Gut Brain Axis (GBA): is the biochemical signaling that takes place between the gastrointestinal tract (GI tract) and the central nervous system (CNS). The term "gut-brain axis" is occasionally used to refer to the role of the gut flora in the interplay as well, whereas the term "microbiome-gut-brain axis" explicitly includes the role of gut flora in the biochemical signaling events that take place between the GI tract and CNS.