Figure 1. Experimental paradigms and readouts of the gut microbiota/brain axis in humans and rodents.

Preclinical studies have used a range of experimental paradigms to study the role of the gut microbiota in gut-brain interactions (blue text). Readouts used in these preclinical studies are listed to the right of the rat brain. Except for GF status, the same experimental paradigms can be used in human studies. In contrast to rodents, subjective responses and structural and functional brain imaging are suitable readouts in human subjects. Notice the considerable difference between the relative proportion of cortical and subcortical structures between the human and rodent brain.