Exacerbation of pain by anxiety is associated with activity in a hippocampal network

Invited commentary: understanding brain mechanisms of pain processing in adolescents' non-suicidal self-injury

Whereas non-suicidal self injury (NSSI) is reported in 13-23% of adolescents and is an increasingly studied topic, there has been little investigation into the pathophysiology behind self-injury. This commentary examines recent research into pain and emotional distress to discuss implications for the manner we should understand, research, and treat NSSI in the future. Research indicates that adolescents may be particularly vulnerable to NSSI behaviors due to neurodevelopmental changes in the processing of distress and pain. Additionally, emotional distress and physical pain neural pathways may have been altered in these individuals, leading to the development of NSSI behaviors during adolescence when changes in ongoing brain development may lead to further emotional dysregulation and poor impulse control. Further studies that directly characterize the relationship between emotional distress and physical pain in adolescence, as well as the neural differences between self-injurers and non-self-injurers, are needed.

Psychological and sensory predictors of experimental thermal pain: a multifactorial model

Although large interindividual differences in pain exist, the underlying factors that contribute to these variations remain poorly understood. Consequently, being able to accurately explain variability in pain ratings in terms of its contributing factors could provide insights into developing a better understanding of individual differences in pain experience. In the present investigation, we show that a significant portion of the variability in experimental heat pain ratings may be predicted using simple quantitative sensory testing and a series of psychological questionnaires including State Trait and Anxiety Inventory (STAI), Center for Epidemiologic Studies - Depression Scale (CES-D), and Positive and Negative Affect Schedule - Expanded form (PANAS-X). A factor analysis was used to reduce individual predictors into sets of composite predictive factors. A multifactorial model that was generated from these factors can reliably predict a significant amount of the variability in heat pain sensitivity ratings (r² = .537, P = .027). Moreover, individual variables including heat pain thresholds and self-assessment of pain sensitivity were found to be poor predictors of heat pain sensitivity. Taken together, these results suggest that a variety of factors underlie individual differences in pain experience and that a reliable model for predicting pain should be constructed from a combination of these factors.

PERSPECTIVE

The present study provides a way to predict subjects' experimental heat pain sensitivity using a multifactorial model generated from a combination of sensory and psychological factors. Future application of such a model in the studies of clinical pain could potentially improve the quality of care provided for patients in pain.

Induction of depressed mood disrupts emotion regulation neurocircuitry and enhances pain unpleasantness

BACKGROUND

Depressed mood alters the pain experience. Yet, despite its clear clinical relevance, little is known about the cognitive and neural mechanisms underlying this phenomenon. We tested an experimental manipulation to unravel the interaction between depressed mood and pain. We hypothesized that dysregulation of the neural circuitry underlying emotion regulation is the mechanism whereby pain processing is affected during depressed mood.

METHODS

Using functional magnetic resonance imaging, we compared the effects of sad and neutral cognitive mood inductions on affective pain ratings, pain-specific cognitions, and central pain processing of a tonic noxious heat stimulus in 20 healthy volunteers.

RESULTS

The increase in negative pain-specific cognitions during depressed mood predicted the perceived increase in pain unpleasantness. Following depressed mood induction, brain responses to noxious thermal stimuli were characterized by increased activity in a broad network including prefrontal areas, subgenual anterior cingulate cortex, and hippocampus, as well as significantly less deactivation when compared with pain responses in a neutral mood. The participants who reported the largest increase in pain unpleasantness after the sad mood induction showed greater inferior frontal gyrus and amygdala activation, linking changes in emotion regulation mechanisms with enhancement of pain affect.

CONCLUSIONS

Our results inform how depressed mood and chronic pain co-occur clinically and may serve to develop and translate effective interventions using pharmacological or psychological treatment.

Temporal summation of heat pain in humans: Evidence supporting thalamocortical modulation

Noxious cutaneous contact heat stimuli (48 degrees C) are perceived as increasingly painful when the stimulus duration is extended from 5 to 10s, reflecting the temporal summation of central neuronal activity mediating heat pain. However, the sensation of increasing heat pain disappears, reaching a plateau as stimulus duration increases from 10 to 20s. We used functional magnetic resonance imaging (fMRI) in 10 healthy subjects to determine if active central mechanisms could contribute to this psychophysical plateau. During heat pain durations ranging from 5 to 20s, activation intensities in the bilateral orbitofrontal cortices and the activation volume in the left primary (S1) somatosensory cortex correlated only with perceived stimulus intensity and not with stimulus duration. Activation volumes increased with both stimulus duration and perceived intensity in the left lateral thalamus, posterior insula, inferior parietal cortex, and hippocampus. In contrast, during the psychophysical plateau, both the intensity and volume of thalamic and cortical activations in the right medial thalamus, right posterior insula, and left secondary (S2) somatosensory cortex continued to increase with stimulus duration but not with perceived stimulus intensity. Activation volumes in the left medial and right lateral thalamus, and the bilateral mid-anterior cingulate, left orbitofrontal, and right S2 cortices also increased only with stimulus duration. The increased activity of specific thalamic and cortical structures as stimulus duration, but not perceived intensity, increases is consistent with the recruitment of a thalamocortical mechanism that participates in the modulation of pain-related cortical responses and the temporal summation of heat pain.

Brain manifestation and modulation of pain from myofascial trigger points

The brain plays a prominent role in the generation and modulation of pain. It contains powerful endogenous pain modulatory systems that can be engaged in a beneficial way by therapeutical intervention. In contrast, pain chronification is associated with maladaptive structural and functional changes that may shift the balance of the modulatory systems. Although pain from myofascial trigger points (MTrPs) is highly prevalent, little is known about its brain manifestations and modulation. Recent neuroimaging data suggest that hyperalgesia from MTrPs is processed in similar regions as hyperalgesia from other pain conditions. However, abnormal hippocampal hypoactivity suggests that dysfunctional stress responses may play an important role in the generation and maintenance of hyperalgesia from MTrPs. Other data suggest that short-term pain relief obtained with intramuscular electrostimulation within an MTrP is partially due to descending pain inhibitory mechanisms.

fMRI study of brain activity elicited by oral parafunctional movements

Parafunctional masticatory activity, such as the tooth clenching and grinding that is associated with bruxism, is encountered by clinicians in many disciplines, including dentistry, neurology and psychiatry. Despite this, little is known about the neurological basis for these activities. To identify the brain network engaged in such complex oromotor activity, functional magnetic resonance imaging (fMRI) was used to elucidate the brain activation patterns of 20 individuals (10 males and 10 females, mean s.d. age of 26.3+/-4.1 years) with (parafunctional, PFx group, 5M/5F) and without (normal functional, NFx group, 5 M/5F) self-reported parafunctional grinding and clenching habits during clenching and grinding tasks. Subject group classification was based on: (i) self-reported history, (ii) clinical examination, (iii) evaluation of dental casts and (iv) positive responses to the temporomandibular disorder (TMD) History Questionnaire [Dworkinand LeResche, Journal of Craniomandibular Disorders, (1992) 6:301]. While subjects performed these oromotor tasks, each wore a custom-designed oral appliance minimizing head motion during imaging. Mean per cent signal changes showed significant between group differences in motor cortical (supplementary motor area, sensorimotor cortex and rolandic operculum) and subcortical (caudate) regions. Supplementary motor area data suggest that motor planning and initiation, particularly during the act of clenching, are less prominent in individuals with oromotor parafunctional behaviours. The overall extent of activated areas was reduced in subjects with self-reported parafunctional masticatory activity compared with the controls. This study's methodology and findings provide an initial step in understanding the neurological basis of parafunctional masticatory activities that are relevant for therapeutic research applications of temporomandibular joint and muscle disorders and associated comorbidities.

Dissection of perceptual, motor and autonomic components of brain activity evoked by noxious stimulation

In the past two decades, functional brain imaging has considerably advanced our knowledge of cerebral pain processing. However, many important links are still missing in our understanding of brain activity in relation to the regulation of pain-related physiological responses. This fMRI study investigates the cerebral correlates of pain (rating), motor responses (RIII-reflex) and autonomic activity (skin conductance response; SCR) evoked by noxious electrical stimulation. Stimulus intensity was adjusted individually based on the RIII threshold to control for differences in peripheral processes and baseline spinal activation. Covariance analyses were used to reveal individual differences in brain activity uniquely associated with individual differences in pain, RIII and SCR. Shock-evoked activity in cingulate, medial orbitofrontal and parahippocampal regions predicted pain sensitivity. Moreover, lateral orbitofrontal and cingulate areas showed strong positive associations with individual differences in motor reactivity but negative associations with autonomic reactivity. Notably, individual differences in OFC activation was almost fully accounted by the combination of individual measures of autonomic and motor reactivity (R(2)=0.93). Additionally, trial-to-trial fluctuations of RIII-reflex and SCR (within-subjects) were proportional to shock-evoked responses in subgenual cingulate cortex (RIII), anterior insula (SCR) and midcingulate cortex (SCR and RIII). Together, these results confirm that individual differences in perceptual, motor, and autonomic components of pain reflect robust individual differences in brain activity. Furthermore, the brain correlates of trial-to-trial fluctuations in pain responses provide additional evidence for a partial segregation of sub-systems involved more specifically in the ongoing monitoring, and possibly the regulation, of pain-related motor and autonomic responses.

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.

Individual sensitivity to pain expectancy is related to differential activation of the hippocampus and amygdala

Anxiety arising during pain expectancy can modulate the subjective experience of pain. However, individuals differ in their sensitivity to pain expectancy. The amygdale and hippocampus were proposed to mediate the behavioral response to aversive stimuli. However, their differential role in mediating anxiety-related individual differences is not clear. Using fMRI, we investigated brain activity during expectancy to cued or uncued thermal pain applied to the wrist. Following each stimulation participants rated the intensity of the painful experience. Activations in the amygdala and hippocampus were examined with respect to individual differences in harm avoidance (HA) personality trait, and individual sensitivity to expectancy, (i.e. response to cued vs. uncued painful stimuli). Only half of the subjects reported on cued pain as being more painful than uncued pain. In addition, we found a different activation profile for the amygdala and hippocampus during pain expectancy and experience. The amygdala was more active during expectancy and this activity was correlated with HA scores. The hippocampal activity was equally increased during both pain expectancy and experience, and correlated with the individual's sensitivity to expectancy. Our findings suggest that the amygdala supports an innate tendency to approach or avoid pain as reflected in HA trait, whereas the hippocampus mediates the effect of context possibly via appraisal of the stimulus value.

The effect of virtual reality on pain and range of motion in adults with burn injuries

Few studies have empirically investigated the effects of immersive virtual reality (VR) on postburn physical therapy pain control and range of motion (ROM). We performed a prospective, randomized controlled study of the effects of adding VR to standard therapy in adults receiving active-assisted ROM physical therapy, by assessing pain scores and maximal joint ROM immediately before and after therapy on two consecutive days. Thirty-nine inpatients, aged 21 to 57 years (mean 35 years), with a mean TBSA burn of 18% (range, 3-60%) were studied using a within-subject, crossover design. All patients received their regular pretherapy pharmacologic analgesia regimen. During physical therapy sessions on two consecutive days (VR one day and no VR the other day; order randomized), each patient participated in active-assisted ROM exercises with an occupational or physical therapist. At the conclusion of each session, patients provided 0 to 100 Graphic Rating Scale measurements of pain after each 10-minute treatment condition. On the day with VR, patients wore a head-position-tracked, medical care environment-excluding VR helmet with stereophonic sound and interacted in a virtual environment conducive to burn care. ROM measurements for each joint exercised were recorded before and after each therapy session. Because of nonsignificant carryover and order effects, the data were analyzed using simple paired t-tests. VR reduced all Graphic Rating Scale pain scores (worst pain, time spent thinking about the pain, and pain unpleasantness by 27, 37, and 31% respectively), relative to the no VR condition. Average ROM improvement was slightly greater with the VR condition; however, this difference failed to reach clinical or statistical significance (P = .243). Ninety-seven percent of patients reported zero to mild nausea after the VR session. Immersive VR effectively reduced pain and did not impair ROM during postburn physical therapy. VR is easily used in the hospital setting and offers a safe, nonpharmacologic adjunctive analgesic treatment.

Roles of the hippocampal formation in pain information processing

Pain is a complex experience consisting of sensory-discriminative, affective-motivational, and cognitive-evaluative dimensions. Now it has been gradually known that noxious information is processed by a widely-distributed, hierarchically- interconnected neural network, referred to as neuromatrix, in the brain. Thus, identifying the multiple neural networks subserving these functional aspects and harnessing this knowledge to manipulate the pain response in new and beneficial ways are challenging tasks. Albeit with elaborate research efforts on the cortical responses to painful stimuli or clinical pain, involvement of the hippocampal formation (HF) in pain is still a matter of controversy. Here, we integrate previous animal and human studies from the viewpoint of HF and pain, sequentially representing anatomical, behavioral, electrophysiological, molecular/biochemical and functional imaging evidence supporting the role of HF in pain processing. At last, we further expound on the relationship between pain and memory and present some unresolved issues.

How neuroimaging studies have challenged us to rethink: is chronic pain a disease?

In this review, we present data from functional, structural, and molecular imaging studies in patients and animals supporting the notion that it might be time to reconsider chronic pain as a disease. Across a range of chronic pain conditions, similar observations have been made regarding changes in structure and function within the brains of patients. We discuss these observations within the framework of the current definition of a disease.

PERSPECTIVE

Neuroimaging studies have made a significant scientific impact in the study of pain. Knowledge of nociceptive processing in the noninjured and injured central nervous system has grown considerably over the past 2 decades. This review examines the information from these functional, structural, and molecular studies within the framework of a disease state.

Feasibility and potential effect of a low-cost virtual reality system on reducing pain and anxiety in adult burn injury patients during physiotherapy in a developing country

OBJECTIVE

The purpose of this study was to ascertain the feasibility and potential effect of a low-cost VR system (eMagin Z800 3DVisor), used in conjunction with pharmacological analgesia, on reducing pain and anxiety in adult burn patients undergoing physiotherapy treatment, compared to pharmacologic analgesia alone at a South African hospital.

STUDY DESIGN

Single-blind, within-subject study design.

METHODS

Pain and anxiety outcome measures were measured by a blinded assessor using the Numeric Pain Rating Scale and Burn Specific Pain and Anxiety Scale. Box-and-whisker plot method, Chi-square tests as well as the Student's paired t-test were used to analyze data.

MAIN FINDINGS

Eleven eligible adult burn patients consented to participate in this study (3 female, 8 male; median age 33 years: range 23-54 years). A marginal (p=0.06) to insignificant (p=0.13) difference between the two sessions (analgesia with VR and analgesia without VR) in reducing pain was found. No significant difference (p=0.58) was found between the two sessions (analgesia with VR and analgesia without VR) for anxiety.

CONCLUSION

There seems to be a trend that the low-cost VR system, when added to routine pharmacological analgesics, is a safe technique and could be of considerable benefit if implemented into the pain management regime of burn units at a South African hospital.

Sadness enhances the experience of pain via neural activation in the anterior cingulate cortex and amygdala: an fMRI study

Pain is a multidimensional experience. Human pain perception can be modulated by subjective emotional responses. We examined this association within the context of a neuroimaging study, using functional MRI to examine neural responses to electrical pain-inducing stimuli in 15 healthy subjects (6 females; age range=20-30 years). Pain-inducing stimuli were presented during different emotional contexts, which were induced via the continuous presentation (5 s) of sad, happy, or neutral pictures of faces. We found that subjective pain ratings were higher in the sad emotional context than in the happy and neutral contexts, and that pain-related activation in the ACC was more pronounced in the sad context relative to the happy and neutral contexts. Psychophysiological interaction (PPI) and dynamic causal modeling (DCM) analyses demonstrated amygdala to ACC connections during the experience of pain in the sad context. These findings serve to highlight the neural mechanisms that may be relevant to understanding the broader relationship between somatic complaints and negative emotion.

Cerebral and spinal modulation of pain by emotions

Emotions have powerful effects on pain perception. However, the brain mechanisms underlying these effects remain largely unknown. In this study, we combined functional cerebral imaging with psychophysiological methods to explore the neural mechanisms involved in the emotional modulation of spinal nociceptive responses (RIII-reflex) and pain perception in healthy participants. Emotions induced by pleasant or unpleasant pictures modulated the responses to painful electrical stimulations in the right insula, paracentral lobule, parahippocampal gyrus, thalamus, and amygdala. Right insula activation covaried with the modulation of pain perception, consistent with a key role of this structure in the integration of pain signals with the ongoing emotion. In contrast, activity in the thalamus, amygdala, and several prefrontal areas was associated with the modulation of spinal reflex responses. Last, connectivity analyses suggested an involvement of prefrontal, parahippocampal, and brainstem structures in the cerebral and cerebrospinal modulation of pain by emotions. This multiplicity of mechanisms underlying the emotional modulation of pain is reflective of the strong interrelations between pain and emotions, and emphasizes the powerful effects that emotions can have on pain.

Painful stimuli evoke potentials recorded from the medial temporal lobe in humans

The role of human medial temporal structures in fear conditioning has led to the suggestion that neurons in these structures might respond to painful stimuli. We have now tested the hypothesis that recordings from these structures will demonstrate potentials related to the selective activation of cutaneous nociceptors by a painful laser stimulus (laser evoked potential, LEP) (Kenton B, Coger R, Crue B, Pinsky J, Friedman Y, Carmon A (1980) Neurosci Lett 17:301-306). Recordings were carried out through electrodes implanted bilaterally in these structures for the investigation of intractable epilepsy. Reproducible LEPs were commonly recorded both bilaterally and unilaterally, while LEPs were recorded at contacts on the left (9/14, P=0.257) as commonly as on the right (5/14), independent of the hand stimulated. Along electrodes traversing the amygdala the majority of LEPs were recorded from dorsal contacts near the central nucleus of the amygdala and the nucleus basalis. Stimulus evoked changes in theta activity were observed at contacts on the right at which isolated early negative LEPs (N2*) responses could be recorded. Contacts at which LEPs could be recorded were as commonly located in medial temporal structures with evidence of seizure activity as on those without. These results demonstrate the presence of pain-related inputs to the medial temporal lobe where they may be involved in associative learning to produce anxiety and disability related to painful stimuli.

Improved characterization of BOLD responses for evoked sensory stimuli

Pain and somatosensory processing involves an interaction of multiple neuronal networks. One result of these complex interactions is the presence of differential responses across brain regions that may be incompletely modeled by a straightforward application of standard general linear model (GLM) approaches based solely on the applied stimulus. We examined temporal blood oxygenation-level dependent (BOLD) signatures elicited by two stimulation paradigms (brush and heat) providing innocuous and noxious stimuli. Data were acquired from 32 healthy male subjects (2 independent cohorts). Regional time courses and model-free analyses of the first cohort revealed distinct temporal features of the BOLD responses elicited during noxious versus innocuous stimulation. Specifically, a biphasic (dual peak) BOLD signal was observed in response to heat but much less so in response to brush stimuli. This signal was characterized by a stimulus-locked response along with a second peak delayed by approximately 12.5 s. A cross-validation error analysis determined a modified design matrix comprising two explanatory variables (EVs) as a parsimonious means to model the biphasic responses within a GLM framework. One EV was directly derived from the stimulation paradigm (EV1), while the second EV (EV2) was EV1 shifted by 12.5 s. The 2EV GLM analysis enabled a more detailed characterization of the elicited BOLD responses, particularly during pain processing. This was confirmed by application of the model to a second, independent cohort[AU1]. Furthermore, the delayed component of the biphasic response was strongly associated with the noxious heat stimuli, suggesting that this may represent a sensitive fMRI link of pain processing.

Hippocampal NMDA receptors and anxiety: at the interface between cognition and emotion

David De Wied had a fundamental interest in the brain and behaviour, with a particular interest in the interface between cognition and emotion, and how impairments at this interface could underlie human psychopathology. The NMDA subtype of glutamate receptor is an important mediator of synaptic plasticity and plays a central role in the neurobiological mechanisms of emotionality, as well as learning and memory. NMDA receptor antagonists affect various aspects of emotionality including fear, anxiety and depression, as well as impairing certain forms of learning and memory. The hippocampus is a key brain structure, implicated in both cognition and emotion. Lesion studies in animals have suggested that dorsal and ventral sub-regions of the hippocampus are differentially involved in dissociable aspects of hippocampus-dependent behaviour. Cytotoxic lesions of the dorsal hippocampus (septal pole) in rodents impair spatial learning but have no effect on anxiety, whereas ventral hippocampal lesions reduce anxiety but are without effect on spatial memory. This role for the ventral hippocampus in anxiety is distinct from the role of the amygdala in other aspects of emotional processing, such as fear conditioning. Recent studies with genetically modified mice have shown that NR1 NMDA receptor subunit deletion, specifically from the granule cells of the dentate gyrus, not only impairs short-term spatial memory but also reduces anxiety. This suggests that NMDA receptors in ventral hippocampus may be a key locus supporting the anxiolytic effects of NMDA receptor antagonists. These data support Gray's neuropsychological account of hippocampal function.

Nociception-induced spatial and temporal plasticity of synaptic connection and function in the hippocampal formation of rats: a multi-electrode array recording

Background

Pain is known to be processed by a complex neural network (neuromatrix) in the brain. It is hypothesized that under pathological state, persistent or chronic pain can affect various higher brain functions through ascending pathways, leading to co-morbidities or mental disability of pain. However, so far the influences of pathological pain on the higher brain functions are less clear and this may hinder the advances in pain therapy. In the current study, we studied spatiotemporal plasticity of synaptic connection and function in the hippocampal formation (HF) in response to persistent nociception.

Results

On the hippocampal slices of rats which had suffered from persistent nociception for 2 h by receiving subcutaneous bee venom (BV) or formalin injection into one hand paw, multisite recordings were performed by an 8 × 8 multi-electrode array probe. The waveform of the field excitatory postsynaptic potential (fEPSP), induced by perforant path electrical stimulation and pharmacologically identified as being activity-dependent and mediated by ionotropic glutamate receptors, was consistently positive-going in the dentate gyrus (DG), while that in the CA1 was negative-going in shape in naïve and saline control groups. For the spatial characteristics of synaptic plasticity, BV- or formalin-induced persistent pain significantly increased the number of detectable fEPSP in both DG and CA1 area, implicating enlargement of the synaptic connection size by the injury or acute inflammation. Moreover, the input-output function of synaptic efficacy was shown to be distinctly enhanced by the injury with the stimulus-response curve being moved leftward compared to the control. For the temporal plasticity, long-term potentiation produced by theta burst stimulation (TBS) conditioning was also remarkably enhanced by pain. Moreover, it is strikingly noted that the shape of fEPSP waveform was drastically deformed or split by a TBS conditioning under the condition of persistent nociception, while that in naïve or saline control state was not affected. All these changes in synaptic connection and function, confirmed by the 2-dimentional current source density imaging, were found to be highly correlated with peripheral persistent nociception since pre-blockade of nociceptive impulses could eliminate all of them. Finally, the initial pharmacological investigation showed that AMPA/KA glutamate receptors might play more important roles in mediation of pain-associated spatiotemporal plasticity than NMDA receptors.

Conclusion

Peripheral persistent nociception produces great impact upon the higher brain structures that lead to not only temporal plasticity, but also spatial plasticity of synaptic connection and function in the HF. The spatial plasticity of synaptic activities is more complex than the temporal plasticity, comprising of enlargement of synaptic connection size at network level, deformed fEPSP at local circuit level and, increased synaptic efficacy at cellular level. In addition, the multi-synaptic model established in the present investigation may open a new avenue for future studies of pain-related brain dysfunctions at the higher level of the neuromatrix.

Genetic vulnerability to affective psychopathology in childhood: a combined voxel-based morphometry and functional magnetic resonance imaging study

BACKGROUND

The majority of affective psychopathology is rooted early in life and first emerges during childhood and adolescence. However, little is known about how genetic vulnerability affects brain structure and function in childhood since the vast majority of studies published so far have been conducted on adult participants. The present investigation examined for the first time the effects of catechol-O-methyltransferase (COMT) valine (val) 158 methionine (met) (val158met) polymorphism, which has been shown to moderate predisposition to negative mood and affective disorders, on brain structure and function in children.

METHODS

Voxel-based morphometry and functional magnetic resonance imaging were used to measure gray matter volume and emotional reactivity in 50 children aged between 10 and 12 years. We tested the hypothesis that met158 allele affects structural brain development and confers heightened reactivity within the affective frontolimbic circuit in children.

RESULTS

The met158 allele was positively associated with gray matter volume in the left hippocampal head where genotype accounted for 59% of interindividual variance. In addition, the met158 allele was positively associated with neuronal responses to fearful relative to neutral facial expressions in the right parahippocampal gyrus where genotype accounted for 14% of the interindividual variance.

CONCLUSIONS

These results indicate that the met158 allele is associated with increased gray matter volume and heightened reactivity during emotional processing within the limbic system in children as young as 10 to 12 years of age. These findings are consistent with the notion that genetic factors affect brain function to moderate vulnerability to affective psychopathology from childhood.

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.

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

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

Models and mechanisms of hyperalgesia and allodynia

Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.

Stress-induced analgesia

For over 30 years, scientists have been investigating the phenomenon of pain suppression upon exposure to unconditioned or conditioned stressful stimuli, commonly known as stress-induced analgesia. These studies have revealed that individual sensitivity to stress-induced analgesia can vary greatly and that this sensitivity is coupled to many different phenotypes including the degree of opioid sensitivity and startle response. Furthermore, stress-induced analgesia is influenced by age, gender, and prior experience to stressful, painful, or other environmental stimuli. Stress-induced analgesia is mediated by activation of the descending inhibitory pain pathway. Pharmacological and neurochemical studies have demonstrated involvement of a large number of neurotransmitters and neuropeptides. In particular, there are key roles for the endogenous opioid, monoamine, cannabinoid, gamma-aminobutyric acid and glutamate systems. The study of stress-induced analgesia has enhanced our understanding of the fundamental physiology of pain and stress and can be a useful approach for uncovering new therapeutic targets for the treatment of pain and stress-related disorders.

Hippocampal Erk mechanisms linking prediction error to fear extinction: roles of shock expectancy and contextual aversive valence

Extinction of fear requires learning that anticipated aversive events no longer occur. Animal models reveal that sustained phosphorylation of the extracellular signal-regulated kinase (Erk) in hippocampal CA1 neurons plays an important role in this process. However, the key signals triggering and regulating the activity of Erk are not known. By varying the degree of expected and delivered aversive reinforcement, we demonstrate that Erk specifically responds to prediction errors of contextual aversive events. An increase of somatonuclear phospho-Erk (pErk) within principal CA1 neurons was observed only when the expectation of contextual foot shock was violated, but not when the context was consistently nonreinforced or reinforced by foot shock. The rate of error detection, Erk signaling, and fear extinction markedly depended on shock expectancy and the aversive valence of the context, as revealed by comparison of groups trained with single, continuous, or partial reinforcement. On the basis of these findings, the hippocampal Erk response to prediction errors of aversive outcome is proposed as a unique mechanism of fear extinction. Improving the detection and processing of these errors has the potential to attenuate fear responses in patients with anxiety disorders.

Placebo analgesia induced by social observational learning

Although it has long been known that psychosocial factors play a crucial role in placebo responses, no attempt has been made to understand if social observation shapes the placebo analgesic effect. To address this question, we compared placebo analgesia induced through social observation (Group 1) with first-hand experience via a typical conditioning procedure (Group 2) and verbal suggestion alone (Group 3). In Group 1, subjects underwent painful stimuli and placebo treatment after they had observed a demonstrator (actually a simulator) showing analgesic effect when the painful stimuli were paired to a green light. In Group 2, subjects were conditioned according to previous studies, whereby a green light was associated to the surreptitious reduction of stimulus intensity, so as to make them believe that the treatment worked. In Group 3, subjects received painful stimuli and were verbally instructed to expect a benefit from a green light. Pain perception was assessed by means of a Numerical Rating Scale (NRS) ranging from 0=no pain to 10=maximum imaginable pain. Empathy trait and heart rate were also measured. We found that observing the beneficial effects in the demonstrator induced substantial placebo analgesic responses, which were positively correlated with empathy scores. Moreover, observational social learning produced placebo responses that were similar to those induced by directly experiencing the benefit through the conditioning procedure, whereas verbal suggestions alone produced significantly smaller effects. These findings show that placebo analgesia is finely tuned by social observation and suggest that different forms of learning take part in the placebo phenomenon.

Representation of UV-B-induced thermal and mechanical hyperalgesia in the human brain: a functional MRI study

Surrogate models of pain and hyperalgesia allow the investigation of underlying mechanisms in healthy volunteers. Here, we investigated brain activation patterns during mechanical and heat hyperalgesia in an inflammatory human pain model using functional magnetic resonance imaging. Heat and mechanical hyperalgesia were induced on the right forearm by UV-B application in 14 healthy subjects. All four conditions (nonsensitized heat and nonsensitized mechanical pain, sensitized heat and sensitized mechanical pain) were perceptually matched. A 2 x 2 factorial analysis was performed. Areas with main effect of sensitization were insula, anterior cingulate cortex (ACC), prefrontal cortices (PFC), parietal association cortices (PA), thalamus, and basal ganglia. A main effect of modality with more activation during heat hyperalgesia was found in primary somatosensory cortex (S1), ACC, PFC, and PA. A main effect of modality with more activation during mechanical hyperalgesia was found in secondary somatosensory cortices, posterior insula, and contralateral inferior frontal cortex (IFC). An interaction of sensitization and modality was found bilaterally in IFC. Areas with similar effects of sensitization in both stimulus modalities were ACC, bilateral anterior insula and bilateral IFC. We conclude that different types of hyperalgesia in a human surrogate model of inflammatory pain produce different brain activation patterns. This is partly due to a differential processing of thermal and mechanical pain and an interaction of sensitization and modality in the caudal portion of the IFC. Finally, the data provide evidence for the existence of a common "sensitization network" consisting of ACC, bilateral anterior insula, and parts of the IFC.

Patients with pain disorder show gray-matter loss in pain-processing structures: a voxel-based morphometric study

OBJECTIVE

To investigate whether the functional changes in pain disorder might be reflected by structural brain changes. Pain disorder assessed with the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criteria is characterized by persistent and distressing chronic pain at one or more body sites which cannot be fully explained by a physiological process or somatic disorder. Psychological factors are thought to play a major role. Recent neuroimaging studies evidenced altered pain processing in patients suffering from this disorder.

METHODS

Fourteen right-handed women fulfilling the DSM-IV criteria for pain disorder and 25 healthy age-matched women were investigated with magnetic resonance imaging. In the voxel-based morphometry analysis, we compared both groups for changes of gray-matter density. We included age and Beck Depression Inventory scores as nuisance variables to minimize possible confounding effects of age or depressive comorbidity.

RESULTS

In the patient group, we found significant gray-matter decreases in the prefrontal, cingulate, and insular cortex. These regions are known to be critically involved in the modulation of subjective pain experiences.

CONCLUSIONS

In the context of similar results in patients with other functional pain syndromes, such as fibromyalgia and chronic back pain, we suggest that structural changes in fronto-limbic brain circuits represent not only an objective marker of these pain syndromes but also constitute a critical pathophysiological element. These findings represent a further proof of the important role of central changes in pain disorder.

Differential brain activation associated with laser-evoked burning and pricking pain: An event-related fMRI study

An important question remains as to how the brain differentially processes first (pricking) pain mediated by Adelta-nociceptors versus second (burning) pain mediated by C-nociceptors. In the present cross-over randomized, within-subjects controlled study, brain activity patterns were examined with event-related fMRI while pricking and burning pain were selectively evoked using a diode laser. Stimuli evoking equivalent pain intensities were delivered to the dorsum of the left foot. Different laser parameters were used to elicit pricking (60ms pulse duration) and burning (2.0s pulse duration) pain. Whole brain group analysis showed that several brain areas were commonly activated by pricking and burning pain, including bilateral thalamus, bilateral anterior insula, bilateral posterior parietal lobule, contralateral dorsolateral prefrontal cortex, ipsilateral cerebellum, and mid anterior cingulate cortex. These findings show that pricking and burning pain were associated with activity in many of the same nociceptive processing brain regions. This may be expected given that Adelta-and C-nociceptive signals converge to a great extent at the level of the dorsal horn. Other brain regions showed differential processing. Stronger activation in the pricking pain condition was found in the ipsilateral hippocampus, bilateral parahippocampal gyrus, bilateral fusiform gyrus, contralateral cerebellum and contralateral cuneus/parieto-occipital sulcus. Stronger activation in the burning pain condition was found in the ipsilateral dorsolateral prefrontal cortex. These differential activation patterns suggest preferential importance of Adelta-fiber signals versus C-fiber signals for these specific brain regions.

Effects of attention on visceral stimulus intensity encoding in the male human brain

BACKGROUND & AIMS

Hypervigilance is considered important in pain perception in functional gastrointestinal disorders. Nonetheless, a comprehensive assessment of the influence of attention on brain processing of visceral sensation has not been performed. We investigated the effects of attention on esophageal pain perception and brain activity.

METHODS

Twelve healthy male volunteers (age range, 21-32 years) underwent 4 functional magnetic resonance imaging scans incorporating 4 levels of esophageal stimulation (ES), ranging from nonpainful to painful, during which they completed a task aimed at distracting them from the esophageal stimulus. The volunteers were then scanned a fifth time, during painful stimulation without distraction.

RESULTS

Following ES during distraction, there was a significant linear trend (P < .05) in which the intensity of cerebral activation in the primary somatosensory cortex (SI) (bilateral) and left mid-anterior cingulate cortex (ACC) increased with stimulation intensity. When pain was delivered during distraction, there was a significant reduction in pain ratings, accompanied by significant decreases (P < .05) in brain activity in the right ACC and right prefrontal cortex. There was no effect of distraction on SI activity (P < .05).

CONCLUSIONS

Our results suggest that the SI is involved in processing sensory-discriminative aspects of visceral sensation. In contrast, activity in the mid-ACC suggests that this region is multifunctional because it appears to be involved in sensory and cognitive appraisal of visceral pain; the right prefrontal cortex seems to be involved in only cognitive responses to pain.

Dynamic activation of the anterior cingulate cortex during anticipatory anxiety

Based on theoretical models, we investigated the dynamics of brain activation during anticipatory anxiety using functional magnetic resonance imaging and a combined parametric/correlational design. Subjects (16 females) anticipated the application of electrical shocks of varying intensity resulting in four different threat levels. The parametric analysis revealed an inverted U-function of activation in the ventral anterior cingulate cortex (ACC) depending on the level of threat. Furthermore, the correlation analysis showed that the association between anxiety and brain activation in the pregenual ACC was, as a tendency, positive during moderate threat but clearly negative during strong threat. Moreover, during strong threat, a positive correlation between anxiety and activation was observed in the dorsal ACC, somatosensory cortex, motor cortex, and hippocampus. These findings suggest threat dependent dynamics of brain activation in the ACC; with increased attentional avoidance during moderate threat and a switch to hypervigilant action readiness in the most anxious subjects during strong threat.

Intra-hippocampal tonic inhibition influences formalin pain-induced pyramidal cell suppression, but not excitation in dorsal field CA1 of rat

It has been hypothesized that intra-hippocampal GABAergic inhibitory interneurons mediate formalin pain-induced suppression of dorsal hippocampal CA1 pyramidal cell discharge. The present study performed on anaesthetized rats tested the hypothesis by disrupting GABAergic mechanisms with intra-hippocampal administration of the GABA(A) receptor antagonist bicuculline methiodide, applied either dorsally into the pyramidal cell layer and stratum oriens (dorsal-bicuculline) or ventrally into the region of apical dendrites (ventral-bicuculline). It was found that ventral-, but not dorsal-bicuculline attenuated formalin-induced suppression of pyramidal cell extracellular discharge. The antagonism was selective in such a way that the excitation of pyramidal cell was unaffected. Interestingly, ventral-bicuculline strongly disinhibited CA1 pyramidal cells and shifted the distribution of their spontaneous discharge to values higher than the control group. However, dorsal-bicuculline disinhibited the local CA1 interneurons that were strongly excited on injection of formalin. Overall, the findings favour the notion that tonic GABA(A) receptor mechanisms located in the region of apical dendrites facilitate formalin-induced pyramidal cell suppression by masking the background excitatory drive impinging on the pyramidal cells. Interestingly, both the attenuation of formalin-induced inhibition and facilitation of basal discharge of CA1 pyramidal cells by ventral-bicuculline are similar to the effects seen previously with the destruction of medial septal cholinergic neurons. This convergence of effects strengthens the proposal that the network of medial septal cholinergic neurons and hippocampal GABAergic interneurons influence formalin pain-induced CA1 pyramidal cell suppression. In addition, the data point to a non-overlapping excitatory drive whose strength is unaffected by the inhibitory drive that underpins formalin suppression.

Preoperative psychologic and demographic predictors of pain perception and tramadol consumption using intravenous patient-controlled analgesia

OBJECTIVES

Postoperative pain is characterized by a wide variability of patients' pain perception and analgesic requirement. The study investigated the extent to which demographic and psychologic variables may influence postoperative pain intensity and tramadol consumption using patient-controlled analgesia (PCA) after cholecystectomy.

METHODS

Eighty patients, aged 18 to 70 years, with an American Society of Anesthesiologists physical status I or II and a body mass index between 18.5 and 24.9, undergoing laparoscopic cholecystectomy were enrolled. Self-rating anxiety scale (SAS) and self-rating questionnaire for depression (SRQ-D) were used--1 day before surgery--to assess patients' psychologic status. General anesthesia was standardized. PCA pump with intravenous tramadol was used for a 24-hour postoperative analgesia. Visual analog scale at rest (VASr) and after coughing (VASi) and tramadol consumption were registered. Pearson's and point biserial correlations, analysis of variance, and step-wise regression were used for statistical analysis.

RESULTS

Pearson r showed positive correlations between anxiety, depression, and pain indicators (P<0.05). Moreover, female patients had higher pain indicators (P<0.05). Analysis of variance showed that anxious (P<0.05) and depressed (P<0.001) patients had higher pain indicators, which significantly decreased during the postoperative 24 hours (P<0.00001). Regression analysis revealed that tramadol consumption was predicted by preoperative depression (P<0.001). VASr was predicted by sex and SRQ-D (P<0.05). VASi was predicted by sex and SAS (P<0.05).

DISCUSSION

Pain perception intensity was primarily predicted by sex with an additional role of depression and anxiety in determining VASr and VASi, respectively. Patients with high depression levels required a larger amount of tramadol.