Table 2.

Main Findings of the Systematic Review Divided up by Brain Areas

Network	Main findings
Sensorimotor network	Resting state: S1 hypoactivation, M1 hyperactivation, increased FC between S1 and thalamus, and aberrant FC between the sensorimotor network and affective-interoceptive areas (amygdala and insula in particular). H-IBS showed increased FC between sensorimotor network and pINS, compared to N-IBS.
Affective and interoceptive areas	Resting state: aberrant FC between the cingulate and the frontal cortices, and between amygdala, insula, sensorimotor network, and hippocampal/para-hippocampal gyri. Amygdala: hyperactivity at resting state; aberrant activation during fear acquisition and during the formation of abdominal pain-related memories. Higher FC of R amygdala positively correlated with pain intensity and decreased gut permeability; FC between L amygdala, bilateral insula, and midbrain positively correlated with symptom severity. Bilateral INS: aberrant activation and FC with limbic and cortical areas at resting-state and during painful and nonpainful rectal distention. R INS: aberrant activation correlated with pain intensity. L INS: abnormal activation correlated with symptom severity and interoceptive awareness; aINS hyperactive during pain anticipation.
Attentional areas	Resting state: decreased activity of the DMN. Rectal stimulation: ACC and PFC hyperactivity. Pain anticipation: mPFC and MFG aberrant activation. Painful distension: greater stress-induced activation in insula and VLPFC, and hypoactivation of DLPFC and subgenual ACC. History of adverse life event was associated with altered FC in the salience network and in the executive control network. Regions of the salience network (MCC, MTG, and STG) were positively correlated with proinflammatory genes (IL-6 and APOL2).

S1, primary somatosensory cortex; M1, primary motor cortex; FC, functional connectivity; H-IBS, hypersensitive IBS; pINS, posterior insula; N-IBS, normosensitive IBS; INS, insula; R, right; L, left; aINS, anterior insula; DMN, default mode network; ACC, anterior cingulate corte; PFC, prefrontal cortex; mPFC, medial prefrontal cortex; MFG, middle frontal gyrus; VLPFC, ventrolateral prefrontal cortex; DLPFC, dorsolateral prefrontal cortex; MCC, mid-cingulate cortex; MTG, middle temporal gyrus; STG, superior temporal gyrus; APOL2, apolipoprotein L2 gene.