For more than 100 years, scientists have known that the vagus nerve carries signals between the organs and the brainstem. As part of the parasympathetic nervous system (rest & digest mode) the vagus regulates functions like heart rate, breathing, and digestion. But new studies have shown signals carried by vagal fibers climb beyond the brainstem, revealing a broad interoceptive network in the brain that interprets internal changes, anticipates the body’s needs, and sends commands to fulfill them. This network includes brain regions involved in more complex cognition. This means the nerves monitoring the basic functions of the body are tightly interwoven with how we remember, process emotion, and even construct our sense of self.
New Research
New techniques for mapping the vagus nerve’s connections and components have revealed new cell types including 37 types of sensory neurons which detect things like stretch, pressure, toxins, and nutrients. These neurons produce signals that may play a role in shaping mood and memory.
Efforts to map the vagus nerve to date have identified a “staggering diversity” of vagal cell types in rodents, including cells that control breathing, trigger coughing, sense changes in blood pressure and oxygen, and detect nutrients in the digestive system. The discovery of vagal-connected cells in the brainstem that trigger nausea could lead to more tolerable chemotherapies that avoid stimulating those nerve pathways. Yet another recently discovered neural pathway seems to indicate a mutual connection between emotional processing and digestion.
Interoception
As the vagus nerve’s role in interoception, or the ability to sense internally, continues to be investigated, one of the questions scientists are asking is whether it’s a positive or a negative to have higher interoceptive awareness. One theory is that people with conditions like generalized anxiety disorder or irritable bowel syndrome may be hyperfocused on sensations from their bodies. If true, specific cognitive training may be effective treatment.
New Therapies
New discoveries surrounding the vagus nerve have also led to new treatments and therapies for conditions such as epilepsy and depression. Vagus nerve stimulation (VNS), which delivers pulses of electricity to the vagus through a device implanted under the collarbone, has been approved to treat these conditions. Similar therapies using an ear-worn VNS device are being tested for use in treating Rheumatoid Arthritis and Alzheimer’s.
VNS and related therapies are being studied for use in assessing consciousness in coma patients who can’t visibly react to external stimuli like sounds or touch. This fascinating realm of study is a new frontier in attempting to understand human consciousness, a mystery some scientists believe is wrapped up in interoception. Converse to Descartes’ 17th century idea that mind and body are separate, the growing body of evidence indicates that body and mind are more intertwined than we ever imagined.