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IIn the 1800s, Alexis St. A French Canadian named Martin was shot in the stomach when someone’s rifle accidentally fired at close range while he was at a fur trading post. He survived, but his injuries caused a hole in his stomach wall. This literally provided an early window into how our emotions and mental health affect the gut. After careful experiments, surgeon William Beaumont discovered that St. He discovered that Martin’s mental state had direct physiological consequences on his stomach activity: when he felt irritable, for example, his digestion slowed down. Somehow their emotional states were manifested in the specific, local biology of their gut.
Most people have experienced the visceral consequences of their emotional feelings. Nerves before the exam may cause you to feel nauseous or even vomit. Deep sadness can cause you to lose your appetite or perhaps lead to a hunger that is impossible to satisfy. Gut symptoms are common in mental health conditions, from depressed appetite changes to debilitating “psychosomatic” stomach pains. Most of our emotions are instinctive feelings.
But the gut not only reacts to emotional feelings, it also influences them. Get disgusted. Disgust is instinctive. Our stomach, like our heart, has a regular electrical rhythm; even just to see Something nasty causes distortions in this electrical signal called “dysrhythmias.” Although disgust is crucial for survival (helping us avoid and survive illness), in many mental health conditions disgust becomes pathological. For example, in obsessive-compulsive disorder (OCD), dirt or germs can occupy a person’s thoughts and cause symptoms such as compulsive hand washing. Self-disgust is common in depression and eating disorders. And even post-traumatic disorder can result from extremely heinous traumas.
Pathological disgust is particularly difficult to treat: Exposure therapy and other psychological approaches are much less effective than for fear-based mental health problems. A few years ago, while working as a neuroscientist at the University of Cambridge, I wondered whether abnormal signals from the stomach caused disgust avoidance. I conducted an experiment to test this hypothesis and found that manipulating one’s bowel activity with a commonly used anti-nausea medication reduced disgust aversion. This may represent a new way to treat pathological disgust in mental health disorders. For example, an anti-nausea medication can be administered immediately before exposure therapy, allowing patients to participate in treatment under a more optimal gut condition.
Read more: How Did I Learn to Listen to What My Instincts Tell Me?
So gut feelings aren’t “all in your mind”—but they’re also not “all in your gut.” Sensations from the gut are transmitted to the brain via the vagus nerve, which is the primary channel of information sent from the body to the brain. The second way to target “gut feelings” is through electrical stimulation of this nerve, which changes the electrical rhythm of the stomach. However, the idea is not new: vagus nerve stimulation for patients with major depression dates back to 2000.
A new theory published in November 2023 suggests that vagus nerve stimulation strengthens signals from the inside of the body to the brain, which helps us adapt our behavior to current challenges and needs. This may explain why the effects of vagus nerve stimulation are so far-reaching, altering learning, memory and motivation. This means that enhancing signals from the gut using vagus nerve stimulation may improve mental health in some cases, but may be ineffective or even harmful in others. After all, before increasing the body’s influence on the brain, we need to take into account the state and needs of the person’s internal body.
But the importance of the vagus nerve extends to even more established treatments: Evidence from mice suggests that the most common type of antidepressant drugs (SSRIs, or selective serotonin reuptake inhibitors) require the vagus nerve to work. This may begin to provide clues as to why antidepressants may or may not work for a particular person, and may even help us understand why they may cause side effects in some people.
If the role of the vagus nerve is to help us tune in to our bodily needs, perhaps the most important internal need is energy. One function of the intestines, along with other organs, is metabolism, which converts food into energy that the body can use. There are mysterious and far-reaching connections between our metabolic system and our mental health. For example, the prevalence of depression in people with diabetes is two or three times higher than in the general population. It’s not clear why: Diabetes may increase the risk of depression and vice versa. My laboratory is currently testing a third possibility: common metabolic factors may increase your risk of both depression and diabetes due to interactions between the body and brain. If we’re right, this could open pathways to metabolic interventions that improve both physical and mental health.
Our brain and broader nervous system adapt to its circumstances, including the body’s internal metabolic needs as well as our experience of the environment around us. Therefore, your gut-brain connection is not static, it changes and adapts over time. A fascinating study from 2021 discovered that brain cells can reactivate gut inflammation an animal had previously experienced. Just the “memory” of intestinal inflammation stored in cells in the brain triggered the physical condition in the body. So sometimes the “gut feeling” actually originates from the brain. This role of the brain in “gut feelings” means that our brain has the capacity to produce dysfunctional gut symptoms through brain changes alone. This ability of the brain may also have positive aspects; Perhaps it could explain why psychological therapy that induces brain changes can treat some gut disorders.
Gut feelings arise from many sources: directly from the gut, from the communication channels between the gut and the brain, and even from the brain itself. In neuroscience, as we unravel the dynamic communication between the gut and the brain, we can begin to understand how these processes helped our ancestors survive and how we can better use them to improve emotional and mental health. A gut feeling can have many possible causes, but each represents a potential solution for mental health.
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