Figure 3: Challenges in Translational Research.

Schematic representation of research approaches aimed to identify a causal role of the gut microbiome in human brain and brain gut disorders. There is extensive evidence for cross sectional differences in the gut microbial composition between defined disease populations and healthy control populations (top row). A number of rodent models of human brain diseases have been developed that mimic certain disease aspects (second row from top). More recently, studies have been reported in which fecal microbial transplants from patients with certain brain diseases into germ free mice have resulted in altered mouse behaviors, mimicking some aspects of the human phenotype (middle row). Fecal microbial transplants from healthy human subjects into individuals with brain disorders have not resulted in consistent improvement in respective symptoms to date (second row from bottom). To date, there is limited evidence for the effectiveness of therapeutic interventions targeted at the microbiome (bottom row).