anterior insula (cAI) correlates with the perceived intensity of allodynic pain across subjects, independent of the level of ongoing pain. However, the peak of activation in the allodynic condition was located in the rostral portion (rAI). This matches the representation of other clinical pain syndromes, confirmed by a literature review. In contrast, experimental pain in healthy volunteers resides predominantly in the cAI, as shown by the same literature review. Taken together, our data and the literature review suggest a functional segregation of anterior insular cortex.

A novel modelling and experimental technique to predict and measure tissue temperature during CO2 laser stimuli for human pain studies

Laser nerve stimulation is now accepted as one of the preferred methods for applying painful stimuli to human skin during pain studies. One of the main concerns, however, is thermal damage to the skin. We present recent work based on using a CO2 laser with a remote infrared (IR) temperature sensor as a feedback system. A model for predicting the subcutaneous skin temperature derived from the signal from the IR detector allows us to accurately predict the laser parameters, thus maintaining an optimum pain stimulus whilst avoiding dangerous temperature levels, which could result in thermal damage. Another aim is to relate the modelling of the CO2 fibre laser interaction to the pain response and compare these results with practical measurements of the pain threshold for various stimulus parameters. The system will also allow us to maintain a constant skin temperature during the stimulus. Another aim of the experiments underway is to review the psychophysics for pain in human subjects, permitting an investigation of the relationship between temperature and perceived pain.

Sex differences in regional brain response to aversive pelvic visceral stimuli

To explore sex differences in the response of seven brain regions to an aversive pelvic visceral stimulus, functional magnetic resonance images were acquired from 13 healthy adults (6 women) during 15 s of cued rectal distension at two pressures: 25 mmHg (uncomfortable), and 45 mmHg (mild pain), as well as during an expectation condition (no distension). Random-effects analyses combining subject data voxelwise found 45-mmHg pressure significantly activated the insular and anterior cingulate cortices in both sexes. In men only, the left thalamus and ventral striatum were also activated. Although all activations appeared more extensive in men, no sex difference attained significance. To explore the presence of deactivations, which are generally cancelled by more numerous activations when subjects are combined for each voxel, the number of activated voxels, number of deactivated voxels, and ratio of deactivated voxels to total voxels affected were assessed via random-effects, mixed-model analyses combining subject data at the region level. Greater insula activation in men compared with women was seen during the expectation condition and during the 25-mmHg distension. Greater deactivations in women were seen in the amygdala (25-mmHg distension) and midcingulate (45-mmHg distension). Women had a significantly higher proportion of deactivated voxels than men in all four subcortical structures during 25-mmHg distension. Greater familiarity of females with physiological pelvic visceral discomfort may have enhanced brain systems that dampen arousal networks during lower levels of discomfort.

Depression and pain: an overview

BACKGROUND

Depression and pain are both burdensome ailments that affect a major proportion of the population. It is evident that depression and pain frequently coexist, with treatment and outcome implications.

OBJECTIVE

To review the literature on the nature, prevalence and co-morbidity of depression and pain, the biological and psychological mechanisms involved and treatment options, thus presenting a broad overview of the current information available.

METHODS

Relevant sources were identified from PubMed and Medline databases using a combination of keywords including depression, pain, prevalence, co-morbidity, biological and psychological mechanisms, serotonin (5-HT), norepinephrine (NE), hypothalamic-pituitary-adrenal (HPA) axis, amygdala, functional magnetic resonance imaging (fMRI), antidepressant and psychological therapy.

RESULTS

It is evident from the research that depression and pain are common co-morbidities. Pain as a physical symptom of depression affects approximately 65% of patients, leading to less favourable outcomes and greater health care utilization. Moreover, depression is a common feature in chronic pain patients and can affect pain threshold and tolerance. Evidence from biological and psychological studies has revealed mechanisms that link chronic pain to depression. Several classes of anti-depressants and psychological interventions have been used successfully in the treatment of somatic symptoms of depression and for a variety of pain syndromes.

CONCLUSIONS

Pain and depression are linked by overlapping phenomenology, neurobiology and therapy. They are mutually interacting, and the interaction has significant treatment and outcome implications.

Hippocampal theta state in relation to formalin nociception

In the present study using extracellular electrophysiological recording techniques, we explored the temporal characteristics of hippocampal theta activation in relation to formalin nociception. Results indicate that, compared to hind paw injection of saline, formalin injection in behaving rat evoked biphasic increase in duration of dorsal CA1 theta. Such an increase broadly paralleled animal biphasic behavioral activation, especially lick and moment-to-moment agitated behaviors. Correspondingly, theta-modulated cell firing was observed following formalin injection in anesthetized rat. The formalin-induced theta activation in behaving rat was most marked during peak of theta activation in the 2nd theta state (11-40 min post-injection) comprising 73% of the time in the 5 min block. An increase in theta peak frequency was also observed with respect to pre-injection control. However, the peak of theta in the 2nd theta state mostly preceded the peak of lick and flinch of the affected paw. In the 41-60 min, following formalin injection while the animals displayed robust nociceptive flinching and lifting, the theta activity approached control levels. Furthermore, the theta peak frequency at peak of theta was higher than the corresponding values of sustained theta observed in correlation with the nociceptive behaviors; in contrast, high frequency theta rhythm was observed during formalin-induced other moment-to-moment agitated behaviors. These findings favor the notion that in the formalin model the theta state of the hippocampus reflects a neural drive that is dissociated from the duration of nociceptive experience and is not selective to the typical nociceptive indices of lick, flinch, and lift of the injured paw.

Slow-Frequency rTMS Reduces Fibromyalgia Pain: Table 1

OBJECTIVE

Evidence suggests that fibromyalgia (FM) is a centrally mediated pain disorder. Antidepressants, including electroconvulsive therapy, provide some symptomatic relief in FM and other pain disorders. Repetitive transcranial magnetic stimulation (rTMS) is a new antidepressant treatment, which may also be useful in treating chronic pain.

DESIGN

As part of a larger study, four women with depression, FM, and borderline personality disorder received 1-Hz rTMS applied to the right dorsolateral prefrontal cortex. Subjects rated pain using an 11-point Likert scale.

RESULTS

Pretreatment pain averaged 8.2 (7-9.5) and reduced to 1.5 (0-3.5) after treatment (P < 0.009). All had improvement in pain, and two had complete resolution of pain. Only one of the four subjects had an antidepressant response.

CONCLUSIONS

These preliminary findings suggest a possible role for rTMS in treating FM.

Reward-aversion circuitry in analgesia and pain: implications for psychiatric disorders

Sensory and emotional systems normally interact in a manner that optimizes an organism's ability to survive using conscious and unconscious processing. Pain and analgesia are interpreted by the nervous system as aversive and rewarding processes that trigger specific behavioral responses. Under normal physiological conditions these processes are adaptive. However, under chronic pain conditions, functional alterations of the central nervous system frequently result in maladaptive behaviors. In this review, we examine: (a) the interactions between sensory and emotional systems involved in processing pain and analgesia in the physiological state; (b) the role of reward/aversion circuitry in pain and analgesia; and (c) the role of alterations in reward/aversion circuitry in the development of chronic pain and co-morbid psychiatric disorders. These underlying features have implications for understanding the neurobiology of functional illnesses such as depression and anxiety and for the development and evaluation of novel therapeutic interventions.

Recollections of one's own past: the effects of aging and gender on the neural mechanisms of episodic autobiographical memory

Episodic autobiographical recollection is the most complex form of human memory. It relies on interactions between episodic memory, associated emotions, and a sense of self-continuity along the time axis of one's personal life history. Evidence exists that autobiographical memory performance as well as its underlying brain mechanisms are influenced by genetic, physiological, psychological, situational, and social-cultural factors. In particular, age (normal cognitive aging as well as age of memories, as defined by the time interval elapsed since information encoding) and gender affect both the performance level and the neural substrates of autobiographical recollection. In this review, studies concerned with aging and gender effects on autobiographical memory are discussed with reference to other age- and gender-related influences on human cognition, as well as clinical data on demented patients. Both age and gender act upon the functional hemispheric lateralization of autobiographical recollection and the prefrontal, hippocampal and parahippocampal engagement in information processing. On the performance level, re-collective qualities such as episodic detail and emotional intensity of autobiographical memories are modulated by both factors. Although the effects of aging and gender on human brain function are built upon different genetic and physiological mechanisms, they influence at least in part the same neurofunctional and behavioral dimensions of autobiographical recollection. Interestingly, age- and gender-related specificities in the neural mechanisms of autobiographical recollection need not be reflected on the performance level.

Unique, common, and interacting cortical correlates of thirst and pain

This study used positron-emission tomography to establish the patterns of brain activity involved in the isolated and concurrent experiences of thirst and pain. Ten subjects were scanned while experiencing pain evoked with noxious pressure, while experiencing thirst after the infusion of hypertonic saline, and while experiencing pain when thirsty. After the onset of thirst, noxious pressure evoked more intense sensations of pain. Noxious pressure did not change subjective ratings of thirst. Thirst caused activation in the anterior cingulate (Brodmann area 32) and the insula. Enhanced pain responses were associated with increased activity in cortical regions that are known to correlate with pain intensity, and also with unique activity in the pregenual anterior cingulate and ventral orbitofrontal cortex. These findings suggest a role for limbic and prefrontal cortices in the modulation of pain during the experience of thirst.

Acute opioid effects on human brain as revealed by functional magnetic resonance imaging

Functional magnetic resonance imaging has been widely used to study brain activation induced either by specific sensory stimulation or motor or cognitive task performance. We demonstrate that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects. The reproducibility of the responses in the predefined regions of interest was confirmed by repeated boluses of ultra-short acting mu-opioid receptor agonist remifentanil and saline. We report spatially and temporally detailed information after remifentanil administration. Areas rich in mu-opioid receptors showed strong activations, whereas primary somatosensory cortex that has the lowest density of mu-opioid receptors showed negligible activation. The cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations that were strongest at 80 to 90 s after drug administration. These areas belong to a circuitry that modulates the affective experience of sensory stimuli.

Cortical responses to pain in healthy individuals depends on pain catastrophizing

The personal experience of pain is complex and depends on physiological and psychological factors. From this latter category, pain catastrophizing plays an important role in pain behavior and response. We aimed to determine the effect of pain catastrophizing on central nociceptive processing in healthy individuals. Functional MRI was performed during two pain intensity levels evoked by electrical median nerve stimulation in 22 healthy individuals. Pain catastrophizing scores were determined for all subjects. Pain catastrophizing was not related to activity in regions associated with sensory-discriminative aspects of pain, such as the primary or secondary somatosensory cortex. Instead, during mild pain, there was a relationship between catastrophizing and activity in cortical regions associated with affective, attention, and motor aspects of pain, including dorsolateral prefrontal, insula, rostral anterior cingulate, premotor, and parietal cortices. During more intense pain, prefrontal cortical regions implicated in the top-down modulation of pain were negatively correlated with catastrophizing. These findings can be viewed from the framework of an attention model of pain catastrophizing, whereby a cortical vigilance network is engaged during mild pain, but diminished prefrontal cortical modulation impedes disengaging from and suppressing pain during more intense pain. These findings may also implicate catastrophizing in the progression to or persistence of chronic pain.

Psychophysics of CNS Pain-Related Activity: Binary and Analog Channels and Memory Encoding

The forebrain neuronal system signaling pain has been poorly characterized. The pain pathway afferent to the thalamus may be a labeled line consisting of neurons in the pain-signaling pathway to the brain (spinothalamic tract, STT) that respond only to painful stimuli. It has recently been proposed that the STT contains a series of analog-labeled lines, each signaling a different aspect of the internal state of the body (interoception), for example, visceral/cold/itch sensations. In this view, pain is the unpleasant emotion produced by disequilibrium of the internal state. The authors now show that stimulation of an STT receiving zone (thalamic principal somatic sensory nucleus, ventral caudal) in awake humans produces two different exteroceptive responses. The first is a binary response signaling the presence of painful stimuli. The second is an analog response in which nonpainful and painful sensations are graded with intensity of the stimulus. Such stimulation can evoke both the sensory and emotional components of previously experienced pain. These results illustrate the diverse functions of human pain signaling pathways.

Mechanisms of central neuropathic pain: a combined psychophysical and fMRI study in syringomyelia

The pathophysiology of central pain syndromes is still poorly understood and their treatment remains a major challenge. It has long been suggested that lesions of the spinothalamic pathways are necessary for developing these pain syndromes. The recently proposed thermosensory disinhibition theory suggests that reduction of the inhibition of thermal sensory afferents that affect nociceptive systems may play a major pathophysiological role. Syringomyelia, which is frequently associated with central neuropathic pain, is characterized by a selective or preferential lesion of the spinothalamic tract resulting in thermosensory deficits of various extents and magnitudes. Thus, syringomyelia represents a unique 'pathological model' particularly suited to investigating the relationship between spinothalamic tract dysfunction, thermosensory deficits and pain. Here, we systematically compared the sensory loss (thermal and mechanical), using quantitative sensory testing, between 46 consecutive syringomyelia patients with or without neuropathic pain. We then further investigated the mechanisms of evoked pains in these patients, using functional MRI (fMRI) in a subgroup of patients with cold or brush-evoked allodynia, compared with patients without pain and healthy volunteers. We found no significant difference in the magnitude or extent of sensory deficits between patients with or without neuropathic pain, suggesting that lesions of the spinothalamic pathways are not sufficient for developing central pain. However, a different pattern of sensory deficits was observed between patients with spontaneous pain only (n = 11) and patients with both spontaneous pain and allodynia (n = 20), suggesting that the mechanisms of central pain are not univocal. In patients with spontaneous pain only, the thermal sensory loss was significantly more asymmetrical and there was a direct relationship between the extent of thermosensory deficits (i.e. deafferentation) and the intensity of burning pain. In contrast, patients with allodynia had reduced thermal deficits, in terms of both magnitude and extent. In addition, the sensory deficits were different between patients with cold or tactile allodynia, suggesting distinct pathophysiological mechanisms related to the sub-modalities of allodynia. Our fMRI study further confirmed this, showing that different sub-types of allodynia were associated with distinct patterns of brain activity, which do not necessarily correspond to the 'pain matrix' involved in acute physiological pain. The prefrontal cortex was the only area consistently activated by pathological evoked pains, suggesting that alteration of high-level pain modulatory mechanisms might play a major role in allodynia due to central lesion.

Modulation of laser-evoked potentials by experimental cutaneous tonic pain

The present study aimed to investigate whether tonic cutaneous pain exerts any effect on the cortical processing of nociceptive input and if this effect may involve only body parts in pain. Tonic cutaneous pain was obtained in nine healthy human subjects by infusion of a hypertonic saline (5%) in the s.c. tissue over the hypothenar muscles (10 ml/h for 20 min). Nociceptive cutaneous CO2 laser-evoked potentials were recorded after stimulation of the right hand dorsum, which was adjacent to the painful area, and the right perioral region, corresponding to the adjacent cortical sensory area. Laser-evoked potentials were obtained before saline injection, at the peak pain and 20 min after pain disappeared. During saline infusion, the laser-evoked pain to right hand stimulation was reduced and the vertex laser-evoked potentials (N2a-P2, mean latency 181 ms and 319 ms for the N2a and the P2 potentials, respectively), which are generated in the anterior cingulate cortex, were significantly decreased in amplitude compared with the baseline. Moreover, the topography of these potentials was modified by cutaneous pain, shifting from the central toward the parietal region. Dipolar modeling showed that the dipolar source in the anterior cingulate cortex moved backward during saline infusion. This result suggests that cutaneous pain may modify the relative activities of the anterior and posterior anterior cingulate cortex parts, which are thought to be devoted to encode different aspects of pain sensation. No laser-evoked potential change was observed after stimulation of the right perioral region, suggesting that functional changes in the nociceptive system are selective for the painful regions and not for areas with cortical proximity.

Mapping brain activity following administration of a nicotinic acetylcholine receptor agonist, ABT-594, using functional magnetic resonance imaging in awake rats

Administration of ABT-594, a potent agonist for nicotinic acetylcholine receptors with selectivity for the alpha4beta2 receptor subtype, is known to modulate a diverse array of behaviors including those associated with nociception, anxiety and motor function. In this study, we sought to gain insight into the neural actions of ABT-594, in vivo, by conducting functional magnetic resonance imaging in awake and anesthetized rats. Using T(2)*-weighted gradient echo imaging and an ultrasmall superparamagnetic iron oxide contrast agent, functional imaging was conducted on a 4.7 T magnet to measure changes in relative cerebral blood volume. In awake, restrained, male Sprague-Dawley rats that were acclimated to the imaging environment, injection of ABT-594 (0.03-0.3 micromol/kg, i.v.) evoked changes to relative cerebral blood volume in several neural regions including the cingulate, somatosensory, motor, auditory, and pre-frontal cortices as well as the thalamus and the periaqueductal gray/dorsal raphe. These effects were typically bimodal with significant decreases in relative cerebral blood volume at the 0.03 micromol/kg dose and increases at the higher doses (0.1 and 0.3 micromol/kg). The decreases and increases in relative cerebral blood volume were often observed within the same region, but triggered by different doses. Both increases and decreases in relative cerebral blood volume were blocked by pretreatment with the noncompetitive nicotinic acetylcholine receptor antagonist, mecamylamine (5 micromol/kg, i.p.) in awake rats. Administration of ABT-594 (0.1 micromol/kg, i.v.) to alpha-chloralose-anesthetized rats did not significantly alter relative cerebral blood volume in any brain region suggesting an anesthetic-related interference with the effects of ABT-594. The neural regions affected by administration of ABT-594 corresponded well to the known pre-clinical behavioral profile for this compound, and demonstrate the utility of using functional magnetic resonance imaging in awake animals to study pharmacological action.

Using FMRI to study the neural correlates of virtual reality analgesia

Excessive pain during medical procedures, such as burn wound dressing changes, is a widespread medical problem and is especially challenging for children. This article describes the rationale behind virtual reality (VR) pain distraction, a new non-pharmacologic adjunctive analgesia, and gives a brief summary of empirical studies exploring whether VR reduces clinical procedural pain. Results indicate that patients using VR during painful medical procedures report large reductions in subjective pain. A neuroimaging study measuring the neural correlates of VR analgesia is described in detail. This functional magnetic resonance imaging pain study in healthy volunteers shows that the large drops in subjective pain ratings during VR are accompanied by large drops in pain-related brain activity. Together the clinical and laboratory studies provide converging evidence that VR distraction is a promising new non-pharmacologic pain control technique.

Cortical representation of experimental tooth pain in humans

Cortical processing of electrically induced pain from the tooth pulp was studied in healthy volunteers with fMRI. In a first experiment, cortical representation of tooth pain was compared with that of painful mechanical stimulation to the hand. The contralateral S1 cortex was activated during painful mechanical stimulation of the hand, whereas tooth pain lead to bilateral activation of S1. The S2 and insular region were bilaterally activated by both stimuli. In S2, the center of gravity of the activation during painful mechanical stimulation was more medial/posterior compared to tooth pain. In the insular region, tooth pain induced a stronger activation of the anterior and medial parts. The posterior part of the anterior cingulate gyrus was more strongly activated by painful stimulation of the hand. Differential activations were also found in motor and frontal areas including the orbital frontal cortex where tooth pain lead to greater activations. In a second experiment, we compared the effect of weak with strong tooth pain. A significantly greater activation by more painful tooth stimuli was found in most of those areas in which tooth pain had induced more activation than hand pain. In the medial frontal and right superior frontal gyri, we found an inverse relationship between pain intensity and BOLD contrast. We concluded that tooth pain activates a cortical network which is in several respects different from that activated by painful mechanical stimulation of the hand, not only in the somatotopically organized somatosensory areas but also in parts of the 'medial' pain projection system.