J Neurogastroenterol Motil  
Understanding Neurogastroenterology From Neuroimaging Perspective: A Comprehensive Review of Functional and Structural Brain Imaging in Functional Gastrointestinal Disorders
Michiko Kano,1,2,3* Patrick Dupont,4 Qasim Aziz,5 and Shin Fukudo2,3
1Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University, Sendai, Japan; 2Behavioral Medicine, Graduate School of Medicine, Tohoku University, Sendai, Japan; 3Psychosomatic Medicine, Tohoku University Hospital, Sendai, Japan; 4Laboratory for Cognitive Neurology, KU Leuven, Belgium; and 5Center for Digestive Diseases, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary College, University of London, UK
Correspondence to: Michiko Kano, MD
Frontier Research Institute for Interdisciplinary Sciences (FRIS), Behavioral Medicine, Graduate School of Medicine, Tohoku University, 2-1 Seiryo, Aoba, Sendai, Japan
Tel: +81-22-717-8218, Fax: +81-717-8161, E-mail address: mkano@med.tohoku.ac.jp
Received: April 10, 2018; Accepted: May 21, 2018; Published online: July 24, 2018.
© The Korean Society of Neurogastroenterology and Motility. All rights reserved.

cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
This review provides a comprehensive overview of brain imaging studies of the brain-gut interaction in functional gastrointestinal disorders (FGIDs). Functional neuroimaging studies during gut stimulation have shown enhanced brain responses in regions related to sensory processing of the homeostatic condition of the gut (homeostatic afferent) and responses to salience stimuli (salience network), as well as increased and decreased brain activity in the emotional response areas and reduced activation in areas associated with the top-down modulation of visceral afferent signals. Altered central regulation of the endocrine and autonomic nervous responses, the key mediators of the brain-gut axis, has been demonstrated. Studies using resting-state functional magnetic resonance imaging reported abnormal local and global connectivity in the areas related to pain processing and the default mode network (a physiological baseline of brain activity at rest associated with self-awareness and memory) in FGIDs. Structural imaging with brain morphometry and diffusion imaging demonstrated altered gray- and white-matter structures in areas that also showed changes in functional imaging studies, although this requires replication. Molecular imaging by magnetic resonance spectroscopy and positron emission tomography in FGIDs remains relatively sparse. Progress using analytical methods such as machine learning algorithms may shift neuroimaging studies from brain mapping to predicting clinical outcomes. Because several factors contribute to the pathophysiology of FGIDs and because its population is quite heterogeneous, a new model is needed in future studies to assess the importance of the factors and brain functions that are responsible for an optimal homeostatic state.
Keywords: Dyspepsia; Homeostasis; Irritable bowel syndrome; Neuroimaging; Visceral pain


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