 Before Thorazine was invented in 1950, mental illness was often treated surgically. In fact, in 1949 the inventor of the lobotomy was awarded the Nobel Prize. But before tens of thousands were lobotomized, colectomy was all the rage. There was this theory that bad bacteria in the gut, intestinal putrefaction was the cause of mental illness, so the cure was to just surgically remove the colon. Yes, the surgery killed about one in three, but when they didn't die, surgeons bragged that, for example, when he resected the colons of schoolchildren as a preventative measure, there was a cessation of abnormal sex practices, such as masturbation, which was viewed at the time as a precursor for mental illness later in life. There were others, though, that took less drastic approaches, suggesting one could instead treat this intestinal putrefaction by changing the intestinal flora. So over a century ago, there were reports of successfully treating psychiatric illnesses like depression with a dietary regimen that included probiotics. Doctors perceived a connection between depression and feces deficient in quantity and moisture, and very offensive in odor. So they gave people probiotics, and not only did people feel better psychologically, but their feces increased in quantity, became softer, more regular consistency, and the offensive smell diminishes. Concurrent with the probiotics, however, all patients were started on a vegetarian diet, so it may not have been the probiotics at all. This field of inquiry remained dormant for about 100 years, but a new discipline has recently emerged known as enteric, meaning intestinal neuroscience. Our enteric nervous system, the collection of nerves in our gut, has been referred to as our second brain, given its size, complexity, and similarity. We've got so many nerves in our gut that as many as in our spinal cord. It kind of makes sense, the size and complexity of our gut brain is not surprising when considering the challenges posed by the interface with our largest body surface. We have 100 times more contact with the outside world through our gut than through our skin, and we also have to deal with our 100 trillion little friends down there. It takes a lot of processing power. Now, anyone who's gotten butterflies in their stomach knows that our mental state can affect our gut. In fact, everyday stressors can affect the integrity of our gut flora. This innovative study looked at feces scraped from used toilet paper and undergrads during exam week. This is how many bacteria they had in their feces before the exam, but look what happens on exam day, and in fact lasted through the whole week. So our mental state can affect our gut, but can our gut affect our mental state? We didn't know until recently. For example, many suffering from chronic fatigue syndrome complain of gut dysfunction, so researchers tried giving people probiotics to see if their mental and emotional state could be improved, and indeed it appeared to help. What about healthy people, though? This is the study that really rocked the scientific establishment. An assessment of the psychotropic properties of probiotics. One month of probiotics was found to significantly decrease symptoms of anxiety, depression, anger, and hostility. How is that possible? Well, a variety of mechanisms has been proposed for how intestinal bacteria may be communicating with our brain. Until that study was published, though, the idea that probiotic bacteria administered to the intestine could influence our brain seemed almost surreal, like science fiction. Science, yes, but fiction, no. Likely, organisms already inside us carry out some degree of influence on our mental well-being. So, might people suffering from certain forms of mental health problems benefit from a fecal transplant, from someone with a more kind of happy-go-lucky bacteria? We don't know, but this ability of probiotics to affect brain processes is perhaps one of the most exciting recent developments in probiotic research.