The enteric nervous system that regulates our gut is often called the body’s “second brain.” Although it can’t compose poetry or solve equations, this extensive network uses the same chemicals and cells as the brain to help us digest and to alert the brain when something is amiss. Gut and brain are in constant communication.
“There is immense crosstalk between these two large nerve centers,” says Braden Kuo, MD, MMSc ’04, co-executive director of the Center for Neurointestinal Health at Massachusetts General Hospital (MGH) and assistant professor of medicine at Harvard Medical School. “This crosstalk affects how we feel and perceive gastrointestinal (GI) symptoms and impacts our quality of life.”
Normally, when we see something tasty, the brain signals the gut to prepare for incoming food. When we feel anxious or stressed, we might experience these as abdominal pain, diarrhea, nausea, or “butterflies.” Messages travel from gut to brain, too. This helps explain why, when we eat something that makes us sick, we instinctively avoid the food and even the place we found it.
These everyday activities can go awry when gut nerves are damaged or malfunction. The Center for Neurointestinal Health treats patients with life-altering conditions such as chronic constipation, extreme bloating, and irritable bowel syndrome (IBS). Center physician-scientists also contribute to the exciting basic, clinical, and translational research happening across HMS to understand the gut-brain connection.
For example, Kuo and colleagues are measuring brain activity in patients with chronic nausea using functional MRI, which detects blood-flow changes. Their discovery that nausea and pain involve similar nerve centers has prompted new treatment plans for certain patients, potentially improving their quality of life.
Center researchers are also investigating how the trillions of bacteria in the gut (the gut microbiome) interact with the enteric nervous system (a component of the autonomic nervous system) and ultimately with the central nervous system, notes center co-leader Allan M. Goldstein, MD ’93, Marshall K. Bartlett Professor of Surgery at HMS and chief of pediatric surgery at MGH. “Increasing evidence is showing that bacteria in the gut, and the byproducts they produce, affect mood, cognition, and behavior.”
HMS Instructor in Medicine Kyle Staller, MD ’09, MPH ’15, is studying how abnormal body image and eating disorders in adolescents influence the likelihood of developing IBS and other GI problems in adulthood. These patients, he says, typically perceive normal digestion sensations, like the gut’s expansion with food and stool, as abnormal and may seek a doctor’s help for bloating.
Kuo has also co-led a pilot study that found the “relaxation response,” a state of deep rest induced by practices such as meditation and yoga, helped relieve symptoms in some patients with IBS and inflammatory bowel disease.
With the brain and gut so intertwined, it makes sense for clinicians treating gastrointestinal disorders to include cognitive approaches such as talk therapy, hypnosis, or relaxation response in their recommendations, and for clinicians treating cognitive symptoms to consider what’s happening in the patient’s gut.
Debra Bradley Ruder is a freelance science writer based in Massachusetts.