Assessing the risk of central post-stroke pain of thalamic origin by lesion mapping.

Central post-stroke pain of thalamic origin is an extremely distressing and often refractory disorder. There are no well-established predictors for pain development after thalamic stroke, and the role of different thalamic nuclei is unclear. Here, we used structural magnetic resonance imaging to identify the thalamic nuclei, specifically implicated in the generation of central post-stroke pain of thalamic origin. Lesions of 10 patients with central post-stroke pain of thalamic origin and 10 control patients with thalamic strokes without pain were identified as volumes of interest on magnetic resonance imaging data. Non-linear deformations were estimated to match each image with a high-resolution template and were applied to each volume of interest. By using a digital atlas of the thalamus, we elucidated the involvement of different nuclei with respect to each lesion. Patient and control volumes of interest were summed separately to identify unique areas of involvement. Voxelwise odds ratio maps were calculated to localize the anatomical site where lesions put patients at risk of developing central post-stroke pain of thalamic origin. In the patients with pain, mainly lateral and posterior thalamic nuclei were affected, whereas a more anterior-medial lesion pattern was evident in the controls. The lesions of 9 of 10 pain patients overlapped at the border of the ventral posterior nucleus and the pulvinar, coinciding with the ventrocaudalis portae nucleus. The lesions of this area showed an odds ratio of 81 in favour of developing thalamic pain. The high odds ratio at the ventral posterior nucleus-pulvinar border zone indicates that this area is crucial in the pathogenesis of thalamic pain and demonstrates the feasibility of identifying patients at risk of developing central post-stroke pain of thalamic origin early after thalamic insults. This provides a basis for pre-emptive treatment studies.

Repeated pain induces adaptations of intrinsic brain activity to reflect past and predict future pain.

Recent neuroimaging studies have revealed a persistent architecture of intrinsic connectivity networks (ICNs) in the signal of functional magnetic resonance imaging (fMRI) of humans and other species. ICNs are characterized by coherent ongoing activity between distributed brain regions during rest, in the absence of externally oriented behavior. While these networks strongly reflect anatomical connections, the relevance of ICN activity for human behavior remains unclear. Here, we investigated whether intrinsic brain activity adapts to repeated pain and encodes an individual's experience. Healthy subjects received a short episode of heat pain on 11 consecutive days. Across this period, subjects either habituated or sensitized to the painful stimulation. This adaptation was reflected in plasticity of a sensorimotor ICN (SMN) comprising pain related brain regions: coherent intrinsic activity of the somatosensory cortex retrospectively mirrored pain perception; on day 11, intrinsic activity of the prefrontal cortex was additionally synchronized with the SMN and predicted whether an individual would experience more or less pain during upcoming stimulation. Other ICNs of the intrinsic architecture remained unchanged. Due to the ubiquitous occurrence of ICNs in several species, we suggest intrinsic brain activity as an integrative mechanism reflecting accumulated experiences.

Metabolic alterations associated with impaired clock drawing in Lewy body dementia.

The clock drawing test (CDT) is a widely used dementia screening instrument that assesses executive and visuospatial abilities; studies in patients with Alzheimer's disease (AD) suggest frontoposterior networks to be involved in clock drawing. Clock drawing errors are also often observed in dementia with Lewy bodies (DLB), but the functional neuroanatomical substrate of impaired clock drawing has not been firmly established in this disorder. The present study was designed to provide initial evidence for brain metabolic alterations associated with CDT performance in DLB. Twenty-one patients with DLB were enrolled. CDT ratings were correlated with the regional cerebral metabolic rate of glucose (rCMRglc) measured by (18)F-fluoro-2-deoxy-glucose positron emission tomography ((18)F-FDG PET) in the statistical parametric mapping software package SPM5, controlling for overall cognitive impairment as measured by the Mini-Mental-State Examination (MMSE) score. There was a significant negative association between test scores and rCMRglc in a left-hemispheric posterofrontal network including the temporoparietal and dorsal pre-motor cortices and the precuneus. The present study provides evidence for a direct association between frontoparietal dysfunction and impaired CDT performance in DLB. These findings also suggest that the CDT is an appropriate screening instrument for this disorder and that metabolic dysfunction, and therefore disease severity, is mirrored by performance on the test.

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.

Positron emission tomography ligand activation studies in the sports sciences: measuring neurochemistry in vivo.

Functional neuroimaging with magnetic resonance imaging (fMRI) or positron emission tomography (PET) provides the methodology to unravel some of the fascinating, but hitherto largely unresolved interactions between physical exercise and brain function. Phenomena such as raised mood, pain modulation, and sport addiction associated with physical exercise are highly interesting psychophysical models that require further in depth understanding at the neurotransmitter level. PET ligand displacement studies allow in vivo monitoring of endogenous transmitter trafficking in the entire brain and, thereby, to identify the link between exercise-induced behavioral measures and the endogenous neurotransmitter release. This review focuses on the methodology of ligand displacement in the opioidergic system, which together with the dopaminergic system has been considered as a central neurotransmitter system underlying diverse sport-induced psychophysical effects. Understanding the basic principles of exercise-induced transmitter release in the brain will potentially aid clinical applications of endurance training, both as a preventative or therapeutic intervention.

The runner's high: opioidergic mechanisms in the human brain.

The runner's high describes a euphoric state resulting from long-distance running. The cerebral neurochemical correlates of exercise-induced mood changes have been barely investigated so far. We aimed to unravel the opioidergic mechanisms of the runner's high in the human brain and to identify the relationship to perceived euphoria. We performed a positron emission tomography "ligand activation" study with the nonselective opioidergic ligand 6-O-(2-[(18)F]fluoroethyl)-6-O-desmethyldiprenorphine ([(18)F]FDPN). Ten athletes were scanned at 2 separate occasions in random order, at rest and after 2 h of endurance running (21.5 +/- 4.7 km). Binding kinetics of [(18)F]FDPN were quantified by basis pursuit denoising (DEPICT software). Statistical parametric mapping (SPM2) was used for voxelwise analyses to determine relative changes in ligand binding after running and correlations of opioid binding with euphoria ratings. Reductions in opioid receptor availability were identified preferentially in prefrontal and limbic/paralimbic brain structures. The level of euphoria was significantly increased after running and was inversely correlated with opioid binding in prefrontal/orbitofrontal cortices, the anterior cingulate cortex, bilateral insula, parainsular cortex, and temporoparietal regions. These findings support the "opioid theory" of the runner's high and suggest region-specific effects in frontolimbic brain areas that are involved in the processing of affective states and mood.

Fronto-Insular Connectivity during Pain Distraction Is Impaired in Patients with Somatoform Pain.

BACKGROUND AND PURPOSE: Somatoform pain disorder is characterized by chronic pain and various psychological symptoms including increased attention to mental and physical processes. Given that the medial prefrontal cortex (mPFC) of the default mode network (DMN) and the anterior insula of the salience network are critically involved in intrinsic and attentional processes, we investigated the involvement of these networks during the distraction from physical pain in somatoform pain patients. METHODS: During painful and nonpainful heat stimulation, attentional distraction from physical processes was modulated with a Stroop task. Thirteen patients were investigated with functional magnetic resonance imaging (fMRI) and compared to 13 controls. Main outcomes were spatial maps of coherent fMRI activity based on independent component analysis and functional connectivity (FC) resulting from psychophysiological interaction analysis. RESULTS: Behavioral pain intensity ratings were reduced during the distraction task in both groups. At brain level, we found deviant network activities in the DMN (particularly in the mPFC) and in the salience network (bilaterally in the anterior insula) in patients. During pain stimulation, Stroop-induced distraction decreased the FC between the mPFC and anterior insula in controls but not in patients. CONCLUSIONS: Modulating the FC between the mPFC and the insula may be highly relevant for shifting the attention away from external stimuli, including nociceptive input. The observed alterations in somatoform pain patients may foster new strategies in cognitive behavioral training tools for these patients.

Imaging pain modulation by subanesthetic S-(+)-ketamine.

Little is known about the effects of low-dose S-(+)-ketamine on the cerebral processing of pain. We investigated the effects of subanesthetic IV S-(+)-ketamine doses on the perception of experimental painful heat stimuli. Healthy volunteers were evaluated with functional magnetic resonance imaging (fMRI) while receiving the painful stimuli in conjunction with placebo and increasing doses (0.05, 0.1, 0.15 mg x kg(-1) x h(-1)) of ketamine infusion. Vital variables were monitored and all subjects rated pain intensity and unpleasantness on a numerical rating scale. Alterations in consciousness were measured using a psycho-behavioral questionnaire. Pain unpleasantness declined as ketamine dosage was increased (55.1% decrease, placebo versus 0.15 mg x kg(-1) x h(-1) ketamine). Pain intensity ratings also decreased with increasing ketamine dosage but to a lesser extent (23.1% decrease). During placebo administration, a typical pain activation network (thalamus, insula, cingulate, and prefrontal cortex) was found, whereas decreased pain perception with ketamine was associated with a dose-dependent reduction of pain-induced cerebral activations. Analysis of the dose-dependent ketamine effects on pain processing showed a decreasing activation of the secondary somatosensory cortex (S2), insula and anterior cingulate cortex. This part of the anterior cingulate cortex (midcingulate cortex) has been linked with the affective pain component that underlines the potency of ketamine in modulating affective pain processing.

SUNCT: bilateral hypothalamic activation during headache attacks and resolving of symptoms after trigeminal decompression.

Short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT) is a primary head-pain syndrome, which is often refractory to any medical treatment. Concerning the pathophysiology of SUNCT, hypothalamic involvement ipsilaterally to the pain has been suggested based on the clinical features and one functional imaging case report. Here we now report a new case with SUNCT and the concomitant cerebral activation pattern (fMRI) during the pain attacks. In addition to an activation of several brain structures known to be generally involved in pain processing, bilateral hypothalamic activation occurred during the pain attacks, arguing for a central origin of the headache. Interestingly, this patient became completely pain free after surgical decompression of the ipsilateral trigeminal nerve. We hypothesize that in this case with a central predisposition for trigeminal autonomic cephalgias, a peripheral trigger with ectopic excitation might have contributed to the clinical picture of SUNCT.

Distraction modulates connectivity of the cingulo-frontal cortex and the midbrain during pain--an fMRI analysis.

Neuroimaging studies with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have delineated a human pain network in vivo. Despite the recognition of cerebral structures engaged in pain transmission, the cerebral mechanisms involved in pain modulation are still not well understood. Here, we investigated healthy volunteers using fMRI during experimental heat pain and distraction induced by a visual incongruent color-word Stroop task. A factorial design permitted categorical and covariation analysis of four conditions, namely innocuous and noxious heat; with and without distraction. Pain without distraction evoked an activation pattern similar to that observed in previous neuroimaging pain studies. Distraction was associated with a significant reduction of the visual analogue scale (VAS) ratings for pain intensity and unpleasantness and a reduction of pain-related activation in multiple brain areas, particularly in the so-called 'medial pain system'. Distraction significantly increased the activation of the cingulo-frontal cortex including the orbitofrontal and perigenual anterior cingulate cortex (ACC), as well as the periaquaeductal gray (PAG) and the posterior thalamus. Covariation analysis revealed functional interaction between these structures during pain stimulation and distraction, but not during pain stimulation per se. According to our results, the cingulo-frontal cortex may exert top-down influences on the PAG and posterior thalamus to gate pain modulation during distraction.

Local and systemic cytokine expression in patients with postherpetic neuralgia.

BACKGROUND: Postherpetic neuralgia (PHN) is the painful complication of a varicella zoster virus reactivation. We investigated the systemic and local gene expression of pro- and anti-inflammatory cytokine expression in patients with PHN. METHODS: Thirteen patients with PHN at the torso (Th4-S1) were recruited. Skin punch biopsies were obtained from the painful and the contralateral painless body area for intraepidermal nerve fiber density (IENFD) and cytokine profiling. Additionally, blood was withdrawn for systemic cytokine expression and compared to blood values of healthy controls. We analyzed the gene expression of selected pro- and anti-inflammatory cytokines (tumor necrosis factor-alpha [TNF] and interleukins [IL]-1ß, IL-2, and IL-8). RESULTS: IENFD was lower in affected skin compared to unaffected skin (p<0.05), while local gene expression of pro- and anti-inflammatory cytokines did not differ except for two patients who had 7fold higher IL-6 and 10fold higher IL-10 gene expression in the affected skin compared to the contralateral unaffected skin sample. Also, the systemic expression of cytokines in patients with PHN and in healthy controls was similar. CONCLUSION: While the systemic and local expression of the investigated pro- and anti-inflammatory cytokines was not different from controls, this may have been influenced by study limitations like the low number of patients and different disease durations. Furthermore, other cytokines or pain mediators need to be considered.

Pain sensitisers exhibit grey matter changes after repetitive pain exposure: a longitudinal voxel-based morphometry study.

Previous research in health and disease has shown that exposure to pain changes the density of cortical grey matter (GM). Such structural changes of the brain might, however, depend crucially on how this pain experience is evaluated and processed in the brain. In the present study we aimed to detect pain-rating patterns and underlying GM changes after the application of repetitive painful stimulation using voxel-based morphometry (VBM). Healthy volunteers were investigated (n=27), receiving 8 noxious and 8 innocuous thermal stimuli on the right forearm for 11 consecutive working days. Data were compared with a control group without any intervention (n=18). Behavioural data demonstrated that a subgroup of volunteers (n=14) sensitised, whereas the others (n=13) habituated over the stimulation days. The VBM analysis revealed no increase but a significant reduction of GM density, eg, in the anterior cingulate cortex, the insular cortex and the frontal cortex, exclusively in the group of sensitisers. By contrast, pain habituaters did not show any density changes in the GM. Depending on the individual perception of pain during the time course of stimulation, the repetitive application of painful stimuli changed the GM density in pain-processing brain regions exclusively in those subjects who were characterised by the lack of habituation. Because VBM studies investigating patients experiencing chronic pain observed similar decreases in GM density and increasing pain ratings over time, the sensitisers in our study may have a higher vulnerability to developing chronic pain syndromes in later life.

Itch and eczema.

Eczema/dermatitis belongs to the most pruritic of skin diseases. Pruritogenic mediators in the skin are still mostly unknown. Recent studies, however, have shown that the histamine 4 receptor plays an important role in itch pathophysiology; tryptase and IL-31 are also involved in atopic eczema itch. Differences in itch perception and itch kinetics between healthy volunteers and eczema patients point towards ongoing central nervous inhibitory activity in patients. Questionnaire studies reported comparatively higher loads in affective items chosen by patients with atopic eczema. In the concept of eczema patient management, the therapy of clinical pruritus has to consider pathophysiology and perception by combining topical and systemic treatment.

Pruritus and atopic dermatitis.

Atopic eczema is one of the most pruritic skin diseases. Mediators of atopic eczema itch in the skin are still mostly unknown, but recent studies showed that the histamine 4 receptor plays an important role in itch pathophysiology; tryptase and interleukin-31 are also involved. Differences in itch perception and itch kinetics between healthy volunteers and eczema patients point towards an ongoing central nervous inhibitory activity in patients. Questionnaire studies reported comparatively higher loads in affective items chosen by patients with atopic eczema. In the concept of patient management, the therapy of clinical pruritus has to consider origin and perception of itch, namely the skin and the central nervous system, by combining topical and systemic treatment.

Neurometabolic correlates of depression and disability in episodic cluster headache.

A close association between pain, depression and disability has been shown. However, the neurometabolic correlates of this association have been barely investigated in disease states. Episodic cluster headache is a severe headache syndrome and represents a suitable disease model for the investigation of episodic pain. The aim of this study was to explore the relationship between depression and disability as well as pain scores and brain metabolism in patients with cluster headache during the disease period with repetitive pain attacks, but outside an acute attack. Thirteen patients with cluster headache underwent 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission (FDG-PET) and completed questionnaires on depression and disability as well as a pain visual analogue rating scale (VAS). A positive correlation between the depression scores and glucose metabolism was observed in the insular cortex. A positive correlation between the pain disability scores and brain metabolism was detected in the amygdala. The same applied to the pain visual analogue rating scores. Our data underline the association between severe episodic pain, depression and disability. In addition to this clinical observation, our results stress the importance of the insula and amygdala in pain processing and suffering.

Test-retest and interobserver reliability of quantitative sensory testing according to the protocol of the German Research Network on Neuropathic Pain (DFNS): a multi-centre study.

Quantitative sensory testing (QST) is an instrument to assess positive and negative sensory signs, helping to identify mechanisms underlying pathologic pain conditions. In this study, we evaluated the test-retest reliability (TR-R) and the interobserver reliability (IO-R) of QST in patients with sensory disturbances of different etiologies. In 4 centres, 60 patients (37 male and 23 female, 56.4±1.9years) with lesions or diseases of the somatosensory system were included. QST comprised 13 parameters including detection and pain thresholds for thermal and mechanical stimuli. QST was performed in the clinically most affected test area and a less or unaffected control area in a morning and an afternoon session on 2 consecutive days by examiner pairs (4 QSTs/patient). For both, TR-R and IO-R, there were high correlations (r=0.80-0.93) at the affected test area, except for wind-up ratio (TR-R: r=0.67; IO-R: r=0.56) and paradoxical heat sensations (TR-R: r=0.35; IO-R: r=0.44). Mean IO-R (r=0.83, 31% unexplained variance) was slightly lower than TR-R (r=0.86, 26% unexplained variance, P<.05); the difference in variance amounted to 5%. There were no differences between study centres. In a subgroup with an unaffected control area (n=43), reliabilities were significantly better in the test area (TR-R: r=0.86; IO-R: r=0.83) than in the control area (TR-R: r=0.79; IO-R: r=0.71, each P<.01), suggesting that disease-related systematic variance enhances reliability of QST. We conclude that standardized QST performed by trained examiners is a valuable diagnostic instrument with good test-retest and interobserver reliability within 2days. With standardized training, observer bias is much lower than random variance. Quantitative sensory testing performed by trained examiners is a valuable diagnostic instrument with good interobserver and test-retest reliability for use in patients with sensory disturbances of different etiologies to help identify mechanisms of neuropathic and non-neuropathic pain.

Interaction of hyperalgesia and sensory loss in complex regional pain syndrome type I (CRPS I).

BACKGROUND: Sensory abnormalities are a key feature of Complex Regional Pain Syndrome (CRPS). In order to characterise these changes in patients suffering from acute or chronic CRPS I, we used Quantitative Sensory Testing (QST) in comparison to an age and gender matched control group. METHODS: 61 patients presenting with CRPS I of the upper extremity and 56 healthy subjects were prospectively assessed using QST. The patients' warm and cold detection thresholds (WDT; CDT), the heat and cold pain thresholds (HPT; CPT) and the occurrence of paradoxical heat sensation (PHS) were observed. RESULTS: In acute CRPS I, patients showed warm and cold hyperalgesia, indicated by significant changes in HPT and CPT. WDT and CDT were significantly increased as well, indicating warm and cold hypoaesthesia. In chronic CRPS, thermal hyperalgesia declined, but CDT as well as WDT further deteriorated. Solely patients with acute CRPS displayed PHS. To a minor degree, all QST changes were also present on the contralateral limb. CONCLUSIONS: We propose three pathomechanisms of CRPS I, which follow a distinct time course: Thermal hyperalgesia, observed in acute CRPS, indicates an ongoing aseptic peripheral inflammation. Thermal hypoaesthesia, as detected in acute and chronic CRPS, signals a degeneration of A-delta and C-fibres, which further deteriorates in chronic CRPS. PHS in acute CRPS I indicates that both inflammation and degeneration are present, whilst in chronic CRPS I, the pathomechanism of degeneration dominates, signalled by the absence of PHS. The contralateral changes observed strongly suggest the involvement of the central nervous system.

Headaches and pineal cyst: a case-control study.

BACKGROUND: Pineal cysts have been suggested to be linked to headache pathogenesis. However, no systematic studies on this topic have been performed so far. OBJECTIVE: The aim of this study was to investigate the relationship between pineal cysts and headache and to determine the relevance of the cyst size in this context. METHODS: We conducted a case-control study of patients who consulted the neurological department between 1999 and 2006 to investigate the relationship between pineal cysts and headache and to determine the relevance of the cyst size. RESULTS: A total of 51 patients with pineal cyst were identified, thereby 51% were suffering from headache (half of them had migraine), whereas in the control group, only 25% had headache (thereof 31% suffered from migraine). There was a significant relationship between headache (as well as migraine) and pineal cysts (chi-square test), but no significant difference in pineal cyst diameter between the patient group with headache versus without headache (t-test). CONCLUSIONS: Our data provide evidence for a causal relationship between pineal cysts and headache, respectively, migraine in this patient cohort.

Recent progress in unraveling central nervous system processing of itch sensation.

Itch is the major symptom of many allergic or inflammatory skin diseases, yet it is still difficult to measure objectively. This article shows and updates the development and approaches of central nervous system investigation of itch.Human neuroimaging studies on the physiology and pathophysiology of itch sensation have been hampered by the lack of a reproducible "on-off" stimulus. Short-term alternating temperature modulation of histamine-induced itch has recently been shown to provide on-off characteristics.Recent studies with functional magnetic resonance imaging demonstrate that itch sensation in healthy volunteers is processed by a network of brain regions contributing to the encoding of sensory, emotional, attentional, evaluative, and motivational aspects of itch.