The Vital Role of the Vagus Nerve in Human Mind Creation

The first version of this story appeared in Quanta Magazine.

It’s late at night. You are alone and wandering the empty streets looking for your parked car when you hear footsteps behind you. Your heart beats faster, your blood pressure rises. Blisters appear on your arms, sweat on your hands. Your stomach knots and muscles contract, ready to run or fight.

Now imagine the same scene, but without the body’s natural response to an external threat. Would you still feel afraid?

Experiences like these reveal a strong connection between the brain and the body in the creation of consciousness—the combination of thoughts, ideas, feelings, and personalities that are unique to each of us. The brain’s capabilities alone are astounding. The upper limb gives most people a clear sense of the world. It can store memories, enable us to learn and speak, generate emotions and consciousness. But those who might try to save their mind by computerizing it miss a key point: The body is important to the mind.

How is this important brain-body connection organized? The answer involves the highly unusual vagus nerve. The longest nerve in the body, it travels from the brain throughout the head and trunk, sending commands to our organs and receiving sensations from them. Many of the complex functions it controls, such as emotions, learning, sexual arousal, and fear, are automatic and operate without conscious control. These complex responses involve a constellation of brain circuits that connect the brain to the body. The vagus nerve, in one way of thinking, is the nerve of the mind.

Sensors are often named for specific functions they perform. Optic nerves carry signals from the eyes to the brain for vision. The auditory nerves process the acoustic information of hearing. The best early anatomists could do with this pathway, however, was to call it the “vagus,” from the Latin for “wandering.” The vagus nerve was recognized by early anatomists, especially Galen, a Greek polymath who lived until about the year 216. But hundreds of years of study were needed to grasp its complex appearance and functionality. This effort continues: Research on the vagus nerve is at the forefront of neuroscience today.

The most powerful current research involves electrical stimulation of this nerve to improve cognition and memory, and a smorgasbord of treatments for neurological and psychological disorders, including migraines, tinnitus, obesity, pain, drug addiction, and more. But how is it possible that stimulating one nerve can have so many psychological and cognitive benefits? To understand this, we must understand the vagus nerve itself.

The vagus nerve originates from four clusters of neurons in the medulla of the brain, where the brain stem attaches to the spinal cord. Most of the nerves in our body branch directly from the spinal cord: They are connected between the vertebrae of our spine in a series of lateral bands to carry information to and from the brain. But not the vagus. The vagus nerve is one of 13 nerves that leave the brain directly through special openings in the skull. From there sprout branches that reach almost everywhere on the head and trunk. The vagus also gives off two large clusters of outpost neurons, called ganglia, located at critical points in the body. For example, a large cluster of vagal neurons clings like a vine to the carotid artery in your neck. Its nerve fibers follow this network of blood vessels throughout your body to reach vital organs, from the heart and lungs to the intestines.