Time Perception & Entrainment by Dopamine, Serotonin & Hormones

The episode opens by presenting time perception as more than a curiosity of cognition. The host, who introduces himself as Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford School of Medicine, argues that how we perceive time may be the most important factor in how we gauge our lives: whether we feel successful or failing, whether we live in fear, and whether we relate to things positively. The proposed reason is that time perception is directly linked to the neurochemical states that control mood, stress, happiness and excitement, and that it frames how we evaluate the past, the present and the future.

Our perception of time is perhaps the most important factor in how we gauge our life.

The stated aim is to cover both the science of time perception and tools and protocols for what the episode calls dilating and contracting time, meaning slowing down or speeding up the experienced pace of life. The host claims this can be done "in a very direct and dynamic way" and that it is "actually not that hard once you understand how time perception works," with applications described across work, sport, relationships and emotional life. These are framing claims at the outset; this section of the episode does not yet present the specific tools for altering the pace of experience.

Before the main topic, the host answers listener questions from an earlier episode on fasting and time-restricted feeding. Time-restricted feeding is described as eating within a fairly regular window in each 24-hour cycle, most often eight hours or ten hours, with some people using shorter windows. The window is supposed to fall at roughly the same time each day. The host says this has positive effects on gene expression that regulate effects on various tissues, and that for some people, though explicitly not all, it makes weight loss easier because they are not eating for large parts of each day.

The core principle offered is that what breaks a fast is "highly contextual." It comes down to whether something ingested raises resting blood glucose, by how much, and for how long. That framing shapes the answers that follow, which are hedged throughout.

• Athletic Greens: the host discloses that it is a sponsor of the podcast and that he had taken it for more than a decade before the show launched. He says that for most people, including himself based on his own measurements, it does not break a fast, and that if it did, the break would be very transient. He adds that without knowing an individual's resting blood glucose he cannot say for sure, but reasons that it likely does not because it contains little carbohydrate or sugar. • Fish oil: described as mainly essential fatty acids, in particular EPA and DHA, which do not tend to raise blood glucose much. Using a continuous glucose monitor, the host reports that fish oil did not change his resting blood glucose, and he says it likely will not for most people. • Pill-type supplements, caffeine, dopamine-raising compounds, vitamins and minerals: the general rule given is that anything without sugar or much carbohydrate will not raise blood glucose very much, with the caveat that protein can raise blood glucose, and fat can too, to a lesser extent.

The limits of this evidence are worth noting. The supporting data are the host's own glucose measurements and a logical argument based on macronutrient content, not a controlled study across individuals. He repeatedly acknowledges that individual resting glucose varies, and the recommended product is a declared sponsor. The conclusion is offered conditionally: by "the logic that I just spelled out," supplements without sugar or protein content "should not break a fast."

The host also notes that the podcast is separate from his teaching and research roles at Stanford and describes it as an effort to provide zero-cost-to-consumer science information to the public, before thanking the sponsors.

The main discussion begins with what the host calls the most fundamental aspect of time perception: entrainment, defined as the way internal processes, both biological and psychological, are linked to something external. The most basic form is the circannual rhythm. The host describes neurons in the eye, brain and body that mark the passage of time through the year, "literally a calendar system in your brain and body."

The mechanism is presented as simple. Light seen by the eyes inhibits the release of melatonin, a hormone with two major functions in this account: making us sleepy at night and regulating other hormones, in particular testosterone and estrogen. As an illustration of how strong this effect is, the host says that if you wake in the middle of the night, when melatonin is typically high, and turn on a bright bathroom light, melatonin levels "crash down to almost zero and stay there."

Because day length varies over the year, so does available sunlight, and therefore melatonin. Long days mean less melatonin released for shorter periods; short days mean more melatonin present for longer. The host adds that the brain and body average light exposure from both artificial sources and sunlight, and that the system tracks not just the day length but its direction of change. An eight-hour day in spring, when days are lengthening, corresponds to progressively less melatonin; an eight-hour day in winter, when days are shortening, corresponds to progressively more. This is offered as the reason most people, though not all, feel more energy in spring and somewhat less energy, sometimes a lot less, and a slightly lower mood in winter.

Every cell and system of your body pays attention to this