Psychobiotics is a new field that studies the effect of bacteria (particularly in the gut) on the mind - it is easy to remember times when an upset tummy gave us a headache, and we “felt awful” and in a bad mood. Apparently the gut contains far more bacteria than the body contains cells, they weigh as much as the brain, and they have vast arrays of genes, producing many hundreds of different chemicals which are used in the body, and also many of the molecules used in brain signalling, such as dopamine and serotonin. If mice are raised in a germ free environment with no exposure to bacteria, they become “autistic”. You could say that we have a symbiosis with our gut bacteria – we need them, and they need us, and in certain circumstances, if medical patients lose much of their population of bacteria, they can be treated with Lactobacillus and a range of other probiotics, although some of the commercial ones are not very effective. In extreme cases where the gut ecosystem has broken down, Faecal Matter Transplantation can be carried out, where microbes are transferred from a person with a healthy gut. This is effective in a range of medical conditions, and it is now being investigated whether this could be a useful therapy for neuropsychiatric cases too.