Neurocognitive Characteristics of Individuals with Irritable Bowel Syndrome

Abstract

In a random community-based telephone survey conducted in Hong Kong, the proportions for the corresponding subtypes were 38%, 20.4%, 6.4%, and 35.2%.2 IBS is a multi-system disorder of the brain-gut axis with multiple biopsychosocial aetiologies.4 Digestive processes are influenced by interactions between hypothalamuspituitary-adrenal (HPA) axis, autonomic nervous system, and inflammatory and central pain modulation systems.5 A core feature of IBS is central visceral hypersensitivity, which is characterised by increased salience and selective attention to sensory input from the gut, descending pain facilitation, impairment of fear conditioning, and extinction learning.6 Interactions of complex systems involving heightened sympathetic output, vagal dysfunction, increased immune activation, increased gastrointestinal epithelial permeability, and reduced gut microbial biodiversity contribute to IBS symptoms and pathophysiology. Frontal Executive Function Working memory was tested using the forward digit span task and Spatial Working Memory task of the Cambridge Neuropsychological Test Automated Battery; no difference was reported between patients with IBS and healthy controls.40,41 The traditional Stroop test was used to evaluate cognitive flexibility and response inhibition, and reported no significant impairment in IBS patients.40-42 Similarly there was no significant impairment in patients with IBS or Crohn's disease (compared with healthy controls) in terms of the Intra-Extra Dimensional Set Shift, but it is uncertain whether most of the IBS patients were of mixed IBS subtype.40 However, IBS patients were found to have increased perseverative errors and set maintenance difficulty (based on the Wisconsin Card Sorting Test) that was associated with reduced dorsolateral prefrontal cortex / pre-supplementary motor area connectivity, implicating impairment in cognitive flexibility.44 The study sample consisted of equal numbers of diarrhoea and constipation predominant types and may explain the discrepancies in executive function, given the heterogeneity in frontal attentional circuits and related physiological parameters in different IBS subtypes. Compatible with learning theory models48 that explain how illness experience can be conditioned with autonomic arousals on subsequent exposures to exacerbate anxiety sensitivity in anxiety disorders, emotional and visceral attentional biases in IBS patients can be understood as the consequence of 'salience computation', as IBS patients developed heightened awareness and sensitivity after recurrent exposure to gastrointestinal symptoms and the associated actual or perceived threats.6 Cold cognitions, especially the frontal executive dysfunction, play a role in the 'top-down' cognitive control of arousal responses in a complex interaction with other brain regions. Anxiety and Depressive Comorbidity Depression and anxiety, on both symptomatic and disorder levels, are common in IBS patients.54 Impairment in cognitive functions in patients with depression, including executive function, episodic memory, semantic memory, visuospatial memory, and information processing speed, has been reported.55-57 Attentional bias for external negative cues is fairly consistent in patients with generalised anxiety disorder.58 Impairment in episodic memory and executive dysfunction has been reported in patients with panic disorder and obsessive-compulsive disorder.59 In IBS studies, self-report anxiety and depressive symptom ratings such as Hospital Anxiety and Depression Scale were commonly used.