Table 1

Brain network alterations in IBS

Default mode network (DMN)	Brain regions	Medial frontal cortex, posterior cingulate or retrosplenial cortex, precuneus, inferior parietal cortex, lateral temporal cortex and hippocampal formation.
	Function	Self-awareness processing. Episodic memory. Monitoring internal thoughts, external goals and future planning.
	Alterations in IBS	Altered functional connectivity and topological reorganisation in various regions, consistent with the network’s dysregulation in chronic visceral pain.148 Higher amygdala and dorsal anterior insula (INS) functional connectivities within DMN in hypersensitive IBS.149
	Sex difference	No reported sex difference in IBS to date.
Sensorimotor network	Brain regions	Thalamus, basal ganglia, sensorimotor cortex and posterior INS.
	Function	Central processing and modulation of visceral and somatic sensory information.
	Alterations in IBS	Increased frequency power of spontaneous brain oscillations.40 Widespread microstructural white matter changes.150 Female IBS greater volume and cortical thickness, correlated with symptom severity.65 147 Greater grey matter in posterior INS, correlated with symptom duration.99 Anterior cingulate and thalamus are hubs in structural network analysis.65 Coupling of cingulate gyrus with thalamus.65
	Sex difference	Higher cortical thickness in sensorimotor cortex in female IBS.147 Lower integrity of sensorimotor region tracts in female IBS.150 Lower fractional anisotropy and mean diffusivity in globus pallidus in female IBS.150
Salience network	Brain regions	Dorsal anterior cingulate cortex (ACC) and anterior INS.
	Function	Response to subjective experience or expectation of any interoceptive and exteroceptive stimulus. Coordination of the appropriate attentional, behavioural, affective and visceral responses to such stimuli.
	Alterations in IBS	Greater engagement of anterior INS and anterior midcingulate cortex in response to actual and expected rectal distension.2 151 Increased affective, central, emotional-arousal processes as well as enhanced visceral stimulus perception.130 152 153 Alterations in the activity and connectivity of anterior INS in women both during the resting state40 145 and abdominal pain threat.146
	Sex difference	Greater pain-related INS response in male IBS.154 155 Greater pain-related ACC response in female IBS.156 More prominent alterations in the connectivity between INS and DMN in female IBS.43 Lower subgenual ACC cortical thickness in female IBS.147 Greater mean diffusivity in cingulate white bundles in female IBS.150
Emotional arousal network	Brain regions	Amygdala, hippocampus, hypothalamus, posterior ACC and subgenual cingulate (sgACC).
	Function	Activated by perceived or real disruption in homeostasis. Generation of rapid feedback inhibition of amygdala, thereby limiting the magnitude and duration of network activity and related activity in the central autonomic network.
	Alterations in IBS	Decrease in inhibitory feedback loop104 152 154; also seen in healthy controls whose central serotonin levels were lowered by acute tryptophan depletion.157 Increased responsiveness to both expected and delivered visceral stimuli in females.158–167 More consistent activation in response to controlled rectal distension.12 Reactivity associated with serotonin (5-hydroxytryptamine)-related gene polymorphisms.49 Functional alterations are accompanied by structural brain alterations.65
	Sex difference	Greater emotional-arousal reactivity and altered connectivity in female IBS.156 168 Greater emotional-arousal reactivity to specific stimuli (faces depicting fear and anger) in male IBS.154
Central autonomic network	Brain regions	Control centres in the pontine-medulla (including periaqueductal grey (PAG) and hypothalamus), the central nucleus of the amygdala and several cortical regions (including the anterior INS, ACC and prefrontal and motor regions).
	Function	Central control and modulation of the autonomic nervous system. Regulation of respiratory, cardiovascular, endocrine and digestive activities during cognitive, affective, and motor tasks and sensations.
	Alterations in IBS	Alterations in the corticotropin releasing factor (CRF) and CRF receptor 1104 105 and norepinephrine–adrenergic receptor signalling system.169
	Sex difference	Greater activation of dorsolateral prefrontal cortex, INS and dorsal pons/PAG in response to visceral stimulus in male IBS.156 Greater activation of ventromedial prefrontal cortex, right anterior cingulate cortex and left amygdala in response to visceral stimulus in female IBS.156
Central executive network	Brain regions	Lateral prefrontal cortices and posterior parietal cortex.
	Function	Activated during tasks involving executive functions such as attention, working memory, planning and response selection. Often coactivated with regions of the salience network, as the brain attempts to focus its limited processing capacity to only salient information via attention, working memory, planning and response selection.
	Alterations in IBS	Deficient activation of inhibitory cortical regions involved in downregulation of pain and emotion as well as attention during expectation and experience of aversive GI stimuli.12 Selective recall of negative and GI sensation words, as well as selective attention to threat-related stimuli.170–173 Reduced effective connectivity during repeated exposure to the anticipation and experience of a threatening GI stimulus, which was linked to was linked to a reduction in IBS hypersensitivity.174 Altered error feedback mechanisms linked to decreased dorsolateral prefrontal cortex activity in Japanese patients with IBS.16 Strong negative association between the cortical thickness and grey matter density of the dorsolateral prefrontal cortex and pain catastrophising.85 175 Altered prepulse inhibition (a process by which an organism can filter the flow of information from its internal and external environments).41
	Sex difference	No reported sex differences in IBS to date.