Although philosophers and scientists have mused over the relationship between mind and body for millennia, modern research on the workings and dysfunctions of the mind has tended to focus on the central nervous system (CNS), composed of the brain and the spinal cord. If something is going wrong with behavior or thought, it follows that the problem likely stems from some anomaly in the CNS, which itself drives behavior and thought. Autism, depression, and anxiety disorder are but three of hundreds of poorly-understood conditions that have been predominantly studied through the lens of the CNS, to nearly no avail. But a growing minority of researchers and medical practitioners is finally making serious headway into developing treatments for some of these maladies, by zooming out from an exclusive focus on the CNS, and shifting the spotlight to the lesser-appreciated, so-called ‘second brain’: the gut.

The brain communicates with the gut via the enteric nervous system.

At first glance, the gut, which is regulated by a large collection of neurons known as the enteric nervous system, has little to do with one’s mental state. Sure, your appetite reflects some interplay between your conscious tasty wants and your subconscious nutritional needs, but beyond digestion, why would the state of the stomach affect the state of the mind? Give it a few more seconds to sink in. Shouldn’t take long. I know I’m not the only person who gets moody and distractible when he’s underfed. Put my digestive system into a state of panic, and you might as well have set off a figurative fire alarm in my brain.

Psychiatrists themselves have long noticed that their patients often suffer from gastrointestinal problems. With the advent of biological psychiatry in the mid-20th century, however, psychiatrists overwhelmingly turned to psychiatric drugs to treat their patients. Yet none of these drugs proved to be a panacea for their intended conditions, and the need for reliable psychiatric treatments has remained, if not grown. Millions of psychiatric patients continue to under- and over-eat, or spend days constipated or on the verge of diarrhea or vomit, to say the least of what might happen if your gut were to malfunction. Moreover, the enteric nervous system contains more neurons than your spinal cord, and produces 95% of the serotonin, and 50% of the dopamine, found in your body. Both serotonin and dopamine are neurotransmitters better known for their roles in the brain, and for their associations with mental illness – perhaps the presence of neurotransmitters in both the brain and the gut is more than coincidence, just like the comorbidity of mental illness with GI dysfunction.