Altered brain responses in subjects with irritable bowel syndrome during cued and uncued pain expectation

BACKGROUND

A majority of the subjects with irritable bowel syndrome (IBS) show increased behavioral and brain responses to expected and delivered aversive visceral stimuli during controlled rectal balloon distension, and during palpation of the sigmoid colon. We aimed to determine if altered brain responses to cued and uncued pain expectation are also seen in the context of a noxious somatic pain stimulus applied to the same dermatome as the sigmoid colon.

METHODS

A task-dependent functional magnetic resonance imaging technique was used to investigate the brain activity of 37 healthy controls (18 females) and 37 IBS subjects (21 females) during: (i) a cued expectation of an electric shock to the abdomen vs a cued safe condition; and (ii) an uncued cross-hair condition in which the threat is primarily based on context vs a cued safe condition.

KEY RESULTS

Regions within the salience, attention, default mode, and emotional arousal networks were more activated by the cued abdominal threat condition and the uncued condition than in the cued safe condition. During the uncued condition contrasted to the cued safe condition, IBS subjects (compared to healthy control subjects) showed greater brain activations in the affective (amygdala, anterior insula) and attentional (middle frontal gyrus) regions, and in the thalamus and precuneus. These disease-related differences were primarily seen in female subjects.

CONCLUSIONS & INFERENCES

The observed greater engagement of cognitive and emotional brain networks in IBS subjects during contextual threat may reflect the propensity of IBS subjects to overestimate the likelihood and severity of future abdominal pain.

Increased attentional network functioning related to symptom severity measures in females with irritable bowel syndrome

BACKGROUND

Increased attention to gastrointestinal (GI) symptoms and disease-specific contexts may play an important role in the enhanced perception of visceral stimuli frequently reported in patients with irritable bowel syndrome (IBS). In this study, we test the hypothesis that altered attentional mechanisms underlie central pain amplification in IBS.

METHODS

To evaluate brain networks that support alerting, orienting, and executive attention, we employed the attention network test (ANT), a modified flanker task which measures the efficiency of functioning of core attentional networks, during functional magnetic resonance imaging in 15 IBS patients (mean age = 31 [11.96]) and 14 healthy controls (HCs; mean age = 31 [10.91]).

KEY RESULTS

Patients with IBS, compared to HCs, showed shorter reaction times during the alerting and orienting conditions which were associated with greater activation of anterior midcingulate and insular cortices, and decreased activity in the right inferior frontal junction and supplementary motor cortex. Patients also showed activation in the dorsal medial prefrontal cortex and concurrent thalamic deactivation during the executive control portion of the ANT relative to HCs, but no group difference in reaction times were found. The activity in brain regions showing group differences during the ANT were associated with measures of GI-specific anxiety, pain catastrophizing, and fear of uncertainty. In IBS, activity in the anterior midcingulate during alerting correlated with duration of GI-symptoms and overall symptom severity.

CONCLUSIONS & INFERENCES

Together, these results suggest that IBS patients have specific abnormalities in attentional network functioning and these deficits may underlie symptom-related anxiety, hypervigilance, and visceral hypersensitivity.

Catecholaminergic Gene Polymorphisms Are Associated with GI Symptoms and Morphological Brain Changes in Irritable Bowel Syndrome

BACKGROUND

Genetic and environmental factors contribute to the pathophysiology of irritable bowel syndrome (IBS). In particular, early adverse life events (EALs) and the catecholaminergic system have been implicated.

AIMS

To investigate whether catecholaminergic SNPs with or without interacting with EALs are associated with: 1) a diagnosis of IBS, 2) IBS symptoms and 3) morphological alterations in brain regions associated with somatosensory, viscerosensory, and interoceptive processes.

METHODS

In 277 IBS and 382 healthy control subjects (HCs), 11 SNPs in genes of the catecholaminergic signaling pathway were genotyped. A subset (121 IBS, 209 HCs) underwent structural brain imaging (magnetic resonance imaging [MRI]). Logistic and linear regressions evaluated each SNP separately and their interactions with EALs in predicting IBS and GI symptom severity, respectively. General linear models determined grey matter (GM) alterations from the SNPs and EALs that were predictive of IBS.

RESULTS

1) DIAGNOSIS: There were no statistically significant associations between the SNPs and IBS status with or without the interaction with EAL after adjusting for multiple comparisons. 2) SYMPTOMS: GI symptom severity was associated with ADRA1D rs1556832 (P = 0.010). 3) Brain morphometry: In IBS, the homozygous genotype of the major ADRA1D allele was associated with GM increases in somatosensory regions (FDR q = 0.022), left precentral gyrus (q = 0.045), and right hippocampus (q = 0.009). In individuals with increasing sexual abuse scores, the ADRAβ2 SNP was associated with GM changes in the left posterior insula (q = 0.004) and left putamen volume (q = 0.029).

CONCLUSION

In IBS, catecholaminergic SNPs are associated with symptom severity and morphological changes in brain regions concerned with sensory processing and modulation and affect regulation. Thus, certain adrenergic receptor genes may facilitate or worsen IBS symptoms.