When it comes to our senses, we frequently focus on the external—the crack of thunder, the glare of sunlight, the fragrance of flowers—that captured our attention in the first place. But our bodies also have a whole host of internal senses that tell our brains whether our hearts are beating at the right speed, for example, or whether our blood pressure is too high. These signals travel constantly via hormones and nerves, including a mysterious 100,000-fiber network called the vagus nerve.
Now, new techniques are helping scientists map the thin, twisting branches of the vagus nerve—which connects the brain to the heart, intestines, and other internal organs—and make surprising discoveries about its role in memory and emotion. These findings have spawned investigations into treatments for everything from Alzheimer’s disease to post-traumatic stress disorder and have led to the approval of medical implants to help treat epilepsy and depression. When it comes to understanding the brain-mind connection, a gut check might not hurt.