Control Your Vagus Nerve to Improve Mood, Alertness & Neuroplasticity

The episode opens with Andrew Huberman introducing himself as a professor of neurobiology and ophthalmology at Stanford School of Medicine and naming the topic: the vagus nerve, which neuroanatomists call cranial nerve 10. He argues against the everyday image of a nerve as a small wire linking one point to another. The vagus is described instead as an extensive set of connections between brain and body, so widespread that in many respects it looks like its own nervous system inside the traditional one.

The host frames the subject as practical as well as anatomical. He says recent years have produced more detailed maps of vagal pathways and a better understanding of how to engage them. He promises tools for becoming more alert without pharmacology, for calming down quickly on demand without pharmacology or devices, for improving mood, and for improving the ability to learn. At this stage these are stated aims of the episode. The excerpt does not yet present the tools themselves or the evidence for them.

He also says the podcast is separate from his teaching and research roles at Stanford, and the episode includes sponsor reads for an electrolyte drink and for red light therapy devices. The health claims in those segments are part of the advertising, not the scientific argument that follows.

The anatomical discussion starts with what sets the vagus apart from the other cranial nerves. Most cranial nerves receive information from, and send connections to, limited regions, typically the head and neck. The vagus does connect to the face, head, neck and throat, but it also reaches the chest, the abdomen and even the lower intestines. The host summarizes it as a nerve of many pathways that both receives and provides information from essentially all areas of the body down to the base of the pelvis.

The name comes from that reach. According to the episode, "vagus" translates roughly to vagabond, meaning wandering, a label early neuroanatomists gave because of the nerve's broad territory. The host warns against reading randomness into the name:

there is nothing random about the wiring of the vagus nerve

Different neurons within the vagus carry different types of information for different purposes. That point sets up the episode's main conceptual move.

To explain what "information" means here, the host separates neuron types. Sensory neurons convert physical events into electrical signals, such as light at the eyes or sound waves in the auditory system. Motor neurons control movement, from the limbs and lips to the opening and closing of airways. He stresses that internal organs need motor control too. The gut contracts and relaxes to move food along, and even the spleen can contract to release red blood cells or immune cells into circulation. A third group, modulatory neurons, adjusts the balance between sensory and motor information, though the episode says it will not focus on them.

The distinction matters because the vagus contains both sensory and motor neurons. The host says that most popular discussion, including what people hear in yoga classes, treats the vagus only as a calming pathway that carries information about the body's state to the brain. He accepts that this is true but calls it one small fraction of what the nerve does, because motor information also travels from the brain to the body. He also mentions that ancient yoga practices separated some important vagal functions without knowing the underlying mechanisms, and says he will return to this later.

His practical claim is that the goal decides the target. Calming effects, energizing effects, immune-enhancing effects and learning-related effects of vagus nerve activation each require knowing whether a sensory or a motor pathway is being engaged. He also presents the sensory pathways as the explanation for why a comfortable or uncomfortable bodily state shapes whether the mind feels comfortable or uncomfortable.

The host then describes the unusual shape of most vagal neurons. A textbook neuron has a cell body, dendrites that receive input, and an axon that sends output. He says some vagal neurons look like that, but about 85% have their cell bodies in the nodose ganglion, a cluster near the neck and back of the head that he compares to a bunch of grapes. One axon runs out to the body. It is short if it ends in the neck, longer if it ends in the chest, and longer still if it reaches the viscera, such as the lungs, pancreas, liver or spleen. A second axon runs up into the brain stem and generally ends in one of three brain stem nuclei. He calls these bipolar neurons and notes that different organs tend, though not always, to be innervated by different neurons.

In his account, these neurons reverse the usual picture of the axon as an output. The branch in an organ collects sensory information, which travels up the axon, past the cell body in the nodose ganglion, into the brain stem and on to the brain. On this basis he describes the vagus as "mostly a sensory pathway" and asks listeners to picture it as a superhighway from body to brain.

Information's coming up those wires in the case of the vagus.

He lists the brain's possible responses to this incoming information. It can become more alert or calmer, be primed to learn better, or turn on a fever that heats the whole body, depending on what the axons sense in the periphery, meaning the organs and tissues outside the brain and spinal cord.

The host contrasts the vagus with senses such as vision and hearing, which typically handle one type of input, photons or sound waves. Vagal sensory signals from organs include both mechanical and chemical information. He uses "gut" broadly, covering the stomach, the large and small intestines, and the structures above the stomach. Mechanical sensing is the easier case. Mechanoreceptors detect stretch in the gut lining when it is distended by food, air or water, and that signal passes up to and through the nodose ganglion, where some processing occurs, before reaching the brain stem.

For chemical sensing, the main example is serotonin. The host says, as something listeners "may have heard," that 90% of the body's serotonin is manufactured in the gut, where it plays a role in gut motility and gut health. He separates gut serotonin from serotonin released in the brain. He previews a later discussion of how gut serotonin levels are conveyed to the brain by the vagus, with the brain in turn making different levels of serotonin that affect mood. He links this pathway to depression and to everyday mood, but the details and supporting evidence are deferred and not part of this excerpt. Gut acidity is a second chemical signal he names.

He briefly introduces technical terms, describing afferents as "the inputs to a structure" and, in the transcript's wording, efferents as "the inputs from a structure." He then extends the mechanical and chemical framework to the lungs. Their expansion and contraction is relayed to the brain stem, along with chemical information about the oxygen and carbon dioxide ratio. He adds the heart and some neck muscles that control airway constriction, and says he is not going through every organ for the sake of time.

He insists this classification is practical rather than academic. Anyone trying to calm down, improve immune function or improve mood through the vagus should first ask which kind of signal is being changed:

Am I going to do that through a mechanical change, or am I going to do that by making a change to the chemical milieu of a given organ or set of organs?

Next the host places the vagus in the autonomic nervous system. Cranial nerve 10 is classified as parasympathetic. The sympathetic branch, which he notes has nothing to do with emotional sympathy, generally raises alertness across a range from ordinary wakefulness to a full-blown panic attack. The parasympathetic branch, often called "rest and digest," controls digestion and the ability to fall asleep. Over-activated, it can cause unwanted sleepiness or fainting, and if hyperactivated it can contribute to coma. He argues that "fight or flight" is too narrow a label for the sympathetic system, because it also produces healthy, non-anxious alertness.