How to Focus to Change Your Brain

The episode opens by framing neuroplasticity as the nervous system's capacity to change in response to experience. Huberman, who introduces himself as a professor of neurobiology and ophthalmology at Stanford School of Medicine, calls it arguably one of the most important aspects of our biology, because it underlies thinking differently, learning new things, forgetting painful experiences and adapting to what life brings. He says he will not review its long history in detail and will instead cover what neuroplasticity is, its different forms, and how access to it depends on age and on the specific kind of change someone is trying to make.

He clarifies that "neuralplasticity" and "neuroplasticity" refer to the same process. Change can be driven by negative events, such as a trauma that creates fear of a particular place, cars or planes, and by positive ones, such as the birth of a first child, a puppy doing something amusing, or witnessing a remarkable athletic performance. The stated reason for starting with an organizing framework is that a web search for the term returns hundreds of thousands of references, mixing scientific sources with "a lot of falsehoods about what neuroplasticity is and how to access it."

The first principle is that humans are born with a nervous system that "isn't just capable of change, but was designed to change." A baby's brain is described as wired very crudely, with imprecise connections, which shows up in the lack of coordinated movement, speech or precision. The episode says we arrive overconnected: axons and dendrites, the neuron parts covered in episode one, form a tangle likened to a mess of small interconnected roads with no highways. From infancy through the ages of 10, 20 and 30, some connections are reinforced and strengthened while others are lost.

From this comes the claim that developmental plasticity, defined here as the plasticity from birth to about age 25, "is mainly a process of removing connections that don't serve our goals well." The exception noted within that window is one-trial learning, in which a single strongly positive or negative experience changes the nervous system permanently, "unless of course we go through some work to undo that experience." The resulting picture is a broadly connected web, poor at any single task, that becomes customized through caregivers, social interactions, thoughts, languages learned and places traveled. This customization applies especially to the brain areas that represent the visual and auditory worlds and the range of possible smells.

Not everything is meant to be plastic. Circuits controlling heartbeat, breathing and digestion are described as wired to resist change, which the episode presents as a benefit: "You never want to have to think about whether or not your heart will beat." Other systems change easily, and language is the main example. Children learn through almost passive experience, going from no language to many words and sentences, including words they have never heard. That leads to the summary that "the young brain is a plasticity machine," followed by the claim that around age 25, "plus or minus a year or two, everything changes."

The episode argues that after about age 25, getting changes in the nervous system, and more importantly getting them "to stick around," takes a completely different set of processes, and that popular discussion largely overlooks this. The slogan "fire together, wire together" is credited to Stanford colleague Carla Shatz and accepted as true for early development, with a qualification: it "doesn't apply in the same way after age 25."

A similar objection is raised against a paraphrased quote from Ramón y Cajal, called the greatest neurobiologist of all time, about people being able to sculpt their own nervous systems. Huberman presents the wording himself as approximate ("I think it goes something like") and argues that such statements leave out how to actually do it. The adult route is described as gated: "you can't just decide to change your brain." Instead, a person has to go through a series of steps that change their internal state in ways that allow the brain to change. Through age 25, refinement is said to happen mainly by removing unhelpful connections and strongly reinforcing those tied to powerful experiences or to skills like walking, talking and doing math.

A brief aside notes that the dog Costello is snoring audibly. Whether listeners can hear it is linked to their hearing sensitivity, a lead-in to later discussion of perfect pitch and range of auditory detection.

The episode takes on the popular idea that exercise like running makes the brain produce new neurons. The "bad news first" is that after puberty, about age 14 or 15, the human brain and nervous system add "very few, if any, new neurons." The evidence is presented by species and region. In rodents and some nonhuman primates, neurogenesis occurs in the olfactory bulb and in the dentate gyrus of the hippocampus, with strong evidence that new neurons can be added there throughout life. In humans, the evidence is called "a little bit more controversial."

Smell is the clearest human example given. A hard blow to the head can shear the axons of olfactory neurons where they pass through the bony cribriform plate, leaving a person anosmic, or unable to smell. Unlike most central nervous system neurons, these can regrow their connections over time, and new neurons can be added to the olfactory bulb after migrating from deeper in the brain through the rostral migratory stream. The episode qualifies this as "some evidence" that smell neurons can be replaced throughout life, "certainly in very young individuals from birth until about age 15 or so."

For the human hippocampus the answer is described as unclear. The episode cites a study from Rusty Gage's lab at the Salk Institute in which terminally ill cancer patients were injected with a dye incorporated only into new neurons, and examination of their brains after death found evidence of new neurons. Huberman says the results "stand over time," but stresses what press coverage left out: very few cells were being added. Later papers, mainly from UCSF labs, are described as showing that any adult neurogenesis involves "an infinitesimal small number of new neurons."

The conclusion is that after birth we largely have the neurons we will use for life, and we lose neurons as some functions decline with age. Yet "all is not lost": circuits can still form new connections and support new memories, abilities and cognitive functions, mainly by strengthening synapses so they are more reliable and more likely to engage, and by removing connections. Removing connections is presented as vital to processes such as grieving or reducing the emotional load of a traumatic experience.