The Science of Making & Breaking Habits

Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford School of Medicine, opens the episode by framing habits as behavior organized into "more or less reflexive action," so that routine acts like brushing teeth do not require much thought. Habits can also be more elaborate, such as exercising at a set time, eating certain foods, or saying or not saying certain things. He acknowledges that some habits undermine immediate and long-term health and psychological goals, and some even undermine overall life goals.

He separates the popular material on habits (books, articles, workshops) from a less widely known neuroscience and psychology of habit formation and breaking. His claim is that the scientific literature holds "some real gems" that, to his knowledge, have not received much popular attention. He says he will reduce two habit formation and habit breaking programs to explicit steps. He ties the timing to New Year's resolutions at the end of 2021, but argues that the programs rest on the biology of habit formation and line up with what psychologists have described.

Before the substance begins, Huberman notes that the podcast is separate from his teaching and research roles at Stanford. He describes it as part of an effort to bring zero-cost-to-consumer science information to the public.

Huberman separates habits from hardwired reflexes. Blinking when something approaches the eye, or pulling away from a sharp or hot object, are reflexes, not habits. Habits are learned by the nervous system, though "not always consciously." Some develop without our noticing until they become a problem. He cites an estimate that "up to 70% of our waking behavior is made up of habitual behavior," and presents it as an estimate rather than a firm measurement.

From there he builds a chain of definitions. Habits are largely learned. Learning is neuroplasticity, "the process by which our nervous system changes in response to experience." What changes is the connections between neurons, which communicate electrically and through chemical signals that make the next neuron more or less likely to be active. In this view, neuroplasticity means forming new circuits and pathways that make some habits more likely to occur and others less likely.

Turning to the popular and psychological literature, Huberman describes a distinction he says others drew first: immediate-goal-based habits versus identity-based habits. An immediate-goal-based habit delivers a specific outcome each time it is done. His example is a goal of 60 minutes of zone 2 cardio daily, or three or four times a week. Each session can be checked off as completed.

He adds context on zone 2 cardio. He says the scientific and health literature points to strongly positive effects of a minimum of 150 to 180 minutes per week. He defines zone 2 as cardiovascular exercise hard enough to get you moving, your heart pumping and your breathing up, but not so hard that you cannot hold a conversation. You can still talk, though it is "a little bit strained," and slightly harder effort would make talking impossible.

Identity-based habits link the same immediate goal to a larger picture of oneself, such as trying to become "a fit person" or an athlete. He says he raises the distinction because the discussion will later cover dopamine, which he describes as a molecule associated with motivation and reward. He states that "different schedules of dopamine release predict whether or not we will stick to a habit or not," and whether a habit forms quickly. This section does not yet supply the evidence for that claim.

Huberman sets aside the popular figures of 18, 21, 30 or 60 days and points to peer-reviewed data. He cites a 2010 study with first author Lally. It found that the same habit took different individuals anywhere from 18 days to 254 days to form. His answer to the common question of whether habits take 21 days, or whether the nervous system changes in six days, is that it is "highly variable."

The behavior studied was taking walks after dinner. Huberman notes that a separate literature shows walks after a meal can speed glucose clearance from the bloodstream and may benefit weight loss and cardiovascular health. In the study, a habit counted as formed when participants did it about 85% of the time and reported not needing much mental effort to start the walk.

And if you can't form one habit easily, it doesn't mean that you can't form other habits easily.

He proposes that why some people form certain habits more easily "probably has something to do with" how well they manage what he calls limbic friction. He hedges this explanation and does not tie it to a specific finding from the Lally study.

Huberman is clear that limbic friction is not a formal term in the biology or psychology literature. It is "a term that I coined" to tie together several pieces of that literature. He defines it as the strain required to overcome one of two body states. One is anxiousness that prevents calming down and engaging in a desired activity or thought pattern. The other is feeling too tired, lazy or unmotivated.

He links both states to the autonomic nervous system, which he describes as a set of neurons, hormones and chemicals that act "as sort of a seesaw" between alertness and calm. He notes the familiar "wired and tired" state but attributes it to prolonged stress that leads to exhaustion. Applied to the Lally study, some people finish dinner and simply go for the walk. Others feel too much limbic friction, either because they are too tired or because they are too anxious and distracted.

He frames limbic friction as "activation energy" and promises to teach ways to measure it, both for executing a new habit and for breaking an unwanted one. Those measurement methods are not given in this part of the episode.

Linchpin habits are the third concept, which Huberman says he names himself while drawing on ideas from books and articles. These are habits that make many other habits easier, and he insists they are "always" things one enjoys. His personal example: he enjoys resistance training and running. He does cardiovascular exercise three or four times per week for roughly 30 to 60 minutes per session, and resistance training three or four times per week for roughly 45 to 60 minutes per session. He typically schedules these early in the day for neurochemical and hormonal reasons he says he will explain later.

He says these enjoyable habits carry over to others: being alert for work, getting good sleep the night before, staying hydrated, and choosing foods that are better for him than ones he would reach for more reflexively without the training. This is his own account of his life, not study data.

Huberman's summary of the three concepts: identity-based versus goal-based habits; different habits take different amounts of time to adopt depending on the person and the habit; and linchpin habits make other habits easier and are always things we enjoy.

He invites listeners to note which habits are easy for them, which are hard, and which they want to break, optionally on paper or by phone dictation. He promises a specific mapping method later in the episode.

Huberman introduces habit strength and stresses that this concept comes from the psychological literature, not from him. He describes two criteria. The first is context dependence: whether you do the same thing in the same way at the same time across environments. His example is that when traveling he brushes his teeth at roughly the same time relative to waking as he does at home. He calls that context independent and a strong habit. Behaviors such as eating or dressing may differ by context. His wording here is somewhat tangled, since he calls them "context independent" while describing behavior that varies by context.

The second criterion is how much limbic friction a habit requires. He defines it more precisely here as top-down control from the forebrain to the limbic system, "the part of your brain that generates autonomic responses": the conscious override of your state needed to act. Habits still being built and consolidated likely require more of it. Early motivation may keep friction low at first, as with a plan for 45 minutes of zone 2 cardio five to seven days a week. Waking up tired and not wanting to get out of bed raises it.