Distinct Alterations in Central Pain Processing of Visceral and Somatic Pain in Quiescent Ulcerative Colitis Compared to Irritable Bowel Syndrome and Health

BACKGROUND AND AIMS

Despite relevance to pain chronicity, disease burden, and treatment, mechanisms of pain perception for different types of acute pain remain incompletely understood in patients with inflammatory bowel disease [IBD]. Building on experimental research across pain modalities, we herein addressed behavioural and neural correlates of visceral versus somatic pain processing in women with quiescent ulcerative colitis [UC] compared to irritable bowel syndrome [IBS] as a patient control group and healthy women [HC].

METHODS

Thresholds for visceral and somatic pain were assessed with rectal distensions and cutaneous thermal pain, respectively. Using functional magnetic resonance imaging, neural and behavioural responses to individually calibrated and intensity-matched painful stimuli from both modalities were compared.

RESULTS

Pain thresholds were comparable across groups, but visceral thresholds correlated with gastrointestinal symptom severity and chronic stress burden exclusively within UC. Upon experience of visceral and somatic pain, both control groups demonstrated enhanced visceral pain-induced neural activation and greater perceived pain intensity, whereas UC patients failed to differentiate between pain modalities at both behavioural and neural levels.

CONCLUSIONS

When confronted with acute pain from multiple bodily sites, UC patients' responses are distinctly altered. Their failure to prioritise pain arising from the viscera may reflect a lack of adaptive behavioural flexibility, possibly resulting from long-lasting central effects of repeated intestinal inflammatory insults persisting during remission. The role of psychological factors, particularly chronic stress, in visceral sensitivity and disease-specific alterations in the response to acute pain call for dedicated mechanistic research as a basis for tailoring interventions for intestinal and extraintestinal pain symptoms in IBD.

Amplified gut feelings under inflammation and depressed mood: A randomized fMRI trial on interoceptive pain in healthy volunteers

BACKGROUND

Inflammation and depressed mood constitute clinically relevant vulnerability factors for enhanced interoceptive sensitivity and chronic visceral pain, but their putative interaction remains untested in human mechanistic studies. We tested interaction effects of acute systemic inflammation and sad mood on the expectation and experience of visceral pain by combining experimental endotoxemia with a mood induction paradigm.

METHODS

The double-blind, placebo-controlled, balanced crossover fMRI-trial in N=39 healthy male and female volunteers involved 2 study days with either intravenous administration of low-dose lipopolysaccharide (LPS, 0.4ng/kg body weight; inflammation condition) or saline (placebo condition). On each study, day two scanning sessions were conducted in an experimentally induced negative (i.e., sad) and in a neutral mood state, accomplished in balanced order. As a model of visceral pain, rectal distensions were implemented, which were initially calibrated to be moderately painful. In all sessions, an identical series of visceral pain stimuli was accomplished, signaled by predictive visual conditioning cues to assess pain anticipation. We assessed neural activation during the expectation and experience of visceral pain, along with unpleasantness ratings in a condition combining an inflammatory state with sad mood and in control conditions. All statistical analyses were accomplished using sex as covariate.

RESULTS

LPS administration led to an acute systemic inflammatory response (inflammation X time interaction effects for TNF-α, IL-6, and sickness symptoms, all p<.001). The mood paradigm effectively induced distinct mood states (mood X time interaction, p<.001), with greater sadness in the negative mood conditions (both p<.001) but no difference between LPS and saline conditions. Significant main and interaction effects of inflammation and negative mood were observed for pain unpleasantness (all p<.05). During cued pain anticipation, a significant inflammation X mood interaction emerged for activation of the bilateral caudate nucleus and right hippocampus (all p_FWE<.05). Main effects of both inflammation and mood were observed in multiple regions, including insula, midcingulate cortex, prefrontal gyri, and hippocampus for inflammation, and midcingulate, caudate, and thalamus for mood (all p_FWE<0.05).

CONCLUSIONS

Results support an interplay of inflammation and sad mood on striatal and hippocampal circuitry engaged during visceral pain anticipation as well as on pain experience. This may reflect a nocebo mechanism, which may contribute to altered perception and interpretation of bodily signals. At the interface of affective neuroscience and the gut-brain axis, concurrent inflammation and negative mood may be vulnerability factors for chronic visceral pain.

Positive Treatment Expectations Shape Perceived Medication Efficacy in a Translational Placebo Paradigm for the Gut-Brain Axis

Placebo research has established the pivotal role of treatment expectations in shaping symptom experience and patient-reported treatment outcomes. Perceived treatment efficacy constitutes a relevant yet understudied aspect, especially in the context of the gut-brain axis with visceral pain as key symptom. Using a clinically relevant experimental model of visceral pain, we elucidated effects of pre-treatment expectations on post-treatment perceived treatment efficacy as an indicator of treatment satisfaction in a translational placebo intervention. We implemented positive suggestions regarding intravenous treatment with a spasmolytic drug (in reality saline), herein applied in combination with two series of individually calibrated rectal distensions in healthy volunteers. The first series used distension pressures inducing pain (pain phase). In the second series, pressures were surreptitiously reduced, modeling pain relief (pain relief phase). Using visual analog scales (VAS), expected and perceived treatment efficacy were assessed, along with perceived pain intensity. Manipulation checks supported that the induction of positive pre-treatment expectations and the modeling of pain relief were successful. Generalized Linear Models (GLM) were implemented to assess the role of inter-individual variability in positive pre-treatment expectations in perceived treatment efficacy and pain perception. GLM indicated no association between pre-treatment expectations and perceived treatment efficacy or perceived pain for the pain phase. For the relief phase, pre-treatment expectations (p = 0.024) as well as efficacy ratings assessed after the preceding pain phase (p < 0.001) were significantly associated with treatment efficacy assessed after the relief phase, together explaining 54% of the variance in perceived treatment efficacy. The association between pre-treatment expectations and perceived pain approached significance (p = 0.057) in the relief phase. Our data from an experimental translational placebo intervention in visceral pain support that reported post-treatment medication efficacy is shaped by pre-treatment expectations. The observation that individuals with higher positive expectations reported less pain and higher treatment satisfaction after pain relief may provide first evidence that perceived symptom improvement may facilitate treatment satisfaction. The immediate experience of symptoms within a given psychosocial treatment context may dynamically change perceptions about treatment, with implications for treatment satisfaction, compliance and adherence of patients with conditions of the gut-brain axis.

Altered Brain Structure in Chronic Visceral Pain: Specific Differences in Gray Matter Volume and Associations With Visceral Symptoms and Chronic Stress

Structural brain alterations in chronic pain conditions remain incompletely understood, especially in chronic visceral pain. Patients with chronic-inflammatory or functional bowel disorders experience recurring abdominal pain in concert with other gastrointestinal symptoms, such as altered bowel habits, which are often exacerbated by stress. Despite growing interest in the gut-brain axis and its underlying neural mechanisms in health and disease, abnormal brain morphology and possible associations with visceral symptom severity and chronic stress remain unclear. We accomplished parallelized whole-brain voxel-based morphometry analyses in two patient cohorts with chronic visceral pain, i.e., ulcerative colitis in remission and irritable bowel syndrome, and healthy individuals. In addition to analyzing changes in gray matter volume (GMV) in each patient cohort vs. age-matched healthy controls using analysis of covariance (ANCOVA), multiple regression analyses were conducted to assess correlations between GMV and symptom severity and chronic stress, respectively. ANCOVA revealed reduced GMV in frontal cortex and anterior insula in ulcerative colitis compared to healthy controls, suggesting alterations in the central autonomic and salience networks, which could however not be confirmed in supplemental analyses which rigorously accounted for group differences in the distribution of sex. In irritable bowel syndrome, more widespread differences from healthy controls were observed, comprising both decreased and increased GMV within the sensorimotor, central executive and default mode networks. Associations between visceral symptoms and GMV within frontal regions were altered in both patient groups, supporting a role of the central executive network across visceral pain conditions. Correlations with chronic stress, on the other hand, were only found for irritable bowel syndrome, encompassing numerous brain regions and networks. Together, these findings complement and expand existing brain imaging evidence in chronic visceral pain, supporting partly distinct alterations in brain morphology in patients with chronic-inflammatory and functional bowel disorders despite considerable overlap in symptoms and comorbidities. First evidence pointing to correlations with chronic stress in irritable bowel syndrome inspires future translational studies to elucidate the mechanisms underlying the interconnections of stress, visceral pain and neural mechanisms of the gut-brain axis.

When gut feelings teach the brain to fear pain: Context-dependent activation of the central fear network in a novel interoceptive conditioning paradigm

The relevance of contextual factors in shaping neural mechanisms underlying visceral pain-related fear learning remains elusive. However, benign interoceptive sensations, which shape patients' clinical reality, may context-dependently become conditioned predictors of impending visceral pain. In a novel context-dependent interoceptive conditioning paradigm, we elucidated the putative role of the central fear network in the acquisition and extinction of pain-related fear induced by interoceptive cues and pain-predictive contexts. In this fMRI study involving rectal distensions as a clinically-relevant model of visceroception, N = 27 healthy men and women underwent differential conditioning. During acquisition training, visceral sensations of low intensity as conditioned stimuli (CS) predicted visceral pain as unconditioned stimulus (US) in one context (Con⁺), or safety from pain in another context (Con^-). During extinction training, interoceptive CS remained unpaired in both contexts, which were operationalized as images of different rooms presented in the MRI scanner. Successful contextual conditioning was supported by increased negative valence of Con⁺ compared to Con^- after acquisition training, which resolved after extinction training. Although interoceptive CS were perceived as comparatively pleasant, they induced significantly greater neural activation of the amygdala, ventromedial PFC, and hippocampus when presented in Con⁺, while contexts alone did not elicit differential responses. During extinction training, a shift from CS to context differentiation was observed, with enhanced responses in the amygdala, ventromedial, and ventrolateral PFC to Con⁺ relative to Con^-, whereas no CS-induced differential activation emerged. Context-dependent interoceptive conditioning can turn benign interoceptive cues into predictors of visceral pain that recruit key regions of the fear network. This first evidence expands knowledge about learning and memory mechanisms underlying interoceptive hypervigilance and maladaptive avoidance behavior, with implications for disorders of the gut-brain axis.

Associative learning and extinction of conditioned threat predictors across sensory modalities

The formation and persistence of negative pain-related expectations by classical conditioning remain incompletely understood. We elucidated behavioural and neural correlates involved in the acquisition and extinction of negative expectations towards different threats across sensory modalities. In two complementary functional magnetic resonance imaging studies in healthy humans, differential conditioning paradigms combined interoceptive visceral pain with somatic pain (study 1) and aversive tone (study 2) as exteroceptive threats. Conditioned responses to interoceptive threat predictors were enhanced in both studies, consistently involving the insula and cingulate cortex. Interoceptive threats had a greater impact on extinction efficacy, resulting in disruption of ongoing extinction (study 1), and selective resurgence of interoceptive CS-US associations after complete extinction (study 2). In the face of multiple threats, we preferentially learn, store, and remember interoceptive danger signals. As key mediators of nocebo effects, conditioned responses may be particularly relevant to clinical conditions involving disturbed interoception and chronic visceral pain.

Polarity-specific modulation of pain processing by transcranial direct current stimulation - a blinded longitudinal fMRI study

Background

To enrich the hitherto insufficient understanding regarding the mechanisms of action of transcranial direct current stimulation (tDCS) in pain disorders, we investigated its modulating effects on cerebral pain processing using functional magnetic resonance imaging (fMRI).

Methods

Thirteen right-handed healthy participants received 20 min of 1.5 mA tDCS applied over the primary motor cortex thrice and under three different stimulation pattern (1.anodal-tDCS, 2.cathodal-tDCS, and 3.sham-tDCS) in a blinded cross-over design. After tDCS neural response to electric trigeminal-nociceptive stimulation was investigated using a block designed fMRI.

Results

Pain stimulation showed a distinct activation pattern within well-established brain regions associated with pain processing. Following anodal tDCS increased activation was detected in the thalamus, basal ganglia, amygdala, cingulate, precentral, postcentral, and dorsolateral prefrontal cortex, while cathodal t-DCS showed decreased response in these areas (p_FWE < 0.05). Interestingly the observed effect was reversed in both control conditions (visual- and motor-stimulation). Behavioral data remained unchanged irrespective of the tDCS stimulation mode.

Conclusions

This study demonstrates polarity-specific modulation of cerebral pain processing, in reconfirmation of previous electrophysiological data. Anodal tDCS leads to an activation of the central pain-network while cathodal tDCS does not. Results contribute to a network-based understanding of tDCS’s impact on cerebral pain-processing.

Cerebral gray matter changes in persistent postural perceptual dizziness

BACKGROUND

Persistent postural perceptual dizziness (PPPD) is the most common vestibular syndrome in middle-aged patients. Multisensory maladjustment involving alterations of sensory response pattern including vestibular, visual and motion stimuli is thought to be a key pathophysiological correlate of this disorder.

OBJECTIVE

We aimed to identify regional gray matter changes in PPPD patients that might be involved in the underlying pathophysiology of this disorder.

METHODS

42 PPPD patients and healthy age and gender matched controls were investigated using magnetic resonance imaging-based voxel-based morphometry. All patients fulfilled the current diagnostic criteria for PPPD, established by the Bárány-Society based on previous criteria for chronic subjective dizziness and phobic postural vertigo.

RESULTS

PPPD patients showed gray matter volume decrease in the temporal cortex, cingulate cortex, precentral gyrus, hippocampus, dorsolateral prefrontal cortex, caudate nucleus and the cerebellum. A negative correlation of disease duration and gray matter volume was observed in the visual cortex, supplementary motor area and somatosensory processing structures.

CONCLUSIONS

In patients with PPPD areas involved in multisensory vestibular processing show gray matter volume decrease. These brain regions resemble those previously described for other vestibular disorders. Longer duration of disease leads to a more pronounced gray matter alteration, which might represent maladaptive mechanisms within the course of disease.

Learning by experience? Visceral pain-related neural and behavioral responses in a classical conditioning paradigm

BACKGROUND

Studies investigating mechanisms underlying nocebo responses in pain have mainly focused on negative expectations induced by verbal suggestions. Herein, we addressed neural and behavioral correlates of nocebo responses induced by classical conditioning in a visceral pain model.

METHODS

In two independent studies, a total of 40 healthy volunteers underwent classical conditioning, consisting of repeated pairings of one visual cue (CS^High ) with rectal distensions of high intensity, while a second cue (CS^Low ) was always followed by low-intensity distensions. During subsequent test, only low-intensity distensions were delivered, preceded by either CS^High or CS^Low . Distension intensity ratings were assessed in both samples and functional magnetic resonance imaging data were available from one study (N=16). As a consequence of conditioning, we hypothesized CS^High -cued distensions to be perceived as more intense and expected enhanced cue- and distension-related neural responses in regions encoding sensory and affective dimensions of pain and in structures associated with pain-related fear memory.

KEY RESULTS

During test, distension intensity ratings did not differ depending on preceding cue. Greater distension-induced neural activation was observed in somatosensory, prefrontal, and cingulate cortices and caudate when preceded by CS^High . Analysis of cue-related responses revealed strikingly similar activation patterns.

CONCLUSIONS & INFERENCES

We report changes in neural activation patterns during anticipation and visceral stimulation induced by prior conditioning. In the absence of behavioral effects, markedly altered neural responses may indicate conditioning with visceral signals to induce hypervigilance rather than hyperalgesia, involving altered attention, reappraisal, and perceptual acuity as processes contributing to the pathophysiology of visceral pain.

Acupuncture-related modulation of pain-associated brain networks during electrical pain stimulation: a functional magnetic resonance imaging study

OBJECTIVE

Findings of existing functional MRI (fMRI) studies on the neural mechanisms that mediate effects of acupuncture analgesia are inconsistent. This study analyzes the effects of manual acupuncture on pain ratings and brain activation in response to experimental, electrical pain stimuli.

DESIGN

Fourteen healthy volunteers were examined by using a 1.5-T MRI scanner. The intensity of pain stimuli was adjusted to individual pain ratings on a numeric rating scale. Baseline fMRI was performed during electrical pain stimulation in a blocked design. For the second session, manual acupuncture with repeated stimulation was performed on contralateral acupoints-large intestine 4, liver 3, and stomach 36-before imaging. After imaging, subjective pain ratings and ratings of the de qi sensation were assessed.

RESULTS

Compared with baseline, volunteers showed modulated brain activity under pain conditions in the cingulate gyrus, insula, primary somatosensory cortex, and prefrontal areas after the acupuncture session. In accordance with the literature, anterior insular and prefrontal activity seemed to be correlated with acupuncture treatment.

CONCLUSION

This study supports the existence of analgesic acupuncture effects that outlast the needling period. Pain-associated brain areas were modulated in direct response to a preceding acupuncture treatment.

Placebo analgesia in patients with functional and organic abdominal pain: a fMRI study in IBS, UC and healthy volunteers

OBJECTIVE

Understanding the neural circuitry of placebo analgesia in the context of visceral pain is increasingly important given evidence of clinical benefit of placebo treatment in IBS. This functional MRI study addressed placebo analgesia in IBS, UC and healthy control (HC) volunteers.

DESIGN

Painful rectal distensions were delivered in N=17 patients with IBS , N=15 patients with UC in remission, and sex-matched and age-matched HCs in an adaptation phase followed by intravenous application of saline combined with either positive instructions of pain relief (placebo) or neutral instructions (control). Neural activation during cued-pain anticipation and pain was analysed along with ratings of expected and perceived pain and measures of negative affectivity and salivary cortisol concentrations. Correlational analyses between placebo analgesia responses and negative affect were accomplished.

RESULTS

HC and UC revealed significant pain inhibition during placebo analgesia, as evidenced by reduced neural activation in pain-related brain areas. In contrast, patients with IBS failed to effectively engage neural downregulation of pain, as evidenced by the absence of placebo-induced changes in distension-induced brain activation, resulting in a significant group difference in the cingulate cortex compared with HC. Depression scores correlated with weaker placebo analgesia, whereas state and trait anxiety were not associated.

CONCLUSIONS

Patients with IBS failed to effectively engage neural downregulation of rectal distension-induced pain during placebo analgesia, indicating a specific deficit in cognitive pain inhibition, which may in part be mediated by depression.

Are there sex differences in placebo analgesia during visceral pain processing? A fMRI study in healthy subjects

BACKGROUND

We explored sex differences in the neural mechanisms mediating placebo analgesia in an established visceral pain model involving painful rectal distensions in healthy volunteers.

METHODS

N = 15 men and N = 15 women underwent three consecutive functional magnetic resonance imaging sessions during which cued painful rectal distensions were delivered. After an adaptation session, positive expectations were induced with deceptive instructions regarding administration of an analgesic drug (placebo session). In the other session (control), truthful information about an inert substance was given. Sex differences in placebo-induced modulation of neural activation during anticipation and pain were analyzed along with ratings of expected and perceived pain intensity.

KEY RESULTS

Placebo-induced reductions in pain ratings were comparable between men and women. At the level of the brain, group comparisons with respect to differences between the placebo and control conditions revealed greater modulation of the posterior insula (regions-of-interest analysis: pFWE < 0.05) and dorsolateral prefrontal cortex (whole-brain analysis: p < 0.001, uncorrected) during pain anticipation in women. During pain, placebo-induced down-regulation of the insula was altered in women compared to men (ROI analysis: pFWE < 0.05).

CONCLUSIONS & INFERENCES

Our data provide first evidence supporting sex differences in pain-induced neural modulation during visceral placebo analgesia despite similar placebo-induced reductions in perceived pain intensity. These preliminary findings might contribute to elucidating mechanisms mediating placebo effects in clinical conditions associated with chronic abdominal pain such as in irritable bowel syndrome.

Central vestibular system modulation in vestibular migraine

Background

Vestibular migraine affects 1% of the general population, and 30%–50% of all migraine patients describe occasionally associated vertigo or dizziness. We aimed to identify brain regions altered in vestibular migraine in order to evaluate the connection between migraine and the vestibular system.

Methods

Seventeen patients with definite vestibular migraine were compared to 17 controls using magnetic resonance imaging-based voxel-based morphometry.

Results

We found grey matter (GM) volume reduction in the superior, inferior and middle (MT/V5) temporal gyrus as well as in the mid. cingulate, dorsolateral prefontal, insula, parietal and occipital cortex. A negative correlation of disease duration and GM volume was observed in areas associated with pain and vestibular processing. Moreover, there was a negative correlation between headache severity and prefrontal cortex volume.

Conclusion

Alterations identified in vestibular migraine resemble those previously described for migraine, but also extend to areas involved in multisensory vestibular control and central vestibular compensation possibly representing the pathoanatomic connection between migraine and the vestibular system.

Visceral sensitivity correlates with decreased regional gray matter volume in healthy volunteers: a voxel-based morphometry study

Regional changes in brain structure have been reported in patients with altered visceral sensitivity and chronic abdominal pain, such as in irritable bowel syndrome. It remains unknown whether structural brain changes are associated with visceral sensitivity. Therefore, we present the first study in healthy individuals to address whether interindividual variations in gray matter volume (GMV) in pain-relevant regions correlate with visceral sensitivity. In 92 healthy young adults (52 female), we assessed rectal sensory and pain thresholds and performed voxel-based morphometry (VBM) to compute linear regression models with visceral sensory and pain thresholds, respectively, as independent variable and GMV in a priori-defined regions of interest (ROIs) as dependent variable. All results were familywise error (FWE) corrected at a level of PFWE<.05 and covaried for age. The mean (±SEM) rectal thresholds were 14.78±0.46mm Hg for first sensation and 33.97±1.13mm Hg for pain, without evidence of sex differences. Lower rectal sensory threshold (ie, increased sensitivity) correlated significantly with reduced GMV in the thalamus, insula, posterior cingulate cortex, ventrolateral and orbitofrontal prefrontal cortices, amygdala, and basal ganglia (all PFWE<.05). Lower rectal pain threshold was associated with reduced GMV in the right thalamus (PFWE=.051). These are the first data supporting that increased visceral sensitivity correlates with decreased gray matter volume in pain-relevant brain regions. These findings support that alterations in brain morphology not only occur in clinical pain conditions but also occur according to normal interindividual variations in visceral sensitivity.

Memory-related hippocampal activity can be measured robustly using FMRI at 7 tesla

High field strength functional magnetic resonance imaging (fMRI) has developed rapidly. However, it suffers from increased artifacts in brain regions such as the medial temporal lobe (MTL), challenging functional imaging of the hippocampus with the objective of high-spatial resolution, which is particularly useful for this region both from a clinical and cognitive neuroscience perspective. We set out to compare a BOLD sequence at 7 T versus 3 T to visualize the MTL activity during an associative memory-encoding task. Twenty-eight healthy volunteers underwent a blocked-design fMRI at either 3 T or 7 T while performing a face-profession associative memory encoding task. Qualitative analyses of overall image quality revealed that functional images at 7 T were of high quality, showing a good white/gray matter contrast, with reasonably acceptable signal dropouts and artifacts at the lower portion of the temporal lobe. Analyses of task-related fMRI data revealed robust activations in the bilateral MTL during associative memory encoding at both field strengths. Notably, we observed significantly stronger memory-related hippocampal activation at 7 T than at 3 T, suggesting higher BOLD sensitivity at 7 T. These results are discussed in the light of the feasibility of 7 T scanning protocols for the MTL.

7 Tesla MPRAGE imaging of the intracranial arterial vasculature: nonenhanced versus contrast-enhanced

PURPOSE

To intraindividually compare the delineation of intracranial arterial vasculature in nonenhanced versus contrast-enhanced magnetization prepared rapid gradient echo (MPRAGE) imaging at 7 Tesla (T).

MATERIALS AND METHODS

Sixteen subjects were examined on a 7 T whole-body magnetic resonance system (Magnetom 7T) equipped with a 32-channel transmit/receive head coil. MPRAGE imaging was performed pre- and postcontrast after the application of 0.1 mmol/kg bodyweight gadobutrol. For qualitative analysis, the delineation of the intracranial arteries, overall image quality, and image impairment were assessed in the nonenhanced and contrast-enhanced datasets using a 5-point scale (5 = excellent to 1 = nondiagnostic). Additionally, contrast ratios (CR) of the middle cerebral artery in correlation to surrounding gray matter in nonenhanced and postcontrast images were obtained. For statistical analysis a Wilcoxon signed-rank test was applied.

RESULTS

Nonenhanced MPRAGE imaging offered an excellent delineation of the central vessel segments of the anterior circulation (mean anterior circulation 4.6) and a moderate- to high-quality assessment of the vessels of the posterior circulation (mean posterior circulation 3.9). Vessel delineation was improved in all assessed segments in the contrast-enhanced datasets, except for the cavernous segment of the internal carotid artery. Quantitative analysis revealed a mild, nonsignificant increase in CR mean values of the M1 segment (CRnonenhanced 0.67; CRcontrast-enhanced 0.69).

CONCLUSION

Our results demonstrate the high diagnostic value of nonenhanced 7 T MPRAGE imaging for the assessment of the intracranial arterial vasculature, with improved assessment of the peripheral segments because of the application of a contrast agent.

Gray matter volume reduction reflects chronic pain in trigeminal neuralgia

Trigeminal neuralgia (TN) is supposedly caused by an ectatic blood vessel affecting the trigeminal nerve at the root entry zone of the brain stem. Recent evidence suggests an additional central component within trigeminal pain-processing in the pathophysiology of TN. Therefore, we aimed to identify specific brain regions possibly associated with the development or maintenance of TN using magnetic resonance imaging (MRI) voxel-based morphometry (VBM). Sixty patients with classical TN were compared to 49 healthy controls. Eighteen patients had TN with concomitant constant facial pain, a condition previously described as a predictor of worse treatment outcome. We found gray matter (GM) volume reduction in TN patients compared to healthy controls in the primary somatosensory and orbitofrontal cortices, as well as the in the secondary somatosensory cortex, thalamus, insula, anterior cingulate cortex (ACC), cerebellum, and dorsolateral prefrontal cortex. GM volume decrease within the ACC, parahippocampus, and temporal lobe correlated with increasing disease duration in TN. There were no differences comparing patients with and without concomitant constant facial pain. No GM increase was found comparing patient subgroups with each other and with healthy controls. The observed changes probably reflect the impact of multiple, daily attacks of trigeminal pain in these patients similar to what was previously described in other chronic pain conditions and may be interpreted as adaptation mechanism to chronic pain in regard to neuronal plasticity. The ACC, parahippocampus and temporal lobe volume reduction in parallel with disease duration may point to a pivotal role of these structures in chronic pain.

Fear conditioning in an abdominal pain model: neural responses during associative learning and extinction in healthy subjects

Fear conditioning is relevant for elucidating the pathophysiology of anxiety, but may also be useful in the context of chronic pain syndromes which often overlap with anxiety. Thus far, no fear conditioning studies have employed aversive visceral stimuli from the lower gastrointestinal tract. Therefore, we implemented a fear conditioning paradigm to analyze the conditioned response to rectal pain stimuli using fMRI during associative learning, extinction and reinstatement.

In N = 21 healthy humans, visual conditioned stimuli (CS⁺) were paired with painful rectal distensions as unconditioned stimuli (US), while different visual stimuli (CS⁻) were presented without US. During extinction, all CSs were presented without US, whereas during reinstatement, a single, unpaired US was presented. In region-of-interest analyses, conditioned anticipatory neural activation was assessed along with perceived CS-US contingency and CS unpleasantness.

Fear conditioning resulted in significant contingency awareness and valence change, i.e., learned unpleasantness of a previously neutral stimulus. This was paralleled by anticipatory activation of the anterior cingulate cortex, the somatosensory cortex and precuneus (all during early acquisition) and the amygdala (late acquisition) in response to the CS⁺. During extinction, anticipatory activation of the dorsolateral prefrontal cortex to the CS⁻ was observed. In the reinstatement phase, a tendency for parahippocampal activation was found.

Fear conditioning with rectal pain stimuli is feasible and leads to learned unpleasantness of previously neutral stimuli. Within the brain, conditioned anticipatory activations are seen in core areas of the central fear network including the amygdala and the anterior cingulate cortex. During extinction, conditioned responses quickly disappear, and learning of new predictive cue properties is paralleled by prefrontal activation. A tendency for parahippocampal activation during reinstatement could indicate a reactivation of the old memory trace. Together, these findings contribute to our understanding of aversive visceral learning and memory processes relevant to the pathophysiology of chronic abdominal pain.

Imaging of Electrode Position after Cochlear Implantation with Flat Panel CT

Background. Postoperative imaging after cochlear implantation is usually performed by conventional cochlear view (X-ray) or by multislice computed tomography (MSCT). MSCT after cochlear implantation often provides multiple metal artefacts; thus, a more detailed view of the implant considering the given anatomy is desirable. A quite new method is flat panel volume computed tomography. The aim of the study was to evaluate the method's clinical use. Material and Methods. After cochlear implantation with different implant types, flat panel CT scan (Philips Allura) was performed in 31 adult patients. Anatomical details, positioning, and resolution of the different electrode types (MedEL, Advanced Bionics, and Cochlear) were evaluated interdisciplinary (ENT/Neuroradiology). Results. In all 31 patients cochlear implant electrode array and topographical position could be distinguished exactly. Spatial resolution and the high degree of accuracy were superior to reported results of MSCT. Differentiation of cochlear scalae by identification of the osseous spiral lamina was possible in some cases. Scanning artefacts were low. Conclusion. Flat panel CT scan allows exact imaging independent of implant type. This is mandatory for detailed information on cochlear electrode position. It enables us to perform optimal auditory nerve stimulation and allows feed back on surgical quality concerning the method of electrode insertion.

Direct visualization of cerebellar nuclei in patients with focal cerebellar lesions and its application for lesion-symptom mapping

As yet, human cerebellar lesion studies have not taken advantage of direct magnetic resonance imaging (MRI) of the cerebellar nuclei in individual patients. In the present study, susceptibility weighted imaging (SWI) was used to visualize lesions of the dentate nuclei in patients with chronic focal lesions. Fifteen patients with cerebellar lesions either due to stroke or tumor surgery underwent SWI imaging using a 1.5T MRI scanner. Dentate nuclei were seen as hypointensities in all patients. Three of the patients underwent additional SWI imaging at 3T and 7T. Compared to 1.5T, corrugation of the dentate wall was seen with greater precision and the dorsal, iron-poorer part was seen more fully. Lesion-symptom mapping was performed based on the 1.5T MR images. Patients were divided into two groups with and without upper limb ataxia. A region-of-interest-(ROI)-driven normalization technique was used which had initially been developed by Diedrichsen et al. (2011) for functional MRI (fMRI) of the dentate nuclei. Compared to conventional normalization of the cerebellum, overlap of dentate lesions improved and lead to increased sensitivity of lesion-symptom maps. Subtraction analysis revealed that the more dorsal and rostral parts of the dentate nuclei were related to upper limb ataxia. Findings were in good accordance with the dentate hand area shown in recent fMRI studies. These data provide evidence that direct identification of dentate lesions together with the ROI-driven normalization technique allows for improved lesion-symptom mapping at the level of the cerebellar nuclei already at conventional 1.5T MRI field strength.

Neural mechanisms mediating the effects of expectation in visceral placebo analgesia: an fMRI study in healthy placebo responders and nonresponders

This functional magnetic resonance imaging study analysed the behavioural and neural responses during expectation-mediated placebo analgesia in a rectal pain model in healthy subjects. In N=36 healthy subjects, the blood oxygen level-dependent (BOLD) response during cued anticipation and painful rectal stimulation was measured. Using a within-subject design, placebo analgesia was induced by changing expectations regarding the probability of receiving an analgesic drug to 0%, 50%, and 100%. Placebo responders were identified by median split based on pain reduction (0% to 100% conditions), and changes in neural activation correlating with pain reduction in the 0% and 100% conditions were assessed in a regions-of-interest analysis. Expectation of pain relief resulted in overall reductions in pain and urge to defecate, and this response was significantly more pronounced in responders. Within responders, pain reduction correlated with reduced activation of dorsolateral and ventrolateral prefrontal cortices, somatosensory cortex, and thalamus during cued anticipation (paired t tests on the contrast 0%>100%); during painful stimulation, pain reduction correlated with reduced activation of the thalamus. Compared with nonresponders, responders demonstrated greater placebo-induced decreases in activation of dorsolateral prefrontal cortex during anticipation and in somatosensory cortex, posterior cingulate cortex, and thalamus during pain. In conclusion, the expectation of pain relief can substantially change perceived painfulness of visceral stimuli, which is associated with activity changes in the thalamus, prefrontal, and somatosensory cortices. Placebo analgesia constitutes a paradigm to elucidate psychological components of the pain response relevant to the pathophysiology and treatment of chronic abdominal pain.

Lesions of the dentate and interposed nuclei are associated with impaired prehension in cerebellar patients

In a recent study using voxel based lesion symptom mapping (VLSM) in cerebellar patients following stroke we found associations of prehensile deficits to lesions of the cerebellar cortex and dentate nucleus (DN). Associations to lesions of the interposed nucleus (IN), which has been shown to contribute to prehension in monkeys, could not be established. One possible reason was that the IN was largely unaffected in the stroke patients. To further address the question of IN involvement in prehension we performed VLSM in patients with surgical cerebellar lesions (n=20), exhibiting high lesion overlap in the medial and intermediate cerebellum including the IN. Prehensile deficits were quantified by analyses of movement kinematics and finger forces. In the patient population prehensile deficits comprised lower movement velocity in reaching and increased lift-off time in grasping. These were associated with lesions of the intermediate and lateral cerebellar cortex together with their output nuclei. Specifically, IN lesions were linked to increased lift-off time in grasping and not to slower reaching movements. Thus, our data support IN contribution particularly for the fluent production of grip forces during dexterous prehension in humans.