Pain affect encoded in human anterior cingulate but not somatosensory cortex

Psychological factors in chronic pain: evolution and revolution

Research has demonstrated the importance of psychological factors in coping, quality of life, and disability in chronic pain. Furthermore, the contributions of psychology in the effectiveness of treatment of chronic pain patients have received empirical support. The authors describe a biopsychosocial model of chronic pain and provide an update on research implicating the importance of people's appraisals of their symptoms, their ability to self-manage pain and related problems, and their fears about pain and injury that motivate efforts to avoid exacerbation of symptoms and further injury or reinjury. They provide a selected review to illustrate treatment outcome research, methodological issues, practical, and clinical issues to identify promising directions. Although there remain obstacles, there are also opportunities for psychologists to contribute to improved understanding of pain and treatment of people who suffer from chronic pain. The authors conclude by noting that pain has received a tremendous amount of attention culminating in the passage of a law by the U.S. Congress designating the period 2001-2011 as the "The Decade of Pain Control and Research."

Painful stimuli evoke different stimulus-response functions in the amygdala, prefrontal, insula and somatosensory cortex: a single-trial fMRI study

Only recently have neuroimaging studies moved away from describing regions activated by noxious stimuli and started to disentangle subprocesses within the nociceptive system. One approach to characterizing the role of individual regions is to record brain responses evoked by different stimulus intensities. We used such a parametric single-trial functional MRI design in combination with a thulium:yttrium-aluminium-granate infrared laser and investigated pain, stimulus intensity and stimulus awareness (i.e. pain-unrelated) responses in nine healthy volunteers. Four stimulus intensities, ranging from warm to painful (300-600 mJ), were applied in a randomized order and rated by the subjects on a five-point scale (P0-4). Regions in the dorsolateral prefrontal cortex and the intraparietal sulcus differentiated between P0 (not perceived) and P1 but exhibited no further signal increase with P2, and were related to stimulus perception and subsequent cognitive processing. Signal changes in the primary somatosensory cortex discriminated between non-painful trials (P0 and P1), linking this region to basic sensory processing. Pain-related regions in the secondary somatosensory cortex and insular cortex showed a response that did not distinguish between innocuous trials (P0 and P1) but showed a positive linear relationship with signal changes for painful trials (P2-4). This was also true for the amygdala, with the exception that, in P0 trials in which the stimulus was not perceived (i.e. 'uncertain' trials), the evoked signal changes were as great as in P3 trials, indicating that the amygdala is involved in coding 'uncertainty', as has been suggested previously in relation to classical conditioning.

Anterior cingulate: single neuronal signals related to degree of reward expectancy

As monkeys perform schedules containing several trials with a visual cue indicating reward proximity, their error rates decrease as the number of remaining trials decreases, suggesting that their motivation and/or reward expectancy increases as the reward approaches. About one-third of single neurons recorded in the anterior cingulate cortex of monkeys during these reward schedules had responses that progressively changed strength with reward expectancy, an effect that disappeared when the cue was random. Alterations of this progression could be the basis for the changes from normal that are reported in anterior cingulate population activity for obsessive-compulsive disorder and drug abuse, conditions characterized by disturbances in reward expectancy.

The rational management of fibromyalgia patients

The exponential increase in pain research over the last 10 years has established fibromyalgia (FM) as a common chronic pain syndrome with similar neurophysiologic aberrations to other chronic pain states. As such, the pathogenesis is considered to involve an interaction of augmented sensory processing (central sensitization) and peripheral pain generators. The notion, that FM symptomatology results from an amplification of incoming sensory impulses, has revolutionized the contemporary understanding of this enigmatic problem and provided a more rational approach to treatment. To date, the management of FM has been mainly palliative, with the aims of reducing pain, improving sleep, maintaining function, treating psychologic distress and diminishing the impact of associated syndromes. The rapidly evolving neurophysiologic, psychophysiologic and molecular biologic basis for chronic pain states has already opened up new avenues for management which should be applicable to this difficult group of patients. Indeed, it is now possible to think about a "rational" approach to managing FM patients that was unthinkable just a few years ago.

Functional magnetic resonance imaging evidence of augmented pain processing in fibromyalgia

OBJECTIVE

To use functional magnetic resonance imaging (fMRI) to evaluate the pattern of cerebral activation during the application of painful pressure and determine whether this pattern is augmented in patients with fibromyalgia (FM) compared with controls.

METHODS

Pressure was applied to the left thumbnail beds of 16 right-handed patients with FM and 16 right-handed matched controls. Each FM patient underwent fMRI while moderately painful pressure was being applied. The functional activation patterns in FM patients were compared with those in controls, who were tested under 2 conditions: the "stimulus pressure control" condition, during which they received an amount of pressure similar to that delivered to patients, and the "subjective pain control" condition, during which the intensity of stimulation was increased to deliver a subjective level of pain similar to that experienced by patients.

RESULTS

Stimulation with adequate pressure to cause similar pain in both groups resulted in 19 regions of increased regional cerebral blood flow in healthy controls and 12 significant regions in patients. Increased fMRI signal occurred in 7 regions common to both groups, and decreased signal was observed in 1 common region. In contrast, stimulation of controls with the same amount of pressure that caused pain in patients resulted in only 2 regions of increased signal, neither of which coincided with a region of activation in patients. Statistical comparison of the patient and control groups receiving similar stimulus pressures revealed 13 regions of greater activation in the patient group. In contrast, similar stimulus pressures produced only 1 region of greater activation in the control group.

CONCLUSION

The fact that comparable subjectively painful conditions resulted in activation patterns that were similar in patients and controls, whereas similar pressures resulted in no common regions of activation and greater effects in patients, supports the hypothesis that FM is characterized by cortical or subcortical augmentation of pain processing.

Cerebral responses to noxious thermal stimulation in chronic low back pain patients and normal controls

Changes in regional cerebral blood flow (rCBF) have previously been demonstrated in a number of cortical and subcortical regions, including the cerebellum, midbrain, thalamus, lentiform nucleus, and the insula, prefrontal, anterior cingulate, and parietal cortices, in response to experimental noxious stimuli. Increased anterior cingulate responses in patients with chronic regional pain and depression to noxious stimulation distant from the site of clinical pain have been observed. We suggested that this may represent a generalized hyperattentional response to noxious stimuli and may apply to other types of chronic regional pain. Here these techniques are extended to a group of patients with nonspecific chronic low back pain. Thirty-two subjects, 16 chronic low back pain patients and 16 controls, were studied using positron emission tomography. Thermal stimuli, corresponding to the experience of hot, mild, and moderate pain, were delivered to the back of the subject's right hand using a thermal probe. Each subject had 12 measurements of rCBF, 4 for each stimulus. Correlation of rCBF with subjective pain experience revealed similar responses across groups in the cerebellum, midbrain (including the PAG), thalamus, insula, lentiform nucleus, and midcingulate (area 24') cortex. These regions represented the majority of activations for this study and those recorded by other imaging studies of pain. Although some small differences were observed between the groups these were not considered sufficient to suggest abnormal nociceptive processing in patients with nonspecific low back pain.

Forebrain-mediated sensitization of central pain pathways: 'non-specific' pain and a new image for MT

Manual therapy (MT-) is moving beyond its empirical origins and into an era of evidence-based practice. Mechanisms for the appearance of clinically observed symptoms and signs are beng incorporated into its clinical reasoning process. The recent, but well-documented phenomenon, central sensitization, is recognized as being one such mechanism. Anatomical, physiological, behavioural and clinical evidence demonstrate that, in addition to input from the periphery, central sensitization can be enhanced or maintained by supraspinal processes involving cognitions, attention ('focussing') and emotions. These forebrain products may, therefore, make a significant contribution to the symptoms and signs of common musculoskeletal presentations such as 'non-specific' back pain and fibromyalgia. The evidence can also be interpreted to provide MT with an acceptable role in the management of these patients.

Rational and targeted pharmacologic treatment of fibromyalgia

Despite disappointing results when subjected to randomized clinical trials, pharmacologic agents remain an important component of FM management. Addressing the main symptoms of pain, disturbed sleep, mood disturbances, fatigue, and associated conditions is essential to improve patient functioning and enhanced quality of life. However, much work remains to design clinical trials which address the complexity of FM, while satisfying evidence based medicine paradigms.

Does anticipation of pain affect cortical nociceptive systems?

Anticipation of pain is a complex state that may influence the perception of subsequent noxious stimuli. We used functional magnetic resonance imaging (fMRI) to study changes of activity of cortical nociceptive networks in healthy volunteers while they expected the somatosensory stimulation of one foot, which might be painful (subcutaneous injection of ascorbic acid) or not. Subjects had no previous experience of the noxious stimulus. Mean fMRI signal intensity increased over baseline values during anticipation and during actual stimulation in the putative foot representation area of the contralateral primary somatosensory cortex (SI). Mean fMRI signals decreased during anticipation in other portions of the contralateral and ipsilateral SI, as well as in the anteroventral cingulate cortex. The activity of cortical clusters whose signal time courses showed positive or negative correlations with the individual psychophysical pain intensity curve was also significantly affected during the waiting period. Positively correlated clusters were found in the contralateral SI and bilaterally in the anterior cingulate, anterior insula, and medial prefrontal cortex. Negatively correlated clusters were found in the anteroventral cingulate bilaterally. In all of these areas, changes during anticipation were of the same sign as those observed during pain but less intense ( approximately 30-40% as large as peak changes during actual noxious stimulation). These results provide evidence for top-down mechanisms, triggered by anticipation, modulating cortical systems involved in sensory and affective components of pain even in the absence of actual noxious input and suggest that the activity of cortical nociceptive networks may be directly influenced by cognitive factors.

Sensory and affective components of orofacial pain: is it all in your brain?

In this paper, we shall review several chronic orofacial pain conditions with emphasis on those that are essentially refractory to treatment. We shall present a review of current and past literature that describes the various pain phenomena as well as their underlying central mechanisms. New data concerning refractory pain will be used to underscore the importance of central processing of pain, with particular emphasis on neuropsychological and cognitive function and capacity that may play important roles in pain processing and maintenance of the pain state. Further, neurophysiological data showing that the anterior cingulate cortex (ACC) and other structures in the brain may play key roles in modulation of chronic pain will also be discussed. Although peripheral triggering events surely play an important role in initiating pain, the development of chronic and, in particular, refractory pain may depend on changes or malfunctions in the central nervous system. These changes may be quite subtle and require sophisticated approaches, such as functional MRI, to study them, as is now being done. New findings obtained therefore may lead to more rational and reliable treatment for orofacial pain.

Imaging attentional modulation of pain in the periaqueductal gray in humans

Pain is an unpleasant sensory and emotional experience usually triggered by stimulation of peripheral nerves and often associated with actual or potential tissue damage. It is well known that pain perception for patients and normal subjects can be modulated by psychological factors, such as attention, stress, and arousal. Our understanding of how this modulation occurs at a neuroanatomical level is poor. Here we neuroanatomically defined a key area in the network of brain regions active in response to pain that is modulated by attention to the painful stimulus. High-resolution functional magnetic resonance imaging was used to define brain activation to painful heat stimulation applied to the hand of nine normal subjects within the periaqueductal gray region. Subjects were asked to either focus on or distract themselves from the painful stimuli, which were cued using colored lights. During the distraction condition, subjects rated the pain intensity as significantly lower compared with when they attended to the stimulus. Activation in the periaqueductal gray was significantly increased during the distraction condition, and the total increase in activation was predictive of changes in perceived intensity. This provides direct evidence supporting the notion that the periaqueductal gray is a site for higher cortical control of pain modulation in humans.

Is fibromyalgia a neurologic disease?

Fibromyalgia (FM) is characterized by abnormal pain sensitivity in response to diverse stimuli as well as persistent widespread pain and other symptoms such as fatigue and sleep disturbance. Progress has been made in identifying factors that contribute to the etiopathogenesis of abnormal pain sensitivity, but there is no single model of pathophysiology or treatment of FM that has gained wide acceptance among health care professionals. We review the literature on the etiopathogenesis of abnormal pain sensitivity in FM and describe an explanatory model that serves as a source of testable hypotheses in our laboratory. This model posits that interactions of exogenous (e.g., environmental stressors) and endogenous (e.g., neuroendocrine dysfunction) abnormalities in genetically predisposed individuals lead to a final common pathway, i.e., alterations in central nervous system function and neuropeptide production that underlie central sensitization and abnormal pain sensitivity. This model also suggests that efforts to develop and evaluate treatments for FM should focus on interventions with direct or indirect effects on central functions that influence pain sensitivity.

Brain mechanisms of pain affect and pain modulation

Recent animal studies reveal ascending nociceptive and descending modulatory pathways that may contribute to the affective-motivational aspects of pain and play a critical role in the modulation of pain. In humans, a reliable pattern of cerebral activity occurs during the subjective experience of pain. Activity within the anterior cingulate cortex and possibly in other classical limbic structures, appears to be closely related to the subjective experience of pain unpleasantness and may reflect the regulation of endogenous mechanisms of pain modulation.

Is there a BOLD response of the visual cortex on stimulation of the vision-related acupoint GB 37?

PURPOSE

To determine whether or not acupuncture of guangming (GB 37) produces a significant response of the visual cortex detectable by means of functional magnetic resonance imaging (fMRI).

MATERIALS AND METHODS

This study investigates the activation of the visual cortex elicited by a soft and an intensified stimulation of GB 37, an acupoint documented to influence vision-related disorders. Three different paradigms were carried out to detect any possible modulation of the Blood Oxygenation Level Dependent (BOLD)-response in the visual cortex to visual stimulation through acupuncture.

RESULTS

The percentage signal changes in the visual stimulation cycles did not significantly differ before vs. during acupuncture.

CONCLUSION

Whereas no BOLD-response correlating with acupuncture was detected in the visual cortex, BOLD-signal-changes in response to needle twisting were detected in different cortical areas. Further studies are necessary to clarify whether these clusters correlate to inevitable somatosensory stimulation accompanying acupuncture or represent an acupuncture-specific response.

Attention and the Stages of Pain Processing

OBJECTIVE

Explore the relationships between the four stages of pain processing and attention in chronic pain sufferers.

DESIGN

A cross-sectional, retrospective study of 736 subjects participating in an outpatient university-based tertiary care pain treatment program.

METHODS

Self-report measures of pain, pain-related unpleasantness, and suffering (Pain Experience Visual Analog Scales) in conjunction with a structured interview assessing illness behavior (adaptation of the Psychosocial Pain Inventory) and attention (Digit Span subtest of the Wechsler Adult Intelligence Scale-Revised) were employed.

OUTCOME MEASURES

Separate step-wise multiple regression analyses were conducted using variables that measure each of the four stages of pain processing as predictors, with Digit Span being the criterion variable.

RESULTS

Multiple regression analyses showed that, of the four pain stages, only suffering and pain behavior were related to attentional performance. Specifically, an individual's perception of lifestyle interference due to pain, level of depression, and the degree of solicitous responses from others each uniquely contributed to Digit Span performance.

CONCLUSIONS

Treatment interventions specifically targeting suffering and pain behavior may prove efficacious in addressing the attentional problems in chronic pain.

Brain activation by central command during actual and imagined handgrip under hypnosis

The purpose was to compare patterns of brain activation during imagined handgrip exercise and identify cerebral cortical structures participating in "central" cardiovascular regulation. Subjects screened for hypnotizability, five with higher (HH) and four with lower hypnotizability (LH) scores, were tested under two conditions involving 3 min of 1) static handgrip exercise (HG) at 30% of maximal voluntary contraction (MVC) and 2) imagined HG (I-HG) at 30% MVC. Force (kg), forearm integrated electromyography, rating of perceived exertion, heart rate (HR), mean blood pressure (MBP), and differences in regional cerebral blood flow distributions were compared using an ANOVA. During HG, both groups showed similar increases in HR (+13 +/- 5 beats/min) and MBP (+17 +/- 3 mmHg) after 3 min. However, during I-HG, only the HH group showed increases in HR (+10 +/- 2 beats/min; P < 0.05) and MBP (+12 +/- 2 mmHg; P < 0.05). There were no significant increases or differences in force or integrated electromyographic activity between groups during I-HG. The rating of perceived exertion was significantly increased for the HH group during I-HG, but not for the LH group. In comparison of regional cerebral blood flow, the LH showed significantly lower activity in the anterior cingulate (-6 +/- 2%) and insular cortexes (-9 +/- 4%) during I-HG. These findings suggest that cardiovascular responses elicited during imagined exercise involve central activation of insular and anterior cingulate cortexes, independent of muscle afferent feedback; these structures appear to have key roles in the central modulation of cardiovascular responses.

Central processing of rectal pain in patients with irritable bowel syndrome: an fMRI study

OBJECTIVES

In healthy subjects, the neural correlates of visceral pain bear much similarity with the correlates of somatic pain. In patients with irritable bowel syndrome, the central nervous system is believed to play a strong modulatory or etiological role in the pathophysiology of the disease. We hypothesize that this role must be reflected in aberrations of central functional responses to noxious visceral stimulation in these patients. To verify this hypothesis, we have induced transient rectal pain in patients and assessed the functional responses of the brain by means of functional magnetic resonance imaging.

METHODS

Twelve right-handed patients (11 female) were examined. Functional imaging (1.5 T) was performed following a block paradigm, alternating epochs with and without noxious stimulation of the rectum. Rectal pain was induced by inflating a latex balloon. Whole-brain coverage was achieved by means of echo-planar magnetic resonance acquisition.

RESULTS

A strong variability of the individual responses to rectal pain was found in patients with irritable bowel syndrome. Significant activations were found in only two patients, and group analysis did not reveal significant activations. In contrast, all patients exhibited significant deactivations. Group analysis revealed significant deactivations within the right insula, the right amygdala, and the right striatum.

CONCLUSIONS

This study reveals aberrant functional responses to noxious rectal stimulation in patients with irritable bowel syndrome. Those results add grounds to the hypothesis that the central nervous system plays a significant role in the pathophysiology of this syndrome.

Dissociable neural responses related to pain intensity, stimulus intensity, and stimulus awareness within the anterior cingulate cortex: a parametric single-trial laser functional magnetic resonance imaging study

Neuroimaging studies have demonstrated activations in the anterior cingulate cortex (ACC) related to the affective component of pain, but not to stimulus intensity. However, it is possible that the low spatial resolution of positron emission tomography, as used in the majority of these studies, obscured areas coding stimulus intensity. We revisited this issue, using a parametric single-trial functional magnetic resonance imaging design, and investigated pain, stimulus intensity, and stimulus awareness (i.e., pain unrelated) responses within the ACC in nine healthy volunteers. Four different stimulus intensities ranging from warm to painful (300-600 mJ) were applied with a thulium yttrium-aluminum granite infrared laser in a randomized order and rated by the subjects on a five point scale (P0-P4). Pain-related regions in the ventral posterior ACC showed a response that did not distinguish between innocuous trials (P0 and P1) but showed a positive linear relationship with the blood oxygenation level-dependent contrast signal for painful trials (P2-P4). Regions in the dorsal anterior ACC along the cingulate sulcus differentiated between P0 (not perceived) and P1 but exhibited no additional signal increase with P2; these regions are related to stimulus awareness and probably to cognitive processing. Most importantly, we identified a region in the dorsal posterior ACC showing a response that discriminated between nonpainful trials (P0 and P1); therefore, this region was simply related to basic sensory processing and not to pain intensity. Stimulus-related activations were all located adjacent to the cingulate motor area, highlighting the strategic link of stimulus processing and response generation in the posterior ACC.

Glutamate receptors and persistent pain: targeting forebrain NR2B subunits

Glutamate is the fast excitatory transmitter in mammalian brains. It binds to two major classes of glutamate receptors: ionotropic and metabotropic receptors. Ionotropic receptors contain three subtype receptors, including N-methyl-d-aspartate (NMDA) receptors. Activation of NMDA receptors is important for initiating long-lasting changes in synapses. In the forebrain structures that are known to contribute to the formation and storage of information, NMDA receptors have an important role in persistent inflammatory pain by reinforcing glutamate sensory transmission. Mice with enhanced forebrain NMDA receptor function demonstrate selective enhancement of persistent pain and allodynia. Drugs targeting NMDA NR2B subunits in the forebrain could serve as a new class of medicine for controlling persistent pain in humans.

Changes in regional cerebral metabolism during systemic hyperthermia in humans

Whole body hyperthermia may produce vasodialation, nausea, and altered cognitive function. Animal research has identified brain regions that have important roles in thermoregulation. However, differences in both the cognitive and sweating abilities of humans and animals implicate the need for human research. Positron emission tomography (PET) was used to identify brain regions with altered activity during systemic hyperthermia. Human subjects were studied under cool (control) conditions and during steady-state hyperthermia induced by means of a liquid-conditioned suit perfused with hot water. PET images were obtained by injecting [(18)F]fluorodeoxyglucose, waiting 20 min for brain uptake, and then scanning for 10 min. Heating was associated with a 23% increase in resting metabolic rate. Significant increases in cerebral metabolic rate occurred in the hypothalamus, thalamus, corpus callosum, cingulate gyrus, and cerebellum. In contrast, significant decreases occurred in the caudate, putamen, insula, and posterior cingulum. These results are important for understanding the mechanisms responsible for altered cognitive and systemic responses during hyperthermia. Novel regions (e.g., lateral cerebellum) with possible thermoregulatory roles were identified.

Imaging how attention modulates pain in humans using functional MRI

Current clinical and experimental literature strongly supports the phenomenon of reduced pain perception whilst attention is distracted away from noxious stimuli. This study used functional MRI to elucidate the underlying neural systems and mechanisms involved. An analogue of the Stroop task, the counting Stroop, was used as a cognitive distraction task whilst subjects received intermittent painful thermal stimuli. Pain intensity scores were significantly reduced when subjects took part in the more cognitively demanding interference task of the counting Stroop than in the less demanding neutral task. When subjects were distracted during painful stimulation, brain areas associated with the affective division of the anterior cingulate cortex (ACC) and orbitofrontal regions showed increased activation. In contrast, many areas of the pain matrix (i.e. thalamus, insula, cognitive division of the ACC) displayed reduced activation, supporting the behavioural results of reduced pain perception.

Cortical mapping of visceral pain in patients with GI disorders using functional magnetic resonance imaging

OBJECTIVE

We sought to identify central loci that activate in response to visceral stimuli (stool and pain). We had a particular interest in observing the anterior cingulate gyrus and frontal cortex in normals and in patients with intestinal disease, including inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).

METHODS

Subjects underwent rectal balloon distention to a sensation of stool and to a sensation of pain while undergoing blood oxygenation level-dependent functional magnetic resonance imaging. Experiments were conducted in a Magnex 3.0-T whole body magnet with a Bruker Biospec console and a quadrature head coil. Four contiguous 5.0-mm oblique axial slices designed to optimize coverage of areas believed to be responsive to noxious stimulation were acquired. Activations were detected by using cross-correlation maps (p < 0.001) for individual subjects. The experimental groups were compared using both an analysis of variance and profile analysis.

RESULTS

A significantly higher percentage of pixels activated in the anterior cingulate gyrus over both pain and stool conditions for the control group than for the IBS group and for the IBS group than for the IBD group (p < 0.035). Deactivation of left somatosensory cortex was greater for the IBS group than for the IBD group and greater for the IBD group than for the controls (p < 0.0065) in the boxcar condition. Frontal deactivation in controls compared with disease groups bordered on statistical significance. Profile analysis of the three groups across six regions of interest revealed that the control and IBD groups were distinguished by different profiles of response (p < 0.005). Nonparametric evaluation of the data suggests that, among the pixels in the anterior cingulate activating to pain, there are two patterns of response to pain-on/off and graded. This was true for both controls and disease groups.

CONCLUSIONS

Normal controls and subjects with IBD and IBS share similar loci of activations to visceral sensations of stool and pain. Both activation and deactivation of particular regions of interest differentiate the three groups, as do profiles of patterned response across six of the regions of interest for the control and IBD groups.

fMRI of thermal pain: effects of stimulus laterality and attention

Brain activity was studied by fMRI in 18 healthy subjects during stimulation of the thenar eminence of the hand with either warm (non-painful, 40 degrees C) or hot (painful, 46-49 degrees C) stimuli using a contact thermode. Experiments were performed on the right and left hand independently and with two attentional contexts: subjects either attended to pain or attended to a visual global motion discrimination task (to distract them from pain). Group analysis demonstrated that attended warm stimulation of the right hand did not produce any significantly activated clusters. Painful thermal stimulation of either hand elicited significant activity over a large network of brain regions, including insula, inferior frontal gyrus, cingulate gyrus, secondary somatosensory cortex, cerebellum, and medial frontal gyrus (corrected P < 0.05). Insula activity was distributed along its anterior-posterior axis and depended on the hand stimulated and attentional context. In particular, activity within the posterior insula was contralateral to the site of stimulation, tested using regions of interest (ROI) analysis: significant side x site interaction (P = 0.001). With attention diverted from the painful stimulus bilateral anterior insula activity moved posteriorly to midinsula and decreased in extent (ROI analysis: significant main effect of attention (P = 0.03)). The role of the insula in thermosensation and attention is discussed.

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

It is common clinical experience that anxiety about pain can exacerbate the pain sensation. Using event-related functional magnetic resonance imaging (FMRI), we compared activation responses to noxious thermal stimulation while perceived pain intensity was manipulated by changes in either physical intensity or induced anxiety. One visual signal, which reliably predicted noxious stimulation of moderate intensity, came to evoke low anxiety about the impending pain. Another visual signal was followed by the same, moderate-intensity stimulation on most of the trials, but occasionally by discriminably stronger noxious stimuli, and came to evoke higher anxiety. We found that the entorhinal cortex of the hippocampal formation responded differentially to identical noxious stimuli, dependent on whether the perceived pain intensity was enhanced by pain-relevant anxiety. During this emotional pain modulation, entorhinal responses predicted activity in closely connected, affective (perigenual cingulate), and intensity coding (mid-insula) areas. Our finding suggests that accurate preparatory information during medical and dental procedures alleviates pain by disengaging the hippocampus. It supports the proposal that during anxiety, the hippocampal formation amplifies aversive events to prime behavioral responses that are adaptive to the worst possible outcome.

The role of operant conditioning in chronic pain: an experimental investigation

The role of operant conditioning for the development and maintenance of chronic pain was examined in 30 chronic back pain patients (CBP) and 30 matched healthy controls. Half of each group was reinforced for increased, half for decreased pain reports while EEG, EOG, heart rate, skin conductance and muscle tension levels were recorded. Both groups showed similar learning rates, however, the CBP patients displayed slower extinction of both the verbal and the cortical (N150) pain response. In addition, the CBP group displayed prolonged elevated electromyogram levels to the task. These data suggest that CBP patients are more easily influenced by operant conditioning factors than healthy controls and this susceptibility may add to the maintenance of the chronic pain problem.

Mind blindness and the brain in autism

Experimental evidence shows that the inability to attribute mental states, such as desires and beliefs, to self and others (mentalizing) explains the social and communication impairments of individuals with autism. Brain imaging studies in normal volunteers highlight a circumscribed network that is active during mentalizing and links medial prefrontal regions with posterior superior temporal sulcus and temporal poles. The brain abnormality that results in mentalizing failure in autism may involve weak connections between components of this system.

Reward circuitry activation by noxious thermal stimuli

Using functional magnetic resonance imaging (fMRI), we observed that noxious thermal stimuli (46 degrees C) produce significant signal change in putative reward circuitry as well as in classic pain circuitry. Increases in signal were observed in the sublenticular extended amygdala of the basal forebrain (SLEA) and the ventral tegmentum/periaqueductal gray (VT/PAG), while foci of increased signal and decreased signal were observed in the ventral striatum and nucleus accumbens (NAc). Early and late phases were observed for signals in most brain regions, with early activation in reward related regions such as the SLEA, VT/PAG, and ventral striatum. In contrast, structures associated with somatosensory perception, including SI somatosensory cortex, thalamus, and insula, showed delayed activation. These data support the notion that there may be a shared neural system for evaluation of aversive and rewarding stimuli.

Reduction in opioid- and cannabinoid-induced antinociception in rhesus monkeys after bilateral lesions of the amygdaloid complex

The amygdaloid complex is a prominent temporal lobe region that is associated with "emotional" information processing. Studies in the rodent have also recently implicated the amygdala in the processing and modulation of pain sensation, the experience of which involves a considerable emotional component in humans. In the present study, we sought to establish the relevance of the amygdala to pain modulation in humans by investigating the contribution of this region to antinociceptive processes in nonhuman primates. Using magnetic resonance imaging guidance, the amygdaloid complex was lesioned bilaterally in six rhesus monkeys (Macaca mulatta) through microinjection of the neurotoxin ibotenic acid. This procedure resulted in substantial neuronal cell loss in all nuclear subdivisions of this structure. In awake unoperated control monkeys, systemic administration of the prototypical opioid morphine or the cannabinoid receptor agonist WIN55,212-2 produced dose-dependent antinociception on a warm-water tail-withdrawal assay. The antinociceptive effects of each drug were reversible with an appropriate antagonist. In monkeys with bilateral amygdala lesions, however, the antinociceptive effects of each drug were significantly reduced. These results constitute the first causal data demonstrating the necessity of neurons in a specific brain region for the full expression of opioid- and cannabinoid-induced antinociception in the primate. Because our amygdala-lesioned monkeys exhibited both a reduction in antinociception and a reduction in behavioral indices of fear (Emery et al., 2001), the possibility should be considered that, in the primate, "antinociceptive circuitry" and "fear circuitry" overlap at the level of the amygdala.

Functional MR imaging of regional brain activation associated with the affective experience of pain

OBJECTIVE

Current models propose that the experience of pain includes both sensory and affective components. Our purpose was to use functional MR imaging to determine areas of the brain engaged by the affective dimension of pain.

SUBJECTS AND METHODS

Twelve healthy adults underwent functional MR imaging using a gradient-echo echoplanar technique while a cold pressor test, consisting of cold and pain tasks, was applied first to one foot and then to the other. The cold task involved the application of cold water (14-20 degrees C) that was not at a painful level. For the pain task, the water temperature was then lowered to a painful temperature (8-14 degrees C) and subsequently to the pain threshold (3-8 degrees C). Images acquired at room temperature before the cold and pain tasks served as a baseline task. Composite maps of brain activation were generated by comparing the baseline task with the cold task and the cold task with the pain task. The significance of signal changes was estimated by randomization of individual activation maps.

RESULTS

Cold-related activation (p < 0.01) was found in the postcentral gyrus bilaterally, laterally, and inferiorly to the primary motor-sensory area of the foot and at a site near the second somatosensory site. Activation also occurred in the frontal lobe (the bilateral middle frontal gyri and the right inferior frontal gyrus), the left anterior insula, the left thalamus, and the superior aspect of the anterior cingulate gyrus (seen at one slice location). Pain-related activation (p < 0.01) included the anterior cingulate gyrus (seen at four slice locations); the superior frontal gyrus, especially on the right; and the right cuneus.

CONCLUSION

Compared with the basic sensory processing of pain, the affective dimension of pain activates a cortical network that includes the right superior frontal gyrus, the right cuneus, and a large area of the anterior cingulate gyrus.

Prefrontal cortical hyperactivity in patients with sympathetically mediated chronic pain

Chronic pain continues to impose a large burden of suffering, yet its neural correlates remain poorly understood. In sympathetically mediated chronic pain (SMP), peripheral sympathetic blockade temporarily relieves this pain, so that related neural activity can be studied without perturbing sensory inputs. We used functional magnetic resonance imaging and thermal painful stimuli applied to the chronically painful body site, before and after sympathetic blockade, to examine the cortical network of chronic pain. The chronic SMP state was associated with a widely spread prefrontal hyperactivity, increased anterior cingulate activity and decreased activity in the thalamus contralateral to the body side suffering from SMP, but was unrelated to sensorimotor activity. Ineffective sympathetic blocks, i.e. blocks that did not diminish the SMP pain, did not change the cortical responses to the painful thermal stimulus; while effective placebo resulted in similar responses to those of effective blocks. These findings provide evidence for abnormal brain responses to pain in patients with chronic SMP, which engages prefrontal/limbic networks more extensively than in acute pain-states.

Distraction modulates anterior cingulate gyrus activations during the cold pressor test

The anterior cingulate gyrus (ACG) is part of a neural network implicated in attention-demanding tasks, such as the experience of pain. However, the regions within the ACG responding to cognitive demands and to painful stimulation are not identical. Since directing attention away from a painful stimulus is known to reduce the perceived pain intensity, we hypothesized that distraction from pain would result both in decreased activation of ACG subregions responsive to painful stimulation and increased activation of ACG subregions responsive to the distraction task. BOLD fMRI has comparatively high spatial resolution and allows for better identification of ACG subregional responses than other neuroimaging techniques. Twelve subjects were tested using the cold pressor test (CPT), a verbal attention task (VAT), and a distraction task (DT) (a combination of the CPT and VAT). Analysis was performed on a voxel-by-voxel basis using a general linear model as implemented in SPM99. In addition to ACG activations common to both the CPT and VAT, we identified one CPT-specific cluster in an area corresponding to BA24'. The modulation effect of distraction on pain was assessed by contrasting (CPT-DT) and (DT-CPT). In support of our hypothesis, contrast (CPT-DT) revealed a decrease in BA24' during the DT and contrast (DT-CPT) showed increased activation in BA32/32'. These data suggest that distraction from pain and concomitant low pain ratings are reflected in distinct ACG subregional responses.

Cognitive interference is associated with neuronal marker N-acetyl aspartate in the anterior cingulate cortex: an in vivo (1)H-MRS study of the Stroop Color-Word task

The neurobiology of cognitive interference is unknown. Previous brain imaging studies using the Stroop Color-Word (SCW) task indicate involvement of the cingulate cortex cognitive division. The present study examines interrelationships between regional brain N-Acetyl aspartate (NAA) levels (as identified by in vivo proton magnetic resonance spectroscopy in the right and left anterior cingulate cortex (ACC), dorsolateral prefrontal cortex, orbitofrontal cortex and thalamus) and cognitive interference (as measured by the SCW task) in 15 normal subjects. The results show that brain chemistry depends on cognitive interference levels (high vs low). Reduction of NAA levels was demonstrated in the right ACC (ie, cognitive midsupracallosal division) of high interference subjects, as compared to the low interference group (P < 0.01, two-tailed t-test). Chemical-cognitive relationships were analyzed by calculating correlations between regional NAA levels and the SCW task scores. Cognitive interference was highly correlated with the right anterior cingulate NAA (r = 0.76, P < 0.001), and was unrelated to other studied regional NAA, including the left ACC (P < 0.025; comparing the difference between r values in the right and left ACC). The interrelationships between NAA across brain regions were examined using correlation analysis (square matrix correlation maps), which detected different connectivity patterns between the two groups. These findings provide evidence of ACC involvement in cognitive interference suggesting a possibility of neuronal reorganization in the physiological mechanism of interference (most likely due to genetically predetermined control of the number of neurons, dendrites and receptors, and their function). We conclude that spectroscopic brain mapping of NAA, the marker of neuronal density and function, to the SCW task measures differentiates between high and low interference in normal subjects. This neuroimaging/cognitive tool may be useful for documentation of interference in studying cognitive control mechanisms, and in diagnosis of neuropsychiatric disorders where dysfunction of cingulate cortex is expected.

Differential coding of pain intensity in the human primary and secondary somatosensory cortex

The primary (SI) and secondary (SII) somatosensory cortices have been shown to participate in human pain processing. However, in humans it is unclear how SI and SII contribute to the encoding of nociceptive stimulus intensity. Using magnetoencephalography (MEG) we recorded responses in SI and SII in eight healthy humans to four different intensities of selectively nociceptive laser stimuli delivered to the dorsum of the right hand. Subjects' pain ratings correlated highly with the applied stimulus intensity. Activation of contralateral SI and bilateral SII showed a significant positive correlation with stimulus intensity. However, the type of dependence on stimulus intensity was different for SI and SII. The relation between SI activity and stimulus intensity resembled an exponential function and matched closely the subjects' pain ratings. In contrast, SII activity showed an S-shaped function with a sharp increase in amplitude only at a stimulus intensity well above pain threshold. The activation pattern of SI suggests participation of SI in the discriminative perception of pain intensity. In contrast, the all-or-none-like activation pattern of SII points against a significant contribution of SII to the sensory-discriminative aspects of pain perception. Instead, SII may subserve recognition of the noxious nature and attention toward painful stimuli.

Somatosensory event-related potential and autonomic activity to varying pain reduction cognitive strategies in hypnosis

OBJECTIVES

The issues of differential effects among cognitive strategies during hypnosis in the control of human pain are under active debate. This study, which employs measures of pain perception, electrocortical and autonomic responses, was aimed at determining these pain-related modulations.

METHODS

Somatosensory event-related potentials (SERPs) to noxious stimuli under an odd-ball paradigm were recorded at the frontal, temporal and parietal regions in 10 high, 9 mid, and 10 low hypnotizable right-handed young women, at waking baseline, varying cognitive strategies (deep relaxation, dissociative imagery, focused analgesia) in hypnosis and placebo conditions. The phasic heart rate (HR) and skin conductance response were also recorded. The analysis was focused on the frequent standard trials of the odd-ball SERPs. Repeated measures analysis of variance was conducted to examine the experimental effects.

RESULTS

Focused analgesia induced the largest reduction in pain rating, more in the high than low hypnotizable subjects. In high hypnotizable subjects, the N2 amplitude was greater over frontal and temporal scalp sites than over parietal and central sites, whereas in moderately and low hypnotizable subjects, N2 was greater over temporal sites than over frontal, parietal, and central sites. These subjects also displayed a larger N2 peak over temporal sites during focused analgesia than in the other conditions. The P3 amplitude was smaller under deep relaxation, dissociative imagery and focused analgesia in the high hypnotizable subjects. For these subjects, the smallest P3 peaks were obtained for dissociated imagery and focused analgesia over frontal and temporal sites. In contrast, for the P3 peak, low hypnotizable subjects failed to show significant condition effects. In all of the subjects, the skin conductance and HR were smaller during hypnotic suggestions than in the waking state.

CONCLUSIONS

The effect of pain modulation is limited to high hypnotizable subjects rather than low hypnotizable ones. Higher frontal-temporal N2 and smaller posterior parietal P3 may indicate active inhibitory processes during cognitive strategies in hypnotic analgesia. These inhibitory processes also regulate the autonomic activities in pain perception.

Cellular and humoral immunity, mood and exam stress: the influences of self-hypnosis and personality predictors

The effects of self-hypnosis training on immune function and mood were examined in medical students at exam time. Hypnosis involved relaxation and imagery directed at improved immune function and increased energy, alertness and concentration. Hypotheses were made about activated and withdrawn personality differences. Eight high and eight low hypnotically susceptible participants were given 10 sessions of hypnosis, one live and nine tape-recorded, and were compared with control subjects (N=12). CD3, CD4, CD8, CD19 and CD56 NK cells and blood cortisol were assayed. Life-style, activated vs. withdrawn temperament, arousal and anxiety questionnaires were administered. Self-hypnosis buffered the decline found in controls in NK (P<0.002) and CD8 cells (P<0.0.07) and CD8/CD4% (P<0.06) (45-35% order of magnitude differences) while there was an increase in cortisol (P<0.05). The change in NK cell counts correlated positively with changes in both CD8 cells and cortisol. Results were independent of changes in life-style. Energy ratings were higher after hypnosis (P<0.01), and increased calmness with hypnosis correlated with an increase in CD4 counts (P<0.01). The activated temperament, notably the cognitive subscale (speaking and thinking quickly), was predictive of exam levels of T and B lymphocytes (P&z.Lt;0.08-P<0.02), and reaching r=0.72 (P<0.001) in the non-intervention control group. The sizeable influences on cell-mediated immunity achieved by a relatively brief, low cost psychological intervention in the face of a compelling, but routine, stress in young, healthy adults have implications for illness prevention and for patients with compromised immunity.

An unusual population of pyramidal neurons in the anterior cingulate cortex of hominids contains the calcium-binding protein calretinin

In the context of an on-going comparative analysis of primate neocortex evolution, we describe the occurrence and distribution of a previously unrecognized group of pyramidal neurons, restricted to the superficial part of layer V in the anterior cingulate cortex of hominids and characterized by immunoreactivity to the calcium-binding protein, calretinin. These neurons were rare in orangutans, more numerous in gorillas and common chimpanzees, while humans had the highest numbers. These calretinin-containing pyramidal cells were not observed in the cingulate cortex of any other primate or mammalian species. This finding, together with other recent observations on the hominoid cingulate cortex, is interesting when considering primate neocortical evolution, as it indicates possible adaptive and anatomical modifications in a cortical region critical for the integration of many aspects of autonomic function, vocalization, and cognitive processes.

Regional mu opioid receptor regulation of sensory and affective dimensions of pain

The endogenous opioid system is involved in stress responses, in the regulation of the experience of pain, and in the action of analgesic opiate drugs. We examined the function of the opioid system and mu-opioid receptors in the brains of healthy human subjects undergoing sustained pain. Sustained pain induced the regional release of endogenous opioids interacting with mu-opioid receptors in a number of cortical and subcortical brain regions. The activation of the mu-opioid receptor system was associated with reductions in the sensory and affective ratings of the pain experience, with distinct neuroanatomical involvements. These data demonstrate the central role of the mu-opioid receptors and their endogenous ligands in the regulation of sensory and affective components of the pain experience.

Subjective ratings of pain correlate with subcortical-limbic blood flow: an fMRI study

Studies investigating the cerebral representations of pain using functional imaging techniques failed to elucidate the affective aspects of pain. This investigation used functional magnetic resonance imaging to measure pain-related changes in cerebral activity during painful stimulation with a strong affective component. Vascular pain was induced via balloon dilatation of a dorsal foot vein of healthy volunteers. The subjects rated their perceived pain uninterruptedly during imaging, allowing cerebral activity to be correlated with both stimulus function (boxcar) and, more importantly, subjective ratings reflecting individual pain experience. The findings indicated signal increases in subcortical-limbic regions, particularly in the amygdala. This region is suggested to be involved in the affective dimension of pain.

The affective component of pain in rodents: direct evidence for a contribution of the anterior cingulate cortex

Numerous human and animal studies indirectly implicate neurons in the anterior cingulate cortex (ACC) in the encoding of the affective consequences of nociceptor stimulation. No causal evidence, however, has been put forth linking the ACC specifically to this function. Using a rodent pain assay that combines the hind-paw formalin model with the place-conditioning paradigm, we measured a learned behavior that directly reflects the affective component of pain in the rat (formalin-induced conditioned place avoidance) concomitantly with "acute" formalin-induced nociceptive behaviors (paw lifting, licking, and flinching) that reflect the intensity and localization of the nociceptive stimulus. Destruction of neurons originating from the rostral, but not caudal, ACC reduced formalin-induced conditioned place avoidance without reducing acute pain-related behaviors. These results provide evidence indicating that neurons in the ACC are necessary for the "aversiveness" of nociceptor stimulation.

Cortical representation of the sensory dimension of pain

It is well accepted that pain is a multidimensional experience, but little is known of how the brain represents these dimensions. We used positron emission tomography (PET) to indirectly measure pain-evoked cerebral activity before and after hypnotic suggestions were given to modulate the perceived intensity of a painful stimulus. These techniques were similar to those of a previous study in which we gave suggestions to modulate the perceived unpleasantness of a noxious stimulus. Ten volunteers were scanned while tonic warm and noxious heat stimuli were presented to the hand during four experimental conditions: alert control, hypnosis control, hypnotic suggestions for increased-pain intensity and hypnotic suggestions for decreased-pain intensity. As shown in previous brain imaging studies, noxious thermal stimuli presented during the alert and hypnosis-control conditions reliably activated contralateral structures, including primary somatosensory cortex (S1), secondary somatosensory cortex (S2), anterior cingulate cortex, and insular cortex. Hypnotic modulation of the intensity of the pain sensation led to significant changes in pain-evoked activity within S1 in contrast to our previous study in which specific modulation of pain unpleasantness (affect), independent of pain intensity, produced specific changes within the ACC. This double dissociation of cortical modulation indicates a relative specialization of the sensory and the classical limbic cortical areas in the processing of the sensory and affective dimensions of pain.

Acupuncture produces central activations in pain regions

Acupuncture is largely used for pain control in several pathological conditions. Its effects on the central nervous system are not well defined. We investigated the effect of the application of acupuncture to 13 normal subjects (males, 21-32 years). H2(15)O bolus PET scans were read before the application of the needles (Rest, R) and after 25 min of needle insertion. Data were acquired by scanning in 3-D mode. The acupuncture application, true acupuncture (TA), was alternated to a placebo needle application (PA) in two different sequences (seven and six subjects, respectively), either R,PA,R, TA or R,TA,R,PA, a period of 15 min being left after every first TA or PA to allow for the recovery of basal conditions. Here we show that classic acupuncture activates the left Anterior Cingulus, the Insulae bilaterally, the Cerebellum bilaterally, the left Superior Frontal Gyrus, and the right Medial and Inferior Frontal Gyri. Most of the activated areas are shared with areas activated in acute and chronic pain states as described in the literature. Thus acupuncture appears to act by activating areas also involved in pain. This indicates that acupuncture could relief pain by unbalancing the equilibrium of distributed pain-related central networks.

Identification of higher brain centres that may encode the cardiorespiratory response to exercise in humans

1. Positron emission tomography (PET) was used to identify the neuroanatomical correlates underlying 'central command' during imagination of exercise under hypnosis, in order to uncouple central command from peripheral feedback. 2. Three cognitive conditions were used: condition I, imagination of freewheeling downhill on a bicycle (no change in heart rate, HR, or ventilation, V(I)): condition II, imagination of exercise, cycling uphill (increased HR by 12 % and V(I) by 30 % of the actual exercise response): condition III, volitionally driven hyperventilation to match that achieved in condition II (no change in HR). 3. Subtraction methodology created contrast A (II minus I) highlighting cerebral areas involved in the imagination of exercise and contrast B (III minus I) highlighting areas activated in the direct volitional control of breathing (n = 4 for both; 8 scans per subject). End-tidal P(CO(2)) (P(ET,CO(2))) was held constant throughout PET scanning. 4. In contrast A, significant activations were seen in the right dorso-lateral prefrontal cortex, supplementary motor areas (SMA), the right premotor area (PMA), superolateral sensorimotor areas, thalamus, and bilaterally in the cerebellum. In contrast B, significant activations were present in the SMA and in lateral sensorimotor cortical areas. The SMA/PMA, dorso-lateral prefrontal cortex and the cerebellum are concerned with volitional/motor control, including that of the respiratory muscles. 5. The neuroanatomical areas activated suggest that a significant component of the respiratory response to 'exercise', in the absence of both movement feedback and an increase in CO(2) production, can be generated by what appears to be a behavioural response.

Parabrachial internal lateral neurons convey nociceptive messages from the deep laminas of the dorsal horn to the intralaminar thalamus

This study investigates the physiological properties of parabrachial internal lateral (PBil) neurons that project to the paracentral thalamic (PC) nucleus using antidromic activation and single-unit recording techniques in anesthetized rat. We reported here that most of these neurons responded exclusively to the nociceptive stimulation of large receptive fields with a sustained firing that often outlasted the stimulus up to several minutes. These responses were depressed by intravenous morphine. Our results demonstrated a novel spino-PBil-PC pathway, which transmits nociceptive messages to the PC nucleus, which in turn projects to the prefrontal cortex. Recent clinical imaging studies showed the important participation of prefrontal cortex in emotional response to pain. This spino-PBil-PC pathway may explain how nociceptive messages reach the prefrontal cortex and thus trigger unbearable aversive aspects of pain.