Altered brain spontaneous activity and connectivity network in irritable bowel syndrome patients: A resting-state fMRI study

Clinical Neurophysiology xxx (2014) xxx–xxx

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Clinical Neurophysiology

journal homepage: www.elsevier .com/locate /c l inph

Altered brain spontaneous activity and connectivity network in irritablebowel syndrome patients: A resting-state fMRI study

http://dx.doi.org/10.1016/j.clinph.2014.10.0041388-2457/� 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

⇑ Corresponding authors at: Department of Medical Imaging, Guangdong No. 2Provincial People’s Hospital, Guangzhou 510317, China. Tel./fax: +86 20 8916 8071(G. Jiang). The Medical Imaging Centre, Nanfang Hospital, Southern MedicalUniversity, Guangzhou 510515, China. Tel./fax: +86 20 6278 7333 (Y. Xu).

E-mail addresses: [email protected] (G. Jiang), [email protected] (Y. Xu).1 Xiaofen Ma and Shumei Li contributed equally to this work.

Please cite this article in press as: Ma X et al. Altered brain spontaneous activity and connectivity network in irritable bowel syndrome patients: A rstate fMRI study. Clin Neurophysiol (2014), http://dx.doi.org/10.1016/j.clinph.2014.10.004

Xiaofen Ma a,1, Shumei Li b,1, Junzhang Tian b, Guihua Jiang b,⇑, Hua Wen b, Tianyue Wang a, Jin Fang b,Wenfeng Zhan b, Yikai Xu a,⇑a Medical Imaging Centre, Nanfang Hospital, Southern Medical University, 1838 Guangzhou Ave North, Guangzhou 510515, Chinab Department of Medical Imaging, Guangdong No. 2 Provincial People’s Hospital, No. 1 Shiliugang Road, Haizhu Distinct, Guangzhou 510317, China

a r t i c l e i n f o

Article history:Accepted 1 October 2014Available online xxxx

Keywords:Irritable bowel syndrome (IBS)Amplitude of low-frequency fluctuate(ALFF)Functional magnetic resonance imaging(fMRI)Functional connectivity (FC)Spontaneous neuronal activity

h i g h l i g h t s

� We aimed to provide evidence that brain functional alterations induced by irritable bowel syndrome(IBS) are not limited to local changes but also express at a level of functional integration using resting-state functional magnetic resonance imaging (R-fMRI).

� IBS patients have decreased amplitude of low-frequency fluctuation (ALFF) in cognitive and pain reg-ulatory and somatosensory regions.

� Functional connectivity analysis revealed the increased connectivity between cingulate and frontalcortex in the IBS patients.

a b s t r a c t

Objective: We aimed to provide additional evidence that brain functional alterations induced by IBS arenot limited to local changes but also express at a level of functional integration within related brainregions involved in processing of visceral afferent information and somatic pain.Methods: With fMRI data acquired from 21 IBS and healthy control (HC) subjects. We investigated theamplitude of low-frequency fluctuation (ALFF) and region of interest (ROI)-based functional connectivity(FC) to reveal the changes of the brain spontaneous activity and the interaction among different relatedregions.Results: IBS patients showed decreased ALFF values in the left superior frontal gyrus, right hippocampus,right middle frontal gyrus, bilateral postcentral, and right superior temporal pole, while increased ALFFvalues in the left median cingulate and left calcarine. There was significant correlation between ALFF val-ues in the altered regions and duration of disease in IBS. FC analysis revealed the increased connectivitybetween cingulate and frontal cortex in IBS.Conclusions: Our findings could provide both regional and brain connectivity spontaneous neuronalactivity properties in IBS.Significance: Our study may lead to a better understanding of intrinsic functional architecture of brainactivity in IBS and highlight the potential for using the ALFF and FC metrics as a disease biomarker.� 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights

reserved.

1. Introduction

The irritable bowel syndrome (IBS), characterized by abdominalpain or discomfort, and disturbed defecation, is the most commonfunctional gastrointestinal disorder detected in gastroenterologicalclinics (Cash et al., 2002; Longstreth et al., 2006; Quigley, 2009). Anincreasing number of people worldwide suffer from IBS, which hasevidently been implicated in the quality of daily life. Some psycho-

esting-

http://dx.doi.org/10.1016/j.clinph.2014.10.004

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2 X. Ma et al. / Clinical Neurophysiology xxx (2014) xxx–xxx

logical factors have been believed to play an important role in theintestinal motility abnormalities in patients with IBS, such as stress,anxiety and anger (Murray et al., 2004; Posserud et al., 2004). Previ-ous studies showed that IBS patients have stronger colonic motilityin response to psychosocial stress (Fukudo et al., 1993, 1998). Inaddition, visceral hypersensitivity or decreased pain thresholds tointestinal distension is apparent in many patients with IBS(Murray et al., 2004; Wilder-Smith and Robert-Yap, 2007). Despitethese findings, the neural mechanisms underlying the physiologicalsymptoms in the patients with IBS remain largely unclear.

In the past decade, an explosion of studies using brain imagingtechniques combined with experimental paradigms have demon-strated that alterations in central sensory processing/modulationexist in IBS subjects’ response to visceral stimulation (Silvermanet al., 1997; Mertz et al., 2000; Naliboff et al., 2001; Drossmanet al., 2003; Ringel et al., 2008). Evidence from positron emissiontomography (PET) studies indicates an alteration in activation ofthe anterior cingulate cortex, prefrontal cortex, insular cortex, andother limbic brain regions during colorectal stimulation(Silverman et al., 1997; Naliboff et al., 2001). Mertz et al. found acti-vated regions in anterior cingulate cortex, prefrontal cortex, thala-mus and insular cortex during nonpainful and painful rectaldistension in IBS patients compared with healthy subjects usingfunctional magnetic resonance imaging (fMRI) technique (Mertzet al., 2000). Similarly, Wilder-Smith et al. demonstrated increasedactivity in anterior cingulate cortex, amygdala, hippocampus,insula, and prefrontal cortex in IBS patients during heterotopic stim-ulation (Wilder-Smith and Robert-Yap, 2007). Song et al. investi-gated brain activation patterns using fMRI during stimulation ofendogenous pain-modulating mechanisms in IBS patients andfound some abnormal activation areas, including the frontal lobe,thalamus, anterior cingulated cortex (Song et al., 2006). Althoughthe experimental paradigms vary between previous studies,advanced brain imaging techniques have been shown to be an effec-tive methodology with reproducible results and mainly demon-strate the effects of physiological symptoms on the neural activityof the frontal cortex and limbic brain regions in IBS patients. How-ever, the variations in experimental paradigms would at least par-tially result in the confusion to elucidate the changes of brainactivity due to IBS. In addition, the commonly used task-based fMRIneeds the patients to cooperate and perform specific tasks and it isvery inconvenient in clinics. At last, the majority of functional stud-ies in IBS using task-based fMRI have focused on the brain’sresponse to a stimulus. However, our brain is very active even inthe absence of explicit stimulus because our brain takes only 2% oftotal body mass but consumes 20% of the body’s energy (Raichleand Mintun, 2006; Fox and Raichle, 2007). Thus the studies usingtask-based fMRI in IBS can reveal only a small fraction of the actualbrain functional activity. Therefore, to understand how the brainoperates in IBS, we must consider the component that consumesmost of the brain’s energy: spontaneous neuronal activity.

Resting state fMRI (R-fMRI), unlike complex task-based fMRI, isa promising branch used to measure spontaneous neural activityand is crucial for uncovering the intrinsic brain functional architec-ture. The spontaneous low-frequency fluctuations (LFF) (0.01–0.08 Hz) in fMRI was first observed by Biswal and was consideredto be of physiological importance (Biswal et al., 1995). Concerningthe amplitude of LFF (ALFF), Biswal et al. found that ALFF may besuggestive of regional spontaneous neuronal activity (Biswalet al., 1995). Zang et al. provided the direct measure of ALFF, inwhich the square root of power spectrum was integrated in alow-frequency range (0.01–0.08 Hz), for observing the regionalintensity of spontaneous fluctuations in BOLD signal (Zang et al.,2007). Since the ALFF (0.01–0.08 Hz) in the resting-state fMRI sig-nal are thought to be of physiologic importance and reflect sponta-neous neuronal activity (Biswal et al., 1995; Zang et al., 2007;

Please cite this article in press as: Ma X et al. Altered brain spontaneous activitystate fMRI study. Clin Neurophysiol (2014), http://dx.doi.org/10.1016/j.clinph.2

Zhang and Raichle, 2010a), this method has been widely used ina range of neurologic and psychiatric diseases , such as Alzheimer’sdisease (Wang et al., 2011), severe depression (Jiao et al., 2011),epilepsy (Zhang et al., 2010b), autism (Kennedy and Courchesne,2008) and schizophrenia (Jafri et al., 2008). Thus, the R-fMRI tech-nique based on ALFF analysis would provide a new insight into theneurophysiology of IBS. However, to our best knowledge, therehave been no previous studies that used ALFF to evaluate regionalspontaneous neural activity in IBS patients. Furthermore, regionalbrain dysfunctions alone are not sufficient to reflect the patho-physiology of IBS. Letzen et al. investigated functional connectivityof the default mode network (DMN) and its association with painnetworks in IBS assessed via lidocaine treatment and found lido-caine significantly changed DMN connectivity and affected its rela-tionship with pain-related networks (Letzen et al., 2013). Tofurther explore the corresponding connectivity network relatedto altered ALFF regions, functional connectivity (FC) analysis wasalso applied to elucidate synchronous ultra-slow frequency oscilla-tion between brain areas from an integrated perspective in thisstudy. ALFF and FC have been widely used in several brain disor-ders and provide us information for better understanding thesediseases (Sorg et al., 2007; Yuan et al., 2010a,b).

In this study, we used r-fMRI to explore the changes in bothregional ALFF intensity and brain connectivity between relatedregions in the IBS patients compared with the healthy controls.We hypothesized the following: (1) IBS patients would havealtered ALFF values in the regions associated with visceral afferentprocessing, somatosensory, and emotional arousal; (2) IBS patientswould have mediated changes of connectivity network within thebrain regions related visceral stimulation and somatic pain.

2. Methods

2.1. Subjects

Twenty-one IBS patients (14M/7F, mean age, 41.82 ±11.92 years, length of education, 10.29 ± 3.05 years) were recruitedfrom the Department of Gastroenterology at Guangdong No. 2 Pro-vincial People’s Hospital during the period from August 2011 toJuly 2012. Each patient was evaluated by one or two gastroenterol-ogists who are experienced in the diagnosis of functional gastroin-testinal disorders, and were confirmed as having IBS according tothe Rome III diagnostic criteria (O’Connor et al., 2012). Patientswere included in the study based on the following criteria: (i) noanxiety or depression mood by patient’s self-report; (ii) no historyof drug, alcohol or smoking abuse; (iii) no stroke or cancer relatedbrain lesions or prior substantial head trauma as verified by con-ventional T1 or T2-FLAIR MR imaging; (iv) no known neurologicalillness or psychiatric disease; (V) not take any centrally actingmedications, such as anxiolytics, antidepressants, or pain medica-tions; (VI) according to the Edinburgh Handedness Inventory, allthe IBS patients were right-handed.

In addition, we also recruited twenty-one ages- , hand- and gen-der-matched healthy subjects (11M/10F, mean age, 35.91 ±14.76 years, length of education, 11.48 ± 4.03 years) from the localcommunity as controls by means of advertisements. None of thecontrol subjects had diseases of the digestive system or other organsystems, or any history of psychiatric or neurological diseases. Thestudy was approved by the Ethics Committee of the GuangdongNo. 2 Provincial People’s Hospital. Informed written consent wasobtained from each participant prior to the MR scanning.

2.2. MRI scanning

MRI data were obtained using a 1.5-T MR imager (AchievaNova-Dual; Philips, Best, the Netherlands) in the Department of

and connectivity network in irritable bowel syndrome patients: A resting-014.10.004


X. Ma et al. / Clinical Neurophysiology xxx (2014) xxx–xxx 3

Medical Imaging, Guang Dong No. 2 Provincial People’s Hospital.Each subject lay supine with the head snugly secured by abelt and foam pads. The r-fMRI dataset was acquired with agradient-echo echo planar imaging (EPI) sequence. During r-fMRIscanning, subjects were asked to close and not move their eye(Pierrot-Deseilligny et al., 2004), lie still, not to think of anythingsystematically or fall asleep. The fMRI acquisition parameterswere as follows: TR/TE = 2000 ms/50 ms, matrix = 128 � 128,FOV = 230 mm � 230 mm, flip angle = 90�, slice thickness = 4.5without gap, interleaved scanning, 22 axonal slices covering thewhole brain were positioned approximately along the AC–PC line,and 240 volumes acquired in approximately 8 min. After scanning,all the participants were asked questions to verify their degree ofcooperation.

2.3. Data processing and ALFF calculation

The fMRI data preprocessing was performed using DPARSF(State Key Laboratory of Cognitive Neuroscience and Learning atBeijing Normal University; http://www.restfmri.net/). The first 10time points for each subject were discarded to avoid the instabilityof the initial MRI signal, and to allow subjects to get used to thefMRI scanning noise. The remaining fMRI data were corrected forthe intra-volume acquisition time delay and head-motion (a leastsquares approach and a 6-parameter spatial transformation), thenwere normalized to the standard Montreal Neurological Institute(MNI) template by applying the EPI template at a 3 � 3 � 3 mm3

resolution. No subjects had head motion exceeding 1.0 mm ofmaximal translation and 1 of maximal rotation in any direction.

The resultant normalized functional images were performedspatial smoothing [4-mm full width at half maximum (FWHM)Gaussian kernel) and then removal of linear trends. After removalof linear trends, fMRI data was filtered using typical temporalbandpass (0.01–0.08 Hz) to reduce the very low-frequency driftand high-frequency respiratory and cardiac noise. Six motionparameters, the cerebrospinal fluid (CSF), the global mean signal,and the white matter signals were regressed out as nuisance covar-iates to reduce the effects of head motion and non-neuronal BOLDfluctuations (Yu et al., 2013). ALFF maps was calculated using RESTsoftware (State Key Laboratory of Cognitive Neuroscience andLearning at Beijing Normal University; http://resting-fmri.source-forge.net). The ALFF calculation procedure was the same as thatreported in previous studies (Zang et al., 2007; Zhang et al.,2010b). After band pass filtering and linear trend removal, the timeseries was transformed to the frequency domain with a fast Fouriertransform (FFT). The power spectrum obtained by FFT was squareroot transformed and averaged across the frequency of 0.01–0.08 Hz at each voxel. The averaged square root of activity wastaken as ALFF averaged square root was taken as the ALFF mea-surement. Rather than directly measure the magnitude of BOLDsignal time series in time domain, ALFF calculates the voxel-wiseaverage amplitude of specific frequency bands (0.01–0.08 Hz) ofthe original fMRI signal in the frequency domain. Therefore, theALFF may reflect the intensity of regional spontaneous brain activ-ity spontaneous brain activity in IBS patients. As a robust method,ALFF can reflect the extent of spontaneous neuronal activity andimplicate the underlying pathophysiology under the IBS patients.

2.4. Functional connectivity analysis

Functional connectivity analysis was performed to investigatethe cortical connectivity patterns between seed regions of interest(seed ROI) and the voxels from the whole brain. Three anatomicalROIs were created according to the coordinates defined in REST(Chen et al., 2012), all of which would be shown abnormal ALFFvalues in IBS patients and demonstrated by previous studies


(Wilder-Smith et al., 2004; Labus et al., 2009; Tillisch et al.,2011). We created spherical seeds (diameter = 5 mm) on the basisof our work showing abnormal ALFF values in the left MCG (x = �3,y = �27, z = 48), right MFG (x = 42, y = 15, z = 57) and HIP (x = 18,y = �9, z = �15). All subsequent analyses were performed sepa-rately for the three ROIs. For each subject, FC correlation mapwas calculated respectively for each seed ROI by a voxel-wise mul-tiple-regression. To reduce the effects of head motion or the phys-iological processes, 9 additional covariates (global signal, whitematter, CSF, and 6 motion parameters for head movement) werecomputed and entered in the general linear model. For each ROI,the seed reference time course was acquired by averaging the timeseries of all voxels in the ROI. Correlation analysis was performedbetween time series from the whole brain and the seed referencetime course in a voxel-wise way. Then, the correlation coefficientswere transformed into Z values using Fisher’s transformation toimprove normality.

2.5. Statistics

A two-sample two-tailed t-tests were performed to assess thedifferences in head motions, age, duration of education betweenthe IBS and control groups using SPSS statistics software (version13.0). A two-tailed Pearson chi-square test was performed todetermine the difference in sex between the two groups. Toexplore the ALFF difference between the two groups, a second leveltwo-sample t-test was performed on the individual normalizedALFF maps in a voxel-by-voxel manner. Whole brain analysis wasconducted with statistical threshold of P < 0.05 (Alphasim cor-rected). Moreover, Pearson correlation analysis was adopted toclarify the relationship between the mean ALFF values in all theregions showing significant differences and the duration of diseasein IBS patients. To explore the between-group differences in func-tional connectivity, the zFC maps of brain regions with significantdifferences between two groups were compared across two groupsusing a statistical threshold of P < 0.01 (Alphasim corrected). Atlast, pearson correlation analysis was also adopted to clarify therelationship between stronger connectivity between couple ofregions showing significant differences and the duration of diseasein IBS patients.

3. Results

3.1. Demographics and clinical characteristics of the participants

The demographics and clinical data of the subjects in this studyare shown in Table 1. The HC and IBS group showed no significantbetween-group differences in demographics data including gender,sex, education and age (P > 0.05). In addition, the head motionparameters for shift and rotation were matched between the IBSgroup and healthy control groups in any direction (P > 0.05). Theaverage duration of disease in the IBS group was 4.92 years.

3.2. Alterations of brain regional spontaneous activity in IBS patients

Results of the two-sample t-test showed significant ALFF alter-ations for several related brain regions in IBS patients compared tothe HC groups (P < 0.05, Alphasim corrected) (Table 2 and Fig. 1).We found that the IBS patients showed a decreased ALFF value,with a peak difference in left superior frontal gyrus (SFG.L), righthippocampus (HIP.R), right middle frontal gyrus (MFG.R), bilateralpostcentral gyrus (PoCG) and right superior temporal pole (STG.R),while the IBS patients showed increased ALFF in the left mediancingulate gyrus (MCG.L) and calcarine (CAL.L). In addition, signifi-cant positive correction was observed between the ALFF values


http://www.restfmri.net/

http://resting-fmri.sourceforge.net

http://resting-fmri.sourceforge.net


Table 1Demographics and clinical characteristics of the participants.

Healthy Control IBS P Value

Gender (M/F) 11/10 14/7 0.21a

Age (years) 35.91 ± 14.76 41.82 ± 11.92 0.15b

Education (years) 11.48 ± 4.03 10.29 ± 3.05 0.29b

Disease duration (years) NA 4.92 ± 3.07 NAHead motion (Shift, mm) 0.295 ± 0.184 0.247 ± 0.123 0.33b

Head motion (Rotation, degree) 0.331 ± 0.250 0.240 ± 0.107 0.13b

The disease duration was obtained by 15 patients for the missing disease durationof 6 patients.

a The P value was obtained using a two-tailed Pearson chi-square test.b The P value was obtained using a two-sample two-tail t test.

Table 2Brain regions showing differences in the ALFF between controls and patients with IBS.

Brain regions MNI coordinates Voxels T Value

x y z

Frontal_Sup_L �30 3 66 809 4.29Temporal_Pole_Sup_R 63 9 �3 58 3.68Hippocampus_R 18 �9 �15 56 3.54Postcentral_R 15 �45 75 69 3.45Frontal_Mid_R 42 15 57 65 3.43Postcentral_L �36 �36 69 138 3.40Calcarine_L �9 �99 �12 530 �4.22Cingulum_Mid_L �3 �27 48 58 �3.51

A positive T value represents decreased ALFF in IBS group. L, R: Left and Right.

Fig. 1. Brain regions showing ALFF differences between IBS and HC groups. (A) The regionand sagittal views of the brain regions showing ALFF difference. (C) The regions showingthreshold (Alphasim corrected, P < 0.05). Warm color represents the IBS patients had dincreased ALFF compared with the HC. (For interpretation of the references to colour in



in the MFG.R with the duration of disease, but significant negativecorrection between the ALFF values in the MCG.L with the durationof disease (Fig. 2).

3.3. Alterations of functional connectivity in IBS patients

Three ROIs, MCG.L, MFG.R and HIP.R, were selected as seedregions, which all of them were shown the significant changes ofALFF in IBS patients. Most importantly, previous neuroimagingstudies demonstrated the common findings in these regions, repre-senting core regions related with the visceral sensory abnormali-ties in IBS patients (Wilder-Smith et al., 2004; Mayer et al., 2009;Tillisch et al., 2011). We found that ROI-based functional connec-tivity analysis revealed increased connectivity between the MCG.Land SFG.L in the IBS group compared with HC group (Fig. 3). Theresults of the functional connectivity showed that the MFG.R inIBS group have increased connectivity with the SFG.L and left pos-terior cingulate gyrus (PCG.L), while decreased connectivity withthe right superior parietal gyrus (SPG.R) and left rectus (REC.L)compared with the HC group (Fig. 3). As for the ROI of HIP.R, no sig-nificant changes of connectivity were found between the IBSpatients and control group after the Alphasim correction(P < 0.05). No significant correlations between the stronger func-tional connectivity and duration of the IBS patients reached signif-icance (correlation coefficient for SFG.L and MFG.R: r = 0.095,p = 0.68; correlation coefficient for PCG.L and MFG.R: r = 0.196,p = 0.40).

s showing ALFF differences display in whole-brain rendering. (B) The axial, coronalALFF differences in axial map from Z = �20 to Z=+76 mm (every 4 mm) at the givenecreased ALFF compared with the HC; Cold color represents the IBS patients hadthis figure legend, the reader is referred to the web version of this article.)



Fig. 2. Relationship between the disease duration and the ALFF values in altered regions in IBS group. From the figure, we can see the significantly negative correlationbetween the ALFF values in the MCG.L and the disease duration; The ALFF values in the MFG.R have significantly positive correlation with the disease duration. There was nocorrelation between the disease duration and other altered ALFF regions in IBS group.


4. Discussion

4.1. Alterations of regional spontaneous activity in IBS patients

The altered ALFF value indicates the abnormal regional activityin the IBS patients. We found significantly increased ALFF values inthe left median cingulum in the IBS patients (Fig. 1 and Table 2).Previous functional neuroimaging studies have found that the cin-gulate cortex is a central player in the neural network governingsomatic and visceral pain. Verne et al. reported that visceral stim-ulation (rectal distension) and somatic pain (cutaneous heat)evoked greater neural activity in several brain regions of IBSpatients, including insular, cingulate cortex (Verne et al., 2003).Mertz et al. studied 18 IBS patients and 16 healthy subjects duringnonpainful and painful rectal distension using fMRI and foundhigher activation of the anterior cingulate cortex during painfulstimulation compared to the controls (Mertz et al., 2000). A quan-titative meta analysis study related to IBS during pelvic visceraldistension have found common increased regional activity in mid-dle cingulate cortex and insula (Labus et al., 2009). Across thesestudies, there were consistent greater activations in cingulate cor-tex associated with visceral stimulation and somatic pain arousal.Using r-fMRI, our current study also found abnormally increasedALFF values in the median cingulum, which implies that resting-state functional increase in IBS patients could be associated withfunctional improvement in pain-processing due to suffering froma long-term somatic and visceral pain. In addition, The ALFF valuein the left median cingulum was negatively related to the diseaseduration, indicating that the longer illness, the lower ALFF valueof the left median cingulum. The gradually decreased ALFF values


in the left median cingulum may suggest that the IBS patientsadapt to the long-term somatic and visceral pain.

Previous studies have shown that IBS group shows smaller reli-able activation primarily in cortical regions involved in modulationof pain as well as attention, including lateral prefrontal cortex,medial prefrontal cortex, and hippocampus and supramarginalgyrus (BA 40) (Bishop et al., 2004; Banks et al., 2007; Schilleret al., 2008). Coen et al. found that prefrontal areas activity undervisceral pain is reduced in a working memory task acting as a dis-tractor in comparison with no distractor, suggesting a cognitiverole of visceral pain in this region (Coen et al., 2008). Aizawaet al. adopted event-related fMRI to evaluate cognitive flexibilityand found IBS patients showed significantly decreased activity ofthe right prefrontal areas and right hippocampus (Aizawa et al.,2012). The hippocampus plays an important role in inhibitingstress responses via hypothalamic regulation, and increased expo-sure to adrenal glucocorticoids can accelerate hippocampal neuronloss and cognitive impairments in aging (Meaney et al., 1988). Thehippocampus contains high levels of glucocorticoid receptors,which make it more vulnerable to long-term stress than mostother brain areas (Joels, 2008). Similar to previous studies, the cur-rent study also found decreased ALFF values in the SFG.L, MFG.Rand HIP.R in the IBS patients (Table 2 and Fig. 1). These regionsare cognitive and pain modulatory brain areas, thus our resultsof lower regional activity in these regions could be related to cog-nitive impairments and weak pain regulation in the long-term vis-ceral sensory abnormalities. Moreover, The ALFF value in theMFG.R was positively related to the disease duration, indicatingthat the longer illness, the greater ALFF value of the MFG.R. Thegradually increased ALFF values in the MFG.R may suggest that



Fig. 3. Functional connectivity differences in the DCG.L and MFG.R between IBS patients and healthy controls. The warm color represent increased connectivity in the IBSpatients group; the cold color represent decreased connectivity in the IBS group patients (Alphasim corrected, p < 0.01). (For interpretation of the references to colour in thisfigure legend, the reader is referred to the web version of this article.)


the IBS patients can effectively modulate the pain evoked by along-term abnormally abdominal pain or discomfort.

The postcentral gyrus is the location of the primary somatosen-sory cortex, the main sensory receptive area for the sense of touch.Song et al. studied abnormal visceral pain processes in IBS patients,by means of fMRI scanning during the following randomized stim-uli: sham and painful rectal distensions using a barostat, with andwithout simultaneous activation of endogenous descending noci-ceptive inhibition using ice water immersion of the foot for hetero-topic stimulation. The above study found that greater activationduring rectal plus heterotopic versus rectal stimulation was seenbilaterally in postcentral and the right superior temporal gyrus incontrols (Song et al., 2006). The postcentral region, secondary(S2) somatosensory cortices, thalamus and prefrontal cortex areknown to process nociceptive information and interception andare most commonly observed to have different activationsbetween the IBS patients and healthy controls (Seminowicz et al.,2010). Thus, it is plausible for us to demonstrate that IBS patientscan impair the left postcentral, which may be responsible for thedisturbed defecation in IBS group.

We also found significantly increased ALFF values in the left cal-carine in the IBS patients (Fig. 1 and Table 2), which was notreported in the previous studies. The exact relationship between


the left calcarine and symptoms in IBS patients was not clear. Inthe opinion of the authors, the findings pertaining to this shouldbe interpreted more cautiously and need more further studies witha large sample size and behavioral evidence.

4.2. Enhanced connectivity network between the cingulate and frontalcortex in IBS patients

The FC approach provides insight into how brain regions worktogether as networks and how these networks can becomestrengthened or weaken in IBS patients. Our study found increasedconnectivity between the MCG.L and SFG.L in the IBS group (Fig. 3).As for the ROI of MFG, we found increased connectivity with theSFG.L and PCG.L in the IBS patients (Fig. 3). From our results, wefound that the increased connectivity network mainly appearbetween the cingulated and frontal cortex (MCG-SFG, PCG-MFG,SFG-MFG). As explained above, previous studies have shown thatthe superior frontal gyrus involved in cognitive modulation, painas well as attention. Besides, it has been demonstrated that theSFG can influence the descending pain modulatory system, notablythrough the modulation of brainstem structures participating inpain modulation (Lorenz et al., 2003; Wager et al., 2004). ThePCG is a central node in the ‘‘default mode’’ network of the brain.




The imaging studies indicate a prominent role for the PCG in painand response to sensory stimuli (Vogt et al., 1992; Nielsen et al.,2005). From our results, we found decreased ALFF values in theSFG.L, MFG.L, which may suggest functional decline in terms ofcognitive functions in IBS patients, while the ALFF value of MCGrelated to pain-processing increased in IBS patients. The increasedconnectivity between the MCG.L and SFG.L, and between PCG.L andMFG.R suggest a elevated synchronization of the connectivity net-work between cingulated and frontal cortex, which may indicate aheightened monitoring of somatic and visceral pain in the IBSgroup through a balanced modulation between cingulated andfrontal cortex. These functional connectivity changes show thecharacteristics of neural activity in IBS patients from the level offunctional integration within related brain regions involved in pro-cessing of visceral afferent information and somatic pain.

Additionally, FC analysis found the right MFG have decreasedconnectivity with SPG.R and REC.L in IBS group (Fig. 3). Decreasedconnectivity between the MFG.R with the SPG.R and REC.L was firstreported in our study. Parietal cortex is considered to be engagedin distinct attention functions such as attention shift, visuo-spatialattention, working memory (Blakemore and Frith, 2005). Previousstudies have suggested that the gyrus rectus may be part of a cir-cuit that mediates some specific emotional functions in humans(Andreasen et al., 1995; Bremner et al., 2002). The decreased con-nectivity may reflect disruption in the network due to the pathol-ogy characteristic in the IBS patients.

4.3. Considerations

Some limitations in the current study are worth mentioning.First, the number of participants in our study is relatively small;a further study including more datasets is needed. We performedmultiple corrections to remedy the first limitation to prevent riska high rate of false positives. Second, this study is a cross-sectionpreliminary study and the experiment cannot per se provide longi-tudinal alteration data on the IBS patients. A future study involvinglong-term longitudinal follow-up with detailed experimental andclinical profiling of a cohort of subjects is required. Third, thepsychological backgrounds of our IBS patients are acquired fromself-report, it would be better to use the structured psychologicalquestionnaires to obtain these information.

5. Conclusion

We found that IBS patients have increased resting-state sponta-neous neuronal activity in visceral afferent processing relatedregions including the left median cingulate and left calcarine, whiledecreased regional brain activity in cognitive and pain regulatoryregions, including the left superior frontal gyrus, right hippocam-pus, right middle frontal gyrus, bilateral postcentral. Importantly,the functional connectivity analysis revealed increased connectiv-ity network between the cingulate and frontal cortex. Our findingsrevealed the alterations of regional brain activity and brain connec-tivity network between the related regions, which may suggest thepossibility of a functional imaging biomarker for IBS. The resting-state fMRI study suggests that the changed spontaneous neuronalactivity of these regions and the corresponding network may beimplicated in the underlying pathophysiology of IBS.

Acknowledgments

The authors thank the PhD Queenie Chan from the clinicalscience manager, MR and Philips healthcare, Greater, China fortechnical support and advice. This work was supported byGuangdong provincial science and technology (Grant Numbers:


2010B031600116 and 2011B031800044), and the National NaturalScience Foundation of China (Grant Number: 81471639).

Conflict of interest: All the authors have no relevant conflicts ofinterest to disclose.

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Altered brain spontaneous activity and connectivity network in irritable bowel syndrome patients: A resting-state fMRI study