The immunology of mind control – exploring the relationship between the microbiome and the brain - part 1 In this series of articles, the relationship between the human species and the human gut microbiome will be evaluated to determine if it is symbiotic, parasitic or somewhere in between. The possibilities, based on animal studies, are explored and compared to studies in human beings. In particular, close attention is paid to the relationship between the gut microbiome and the central nervous system, especially its effect on human behaviour. This relationship is termed the ‘microbiome–gut–brain axis’. The gut microbiome has an influence on stress (both acute and chronic), anxiety, loneliness and depression, through a number of pathways. It has also been associated with the development of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, with associated cognitive decline. The concept of ‘mind control’ of human beings by organisms in the microbiome is relatively new, but has been demonstrated with multiple examples in the animal kingdom. Therefore, it is not surprising that certain components of the microbiome have also been associated with the development of schizophrenia. Since the common treatments used for these conditions are not equally effective in all patients, it is vital for clinicians to explore other avenues to be used as therapeutic targets. Recent research has also evaluated the impact of vitamin D and olfaction on the brain, and its possible use as adjunctive therapy. The gut microbiome, in particular, requires further research to aid in the development of future therapies for certain conditions. Animal studies in this regard have shown promising results, but human studies are infrequent, often with disappointing results. Randomised control trials in human beings are required to prove or disprove the effects of the gut microbiome on complex psychiatric diseases.