Abnormal Amygdala Resting-State Functional Connectivity in Irritable Bowel Syndrome

Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress

AIMS

Basolateral amygdala (BLA), as a center for stress responses and emotional regulation, is involved in visceral hypersensitivity of irritable bowel syndrome (IBS) induced by stress. In the present study, we aimed to investigate the role of EphB2 receptor (EphB2) in BLA and explore the underlying mechanisms in this process.

METHODS

Visceral hypersensitivity was induced by water avoidance stress (WAS). Elevated plus maze test, forced swimming test, and sucrose preference test were applied to assess anxiety- and depression-like behaviors. Ibotenic acid or lentivirus was used to inactivate BLA in either the induction or maintenance stage of visceral hypersensitivity. The expression of protein was determined by quantitative PCR, immunofluorescence, and western blot.

RESULTS

EphB2 expression was increased in BLA in WAS rats. Inactivation of BLA or downregulation of EphB2 in BLA failed to induce visceral hypersensitivity as well as anxiety-like behaviors. However, during the maintenance stage of visceral pain, visceral hypersensitivity was only partially relieved but anxiety-like behaviors were abolished by inactivation of BLA or downregulation of EphB2 in BLA. Chronic WAS increased the expression of EphB2, N-methyl-D-aspartate receptors (NMDARs), and postsynaptic density protein (PSD95) in BLA. Downregulation of EphB2 in BLA reduced NMDARs and PSD95 expression in WAS rats. However, activation of NMDARs after the knockdown of EphB2 expression still triggered visceral hypersensitivity and anxiety-like behaviors.

CONCLUSIONS

Taken together, the results suggest that EphB2 in BLA plays an essential role in inducing visceral hypersensitivity. In the maintenance stage, the involvement of EphB2 is crucial but not sufficient. The increase in EphB2 induced by WAS may enhance synaptic plasticity in BLA through upregulating NMDARs, which results in IBS-like symptoms. These findings may give insight into the treatment of IBS and related psychological distress.

Percutaneous Electrical Nerve Field Stimulation in Children and Adolescents With Functional Dyspepsia-Integrating a Behavioral Intervention

OBJECTIVES

Functional dyspepsia (FD) includes postprandial distress and epigastric pain syndrome. Percutaneous electrical nerve field stimulation (PENFS) in addition to behavioral interventions (BI) has shown benefits in children with functional abdominal pain but not specifically in FD. We aimed to assess the efficacy of PENFS for treating FD and compare the outcomes with those who received the combination of PENFS + BI.

MATERIALS AND METHODS

Charts of patients with FD who completed four weeks of PENFS were evaluated. A subset of patients received concurrent BI. Demographic data, medical history, and symptoms were documented. Outcomes at different time points included subjective symptom responses and validated questionnaires collected clinically (Abdominal Pain Index [API], Nausea Severity Scale [NSS], Functional Disability Inventory [FDI], Pittsburgh Sleep Quality Index [PSQI], Children's Somatic Symptoms Inventory [CSSI], Patient-Reported Outcomes Measurement Information Systems [PROMIS] Pediatric Anxiety and Depression scales).

RESULT

Of 84 patients, 61% received PENFS + BI, and 39% received PENFS alone. In the entire cohort, API (p < 0.0001), NSS (p = 0.001), FDI (p = 0.001), CSSI (p < 0.0001), PSQI (p = 0.01), PROMIS anxiety (p = 0.02), and depression (p = 0.01) scores improved from baseline to three weeks and at three months. Subjective responses showed nausea improvement (p = 0.01) and a trend for improvement in abdominal pain (p = 0.07) at week three. Abdominal pain subjectively improved at week three and three months (p = 0.003 and 0.02, respectively), nausea at week three and three months (p = 0.01 and 0.04, respectively), and a trend for improvement in sleep disturbances at week three and three months (p = 0.08 and p = 0.07, respectively) in the PENFS + BI group vs PENFS alone.

CONCLUSION

Abdominal pain, nausea, functioning, somatization, sleep disturbances, anxiety, and depression improved at three weeks and three months after PENFS in pediatric FD. Subjective pain and nausea improvement were greater in the PENFS + BI group than in the group with PENFS alone, suggesting an additive effect of psychologic therapy.

Cognitive function in patients with irritable bowel syndrome: impairment is common and only weakly correlated with depression/anxiety and severity of gastrointestinal symptoms

OBJECTIVE

To investigate cognitive function in patients with irritable bowel syndrome (IBS) and its relation to anxiety/depression and severity of gastrointestinal (GI) symptoms.

METHODS

Patients with IBS (n = 65) and healthy controls (HCs, n = 37) performed the ten subtests of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Age-normed index scores of five cognitive domains (Immediate memory, Visuospatial function, Language function, Attention, Recall) and a total (Fullscale) score were derived from the performance. Emotional function was assessed using the Hospital Anxiety and Depression Scale (HADS), and the IBS Symptom Scoring System (IBS-SSS) was used to define the severity of GI symptoms.

RESULTS

Patients with IBS reported significantly higher scores than the HC group on symptom measures of anxiety and depression, and significantly lower scores on the Immediate memory, Recall, and Fullscale RBANS indexes. Approximately 30% of the IBS patients obtained index scores at least one standard deviation below the population mean, and more than 50% scored above the screening threshold for an anxiety disorder. The severity of GI symptoms was significantly correlated with the severity level of anxiety symptoms (p=.006), but neither the severity level of emotional nor GI symptoms was significantly correlated with the RBANS index scores in the IBS group.

CONCLUSION

Cognitive and emotional function were more severely affected in patients with IBS than in HCs. The weak correlation between the two functional areas suggests that both should be assessed as part of a clinical examination of patients with IBS.

Hypoconnectivity of the Amygdala in Patients with Low-Back-Related Leg Pain Linked to Individual Mechanical Pain Sensitivity: A Resting-State Functional MRI Study

Purpose

To explore resting-state functional connectivity (rsFC) of the amygdala in patients with low-back-related leg pain (LBLP).

Patients and Methods

For this prospective study, a total of 35 LBLP patients and 30 healthy controls (HCs) were included and underwent functional MRI and clinical assessments. Then, patients with LBLP were divided into acute LBLP (aLBLP) and chronic LBLP (cLBLP) subgroups. We further evaluated the between-group rsFC differences using left and right amygdala seeds in a whole-brain voxel analysis strategy. Finally, we performed correlation analysis between the rsFC values of altered regions and clinical indices.

Results

Compared to HCs, hypoconnectivity of the amygdala was observed in LBLP patients (P < 0.01, with correction). The amygdala's rsFC pattern was different between aLBLP and cLBLP patients: decreased the amygdala's FC to the right putamen, to the right paracentral lobule (PCL), or to the right posterior temporal lobe in aLBLP patients, while right amygdala to the bilateral anterior cingulate cortex (ACC) and the left postcentral gyrus (PoCG) in cLBLP patients. Correlation analysis showed that lower rsFC of the left amygdala to the right PCL was correlated with the von Frey filament (vF) test values of the left lumbar (p = 0.025) and right lumbar (p = 0.019) regions, and rsFC of the right amygdala to the left PoCG was correlated with lower vF test values of the left lumbar (p = 0.017), right lumbar spine (p = 0.003); to right PoCG was correlated with calf (p = 0.015); the rsFC of the right amygdala to bilateral ACC was negatively correlated with the pain rating index (p = 0.003).

Conclusion

LBLP patients showed amygdala hypoconnectivity, and the altered pattern of amygdala rsFC was different in the acute and chronic phases. Moreover, the amygdala hypoconnectivity was related to individual mechanical sensitivity (vF test) in LBLP patients.

Percutaneous electrical nerve field stimulation compared to standard medical therapy in adolescents with functional abdominal pain disorders

Introduction

Standard medical therapy (SMT) in children with functional abdominal pain disorders (FAPD) includes cyproheptadine and amitriptyline. While percutaneous electrical nerve field stimulation (PENFS) has shown benefit, no study has compared outcomes of PENFS to SMT. We aimed to examine changes in abdominal pain, nausea and disability before and after treatment and compare outcomes between treatments.

Methods

The records of FAPD patients ages 11-21 years, treated with 4 weeks of PENFS, cyproheptadine or amitriptyline were reviewed. Outcomes were evaluated using validated questionnaires [Abdominal Pain Index (API), Nausea Severity Scale (NSS), and the Functional Disability Inventory (FDI)] at baseline and follow-up within 3 months (FU).

Result

Of 101 patients, 48% received PENFS, 31% cyproheptadine and 21% received amitriptyline. Median ages were 17 (15-19), 16 (15-18) and 15 (11-16) years respectively and the majority were females (75%, 90% and 52% respectively). In the PENFS group, API (p = 0.001), NSS (p = 0.059) and FDI (p = 0.048) were significantly lower at FU. API (p = 0.034) but not NSS and FDI (p > 0.05) decreased significantly at FU in the amitriptyline group. API, NSS and FDI did not change significantly with cyproheptadine at FU (p > 0.05). FU API scores were lower in PENFS vs. cyproheptadine (p = 0.04) but not vs. amitriptyline (p = 0.64). The FDI scores were significantly lower in the amitriptyline vs. cyproheptadine group (p = 0.03).

Conclusion

Therapy with PENFS showed improvements in abdominal pain, nausea and disability while amitriptyline showed improvements in abdominal pain within 3 months of treatment. PENFS was more effective than cyproheptadine in improving abdominal pain. Amitriptyline improved disability scores more than cyproheptadine and showed promise for treatment. PENFS may be a good non-pharmacologic alternative for FAPD.

Anatomical and Functional Connectivity of Critical Deep Brain Structures and Their Potential Clinical Application in Brain Stimulation

Subcortical structures, such as the hippocampus, amygdala, and nucleus accumbens (NAcc), play crucial roles in human cognitive, memory, and emotional processing, chronic pain pathophysiology, and are implicated in various psychiatric and neurological diseases. Interventions modulating the activities of these deep brain structures hold promise for improving clinical outcomes. Recently, non-invasive brain stimulation (NIBS) has been applied to modulate brain activity and has demonstrated its potential for treating psychiatric and neurological disorders. However, modulating the above deep brain structures using NIBS may be challenging due to the nature of these stimulations. This study attempts to identify brain surface regions as source targets for NIBS to reach these deep brain structures by integrating functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). We used resting-state functional connectivity (rsFC) and probabilistic tractography (PTG) analysis to identify brain surface stimulation targets that are functionally and structurally connected to the hippocampus, amygdala, and NAcc in 119 healthy participants. Our results showed that the medial prefrontal cortex (mPFC) is functionally and anatomically connected to all three subcortical regions, while the precuneus is connected to the hippocampus and amygdala. The mPFC and precuneus, two key hubs of the default mode network (DMN), as well as other cortical areas distributed at the prefrontal cortex and the parietal, temporal, and occipital lobes, were identified as potential locations for NIBS to modulate the function of these deep structures. The findings may provide new insights into the NIBS target selections for treating psychiatric and neurological disorders and chronic pain.

Regulation of the central amygdala on intestinal motility and behavior via the lateral hypothalamus in irritable bowel syndrome model mice

BACKGROUND

Impaired bidirectional communication between the gastrointestinal tract and the central nervous system (CNS) is closely related to the development of irritable bowel syndrome (IBS). Studies in patients with IBS have also shown significant activation of the hypothalamus and amygdala. However, how neural circuits of the CNS participate in and process the emotional and intestinal disorders of IBS remains unclear.

METHODS

The GABAergic neural pathway projecting from the central amygdala (CeA) to the lateral hypothalamus (LHA) in mice was investigated by retrograde tracking combined with fluorescence immunohistochemistry. Anxiety, depression-like behavior, and intestinal motility were observed in the water-immersion restraint stress group and the control group. Furthermore, the effects of the chemogenetic activation of the GABAergic neural pathway of CeA-LHA on behavior and intestinal motility, as well as the co-expression of orexin-A and c-Fos in the LHA, were explored.

KEY RESULTS

In our study, Fluoro-Gold retrograde tracking combined with fluorescence immunohistochemistry showed that GABAergic neurons in the CeA were projected to the LHA. The microinjection of the gamma-aminobutyric acid (GABA) receptor antagonist into the LHA relieved anxiety, depression-like behavior, and intestinal motility disorder in the IBS mice. The chemogenetic activation of GABAergic neurons in the CeA-LHA pathway led to anxiety, depression-like behavior, and intestinal motility disorder. In addition, GABAergic neurons in the CeA-LHA pathway inhibited the expression of orexin-A in the LHA, and orexin-A was co-expressed with GABAA receptors.

CONCLUSIONS & INFERENCES

The CeA-LHA GABAergic pathway might participate in the occurrence and development of IBS by regulating orexin-A neurons.

Sex-specific brain microstructural reorganization in irritable bowel syndrome

ABSTRACT

Preliminary evidence suggests that there are sex differences in microstructural brain organization among individuals with irritable bowel syndrome (IBS). The aim of this study was to further investigate sex-dependent differences in brain microstructure and organization in a large sample of well-phenotyped participants with IBS compared with healthy controls. We hypothesized that female patients with IBS would show evidence for increased axonal strength and myelination within and between brain regions concerned with pain and sensory processing, when compared with males with IBS. We also hypothesized that female compared with male IBS subjects show greater levels of somatic awareness and sensory sensitivity consistent with multisystem sensory sensitivity. Diffusion tensor images and clinical assessments were obtained in 100 healthy controls (61 females) and 152 IBS (107 females) on a 3T Siemens Trio. Whole brain voxel-wise differences in fractional anisotropy, mean, radial and axial diffusivity, and track density as differences in somatic awareness and sensory sensitivity were assessed using the general linear model. Female compared with male IBS participants showed extensive microstructural alterations in sensorimotor, corticothalamic, and basal ganglia circuits involved in pain processing and integration of sensorimotor information. Together with the observed increases in symptom severity, somatic awareness, and sensory sensitivity, the findings support the hypotheses that the etiology and maintenance of symptoms in females with IBS may be driven by greater central sensitivity for multiple sensory stimuli.

Increased GABAergic projections in the paraventricular nucleus regulate colonic hypersensitivity via oxytocin in a rat model of irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized by gastrointestinal dysmotility and visceral hyperalgesia, and the impaired brain-gut axis is accepted as a crucial cause for the onset of IBS. The objective of this study is to investigate the effects of the adaptive changes in the central neural system induced by stress on IBS-like syndromes in rats. Long-term water avoidance stress (WAS) was used to prepare IBS animals. The changes in neuronal excitation and GABA expression were shown by immunohistochemistry. The mRNA and protein expressions of neurotransmitters were detected with Quantitative reverse-transcription PCR (qRT-PCR) and Enzyme-linked immunosorbent assay (ELISA). The intestinal transit time, fecal moisture content, and abdominal withdrawal reflex scores of rats were recorded to monitor intestinal motility and visceral hyperalgesia. In the WAS-treated rats with enhanced intestinal motility and visceral hypersensitivity, more GABAergic projections were found in the paraventricular nucleus (PVN) of the hypothalamus, which inhibited the firing rate of neurons and decreased the expression of oxytocin. Exogenous oxytocin improved gut motility and decreased AWR scores. The inhibition of oxytocin by the adaptive GABAergic projection in the PVN might be an important mediator of IBS, which indicates a potential novel therapeutic target.

Fatty Acid Amide Hydrolase: An Integrative Clinical Perspective

Introduction: Fatty acid amide hydrolase (FAAH) is one of the main terminating enzymes of the endocannabinoid system (ECS). Since being discovered in 1996, the modulation of FAAH has been viewed as a compelling alternative strategy to obtain the beneficial effect of the ECS. With a considerable amount of FAAH-related publication over time, the next step would be to comprehend the proximity of this evidence for clinical application. Objective: This review intends to highlight the rationale of FAAH modulation and provide the latest evidence from clinical studies. Methods: Publication searches were conducted to gather information focused on FAAH-related clinical evidence with an extension to the experimental research to understand the biological plausibility. The subtopics were selected to be multidisciplinary to offer more perspective on the current state of the arts. Discussion: Experimental and clinical studies have demonstrated that FAAH was highly expressed not only in the central nervous system but also in the peripheral tissues. As the key regulator of endocannabinoid signaling, it would appear that FAAH plays a role in the modulation of mood and emotional response, reward system, pain perception, energy metabolism and appetite regulation, inflammation, and other biological processes. Genetic variants may be associated with some conditions such as substance/alcohol use disorders, obesity, and eating disorder. The advancement of functional neuroimaging has enabled the evaluation of the neurochemistry of FAAH in brain tissues and this can be incorporated into clinical trials. Intriguingly, the application of FAAH inhibitors in clinical trials seems to provide less striking results in comparison with the animal models, although some potential still can be seen. Conclusion: Modulation of FAAH has an immense potential to be a new therapeutic candidate for several disorders. Further exploration, however, is still needed to ensure who is the best candidate for the treatment strategy.

Amygdalar Functional Connectivity Differences Associated With Reduced Pain Intensity in Pediatric Peripheral Neuropathic Pain

Background

There is evidence of altered corticolimbic circuitry in adults with chronic pain, but relatively little is known of functional brain mechanisms in adolescents with neuropathic pain (NeuP). Pediatric NeuP is etiologically and phenotypically different from NeuP in adults, highlighting the need for pediatric-focused research. The amygdala is a key limbic region with important roles in the emotional-affective dimension of pain and in pain modulation.

Objective

To investigate amygdalar resting state functional connectivity (rsFC) in adolescents with NeuP.

Methods

This cross-sectional observational cohort study compared resting state functional MRI scans in adolescents aged 11–18 years with clinical features of chronic peripheral NeuP (n = 17), recruited from a tertiary clinic, relative to healthy adolescents (n = 17). We performed seed-to-voxel whole-brain rsFC analysis of the bilateral amygdalae. Next, we performed post hoc exploratory correlations with clinical variables to further explain rsFC differences.

Results

Adolescents with NeuP had stronger negative rsFC between right amygdala and right dorsolateral prefrontal cortex (dlPFC) and stronger positive rsFC between right amygdala and left angular gyrus (AG), compared to controls (P_FDR<0.025). Furthermore, lower pain intensity correlated with stronger negative amygdala-dlPFC rsFC in males (r = 0.67, P = 0.034, n = 10), and with stronger positive amygdala-AG rsFC in females (r = −0.90, P = 0.006, n = 7). These amygdalar rsFC differences may thus be pain inhibitory.

Conclusions

Consistent with the considerable affective and cognitive factors reported in a larger cohort, there are rsFC differences in limbic pain modulatory circuits in adolescents with NeuP. Findings also highlight the need for assessing sex-dependent brain mechanisms in future studies, where possible.

Altered Resting Brain Functions in Patients With Irritable Bowel Syndrome: A Systematic Review

Background

The neural activity of irritable bowel syndrome (IBS) patients in the resting state without any intervention has not been systematically studied. The purpose of this study was to compare the resting-state brain functions of IBS patients with healthy controls (HCs).

Methods

The published neuroimage studies were obtained from electronic databases including PubMed, EMBASE, PsycINFO, Web of Science Core, CNKI Database, Wanfang Database, VIP Database, and CBMdisc. Search dates were from inception to March 14th, 2022. The studies were identified by the preidentified inclusion and exclusion criteria. Two independent reviewers compiled the studies and evaluated them for quality and bias.

Results

Altogether 22 fMRI studies were included in this review. The risk of bias of the included studies was generally low. The findings indicated that in IBS patients, increased or decreased brain areas were mostly associated with visceral sensations, emotional processing, and pain processing. According to brain network research, IBS may exhibit anomalies in the DMN, CEN, and emotional arousal networks. The fluctuations in emotion (anxiety, sadness) and symptoms in IBS patients were associated with alterations in the relevant brain regions.

Conclusion

This study draws a preliminary conclusion that there are insufficient data to accurately distinguish the different neurological features of IBS in the resting state. Additional high-quality research undertaken by diverse geographic regions and teams is required to reach reliable results regarding resting-state changed brain regions in IBS.

Increased functional connectivity between limbic brain areas in healthy individuals with high versus low sensitivity to cold pain: A resting state fMRI study

Background

The representation of variability in sensitivity to pain by differences in neural connectivity patterns and its association with psychological factors needs further investigation. This study assessed differences in resting-state functional connectivity (rsFC) and its association to cognitive-affective aspects of pain in two groups of healthy subjects with low versus high sensitivity to pain (LSP vs. HSP). We hypothesized that HSP will show stronger connectivity in brain regions involved in the affective-motivational processing of pain and that this higher connectivity would be related to negative affective and cognitive evaluations of pain.

Methods

Forty-eight healthy subjects were allocated to two groups according to their tolerability to cold stimulation (cold pressor test, CPT, 1°C). Group LSP (N = 24) reached the cut-off time of 180±0 sec and group HSP tolerated the CPT for an average of 13±4.8 sec. Heat, cold and mechanical evoked pain were measured, as well as pain-catastrophizing (PCS), depression, anxiety and stress (DASS-21). All subjects underwent resting state fMRI. ROI-to-ROI analysis was performed.

Results

In comparison to the LSP, the HSP had stronger interhemispheric connectivity of the amygdala (p = 0.01) and between the amygdala and nucleus accumbens (NAc) (p = 0.01). Amygdala connectivity was associated with higher pain catastrophizing in the HSP only (p<0.01).

Conclusions

These findings suggest that high sensitivity to pain may be reflected by neural circuits involved in affective and motivational aspects of pain. To what extent this connectivity within limbic brain structures relates to higher alertness and more profound withdrawal behavior to aversive events needs to be further investigated.

Melanocortin-4 receptor signaling in the central amygdala mediates chronic inflammatory pain effects on nociception

Chronic inflammatory pain represents one of the largest subsets of chronic pain diagnoses, which affect nearly a quarter of individuals in the United States and cost nearly $600 billion dollars annually. Chronic pain leads to persistent sensory hypersensitivities, as well as emotional and cognitive disturbances. Evidence suggests that melanocortin 4 receptors (MC4Rs) mediate pain-signaling and pain-like behaviors via actions at various nodes in the pain-neural axis, but the field lacks a complete understanding of the potential role of MC4Rs in chronic inflammatory pain in males and females. The central amygdala (CeA) expresses high quantities of MC4R and receives pain-related information from the periphery, and in vivo CeA manipulations alter nociceptive behavior in pain-naïve and in animals with chronic pain. Here, we tested the hypothesis that MC4Rs in the CeA modulate thermal nociception and mechanical sensitivity, as well as pain avoidance, in male and female Wistar rats, using a model of chronic inflammatory pain (Complete Freud's Adjuvant; CFA). First, we report that CFA produces long-lasting hyperalgesia in adult male and female Wistar rats, and long-lasting pain avoidance in male Wistar rats. Second, we report that MC4R antagonism in the CeA reduces thermal nociception and mechanical sensitivity in male and female Wistar rats treated with CFA. Finally, we report that MC4R antagonism in the CeA reduces pain avoidance in male, and that this effect is not due to drug effects on locomotor activity. Our results indicate that a model of chronic inflammatory pain produces long-lasting increases in pain-like behaviors in adult male and female Wistar rats, and that antagonism of MC4Rs in the CeA reverses those effects.

Functional neuroimaging in Irritable Bowel Syndrome: a systematic review highlights common brain alterations with Functional Movement Disorders

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurring abdominal pain and altered bowel habits without detectable organic causes. This study aims to provide a comprehensive overview of the literature on functional neuroimaging in IBS and to highlight brain alterations similarities with other functional disorders - functional movement disorders in particular. We conducted the bibliographic search via PubMed in August 2020 and included 50 studies following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines for systematic reviews. Overall, our findings showed an aberrant activation and functional connectivity of the insular, cingulate, sensorimotor and frontal cortices, the amygdala and the hippocampus, suggesting an altered activity of the homeostatic and salience network and of the autonomous nervous system. Moreover, glutamatergic dysfunction in the anterior insula and hypothalamic pituitary axis dysregulation were often reported. These alterations seem to be very similar to those observed in patients with functional movement disorders. Hence, we speculate that different functional disturbances might share a common pathophysiology and we discussed our findings in the light of a Bayesian model framework.

Irritable bowel syndrome in women: Association between decreased insular subregion volumes and gastrointestinal symptoms

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All insular subregions are smaller in IBS compared to healthy women.

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Insular volume associates with GI symptoms independent of psychiatric comorbidity.

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GI symptoms associate with anterior but not posterior insular volume.

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More nausea associated with smaller dorsal anterior insula bilaterally.

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Insula in major depression is not significantly smaller than in healthy women.

Objective

Irritable bowel syndrome (IBS) is a chronic pain disorder characterized by disturbed interactions between the gut and the brain with depression as a common comorbidity. In both IBS and depression, structural brain alterations of the insular cortices, key structures for pain processing and interoception, have been demonstrated but the specificity of these findings remains unclear. We compared the gray matter volume (GMV) of insular cortex (IC) subregions in IBS women and healthy controls (HC) and examined relations to gastrointestinal (GI) symptoms and glutamate + glutamine (Glx) concentrations. We further analyzed GMV of IC subregions in women with major depression (MDD) compared to HC and addressed possible differences between depression, IBS, IBS with depression and HC.

Design

Women with IBS (n = 75), MDD (n = 41) and their respective HC (n = 39 and n = 43) underwent structural brain MRI. IC subregion volumes were estimated using statistical parametric mapping software. General linear model approaches were applied to IC volumetric data and FDR-corrected partial correlation analyses assessed relations between GMV, GI symptoms and Glx concentrations.

Results

IBS patients had significantly smaller IC subregions than HC in both hemispheres but there was no significant difference between MDD compared with IBS and HC for any insular subregion. In IBS, the dorsal anterior insular volumes were negatively correlated with symptoms of nausea and pain, and the left ventral subregion showed a positive correlation with straining to defecate, while the posterior subregion volumes showed no relation to symptoms. In the anterior insula, concentration of Glx showed positive correlations with GMV bilaterally in HC and with GMV of the right anterior insula in IBS.

Conclusion

As the interoceptive cortex, the insula shows substantial and disease-specific structural differences in patients with chronic interoceptive visceral pain. Particularly changes in the anterior proportions might be related to chronic exposure to or enhanced salience towards adverse interoceptive visceral signals and could be linked to biochemical changes, calling for further multimodal and longitudinal work.

Irritable Bowel Syndrome, Depression, and Neurodegeneration: A Bidirectional Communication from Gut to Brain

Patients with irritable bowel syndrome (IBS) are increasingly presenting with a wide range of neuropsychiatric symptoms, such as deterioration in gastroenteric physiology, including visceral hypersensitivity, altered intestinal membrane permeability, and gastrointestinal motor dysfunction. Functional imaging of IBS patients has revealed several abnormalities in various brain regions, such as significant activation of amygdala, thinning of insular and anterior cingulate cortex, and increase in hypothalamic gray matter, which results in poor psychiatric and cognitive outcomes. Interrelations between the enteric and central events in IBS-related gastrointestinal, neurological, and psychiatric pathologies have compelled researchers to study the gut-brain axis-a bidirectional communication that maintains the homeostasis of the gastrointestinal and central nervous system with gut microbiota as the protagonist. Thus, it can be disrupted by any alteration owing to the gut dysbiosis or loss of diversity in microbial composition. Available evidence indicates that the use of probiotics as a part of a balanced diet is effective in the management of IBS and IBS-associated neurodegenerative and psychiatric comorbidities. In this review, we delineate the pathogenesis and complications of IBS from gastrointestinal and neuropsychiatric standpoints while also discussing the neurodegenerative events in enteric and central nervous systems of IBS patients and the therapeutic potential of gut microbiota-based therapy established on clinical and preclinical data.

Inter-hemispheric Functional Connections Are More Vulnerable to Attack Than Structural Connection in Patients With Irritable Bowel Syndrome

Background/Aims

Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disease characterized by recurrent abdominal pain and bowel dysfunction. However, the majority of previous neuroimaging studies focus on brain structure and connections but seldom on the inter-hemispheric connectivity or structural asymmetry. This study uses multi-modal imaging to investigate the abnormal changes across the 2 cerebral hemispheres in patients with IBS.

Methods

Structural MRI, resting-state functional MRI, and diffusion tensor imaging were acquired from 34 patients with IBS and 33 healthy controls. The voxel-mirrored homotopic connectivity, fractional anisotropy, fiber length, fiber number, and asymmetry index were calculated and assessed for group differences. In addition, we assessed their relevance for the severity of IBS.

Results

Compared with healthy controls, the inter-hemispheric functional connectivity of patients with IBS showed higher levels in bilateral superior occipital gyrus, middle occipital gyrus, precuneus, posterior cingulate gyrus, and angular gyrus, but lower in supplementary motor area. The statistical results showed no significant difference in inter-hemispheric anatomical connections and structural asymmetry, however negative correlations between inter-hemispheric connectivity and the severity of IBS were found in some regions with significant difference.

Conclusions

The functional connections between cerebral hemispheres were more susceptible to IBS than anatomical connections, and brain structure is relatively stable. Besides, the brain areas affected by IBS were concentrated in default mode network and sensorimotor network.

Abnormalities in the thalamo-cortical network in patients with functional constipation

Functional constipation (FCon) is a common functional gastrointestinal disorder (FGID); neuroimaging studies have shown brain functional abnormalities in thalamo-cortical regions in patients with FGID. However, association between FCon and topological characteristics of brain networks remains largely unknown. We employed resting-state functional magnetic resonance imaging (RS-fMRI) and graph theory approach to investigate functional brain topological organization in 42 patients with FCon and 41 healthy controls (HC) from perspectives of global, regional and modular levels. Results showed patients with FCon had a significantly lower normalized clustering coefficient and small-worldness, implying decreased brain functional connectivity. Regions showed altered nodal degree and efficiency mainly located in the thalamus, rostral anterior cingulate cortex (rACC), and supplementary motor area (SMA), which are involved in somatic/sensory, emotional processing and motor-control. For the modular analysis, thalamus, rACC and SMA had an aberrant within-module nodal degree and nodal efficiency, and thalamus-related network exhibited abnormal interaction with the limbic network (amygdala and hippocampal gyrus). Nodal degree in the thalamus was negatively correlated with difficulty of defecation, and nodal degree in the rACC was negatively correlated with sensation of incomplete evacuation. These findings indicated that FCon was associated with abnormalities in the thalamo-cortical network.

Association between Chronic Pain and Alterations in the Mesolimbic Dopaminergic System

Chronic pain (pain lasting for >3 months) decreases patient quality of life and even occupational abilities. It can be controlled by treatment, but often persists even after management. To properly control pain, its underlying mechanisms must be determined. This review outlines the role of the mesolimbic dopaminergic system in chronic pain. The mesolimbic system, a neural circuit, delivers dopamine from the ventral tegmental area to neural structures such as the nucleus accumbens, prefrontal cortex, anterior cingulate cortex, and amygdala. It controls executive, affective, and motivational functions. Chronic pain patients suffer from low dopamine production and delivery in this system. The volumes of structures constituting the mesolimbic system are known to be decreased in such patients. Studies on administration of dopaminergic drugs to control chronic pain, with a focus on increasing low dopamine levels in the mesolimbic system, show that it is effective in patients with Parkinson’s disease, restless legs syndrome, fibromyalgia, dry mouth syndrome, lumbar radicular pain, and chronic back pain. However, very few studies have confirmed these effects, and dopaminergic drugs are not commonly used to treat the various diseases causing chronic pain. Thus, further studies are required to determine the effectiveness of such treatment for chronic pain.

Efficacy of Auricular Neurostimulation in Adolescents With Irritable Bowel Syndrome in a Randomized, Double-Blind Trial

BACKGROUND & AIMS

Auricular neurostimulation therapy, in which a noninvasive device delivers percutaneous electrical nerve field stimulation (PENFS) to the external ear, is effective in pediatric patients with functional abdominal pain disorders. Preclinical studies showed that PENFS modulates central pain pathways and attenuates visceral hyperalgesia. We evaluated the efficacy of PENFS in adolescents with irritable bowel syndrome (IBS).

METHODS

We analyzed data from pediatric patients with IBS who participated in a double-blind trial at a tertiary care gastroenterology clinic from June 2015 through November 2016. Patients were randomly assigned to groups that received PENFS (n = 27; median age, 15.3 y; 24 female) or a sham stimulation (n = 23; median age, 15.6 y; 21 female), 5 days/week for 4 weeks. The primary endpoint was number of patients with a reduction of 30% or more in worst abdominal pain severity after 3 weeks. Secondary endpoints were reduction in composite abdominal pain severity score, reduction in usual abdominal pain severity, and improvement in global symptom based on a symptom response scale (-7 to +7; 0 = no change) after 3 weeks.

RESULTS

Reductions of 30% or more in worst abdominal pain were observed in 59% of patients who received PENFS vs 26% of patients who received the sham stimulation (P = .024). The patients who received PENFS had a composite pain median score of 7.5 (interquartile range [IQR], 3.6-14.4) vs 14.4 for the sham group (IQR, 4.5-39.2) (P = .026) and a usual pain median score of 3.0 (IQR, 3.0-5.0) vs 5.0 in the sham group (IQR, 3.0-7.0) (P = .029). A symptom response scale score of 2 or more was observed in 82% of patients who received PENFS vs 26% of patients in the sham group (P ≤ .001). No significant side effects were reported.

CONCLUSIONS

Auricular neurostimulation reduces abdominal pain scores and improves overall wellbeing in adolescents with IBS. PENFS is a noninvasive treatment option for pediatric patients with functional bowel disorders. ClinicalTrials.gov no: NCT02367729.

Resting state functional connectivity of the pain matrix and default mode network in irritable bowel syndrome: a graph theoretical analysis

Irritable bowel syndrome (IBS) is a functional disorder of brain-gut interactions. Differential brain responses to rectal distention between IBS and healthy controls (HCs) have been demonstrated, particularly in the pain matrix and the default mode network. This study aims to compare resting-state functional properties of these networks between IBS patients and HCs using graph analysis in two independent cohorts. We used a weighted graph analysis of the adjacency matrix based on partial correlations between time series in the different regions in each subject to determine subject specific graph measures. These graph measures were normalized by values obtained in equivalent random networks. We did not find any significant differences between IBS patients and controls in global normalized graph measures, hubs, or modularity structure of the pain matrix and the DMN in any of our two independent cohorts. Furthermore, we did not find consistent associations between these global network measures and IBS symptom severity or GI-specific anxiety but we found a significant difference in the relationship between measures of psychological distress (anxiety and/or depressive symptoms) and normalized characteristic path length. The responses of these networks to visceral stimulation rather than their organisation at rest may be primarily disturbed in IBS.

Altered resting-state functional connectivity and effective connectivity of the habenula in irritable bowel syndrome: A cross-sectional and machine learning study

Irritable bowel syndrome (IBS) is a disorder involving dysfunctional brain–gut interactions characterized by chronic recurrent abdominal pain, altered bowel habits, and negative emotion. Previous studies have linked the habenula to the pathophysiology of negative emotion and pain. However, no studies to date have investigated habenular function in IBS patients. In this study, we investigated the resting‐state functional connectivity (rsFC) and effective connectivity of the habenula in 34 subjects with IBS and 34 healthy controls and assessed the feasibility of differentiating IBS patients from healthy controls using a machine learning method. Our results showed significantly enhanced rsFC of the habenula‐left dorsolateral prefrontal cortex (dlPFC) and habenula‐periaqueductal grey (PAG, dorsomedial part), as well as decreased rsFC of the habenula‐right thalamus (dorsolateral part), in the IBS patients compared with the healthy controls. Habenula‐thalamus rsFC was positively correlated with pain intensity (r = .467, p = .005). Dynamic causal modeling (DCM) revealed significantly decreased effective connectivity from the right habenula to the right thalamus in the IBS patients compared to the healthy controls that was negatively correlated with disease duration (r = −.407, p = .017). In addition, IBS was classified with an accuracy of 71.5% based on the rsFC of the habenula‐dlPFC, habenula‐thalamus, and habenula‐PAG in a support vector machine (SVM), which was further validated in an independent cohort of subjects (N = 44, accuracy = 65.2%, p = .026). Taken together, these findings establish altered habenular rsFC and effective connectivity in IBS, which extends our mechanistic understanding of the habenula's role in IBS.

Amygdala physiology in pain

The amygdala has emerged as an important brain area for the emotional-affective dimension of pain and pain modulation. The amygdala receives nociceptive information through direct and indirect routes. These excitatory inputs converge on the amygdala output region (central nucleus) and can be modulated by inhibitory elements that are the target of (prefrontal) cortical modulation. For example, inhibitory neurons in the intercalated cell mass in the amygdala project to the central nucleus to serve gating functions, and so do inhibitory (PKCdelta) interneurons within the central nucleus. In pain conditions, synaptic plasticity develops in output neurons because of an excitation-inhibition imbalance and drives pain-like behaviors and pain persistence. Mechanisms of pain related neuroplasticity in the amygdala include classical transmitters, neuropeptides, biogenic amines, and various signaling pathways. An emerging concept is that differences in amygdala activity are associated with phenotypic differences in pain vulnerability and resilience and may be predetermining factors of the complexity and persistence of pain.

Larger regional volume of the thalamus in diarrhea-predominant irritable bowel syndrome: a cross-sectional study

As a relay center between the cerebral cortex and various subcortical brain areas, the thalamus is repeatedly associated with the dysfunction of brain-gut interaction in patients with irritable bowel syndrome (IBS). However, the regional morphological alterations of the thalamus in IBS are not well defined. We acquired structural magnetic resonance data from 34 patients with IBS and 34 demographically similar healthy subjects. Data processing was performed using FMRIB's Integrated Registration and Segmentation Tool (FIRST). Volumetric analysis and surface-based vertex analysis were both carried out to characterize the morphology of the thalamus and other subcortical structures. Our results suggested that the majority (31 cases) of the patients with IBS had diarrhea-predominant symptoms. Volumetric analysis revealed a larger normalized volume of the right thalamus and left caudate nucleus in patients with IBS than in healthy controls. Surface analysis indicated that the difference arose mainly from the laterodorsal nucleus of the right thalamus, and the body of the left caudate nucleus. In addition, patients with IBS had different hemispheric asymmetries of the thalamus (rightward) and caudate nucleus (leftward) from controls (leftward for the thalamus and rightward for the caudate nucleus). In general, our results indicated that patients with diarrhea-predominant IBS had enlarged thalamus and caudate nucleus volumes, as well as altered hemispheric asymmetries of these two structures, compared with healthy controls. The neuroimaging evidence of these structural alterations helps clarify the underlying pathophysiology of diarrhea-predominant IBS.

Resting-State Functional Connectivity Between Centromedial Amygdala and Insula as Related to Somatic Symptoms in Depressed Patients: A Preliminary Study

OBJECTIVE

Somatic symptoms are prevalent in patients with depression. The centromedial amygdala (CMA) is a key brain region that mediates autonomic and somatic responses. Abnormal function in the CMA may contribute to the development of somatic symptoms in depressed patients.

METHODS

We compared the resting-state functional connectivity (RSFC) based on the seed of the left and right CMA between 37 patients with depression and 30 healthy controls. The severity of depressive and somatic symptoms was assessed using the Hamilton Depression Rating Scale (HDRS) and the 15-item somatic symptom severity scale of the Patient Health Questionnaire (PHQ-15). Correlation analysis was performed to investigate the relationship between the RSFC and clinical variables (HDRS and PHQ-15) in depressed patients.

RESULTS

Compared with healthy controls, patients with depression exhibited decreased RSFC between the CMA and insula, and superior temporal gyrus. In addition, functional connectivity between the left CMA and left insula was negatively correlated with PHQ-15 (r = -0.348, p = .037) in depressed patients. No significant relation was found between the RSFC and HDRS in depressed patients.

CONCLUSIONS

Functional connectivity between the CMA and insula is reduced in depressive patients, which is associated with the severity of somatic symptoms. Our findings may provide a potential neural substrate to interpret the co-occurrence of depression with somatic symptoms.

Abnormal reward system network in primary dysmenorrhea

Neuroimaging studies have demonstrated that reward system is associated with chronic pain diseases. In addition, previous studies have also demonstrated abnormal functional and structural brain regions in primary dysmenorrhea. However, the relation of reward system and primary dysmenorrhea is still unknown. Using the resting state functional magnetic resonance imaging, we aimed to investigate the functional connectivity changes of reward system during periovulatory phase in primary dysmenorrhea. Forty-one primary dysmenorrhea patients and 39 matched female healthy controls participated in this study. Compared to healthy controls, primary dysmenorrhea patients showed decreased connectivity of left nucleus accumbens with the bilateral anterior insula and the left amygdala and decreased connectivity of right nucleus accumbens with ventral tegmental area, the left hippocampus, the right orbital frontal cortex, and the right anterior insula. In addition, the decreased functional connectivity between the right nucleus accumbens-ventral tegmental area negatively correlated with the level of prostaglandin F2 alpha. Our findings provide neuroimaging evidence in support of the abnormal reward system connectivity in primary dysmenorrhea patients, which might contribute to a better understanding of the cerebral pathophysiology of primary dysmenorrhea.

Understanding Neurogastroenterology From Neuroimaging Perspective: A Comprehensive Review of Functional and Structural Brain Imaging in Functional Gastrointestinal Disorders

This review provides a comprehensive overview of brain imaging studies of the brain-gut interaction in functional gastrointestinal disorders (FGIDs). Functional neuroimaging studies during gut stimulation have shown enhanced brain responses in regions related to sensory processing of the homeostatic condition of the gut (homeostatic afferent) and responses to salience stimuli (salience network), as well as increased and decreased brain activity in the emotional response areas and reduced activation in areas associated with the top-down modulation of visceral afferent signals. Altered central regulation of the endocrine and autonomic nervous responses, the key mediators of the brain-gut axis, has been demonstrated. Studies using resting-state functional magnetic resonance imaging reported abnormal local and global connectivity in the areas related to pain processing and the default mode network (a physiological baseline of brain activity at rest associated with self-awareness and memory) in FGIDs. Structural imaging with brain morphometry and diffusion imaging demonstrated altered gray- and white-matter structures in areas that also showed changes in functional imaging studies, although this requires replication. Molecular imaging by magnetic resonance spectroscopy and positron emission tomography in FGIDs remains relatively sparse. Progress using analytical methods such as machine learning algorithms may shift neuroimaging studies from brain mapping to predicting clinical outcomes. Because several factors contribute to the pathophysiology of FGIDs and because its population is quite heterogeneous, a new model is needed in future studies to assess the importance of the factors and brain functions that are responsible for an optimal homeostatic state.

Disrupted functional connectivity density in irritable bowel syndrome patients

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder resulting from a dysregulation of the brain-gut axis. However, its exact neural substrate still remains unclear. This study investigated the changes of intrinsic whole brain functional connectivity pattern in IBS using functional connectivity density (FCD). We acquired resting-state functional magnetic resonance imaging (rs-fMRI) data from thirty-two IBS patients and thirty-two healthy controls. Functional connectivity density, a data-driven algorithm, was used to compute the long-range and short-range FCD values for each voxel in the brain of each subject, implying the amount of distant and local functional connections of cortical hubs. The FCD maps were compared between IBS patients and healthy controls. Pearson correlations analysis was also performed between abnormal FCD values and clinical/psychometric scores in patients. Compared to healthy controls, IBS patients showed concurrently decreased long- and short-range FCD in bilateral anterior midcingulate cortices (aMCC) and inferior parietal lobules (IPL), and decreased long-range FCD in right anterior insula, and decreased short-range FCD in bilateral prefrontal cortices, subgenual anterior cingulate cortices and caudates. IBS patients also had concurrently increased long- and short-range FCD mainly in primary sensorimotor cortices, as well as increased long-range FCD in right supplementary motor area and increased short-range FCD in occipital lobe. In addition, some regions with altered FCD showed abnormal functional connectivity in brain regions involved in pain matrix of IBS patients. Furthermore, the abnormal FCD values in right anterior insula and left caudate showed significant correlation with severity of symptoms and disease duration of IBS patients respectively. In conclusion, patients with IBS have widely disrupted FCD, which decreased in brain regions involved in homeostatic afferent network, emotional arouse, and cognitive regulation, while increased in regions associated with sensorimotor modulation. And the observed functional connectivity alterations unveiled complicated working patterns of pain matrix in IBS patients. This study may provide us with new insight into the underlying brain network topology of IBS.

Amygdala Plasticity and Pain

The amygdala is a limbic brain region that plays a key role in emotional processing, neuropsychiatric disorders, and the emotional-affective dimension of pain. Preclinical and clinical studies have identified amygdala hyperactivity as well as impairment of cortical control mechanisms in pain states. Hyperactivity of basolateral amygdala (BLA) neurons generates enhanced feedforward inhibition and deactivation of the medial prefrontal cortex (mPFC), resulting in pain-related cognitive deficits. The mPFC sends excitatory projections to GABAergic neurons in the intercalated cell mass (ITC) in the amygdala, which project to the laterocapsular division of the central nucleus of the amygdala (CeLC; output nucleus) and serve gating functions for amygdala output. Impairment of these cortical control mechanisms allows the development of amygdala pain plasticity. Mechanisms of abnormal amygdala activity in pain with particular focus on loss of cortical control mechanisms as well as new strategies to correct pain-related amygdala dysfunction will be discussed in the present review.

Stress-Induced Chronic Visceral Pain of Gastrointestinal Origin

Visceral pain is generally poorly localized and characterized by hypersensitivity to a stimulus such as organ distension. In concert with chronic visceral pain, there is a high comorbidity with stress-related psychiatric disorders including anxiety and depression. The mechanisms linking visceral pain with these overlapping comorbidities remain to be elucidated. Evidence suggests that long term stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic visceral pain disorders such as irritable bowel syndrome (IBS). Early life stress (ELS) is a risk-factor for the development of IBS, however the mechanisms responsible for the persistent effects of ELS on visceral perception in adulthood remain incompletely understood. In rodent models, stress in adult animals induced by restraint and water avoidance has been employed to investigate the mechanisms of stress-induce pain. ELS models such as maternal separation, limited nesting, or odor-shock conditioning, which attempt to model early childhood experiences such as neglect, poverty, or an abusive caregiver, can produce chronic, sexually dimorphic increases in visceral sensitivity in adulthood. Chronic visceral pain is a classic example of gene × environment interaction which results from maladaptive changes in neuronal circuitry leading to neuroplasticity and aberrant neuronal activity-induced signaling. One potential mechanism underlying the persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in visceral nociception, stress-induced visceral pain has been linked to alterations in DNA methylation and histone acetylation patterns within the brain, leading to increased expression of pro-nociceptive neurotransmitters. This review will discuss the potential neuronal pathways and mechanisms responsible for stress-induced exacerbation of chronic visceral pain. Additionally, we will review the importance of specific experimental models of adult stress and ELS in enhancing our understanding of the basic molecular mechanisms of pain processing.

The Increased Level of Depression and Anxiety in Irritable Bowel Syndrome Patients Compared with Healthy Controls: Systematic Review and Meta-analysis

BACKGROUND/AIMS

Irritable bowel syndrome (IBS) patients commonly experience psychiatric disorders, such as depression and anxiety. This meta-analysis sought to compare depression and anxiety levels between IBS patients and healthy controls.

METHODS

We searched major electronic databases (PubMed, EMBASE, MEDLINE, and Cochrane library) to find comparative studies on IBS patients and healthy controls. The primary outcome was a standardized mean difference (SMD) of anxiety and depression levels; sub-group analyses were conducted according to IBS-subtypes.

RESULTS

In total, 2293 IBS patients and 4951 healthy controls from 27 studies were included. In random effect analysis, depression and anxiety levels were significantly higher in IBS patients (pooled SMD = 0.76; 95% CI, 0.62-0.90; P < 0.001; I2 = 77.2% and pooled SMD = 0.84; 95% CI, 0.67-1.01; P < 0.001; I2 = 85.6%, respectively). Both analyses' funnel plots showed symmetry. In meta-regression analysis, heterogeneity was due to the studied region and questionnaire type for both depression and anxiety. In sub-group analyses of IBS-subtype, the pooled SMDs of depression and anxiety levels (IBS with predominant constipation: 0.83 and 0.81, IBS with predominant diarrhea: 0.73 and 0.65, and IBS with mixed bowel habits: 0.62 and 0.75; P < 0.001, respectively) were significantly higher in all IBS-subtypes.

CONCLUSIONS

The present meta-analysis showed depression and anxiety levels to be higher in IBS patients than in healthy controls, regardless of IBS-subtype. However, the gender effect on psychological factors among IBS patients could not be determined and should be evaluated in prospective studies.

Brain functional connectivity is associated with visceral sensitivity in women with Irritable Bowel Syndrome

Increased perception of visceral stimuli is a key feature of Irritable Bowel Syndrome (IBS). While altered resting-state functional connectivity (rsFC) has been also reported in IBS, the relationship between visceral hypersensitivity and aberrant rsFC is unknown. We therefore assessed rsFC within the salience, sensorimotor and default mode networks in patients with and without visceral hypersensitivity and in healthy controls (HCs).

An exploratory resting-state functional magnetic resonance imaging study was performed in 41 women with IBS and 20 HCs. Group independent component analysis was used to derive intrinsic brain networks. Rectal thresholds were determined and patients were subdivided into groups with increased (hypersensitive IBS, N = 21) or normal (normosensitive IBS, N = 20) visceral sensitivity. Between-group comparisons of rsFC were carried-out using region-of-interest analyses and peak rsFC values were extracted for correlational analyses.

Relative to normosensitive IBS, hypersensitive patients showed increased positive rsFC of pregenual anterior cingulate cortex and thalamus within the salience network and of posterior insula within the sensorimotor network. When compared to both hypersensitive IBS and HCs, normosensitive IBS showed decreased positive rsFC of amygdala and decreased negative rsFC in dorsal anterior insula within the DMN. DMN and sensorimotor network rsFC were associated with rectal perception thresholds, and rsFC in posterior insula was correlated with reported symptom severity in IBS.

Our exploratory findings suggest that visceral sensitivity in IBS is related to changes in FC within resting-state networks associated with interoception, salience and sensory processing. These alterations may play an important role in hypervigilance and hyperalgesia in IBS.

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Functional connectivity (FC) was compared between hyper- and normosensitive IBS.

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Hypersensitive IBS showed enhanced salience and sensorimotor network FC.

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Normosensitive IBS had decreased amygdala and anterior insula FC within the DMN.

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Changes in FC were associated with visceral sensitivity and symptom severity.

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Altered FC may play a key role in hypervigilance and hyperalgesia in IBS.

Disturbed Interhemispheric Functional Connectivity Rather than Structural Connectivity in Irritable Bowel Syndrome

Neuroimaging studies have demonstrated that irritable bowel syndrome (IBS)-a relapsing functional bowel disorder-presents with disrupted brain connections. However, little is known about the alterations of interhemispheric functional connectivity and underlying structural connectivity in IBS. This study combined resting-state functional magnetic resonance imaging (rs-fMRI) and diffusion tensor imaging (DTI) to investigate changes in interhemispheric coordination in IBS patients. Resting-state functional and structural magnetic resonance images were acquired from 65 IBS patients and 67 healthy controls (HCs; matched for age, sex and educational level). Interhemispheric voxel-mirrored homotopic connectivity (VMHC) was calculated and compared between groups. Homotopic regions showing abnormal VMHC in patients were targeted as regions of interest (ROIs) for analysis of DTI tractography. The fractional anisotropy (FA), fiber number and fiber length were compared between groups. Statistical analysis was also performed by including anxiety and depression as covariates to evaluate their effect. A Pearson correlation analysis between abnormal interhemispheric connectivity and clinical indices of IBS patients was performed. Compared to HCs, IBS patients had higher interhemispheric functional connectivity between bilateral thalami, cuneus, posterior cingulate cortices (PCC), lingual gyri and inferior occipital/cerebellum lobes, as well as lower interhemispheric functional connectivity between bilateral ventral anterior cingulate cortices (vACC) and inferior parietal lobules (IPL). The inclusion of anxiety and depression as covariates abolished VMHC difference in vACC. Microstructural features of white matter tracts connecting functionally abnormal regions did not reveal any differences between the groups. VMHC values in vACC negatively correlated with the quality of life (QOL) scores of patients. In conclusion, this study provides preliminary evidence of the disrupted functional coordination rather than anatomic coordination between interhemispheric regions within the cortex-thalamus circuit in IBS patients, which could partly account for the enhanced visceral information processing and impaired endogenous pain or emotion inhibition associated with IBS.