Functional brain imaging in irritable bowel syndrome with rectal balloon-distention by using fMRI

Brain activity in response to food images in patients with irritable bowel syndrome and functional dyspepsia

BACKGROUND

Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are caused and exacerbated by consumption of fatty foods. However, no study has evaluated brain activity in response to food images in patients with disorders of gut-brain interaction (DGBI). This study aimed to compare food preference and brain activity when viewing food images between patients with DGBI and healthy controls.

METHODS

FD and IBS were diagnosed using the ROME IV criteria. Food preference was assessed using a visual analog scale (VAS). Brain activity in the prefrontal cortex (PFC) in response to food images was investigated using functional near-infrared spectroscopy (fNIRS).

RESULTS

Forty-one patients were enrolled, including 25 with DGBI. The mean VAS scores for all foods (controls vs. FD vs. IBS: 69.1 ± 3.3 vs. 54.8 ± 3.8 vs. 62.8 ± 3.7, p = 0.02), including fatty foods (78.1 ± 5.4 vs. 43.4 ± 6.3 vs. 64.7 ± 6.1, p < 0.01), were the lowest in patients with FD among all groups. Patients with FD had significantly higher brain activity in the left PFC than those with IBS and healthy controls (mean z-scores in controls vs. FD vs. IBS: - 0.077 ± 0.03 vs. 0.125 ± 0.04 vs. - 0.002 ± 0.03, p < 0.001).

CONCLUSIONS

Patients with DGBI, particularly those with FD, disliked fatty foods. The brain activity in patients with DGBI differed from that in healthy controls. Increased activity in the PFC of patients with FD was confirmed.

Sensory brain activation during rectal balloon distention: a pilot study in healthy volunteers to assess safety and feasibility at 1.5T

OBJECTIVE

Although increasing evidence suggests a central mechanism of action for sacral neuromodulation, the exact mechanism remains unclear. We set up a scanning paradigm to measure brain activation related to various stages of rectal filling using rectal balloon distention.

MATERIALS AND METHODS

Six healthy volunteers underwent rectal balloon distention during MRI scanning at a 1.5T scanner with a Tx/Rx head coil. MR images were collected at four levels of distention: empty balloon (EB), first sensation volume (FSV), desire to defecate volume (DDV), maximum tolerable volume (MTV). Data were analyzed using BrainVoyager 20.4. Whole brain and ROI-based fixed-effects general linear model analyses were performed on the fMRI time-course data from all participants.

RESULTS

Rectal filling until FSV evoked the most blood-oxygen-level-dependent responses in several clusters throughout the cortex, followed by the responses evoked by rectal filling until DDV. Interestingly, rectal filling until MTV evoked negative responses compared to baseline throughout the cortex. No negative side effects were found.

DISCUSSION

This study shows that a standardized paradigm for functional MRI combined with rectal filling is feasible and safe in healthy volunteers and is ready to be used in fecal incontinent patients to assess whether their brain activity differs from healthy controls.

Relationship Between Sensitivity to Disgust and Irritable Bowel Syndrome: A Study on Healthy Individuals

OBJECTIVE

Irritable bowel syndrome (IBS) is a psychosomatic gastrointestinal disorder involving the dysfunctional activation of specific brain regions crucial for interoception and disgust processing. Yet, no study has ever investigated the link between this socio-affective/visceral experience and IBS.

METHOD

The present study investigated whether disgust sensitivity and disgust propensity, which can be socially relevant, relate with IBS symptoms in a nonclinical population.105 healthy participants were asked to complete the Disgust Propensity and Sensitivity Scale-Revised (DPSS-R), the Irritable Bowel Syndrome-Quality of Life Measure (IBS-QOL), and the Chronic Urticaria Quality of Life Measure (CU-Q2OL), as control condition.

RESULTS

Results showed higher disgust sensitivity scores in individuals with high IBS-QOL score, compared to individuals with low IBS-QOL score. The correlation analysis corroborates this result by showing a positive relationship between disgust sensitivity and respective IBS-QOL scores.

CONCLUSIONS

This research provides new insights into understanding the etiopathogenesis of IBS, suggesting the relevance of a socially relevant personality trait such as disgust sensitivity as a potential trigger and / or predisposition factor for this chronic inflammatory disease.

Spontaneous pain as a challenge of research and management in chronic pain

Spontaneous pain occurring without apparent external stimuli, is a significant complaint of individuals with chronic pain whose mechanisms, somewhat surprisingly, remain poorly understood. Over the past decades, neuroimaging studies start to reveal brain activities accompanying spontaneous pain. Meanwhile, a variety of animal models and behavioral tests have been established, including non-reflexive tests and free-choice tests, which have been shown to be effective in assessing spontaneous pain. For the spontaneous pain mechanisms, multiple lines of research mainly focus on three aspects: (1) sensitization of peripheral nociceptor receptors and ion channels, (2) spontaneous neuronal firing and abnormal activity patterns at the dorsal root ganglion and spinal cord level, (3) functional and structural alterations in the brain, particularly the limbic system and the medial pain pathway. Despite accumulating evidence revealing distinct neuronal mechanisms from evoked pain, we are still far from full understanding of spontaneous pain, leaving a big gap between bench and bedside for chronic pain treatment. A better understanding of the neural processes in chronic pain, with specific linkage as to which anatomical structures and molecules related to spontaneous pain perception and comorbidities, will greatly improve our ability to develop novel therapeutics.

Abnormal resting-state local spontaneous functional activity in irritable bowel syndrome patients: A meta-analysis

BACKGROUND

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder. The current understanding of the pathogenesis underlying IBS is still unclear. Numerous studies have reported local abnormal resting state spontaneous functional activity in IBS patients in widespread brain regions. However, the results have not yet yielded consistent conclusions. Thus, we investigated common spontaneous functional activity abnormalities in patients with IBS by conducting a voxel-based meta-analysis.

METHODS

Up to December 2021, we performed a systematic search of IBS studies in five databases. These studies investigated the differences of resting state spontaneous brain activity between patients with IBS and healthy controls (HCs). The reference lists of included studies, relevant reviews and meta-analyses were investigated manually. Anisotropic effect-size signed differential mapping (AES-SDM) was applied in this meta-analysis.

RESULTS

Twelve studies encompassing 335 patients with IBS and 327 HCs were included in this meta-analysis. The local brain activities of the left calcarine fissure and surrounding cortex, right postcentral gyrus, left postcentral gyrus, left cerebellum, left inferior temporal gyrus, and left inferior frontal gyrus of triangular part in IBS patients were significantly increased compared with HCs, while the brain activities of the left anterior cingulate and paracingulate gyrus, right middle frontal gyrus, right supramarginal gyrus, left middle frontal gyrus, left precuneus, right putamen and right insula were significantly decreased compared with HCs.

CONCLUSION

The current study expands on a growing literature exploring resting state activity in IBS, which provides useful insights for understanding the underlying pathophysiology of nonorganic functional bowel disease and developing more targeted treatment and intervention strategies.

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.

A Broader Perspective: Functional Symptoms Beyond Neurology

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Functional (psychogenic) symptoms exist in all specialties.

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They are by definition not under voluntary control, unlike factitious disorders and malingering.

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The diagnostic approach to functional symptoms varies among specialties.

Antibiotic use but not gastrointestinal infection frequently precedes first diagnosis of functional gastrointestinal disorders

INTRODUCTION

While the etiopathogenesis of functional gastrointestinal disorders (FGIDs) is not completely understood, alterations of the intestinal microbiome have been observed. Antibiotics can induce dysbiosis, but whether antibiotics are a risk factor for the onset of FGIDs is uncertain. Antibiotics have been reported as both a risk factor for new onset FGID but also as a therapy for existing FGID. This study aimed to estimate the fraction of cases where antibiotics provoked the onset of FGID.

METHOD

Electronic medical records were obtained from general practices (primary care) in the United Kingdom. Dates of antibiotic prescription (AP) were compared with first date of FGID diagnosis and contrasted across three prevalent FGIDs and controls without gastrointestinal disorders.

RESULTS

There were 10,926 GI healthy controls, 4326 IBS alone, 3477 FD alone, 340 chronic constipation and 4402 with overlap of multiple conditions. Both the prevalence of AP and rate were higher in FGID patients and increased with diagnosis of multiple FGIDs. 7%-14% of FGID patients were prescribed their first recorded antibiotic in the 12 months prior to their first FGID diagnosis and 20%-33% were prescribed an antibiotic in the same period. Differences between FGID groups were not accounted for by social deprivation and only rate of AP was moderated by social deprivation. In contrast, only 5%-10% of patients ever had a gastrointestinal infection recorded and only 1.5%-3.5% prior to their first FGID diagnosis.

CONCLUSION

These data indicate that antibiotics are prescribed prior to FGID diagnosis in a significant minority of care-seeking FGID patients, opening the potential for this medication to contribute to the pathophysiology. APs appears to mostly be for non-gastrointestinal conditions.

Altered brain structural connectivity in patients with longstanding gut inflammation is correlated with psychological symptoms and disease duration

OBJECTIVE

We aimed to identify differences in network properties of white matter microstructure between asymptomatic ulcerative colitis (UC) participants who had a history of chronic gut inflammation, healthy controls (HCs) and a disease control group without gut inflammation (irritable bowel syndrome; IBS).

DESIGN

Diffusion weighted imaging was conducted in age and sex-matched participants with UC, IBS, and HCs (N = 74 each), together with measures of gastrointestinal and psychological symptom severity. Using streamline connectivity matrices and graph theory, we aimed to quantify group differences in brain network connectivity. Regions showing group connectivity differences were correlated with measures showing group behavioral and clinical differences.

RESULTS

UC participants exhibited greater centrality in regions of the somatosensory network and default mode network, but lower centrality in the posterior insula and globus pallidus compared to HCs (q < 0.05). Hub analyses revealed compromised hubness of the pallidus in UC and IBS compared to HCs which was replaced by increased hubness of the postcentral sulcus. Surprisingly, few differences in network matrices between UC and IBS were identified. In UC, centrality measures in the secondary somatosensory cortex were associated with depression (q < 0.03), symptom related anxiety (q < 0.04), trait anxiety (q < 0.03), and symptom duration (q < 0.05).

CONCLUSION

A history of UC is associated with neuroplastic changes in several brain networks, which are associated with symptoms of depression, trait and symptom-related anxiety, as well as symptom duration. When viewed together with the results from IBS subjects, these findings suggest that chronic gut inflammation as well as abdominal pain have a lasting impact on brain network organization, which may play a role in symptoms reported by UC patients, even when gut inflammation has subsided.

Evidence-based clinical practice guidelines for irritable bowel syndrome 2020

Managing irritable bowel syndrome (IBS) has attracted international attention because single-agent therapy rarely relieves bothersome symptoms for all patients. The Japanese Society of Gastroenterology (JSGE) published the first edition of evidence-based clinical practice guidelines for IBS in 2015. Much more evidence has accumulated since then, and new pharmacological agents and non-pharmacological methods have been developed. Here, we report the second edition of the JSGE-IBS guidelines comprising 41 questions including 12 background questions on epidemiology, pathophysiology, and diagnostic criteria, 26 clinical questions on diagnosis and treatment, and 3 questions on future research. For each question, statements with or without recommendations and/or evidence level are given and updated diagnostic and therapeutic algorithms are provided based on new evidence. Algorithms for diagnosis are requisite for patients with chronic abdominal pain or associated symptoms and/or abnormal bowel movement. Colonoscopy is indicated for patients with one or more alarm symptoms/signs, risk factors, and/or abnormal routine examination results. The diagnosis is based on the Rome IV criteria. Step 1 therapy consists of diet therapy, behavioral modification, and gut-targeted pharmacotherapy for 4 weeks. For non-responders, management proceeds to step 2 therapy, which includes a combination of different mechanistic gut-targeted agents and/or psychopharmacological agents and basic psychotherapy for 4 weeks. Step 3 therapy is for non-responders to step 2 and comprises a combination of gut-targeted pharmacotherapy, psychopharmacological treatments, and/or specific psychotherapy. These updated JSGE-IBS guidelines present best practice strategies for IBS patients in Japan and we believe these core strategies can be useful for IBS diagnosis and treatment globally.

Detection of microstructural white matter alterations in functional gastrointestinal disorders assessed by diffusion kurtosis imaging

BACKGROUND AND AIM

We evaluated whether diffusion kurtosis and tensor imaging (DKI/DTI) could reveal microstructural alterations in the brains of patients with functional gastrointestinal disorders (FGIDs), and whether imaging findings were correlated with health-related quality of life (HRQOL).

METHODS

Twelve patients with FGIDs fulfilling the Rome IV criteria, and seven healthy controls were examined using a 3 T magnetic resonance (MR) scanner. Tract-based spatial statistics and regions of interest analyses were performed to compare the mean kurtosis (MK), fractional anisotropy (FA), and mean diffusivity (MD) between patients with FGIDs versus controls. HRQOL was assessed in patients with FGIDs using the eight-item short form of the Medical Outcome Study Questionnaire (SF-8) and the Gastrointestinal Symptom Rating Scale.

RESULTS

Patients with FGIDs had extensive, widespread regions of reduced MD in the white matter in comparison with healthy controls, whereas no significant differences were observed in MK and FA. No significant differences in deep gray matter for the MK, FA, and MD values were observed between patients with FGIDs and controls. In patients with FGIDs, the FA values in the globus pallidus had a significant and negative correlation with SF-8 (a mental component summary) (r = -0.797, P = 0.01 uncorrected for multiple comparisons).

CONCLUSIONS

DKI/DTI can help identify microstructural white matter alterations in patients with FGIDs. The FA values in the globus pallidus may be useful for a severity assessment of FGIDs.

Second Asian Consensus on Irritable Bowel Syndrome

BACKGROUND/AIMS

There has been major progress in our understanding of the irritable bowel syndrome (IBS), and novel treatment classes have emerged. The Rome IV guidelines were published in 2016 and together with the growing body of Asian data on IBS, we felt it is timely to update the Asian IBS Consensus.

METHODS

Key opinion leaders from Asian countries were organized into 4 teams to review 4 themes: symptoms and epidemiology, pathophysiology, diagnosis and investigations, and lifestyle modifications and treatments. The consensus development process was carried out by using a modified Delphi method.

RESULTS

Thirty-seven statements were developed. Asian data substantiate the current global viewpoint that IBS is a disorder of gut-brain interaction. Socio-cultural and environmental factors in Asia appear to influence the greater overlap between IBS and upper gastrointestinal symptoms. New classes of treatments comprising low fermentable oligo-, di-, monosacharides, and polyols diet, probiotics, non-absorbable antibiotics, and secretagogues have good evidence base for their efficacy.

CONCLUSIONS

Our consensus is that all patients with functional gastrointestinal disorders should be evaluated comprehensively with a view to holistic management. Physicians should be encouraged to take a positive attitude to the treatment outcomes for IBS patients.

Altered white matter microstructure identified with tract-based spatial statistics in irritable bowel syndrome: a diffusion tensor imaging study

The neural mechanisms underlying the pathophysiology of irritable bowel syndrome(IBS) are far from being completely understood. The purpose of the present study was to investigate potential white matter (WM) microstructural changes and underlying causes for WM impairment in IBS using diffusion tensor imaging. The present prospective study involved 19 patients with IBS and 20 healthy controls. Whole-brain voxel-wise analyses of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were performed by tract-based spatial statistics (TBSS) to localize abnormal WM regions between the 2 groups. We found that IBS patients had significantly reduced FA (P < 0.05) in the splenium of the corpus callosum, the right retrolenticular area of the internal capsule and the right superior corona radiata. We also found increased MD (P < 0.05) in the splenium and body of the corpus callosum, the right retrolenticular area of the internal capsule, the right superior corona radiata and the right posterior limb of the internal capsule. In addition, IBS patients had significantly increased AD (P < 0.05) in the splenium of the corpus callosum, the bilateral retrolenticular area of the internal capsule and the left posterior limb of the internal capsule. We conclude that the WM microstructure is changed in IBS and the underlying pathological basis may be attributed to the axonal injury and loss. These results may lead to a better understanding of the pathophysiology of IBS.

Functional abdominal pain disorders in children

Chronic abdominal pain is a common problem in pediatric practice. The majority of cases fulfill the Rome IV criteria for functional abdominal pain disorders (FAPDs). At times, these disorders may lead to rather serious repercussions. Area covered: We have attempted to cover current knowledge on epidemiology, pathophysiology, risk factors related to pathophysiology, clinical evaluation and management of children with FAPDs. Expert commentary: FAPDs are a worldwide problem with a pooled prevalence of 13.5%. There are a number of predisposing factors and pathophysiological mechanisms including stressful events, child maltreatment, visceral hypersensitivity, altered gastrointestinal motility and change in intestinal microbiota. It is possible that the environmental risk factors intricately interact with genes through epigenetic mechanisms to contribute to the pathophysiology. The diagnosis mainly depends on clinical evaluation. Commonly used pharmacological interventions do not play a major role in relieving symptoms. Centrally directed, nonpharmacological interventions such as hypnotherapy and cognitive behavioral therapy have shown both short and long term efficacy in relieving pain in children with FAPDs. However, these interventions are time consuming and need specially trained staff and therefore, not currently available at grass root level. Clinicians and researchers should join hands in searching for more pragmatic and effective therapeutic modalities to improve overall care of children with FAPDs.

Magnetic resonance imaging analysis of brain function in patients with irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a common functional disease of the gastrointestinal tract. The current study aimed to examine the association between visceral hypersensitivity in IBS and cortical activation using functional magnetic resonance imaging (fMRI), and to elucidate the role of psychological factors in the pathogenesis of IBS.

METHODS

The present study included 31 patients with IBS and 20 healthy controls. Cerebral function was assessed using fMRI. During imaging, a Sengstaken-Blakemore tube was placed within the rectum approximately 10 cm from the anus, following which gas was rapidly injected into the airbag using a 150-ml syringe. Images were obtained at 40 ml, 80 ml, and 120 ml of expansion. Psychological status was evaluated using the Hospital Anxiety and Depression Scale (HADS).

RESULTS

Anxiety and depression scores were higher among patients with IBSthan among controls (both P < 0.05), although scores in both groups were below the level of clinical diagnosis. Brain activation in regions of interest (parietal areas, prefrontal cortex, cerebellum, anterior cingulate cortex, insular cortex, and thalamus) increased along with increases in rectal balloon dilation, except in women with IBS and patients with disease duration less than 5 years. Furthermore, region of interest (ROI) activation (such as the parietal region, prefrontal cortex, cerebellum, anterior cingulate cortex, insular cortex, and thalamus) differed significantly between the 40-ml and 120-ml conditions, and between the 80-ml and 120-ml conditions (P < 0.05), among patients with IBS with anxiety or depression scores less than 9 points.

CONCLUSIONS

Overall, our findings indicate that changes in brain activation due to changes in rectal balloon distension can be objectively and accurately measured using fMRI. Although our results indicated that visceral hypersensitivity during IBS is associated with changes in cortical activation, further studies utilizing larger sample sizes are required to more fully elucidate the association between psychological factors and visceral hypersensitivity in IBS.

Intrinsic brain abnormalities in irritable bowel syndrome and effect of anxiety and depression

This resting-state functional magnetic resonance imaging (rs-fMRI) study investigated intrinsic brain abnormalities in irritable bowel syndrome (IBS) and effect of anxiety and depression. Thirty IBS patients and 31 matched healthy controls underwent rs-fMRI scanning. Regional brain activity was evaluated by measuring the amplitude of low-frequency fluctuation (ALFF) and compared between IBS patients and healthy controls with a two-sample t-test. Areas with abnormal ALFF were further used as seeds in subsequent inter-regional functional connectivity (FC) analysis. Statistical analyses were also performed by including anxiety and depression as covariates to evaluate their effect. Compared to healthy controls, IBS patients showed decreased ALFF in several core default mode network regions (medial prefrontal cortex [MPFC], posterior cingulate cortex [PCC], bilateral inferior parietal cortices [IPC]), and in middle frontal cortex, right orbital part of the superior frontal gyrus (ORBsup), dorsal anterior cingulate cortex (dACC), and ventral anterior cingulated cortex (vACC), while they showed increased ALFF in bilateral posterior insula and cuneus. In addition, IBS patients revealed decreased inter-regional positive FC between MPFC and right ORBsup, between vACC and PCC, as well as decreased negative FC between MPFC and left posterior insula, while they showed increased negative FC between MPFC and cuneus. The inclusion of anxiety and depression as covariates abolished ALFF differences in dACC and vACC, but none of the FC differences.

IN CONCLUSION

IBS patients had disturbed intrinsic brain function. High levels of anxiety and depression in IBS patients could account for their decreased intrinsic brain activity in regions (the ACC) involved in affective processing.

Cross-cultural and psychological issues in irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders encountered by gastroenterologists worldwide. Of all the etiological factors that had been postulated to explain the pathophysiology of IBS, cultural and psychological factors are unique and difficult to understand. Culture plays an important role in coloring the presentation of IBS, and many a times, it has a significant role in several treatment aspects too. Psychological aspects like personality profiles, family relationships, societal myths, and abuse in any form are equally important in the management perspectives of IBS. In this brief review, we had tried to specifically focus on these aspects in IBS and have explained the evidences in favor of these factors. Knowledge about various cross-cultural aspects and psychological factors in patients with IBS is essential for taking an appropriate history and for undertaking a holistic approach for the management of the same. A collaborative team effort by psychiatrists and gastroenterologists could help in reducing the burden of this difficult to treat functional bowel disorder.

Mapping of Brain Activations to Rectal Balloon Distension Stimuli in Male Patients with Irritable Bowel Syndrome Using Functional Magnetic Resonance Imaging

Background/Aims

Irritable bowel syndrome (IBS) is associated with exaggerated cerebral response including emotional processing following visceral stimulation; though data on this issue is available in female IBS patients, it is scanty among males. Hence, we aimed to study brain response of male IBS patients following rectal balloon distension as compared to healthy controls using functional magnetic resonance imaging (fMRI). Data between diarrhea and constipation predominant IBS (IBS-D and IBS-C) were also compared.

Methods

Rectal balloon distension threshold was assessed in 20 male IBS patients (10 IBS-C and 10 IBS-D) and 10 age-matched male healthy controls. Subsequently, fMRI on all the participants was performed at their respective rectal pain threshold. The fMRI data were analysed using the Statistical Parametric Mapping software.

Results

IBS patients showed greater cerebral activations in insula, middle temporal gyrus, and cerebellum in the left hemisphere compared to healthy controls. Neural activation was found in bilateral precuneus/superior parietal lobules in controls but not in patients with IBS. The brain activation differed among IBS-C and IBS-D patients; while the right mid-cingulate cortex was activated in IBS-C, the left inferior orbito-frontal cortex, left calcarine, and bilateral fusiform gyri were activated among patients with IBS-D following rectal balloon distension.

Conclusions

Brain response to rectal balloon distension differed among male patients with IBS and controls and among patients with IBS-C and IBS-D. Differential activation among patients with IBS-C and IBS-D was seen in the brain regions controlling affective motivation, homeostatic emotions, and autonomic responses to pain.

How to Perform and Interpret Functional Magnetic Resonance Imaging Studies in Functional Gastrointestinal Disorders

Functional neuroimaging studies have revealed the importance of the role of cognitive and psychological factors and the dysregulation of the brain-gut axis in functional gastrointestinal disorder patients. Although only a small number of neuroimaging studies have been conducted in functional gastrointestinal disorder patients, and despite the fact that the neuroimaging technique requires a high level of knowledge, the technique still has a great deal of potential. The application of functional magnetic resonance imaging (fMRI) technique in functional gastrointestinal disorders should provide novel methods of diagnosing and treating patients. In this review, basic knowledge and technical/practical issues of fMRI will be introduced to clinicians.

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.

Role of 5-HT1A receptor in insular cortex mediating stress - induced visceral sensory dysfunction

BACKGROUND

5-HT1A receptors (HTR1As) in the insular cortex are thought to be related with the generation of stress-induced functional gastrointestinal disorders (FGIDs), but its mechanism is not clear. Visceral hypersensitivity is one important pathophysiological mechanism of FGIDs. This study aimed to explore the role of HTR1As in mediating stress-induced visceral hypersensitivity and its mechanism in the insular cortex.

METHODS

Visceral hypersensitivity rat model was established by water avoidance stress (WAS) and the visceral sensitivity was measured by electromyogram. The activities of HTR1As were regulated by microinjecting the HTR1A agonist and antagonist into the insular cortex. The expression levels of 5-HT, HTR1A, N-methyl-d-aspartic acid receptor subtype 2B (NR2B) and c-fos were observed by RT-PCR, Western Blot and immunohistochemical staining.

KEY RESULTS

In WAS rats, the expression levels of 5-HT and HTR1As in the insular cortex were significantly lower (p < 0.05) than that in sham WAS and normal rats, but the levels of c-fos and NR2B were significantly higher (p < 0.05). After microinjecting HTR1As agonist into the insular cortex of WAS rats, the visceral sensitivity and the expression levels of NR2B and c-fos in insular cortex significantly decreased (p < 0.05).

CONCLUSIONS & INFERENCES

The HTR1As-NR2B signal pathway of insular cortex plays an important role in regulating stress-induced visceral hypersensitivity.

Stress and the Microbiota-Gut-Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut-brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut-brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

Abnormal Amygdala Resting-State Functional Connectivity in Irritable Bowel Syndrome

BACKGROUND AND PURPOSE

Functional neuroimaging studies in irritable bowel syndrome have revealed abnormalities in the corticolimbic regions, specifically, hyperactivity of the amygdala during visceral and somatic stimulation. This study investigated changes in the neural circuitry of the amygdala in patients with irritable bowel syndrome based on resting-state functional connectivity.

MATERIALS AND METHODS

Functional MR imaging data were acquired from 31 patients with irritable bowel syndrome and 32 healthy controls (matched for age, sex, and educational level) during rest, and the resting-state functional connectivity of bilateral amygdalae was compared. Multiple regression was performed to investigate the relationship between clinical indices of patients with irritable bowel syndrome and resting-state functional connectivity.

RESULTS

Compared with healthy controls, patients with irritable bowel syndrome had higher positive resting-state functional connectivity between the amygdala and insula, midbrain, parahippocampal gyrus, pre- and postcentral gyri, and supplementary motor area. The inclusion of anxiety and depression as covariates did not alter amygdala resting-state functional connectivity differences between the study groups. Multiple covariate regression results showed that the pain intensity in patients with irritable bowel syndrome positively correlated with resting-state functional connectivity between the amygdala and supplementary motor area, pre- and postcentral gyri, and insula, while the Irritable Bowel Syndrome-Symptom Severity Score positively correlated with resting-state functional connectivity between the amygdala and insula and midbrain.

CONCLUSIONS

Patients with irritable bowel syndrome showed disturbed amygdala resting-state functional connectivity with the corticolimbic regions, which could partly account for the enhanced emotional arousal and visceral information processing associated with irritable bowel syndrome.

Comparison of electroacupuncture and moxibustion on brain-gut function in patients with diarrhea-predominant irritable bowel syndrome: A randomized controlled trial

OBJECTIVE

To compare the effects of electroacupuncture (EA) and moxibustion therapies on patients with diarrhea-predominant irritable bowel syndrome (D-IBS).

METHODS

A total of 60 D-IBS patients were randomly allocated to the EA group (30 cases) and moxibustion group (30 cases). Before and after treatment, the gastrointestinal symptoms and psychological symptoms were scored by Visual Analogue Scale, Bristol Stool Form Scale, Hamilton Anxiety Rating Scale (HAMA), and Hamilton Depression Rating Scale (HAMD); the expressions of 5-hydroxytryptamine (5-HT), 5-HT3 receptor (5-HT3R), and 5-HT4 receptor (5-HT4R) in the sigmoid mucosal tissue were measured by immunohistochemical staining. Additionally, the effects on the functional brain areas of the anterior cingulate cortex (ACC), insular cortex (IC) and prefrontal cortex (PFC) were observed by functional magnetic resonance imaging.

RESULTS

Compared with before treatment, both EA and moxibustion groups reported significant improvements in abdominal pain and abdominal bloating after treatment (P<0.01 or P<0.05). The moxibustion group reported greater improvements in defecation emergency, defecation frequency, and stool feature than the EA group (P<0.01). Both HAMA and HAMD scores were significantly decreased in the moxibustion group than in the EA group (P<0.01). Both groups demonstrated significantly reduced expressions of 5-HT, 5-HT3R and 5-HT4R in the colonic mucosa after treatment (P<0.01), with a greater reduction of 5-HT in the moxibustion group (P<0.05). Finally, decreased activated voxel values were observed in the left IC, right IC and PFC brain regions of patients in the moxibustion group under stimulation with 150 mL colorectal distension after treatment (P<0.05 or P<0.01), while in the EA group only PFC area demonstrated a reduction (P<0.05).

CONCLUSION

Moxibustion can significantly improve the symptoms of D-IBS, suggesting that moxibustion may be a more effective therapy than EA for D-IBS patients.

Altered viscerotopic cortical innervation in patients with irritable bowel syndrome

BACKGROUND

Studies have demonstrated the existence of regional gray matter and white matter (WM) alterations in the brains of patients with irritable bowel syndrome (IBS), but the extent to which altered anatomical connectivity between brain regions is altered in IBS remains incompletely understood.

METHODS

In this study, magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) were used to identify significant brain connectivity differences between IBS patients and healthy control (HC) subjects. Based on MRI and DTI volumes acquired from 66 IBS patients and 23 HC subjects, multivariate regression was used to investigate whether subject age, sex, cortical thickness, or the mean fractional anisotropy (FA) of WM connections innervating each location on the cortex could predict IBS diagnosis.

KEY RESULTS

HC and IBS subjects were found to differ significantly within both left and right viscerotopic portions of the primary somatosensory cortex (S1), with the mean FA of WM bundles innervating S1 being the predictor variable responsible for these significant differences.

CONCLUSIONS & INFERENCES

These preliminary findings illustrate how a chronic visceral pain syndrome and brain structure are related in the cohort examined, and because of their indication that IBS diagnosis is associated with anatomic neuropathology of potential neurological relevance in this patient sample.

Post-traumatic Stress Disorder Is Associated With Irritable Bowel Syndrome in African Americans

Background/Aims

Psychosocial stressors likely play an important role in irritable bowel syndrome (IBS). The association between IBS and post-traumatic stress disorder (PTSD) in non-minorities has been described. Our aim was to investigate the potential association between IBS and PTSD in an urban African American population.

Methods

Our institution maintains a longitudinal population-based survey of African Americans (AA). The survey utilizes a complex, stratified sampling design. The study group consisted of adult AA meeting Rome III criteria for IBS of any subtype. The 4-item Primary Care PTSD screener was administered; score of ≥ 3 (range, 0–4) was considered positive for PTSD. Depression (Public Health Questionnaire-9 depression) and anxiety (generalized anxiety disorder-7) levels were measured using standardized scales. To assess quality of life, norm-based physical and mental component summary scores from the short-form 36 health survey version 2 were obtained. Descriptive and inferential statistics were calculated using Complex Sample Module of SPSS after weighting of the study sample.

Results

Four hundred nineteen subjects included corresponded to a weighted 21,264 (95% CI, 19,777–22,751) individuals. The prevalence of IBS in our sample of urban AA was 8.2%. In multivariate regression analysis, female gender, age > 40, higher educational attainment and divorce were independently associated with IBS. Those with IBS were considerably more likely to suffer from PTSD (OR, 4.54; 95% CI, 4.07–5.06). PTSD was independently associated with depression, anxiety, harmful drinking and substance abuse.

Conclusions

In AA, PTSD is independently associated with IBS. PTSD has a significantly negative impact on physical and mental self-assessment of quality of life. Evaluation of minorities presenting with functional gastrointestinal disorders should include screening for PTSD.

Diffusion tensor imaging detects microstructural reorganization in the brain associated with chronic irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterized by recurring abdominal pain associated with alterations in bowel habits. We hypothesized that patients with chronic visceral pain associated with IBS may have microstructural differences in the brain compared with healthy control subjects (HCs), indicative of long-term neural reorganization of chronic pain pathways and regions associated with sensory integration. In the current study we performed population-based voxel-wise diffusion tensor imaging (DTI) comparisons and probabilistic tractography in a large sample of phenotyped patients with IBS (n=33) and in HCs (n=93). Patients had lower fractional anisotropy (FA) in thalamic regions, the basal ganglia (BG) and sensory/motor association/integration regions as well as higher FA in frontal lobe regions and the corpus callosum. In addition, patients had reduced mean diffusivity (MD) within the globus pallidus (GP) and higher MD in the thalamus, internal capsule, and coronal radiata projecting to sensory/motor regions, suggestive of differential changes in axon/dendritic density in these regions. Sex differences in FA and MD were also observed in the patients but not in HCs. Probabilistic tractography in patients confirmed a higher degree of connectivity between the thalamus and prefrontal cortex, as well as between the medial dorsal thalamic nuclei and anterior cingulate cortex, and a lower degree of connectivity between the GP and thalamus. Together, these results support the hypothesis that patients with chronically recurring visceral pain from IBS have long-term microstructural changes within the brain, particularly in regions associated with integration of sensory information and corticothalamic modulation.

Interoception across modalities: on the relationship between cardiac awareness and the sensitivity for gastric functions

The individual sensitivity for ones internal bodily signals ("interoceptive awareness") has been shown to be of relevance for a broad range of cognitive and affective functions. Interoceptive awareness has been primarily assessed via measuring the sensitivity for ones cardiac signals ("cardiac awareness") which can be non-invasively measured by heartbeat perception tasks. It is an open question whether cardiac awareness is related to the sensitivity for other bodily, visceral functions. This study investigated the relationship between cardiac awareness and the sensitivity for gastric functions in healthy female persons by using non-invasive methods. Heartbeat perception as a measure for cardiac awareness was assessed by a heartbeat tracking task and gastric sensitivity was assessed by a water load test. Gastric myoelectrical activity was measured by electrogastrography (EGG) and subjective feelings of fullness, valence, arousal and nausea were assessed. The results show that cardiac awareness was inversely correlated with ingested water volume and with normogastric activity after water load. However, persons with good and poor cardiac awareness did not differ in their subjective ratings of fullness, nausea and affective feelings after drinking. This suggests that good heartbeat perceivers ingested less water because they subjectively felt more intense signals of fullness during this lower amount of water intake compared to poor heartbeat perceivers who ingested more water until feeling the same signs of fullness. These findings demonstrate that cardiac awareness is related to greater sensitivity for gastric functions, suggesting that there is a general sensitivity for interoceptive processes across the gastric and cardiac modality.

Brain responses to visceral stimuli reflect visceral sensitivity thresholds in patients with irritable bowel syndrome

BACKGROUND & AIMS

Only a fraction of patients with irritable bowel syndrome (IBS) have increased perceptual sensitivity to rectal distension, indicating differences in processing and/or modulation of visceral afferent signals. We investigated the brain mechanisms of these perceptual differences.

METHODS

We analyzed data from 44 women with IBS and 20 female healthy subjects (controls). IBS symptom severity was determined by a severity scoring system. Anxiety and depression symptoms were assessed using the hospital anxiety and depression score. Blood oxygen level-dependent signals were measured by functional magnetic resonance imaging during expectation and delivery of high (45 mmHg) and low (15 mmHg) intensity rectal distensions. Perception thresholds to rectal distension were determined in the scanner. Brain imaging data were compared among 18 normosensitive and 15 hypersensitive patients with IBS and 18 controls. Results were reported significant if peak P-values were ≤.05, with family-wise error correction in regions of interest.

RESULTS

The subgroups of patients with IBS were similar in age, symptom duration, psychological symptoms, and IBS symptom severity. Although brain responses to distension were similar between normosensitive patients and controls, hypersensitive patients with IBS had greater activation of insula and reduced deactivation in pregenual anterior cingulate cortex during noxious rectal distensions, compared to controls and normosensitive patients with IBS. During expectation of rectal distension, normosensitive patients with IBS had more activation in right hippocampus than controls.

CONCLUSIONS

Despite similarities in symptoms, hyper- and normosensitive patients with IBS differ in cerebral responses to standardized rectal distensions and their expectation, consistent with differences in ascending visceral afferent input.

Pathophysiologic findings of irritable bowel syndrome in china

The mechanism of irritable bowel syndrome (IBS) is still incompletely understood in the world although large amount of investigations have been carried out on it. There are many studies on the pathophysiology of IBS in China, which has huge amount of population suffering from IBS with special ethnicity and culture, including Mainland China, Hong Kong and Taiwan. We collected the literatures to show the results and discuss whether there were any differences in the pathophysiologic findings between China and other countries, whether there were any differences among different subtypes and how the pathophysiology correlated with the manifestations of patients. Gene polymorphism, disturbances of gastrointestinal motility, visceral hypersensitivity, intestinal infection and inflammation, psychological disturbances, food hypersensitivity and intolerance, and altered gut microflora were reviewed in this paper. Some conflicting outcomes between China and other countries were noted although most of them were similar.

White matter abnormalities in irritable bowel syndrome and relation to individual factors

Patients with irritable bowel syndrome (IBS) have abnormal cortical responses to rectal distension and grey matter thinning in brain areas associated with nociception. These abnormalities may be driven by white matter changes and individual factors. Therefore, we tested the hypothesis that WM subserving the pain system is compromised in IBS, and that disease characteristics and personality contribute to these abnormalities. MRI diffusion tensor imaging (DTI) images were obtained from 10 female IBS patients (20-54 years old, mean±SD 32.8±10.4), and 16 female healthy controls (20-44 years old, mean±SD 29.1±7.9). Mean fractional anisotropy (FA) was extracted from WM regions associated with nociception. The IBS group had higher FA in the fornix and external capsule adjacent to the right posterior insula. IBS chronic pain severity correlated with FA of the bilateral anterior insula and lateral thalamus and left anterior insula FA correlated with pain unpleasantness. IBS duration correlated with FA in the external capsule adjacent to the left posterior insula. Neuroticism correlated with FA in the left medial thalamus in IBS patients only. Pain catastrophizing correlated negatively to cingulum FA in IBS, whereas controls showed correlation between pain catastrophizing and FA of the external capsule adjacent to the left anterior and posterior insula. Thus, fornix and insular white matter is related to IBS symptoms. These data suggest that dysregulation of brain-gut communication via the neuroendocrine pathway or via abnormal visceral sensory and homeostatic input has a role in the pathology of IBS chronic pain.

Pooled analysis of brain activity in irritable bowel syndrome and controls during rectal balloon distension

BACKGROUND

Brain-imaging literature of irritable bowel syndrome (IBS) suggests an abnormal brain-gut communication. We analyzed the literature to evaluate and compare the aspects of brain activity in individuals with IBS and control subjects experiencing controlled rectal stimulation.

METHODS

PubMed was searched until September 2010. Data from 16 articles reporting brain activity during rectal balloon distensions in IBS compared to control groups was analyzed. Prevalence rates and pairwise activations were assessed using binomial distributions for 11 selected regions of interest. The data were aggregated to adjust for center effect.

KEY RESULTS

There was considerable variability in the literature regarding regions and their activity patterns in controls and individuals with IBS. There was no significant difference found in the thalamus, anterior cingulate cortex, posterior cingulate cortex, and prefrontal cortex, however, results show limited evidence of consensus for the anterior insula (AI) (P = 0.22). Pairwise activity results suggest that pairs involving the AI tend to have more consistent activity together than pairs which do not involve the AI (posterior insula and AI, P = 0.08; posterior cingulate cortex and AI, P = 0.16), however, no pairwise evaluation reached significance.

CONCLUSIONS & INFERENCES

Our pooled analysis demonstrates that the literature reports are quite heterogeneous but there is some evidence that there may be patterns of higher activity more common in individuals with IBS than in controls. A consensus, though, regarding study designs, analysis approach and reporting could create a clearer understanding of brain involvement in IBS pathophysiology.

Asian consensus on irritable bowel syndrome

BACKGROUND AND AIMS

Many of the ideas on irritable bowel syndrome (IBS) are derived from studies conducted in Western societies. Their relevance to Asian societies has not been critically examined. Our objectives were to bring to attention important data from Asian studies, articulate the experience and views of our Asian experts, and provide a relevant guide on this poorly understood condition for doctors and scientists working in Asia.

METHODS

A multinational group of physicians from Asia with special interest in IBS raised statements on IBS pertaining to symptoms, diagnosis, epidemiology, infection, pathophysiology, motility, management, and diet. A modified Delphi approach was employed to present and grade the quality of evidence, and determine the level of agreement.

RESULTS

We observed that bloating and symptoms associated with meals were prominent complaints among our IBS patients. In the majority of our countries, we did not observe a female predominance. In some Asian populations, the intestinal transit times in healthy and IBS patients appear to be faster than those reported in the West. High consultation rates were observed, particularly in the more affluent countries. There was only weak evidence to support the perception that psychological distress determines health-care seeking. Dietary factors, in particular, chili consumption and the high prevalence of lactose malabsorption, were perceived to be aggravating factors, but the evidence was weak.

CONCLUSIONS

This detailed compilation of studies from different parts of Asia, draws attention to Asian patients' experiences of IBS.

Anatomical connections between brain areas activated during rectal distension in healthy volunteers: a visceral pain network

Diffusion Tensor Imaging (DTI) is a promising new imaging method allowing in vivo mapping of anatomical connections in the living human brain. We combined DTI with functional magnetic resonance imaging (fMRI) to investigate the anatomical relationships between areas involved in visceral sensations in humans. Non-painful and moderately painful rectal distensions were performed in 11 healthy women (38.4+/-3.1years). fMRI was used to analyse the changes in brain activity during both types of distension. Then, DTI was applied for tracking fibers between the main activated regions. Non-painful distension bilaterally activated the PreFrontal Cortex (PFC), the Anterior Cingulate Cortex (ACC) and the right insula. Painful distension bilaterally activated the primary (S1) and secondary (S2) somatosensory cortices, the motor cortex, the frontal inferior gyrus, the thalamus, the insula, the striatum and the cerebellum. DTI revealed direct connections between insula, and the four areas more frequently activated in this study, i.e. ACC, thalamus, S1, S2 and PFC. The combined use of fMRI and DTI in healthy subjects during rectal distension revealed a neural network of visceral sensory perception involving the insula, thalamus, somatosensory cortices, ACC and PFC.

Affective neural circuitry and mind-body influences in asthma

Individuals with asthma have twice the risk of developing mood and anxiety disorders as individuals without asthma and these psychological factors are associated with worse outcomes and greater need for medical intervention. Similarly, asthma symptom onset and exacerbation often occur during times of increased psychological stress. Remission from depression, on the other hand, is associated with improvement in asthma symptoms and decreased usage of asthma medication. Yet research aimed at understanding the biological underpinnings of asthma has focused almost exclusively on the periphery. An extensive literature documents the relationship between emotion and asthma, but little work has explored the function of affective neural circuitry in asthma symptom expression. Therefore, the following review integrates neuroimaging research related to factors that may impact symptom expression in asthma, such as individual differences in sensitivity to visceral signals, the influence of expectation and emotion on symptom perception, and changes related to disease chronicity, such as conditioning and plasticity. The synthesis of these literatures suggests that the insular and anterior cingulate cortices, in addition to other brain regions previously implicated in the regulation of emotion, may be both responsive to asthma-related bodily changes and important in influencing the appearance and persistence of symptom expression in asthma.

Neuromodulatory processes of the brain-gut axis

Brain-gut axis represents a complex reflex circuit that integrates the communication between cortex and the digestive system. Disturbances of the neuromodulatory processes in the brain-gut axis generate functional digestive disorders mainly centered on the pain symptoms and motility disorders. This article reviews structural and patho-physiological aspects of the brain-gut axis and explains how the neuromodulatory interventions currently used in order to treat GI conditions related to the brain-gut axis disturbances. The neuromodulation can be realized by pharmacological targeting mainly receptors in the periphery or using electrical stimulation applied at different levels of the nervous system or directly in the muscular layers of the bowels resulting in modulation of the digestive system activity. The efficacy of the methods using electrostimulation is dependent on the parameters of the physical system used: amplitude, frequency, burst time of the electrical current and also the positioning of the electrodes. While pharmacological interventions are largely used at the moment, neuromodulatory interventions involving electrical stimulation showed clinical efficacy in research trials and have promise.

Neural and psychological predictors of treatment response in irritable bowel syndrome patients with a 5-HT3 receptor antagonist: a pilot study

BACKGROUND

Symptom improvement in irritable bowel syndrome (IBS) treatment trials varies widely, with only 50-70% of patients qualifying as responders. Factors predicting treatment responsiveness are not known, although we have demonstrated that symptom improvement with the 5-HT3R antagonist alosetron is correlated with reduced amygdala activity.

AIM

To determine whether neural activity during rectal discomfort or psychological distress predicts symptom improvement following treatment with alosetron.

METHODS

Basal psychological distress and neural activity (15O PET) during uncomfortable rectal stimulation were measured in 17 nonconstipated IBS patients who then received 3 weeks of alosetron treatment.

RESULTS

Greater symptom improvement was predicted by less activity in bilateral orbitofrontal cortex (OFC) and medial temporal gyrus during pre-treatment scans. Lower levels of interpersonal sensitivity predicted greater symptom improvement and were positively related to activity in left OFC. Connectivity analysis revealed a positive relationship between activity in the left OFC and right amygdala.

CONCLUSIONS

Irritable bowel disease symptom improvement with 5-HT3R antagonist alosetron is related to pre-treatment reactivity of the left OFC, which may be partially captured by subjective measures of interpersonal sensitivity. The left OFC may fail to modulate amygdala response to visceral stimulation, thereby diminishing effectiveness of treatment. Psychological factors and their neurobiological correlates are plausible predictors of IBS treatment outcome.

Brain imaging of visceral functions in healthy volunteers and IBS patients

From experience, most people know about a link between psychological processes and gastrointestinal sensory and motor functions. Cognitive processes (e.g., attention) as well as affective processes (e.g., fear) play a role in gastrointestinal sensations in healthy controls and patients with irritable bowel syndrome (IBS) alike. However, the exact nature of this relationship has not been completely understood yet. Brain imaging techniques allow for the study of brain-gut interactions in vivo. Accordingly, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been widely used to study neural mechanisms underlying visceral sensations. This article will summarize the results of functional brain imaging studies in healthy controls and selected studies assessing the influence of psychological processes on gastrointestinal functions. Subsequently, this article will deal with those brain areas activated by visceral stimulation in IBS patients. Special attention will be paid to recently published studies concerning psychological factors and novel research questions.

Sex differences in brain activity during aversive visceral stimulation and its expectation in patients with chronic abdominal pain: a network analysis

Differences in brain responses to aversive visceral stimuli may underlie previously reported sex differences in symptoms as well as perceptual and emotional responses to such stimuli in patients with irritable bowel syndrome (IBS). The goal of the current study was to identify brain networks activated by expected and delivered aversive visceral stimuli in male and female patients with chronic abdominal pain, and to test for sex differences in the effective connectivity of the circuitry comprising these networks. Network analysis was applied to assess the brain response of 46 IBS patients (22 men and 24 women) recorded using [15O] water positron emission tomography during rest/baseline and expected and delivered aversive rectal distension. Functional connectivity results from partial least squares analyses provided support for the hypothesized involvement of 3 networks corresponding to: 1) visceral afferent information processing (thalamus, insula and dorsal anterior cingulate cortex, orbital frontal cortex), 2) emotional-arousal (amygdala, rostral and subgenual cingulate regions, and locus coeruleus complex) and 3) cortical modulation (frontal and parietal cortices). Effective connectivity results obtained via structural equation modeling indicated that sex-related differences in brain response are largely due to alterations in the effective connectivity of emotional-arousal circuitry rather than visceral afferent processing circuits. Sex differences in the cortico-limbic circuitry involved in emotional-arousal, pain facilitation and autonomic responses may underlie the observed differences in symptoms, and in perceptual and emotional responses to aversive visceral stimuli.

Neonatal maternal separation enhances central sensitivity to noxious colorectal distention in rat

Psychological stress experienced in early life plays an important role in the development of visceral hyperalgesia in irritable bowel syndrome (IBS). Neonatal maternal separation has been shown to trigger a long-term alternation in stress-induced responses to visceral nociceptive stimuli in rats. The aim of the present study was to show a direct evidence of stress-induced alteration in central neuronal responses to colorectal distention (CRD) in rats by a quantitative study of c-fos expression in relevant brain structures. Male Wistar rat pups were subjected to 180-min daily neonatal maternal separation (NMS) for 13 consecutive days (from PND 2 to PND 14). The expression of c-fos was examined by using immunohistochemistry. Increased c-fos expression was observed, for the first time, in the cingulate cortex (3-fold) in NMS rats in comparison with the control group at basal condition. At noxious CRD (80 mm Hg), c-fos expression was induced in the supraspinal centers and in both the superficial (laminae I-II) and the deeper laminae (laminae V-VI and X) of the spinal cord in rats. Significantly more Fos-IR nuclei were found in the laminae I and II, and laminae V-VI of the lumbarsacral spinal cord, the paraventricular thalamic nucleus, the cingulate cortex, the amygdaloid central nucleus in NMS rats, but not in the solitary tract, the central medial thalamic nucleus, the ventromedial hypothalamic nucleus, and the periaquaductal gray. The present results indicate that NMS has sensitized the cingulate cortex and upregulated the activity of the ascending pathway at spinal level as well as the thalamo-cortico-amydala pathway to CRD. The upregulation and sensitization of these pathways may be responsible for the development of visceral hypersensitivity in IBS.

Regional cerebral blood flow during gastric balloon distention in functional dyspepsia

BACKGROUND & AIMS

Hypersensitivity to proximal gastric distention as a result of abnormal central nervous system processing of visceral stimuli is a possible pathophysiologic mechanism in functional dyspepsia (FD). Increasing evidence suggests involvement of both lateral and medial pain systems in normal visceral sensitivity and aberrant brain activation patterns in visceral hypersensitivity. We hypothesized that there is involvement of aberrant brain activation in FD with hypersensitivity to gastric distention. Our aim was to investigate regional cerebral blood flow during painful proximal gastric distention in hypersensitive FD.

METHODS

Brain (15)O-water positron emission tomography was performed in 13 FD patients with symptoms of gastric hypersensitivity during 3 conditions: no distention, sham distention, and isobaric distention to unpleasant or painful sensation. Pain, discomfort, nausea, and bloating during maximal distention were rated on visual analogue scales. Data were analyzed using statistical parametric mapping.

RESULTS

The threshold for painful distention was 6.6 +/- 3.8 mm Hg greater than the minimal distending pressure. At the corrected P level of less than .05, subtraction analysis (painful distention - no distention) showed activations in bilateral gyrus precentralis, bilateral gyrus frontalis inferior, bilateral gyrus frontalis medialis, bilateral gyrus temporalis superior, bilateral cerebellar hemisphere, and left gyrus temporalis inferior. Sham distention minus no distention showed no activations.

CONCLUSIONS

Similar to healthy volunteers, proximal stomach distention in FD activates components of the lateral pain system and bilateral frontal inferior gyri, putatively involved in regulation of hunger and satiety. In hypersensitive FD, these activations occur at significantly lower distention pressures. In contrast to findings in normosensitivity, none of the components of the medial pain system were significantly activated.

New insights into the pathogenesis and pathophysiology of irritable bowel syndrome

The pathogenesis and pathophysiology of irritable bowel syndrome is complex and still incompletely known. Potential pathogenetic factors include genes, infectious events, psychological symptoms and other loosely defined environmental factors. Both alterations at the central and peripheral level are thought to contribute to the symptoms of irritable bowel syndrome, including psychosocial factors, abnormal gastrointestinal motility and secretion, and visceral hypersensitivity. Today irritable bowel syndrome is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral abnormalities probably dominating in some patients and disturbed central processing of signals from the periphery in others. Lines of evidence also suggest that inflammation within the gastrointestinal tract may be of great importance in at least subgroups of irritable bowel syndrome patients. To conclude, a complex picture of the pathogenesis and pathophysiology of irritable bowel syndrome is emerging, with interactions between several different alterations resulting in the divergent symptom pattern in these patients.

Functional findings in irritable bowel syndrome

The pathophysiology of IBS is complex and still incompletely known. Both central and peripheral factors, including psychosocial factors, abnormal GI motility and secretion, and visceral hypersensitivity, are thought to contribute to the symptoms of IBS. Several studies have demonstrated altered GI motor function in IBS patients and the pattern differs between IBS subgroups based on the predominant bowel pattern. Few studies have so far addressed GI secretion in IBS, but there are some evidence supporting altered secretion in the small intestine of IBS patients. Visceral hypersensitivity is currently considered to be perhaps the most important pathophysiological factor in IBS. Importantly, several external and internal factors can modulate visceral sensitivity, as well as GI motility, and enhanced responsiveness within the GI tract to for instance stress and nutrients has been demonstrated in IBS patients. Today IBS is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral alterations probably dominating in some patients and disturbed central processing of signals from the periphery in others.

Repetitive rectal painful distention induces rectal hypersensitivity in patients with irritable bowel syndrome

BACKGROUND

A reduced rectal perceptual threshold has been reported in patients with irritable bowel syndrome (IBS), but this phenomenon may be induced by a comorbid psychological state. We evaluated the rectal pain threshold at baseline and after conditioning (repetitive rectal painful distention: RRD) in patients with IBS or functional abdominal pain syndrome (FAPS), which is an abdominal pain disorder, and in healthy controls, and determined whether rectal hypersensitivity is a reliable marker for IBS.

METHODS

The rectal sensory threshold was assessed by a barostat. First, a ramp distention of 40 ml/min was induced, and the threshold of pain and the maximum tolerable pressure (mmHg) were measured. Next, RRD (phasic distentions of 60-s duration separated by 30-s intervals) was given with a tracking method until the subjects had complained of pain six times. Finally, ramp distention was induced again, and the same parameters were measured. The normal value was defined by calculating the 95% confidence intervals of controls.

RESULTS

Five or six of the seven IBS patients showed a reduced rectal pain threshold or maximum tolerable pressure, respectively, at baseline. In all patients with IBS, both thresholds were reduced after RRD load, but they were reduced in none of the patients with FAPS. RRD significantly reduced both thresholds in the IBS group (P < 0.05), but it had no effect in the control or FAPS groups.

CONCLUSIONS

Rectal hypersensitivity induced by RRD may be a reliable marker for IBS. Conditioning-induced visceral hypersensitivity may play a pathophysiologic role in IBS.