Time Perception & Entrainment by Dopamine, Serotonin & Hormones

High-Level Overview

In this solo episode, Andrew Huberman takes on a subject he calls perhaps the most important factor in how we judge our lives: our perception of time. Whether we see our past as a success or a failure, whether we feel on track in the present, and whether the future looks bright or uncertain are all framed, he argues, by the neurochemical states that set our internal clocks. His promise is practical: "We can control the speed at which we experience life." Once you understand the machinery, he says, you can deliberately dilate or contract time.

The tone is classic Huberman teaching: technical but conversational, building from slow, subconscious rhythms (the seasons, the 24-hour day, 90-minute cycles) up to the fast, moment-to-moment chemistry of dopamine and serotonin, then out to trauma, blinking, cold exposure, vacations, relationships and habits. Before the main topic he also answers listener questions about whether supplements break a fast. The conversation moves from biology to everyday tools, with each layer of timekeeping yielding a protocol you can try.

The Discussion Explores:

• Entrainment: how the body matches itself to external cycles, starting with yearly (circannual) rhythms driven by light and melatonin
• Seasonal hormones: a study showing sunlight on the skin raises testosterone and estrogen
• Circadian entrainment: the clock genes in every cell and the light, exercise and meal-timing tools that keep them aligned
• Ultradian 90-minute cycles: why focused work caps out at about 90 minutes and how to use these blocks
• Dopamine versus serotonin: dopamine raises the brain's "frame rate" and makes us overestimate elapsed time; serotonin lowers it
• Matching tasks to time of day: rigid, precise work early; creative, brainstorming work later
• Trauma and overclocking: why extreme arousal stamps memories in slow motion, and how treatment works on playback rate
• Fun versus boredom: why good times fly by but are remembered as long, and how novelty deepens bonds with places and people
• Habits as time markers: using dopamine-releasing routines to carve the day into functional units

Deep Dive into Main Ideas

A Quick Detour: Do Supplements Break a Fast?

Opening with listener questions from his earlier episode on fasting and time-restricted feeding, Huberman recaps that time-restricted feeding means eating within a regular window (most often eight or ten hours) at roughly the same point in each 24-hour day. Whether something breaks a fast, he says, comes down to whether it raises resting blood glucose, by how much, and for how long.

Applying that logic, he says his own glucose monitoring shows that Athletic Greens (a sponsor he has used for more than a decade) and fish oil, which is mainly the fatty acids EPA and DHA, do not change his resting blood glucose, and that chances are they won't for most people either. His rule of thumb is that supplements without sugar, much carbohydrate or protein should not, in his words, quote unquote break a fast, while noting that protein and, to a lesser extent, fat can raise blood glucose and that it all depends on the individual.

Circannual Entrainment: A Calendar Written in Melatonin

The foundation of time perception, Huberman explains, is entrainment: the linking of our internal biology and psychology to some external event. The slowest version is the circannual rhythm, in which neurons in the eye, brain and body track the passage of the year. He calls it "Literally a calendar system in your brain and body." The mechanism is simple: light seen by the eyes suppresses the hormone melatonin, which both makes us sleepy at night and regulates other hormones such as testosterone and estrogen. Flip on a bright bathroom light in the middle of the night, he notes, and melatonin crashes to almost zero.

Because day length changes through the year, so does melatonin output. Long days mean less melatonin released for shorter periods; short days mean more for longer. The brain averages the light it sees from both sunlight and artificial sources, and the trend matters: an eight-hour day in spring, when days are lengthening, sends a signal of falling melatonin, while the same eight hours in winter signals rising melatonin. Huberman says this is why most people, though not all, feel more energy in spring and lower energy and mood in winter, with effects reaching mood, energy and even appetite.

He then describes a paper published last year in Cell Reports showing that across the calendar year people make more testosterone and estrogen when days are longer, correlated with interest in romantic interactions, a mild willingness to argue, and energy and mood. The surprise was that the skin, not only the eyes, drives this: about two hours a day of sunlight on exposed arms, upper back, neck and face produced significant increases in both hormones. It did not need to be very bright, cloud cover was fine, and sunscreen did not appear to block the effect, though he stresses prioritizing skin health.

Circadian Entrainment and the First Tools

The next and, he says, most powerful rhythm is the 24-hour circadian cycle. A master clock sits above the roof of the mouth, and every cell runs its own molecular timer: a clock gene (names like per, BMAL and clock) is expressed, its RNA becomes a protein, the protein builds up and shuts the gene down, and as the protein is used up the gene switches back on, a loop lasting about 24 hours. Morning light, evening light and darkness at night keep these cellular clocks locked to the Earth's rotation.

Huberman insists precise circadian entrainment matters enormously, saying disruption increases cancer risk, obesity and mental health issues, slows wound healing and disrupts hormones. His protocols: view 10 to 30 minutes of bright light, ideally sunlight, within an hour of waking; do it again in the afternoon or evening; get as much bright light as possible through the day and as little as possible at night (any bright light, not just blue light); and avoid sunglasses when it is safe to do so, while eyeglasses and contacts are fine. He adds exercising at fairly consistent times, within plus or minus two hours from day to day, and eating within a consistent window. The encouraging part is that exact meal times don't matter as much as keeping meals within roughly the same phase of each day.

Why this matters for time perception: he cites a classic 1985 study by Aschoff, since repeated many times, in which people lived without clocks, windows or regular light. After around 42 days they guessed they had been there 28 or 36 days, and their ability to measure short intervals, such as two minutes, which people normally judge to within about five to 15 seconds, was badly disrupted. Because accurate time perception predicts how well we perform a task, Huberman treats solid circadian entrainment as the base layer for everything else.

Ultradian Cycles: Working in 90-Minute Blocks

Ultradian rhythms of about 90 minutes divide sleep, with more slow-wave sleep early in the night and more REM later, and, Huberman says, the literature supports that they also govern waking focus. The idea began as the basic rest-activity cycle proposed by Nathaniel Kleitman. After roughly 90 minutes of hard mental or physical work, the release of acetylcholine and dopamine (and to some extent norepinephrine), the chemicals behind narrow focus, motivation and drive, drops, and performance falls off.

The key point for listeners who ask when the cycle begins: unlike sleep cycles, waking ultradian cycles are something you initiate. You set a timer and decide the focus starts now. Huberman does this mid-morning and sometimes again in the afternoon, putting away his phone and often turning off the internet. He is clear that you should not expect to drop into deep focus immediately, that no one can negotiate the decline at around 100 to 120 minutes, and that back-to-back cycles don't work. He recommends spacing them by at least two to four hours, ideally doing one or two a day and no more than three, and he stresses these are for truly hard problems, not email or social media.

Dopamine, Serotonin and the Brain's Frame Rate

Huberman then turns to conscious time perception, which he breaks into three forms: the passage of time in the present (an interval timer ticking finely or coarsely), prospective timing (measuring off an interval into the future, like a stopwatch), and retrospective timing (reconstructing from memory how long things took). All of it, he says, boils down to a few neuromodulators.

In human and animal experiments, raising dopamine makes people overestimate elapsed time: as he puts it, "the more dopamine that is released into our brain, the more we tend to overestimate how much time has passed". Asked to signal when a minute is up, people with elevated dopamine might call it at the 38-second mark. Norepinephrine, which can be made from dopamine, acts similarly. His analogy is a camera's frame rate: slow motion comes from shooting at high frame rates, such as 4,000 frames per second instead of 30, and dopamine and norepinephrine fine-slice experience the same way. Serotonin does the opposite. Drugs that raise serotonin, and cannabis, make people underestimate time, letting six minutes pass when asked to mark five, because they lower the frame rate.

He also emphasizes there is no single brain area for time: "time perception is what we call a distributed phenomenon", involving the striatum and other regions working as a network, with the cerebellum involved in the timing of movement.

Tool 7: Precise Work in the Morning, Creative Work Later

Emerging evidence suggests dopamine and norepinephrine dominate roughly the first half of the waking day and serotonin rises toward evening, and that people overestimate elapsed time early in the day and underestimate it later, even without any substances. Huberman argues this adds a second reason to the familiar advice of doing your hardest task first: "early in the day you are a much more high resolution camera, so to speak, then you are later in the day."

His recommendation is to match task to state. Work with rigid rules and right-or-wrong answers, such as math, following a recipe, executing musical or physical skills, or accounting, belongs early. Brainstorming and creative work, which benefit from blending memories and looser batching of time, may suit the more serotonergic afternoon and evening. He adds that poor, short or fragmented sleep blurs these daily dopamine and serotonin phases, which may be part of why we can't concentrate after bad nights.

Trauma, Overclocking and Memory Playback

The dark side of a high frame rate is what Huberman calls overclocking. In car accidents and other trauma, dopamine and norepinephrine surge so high that events are perceived in ultra slow motion. The problem is how that gets stored. The hippocampus and neocortex act as a space-time recorder: a memory is coded both by which neurons fire (a space code) and by their timing (a rate code). Using rates lets the same neurons store many more memories, but an overclocked memory is stamped down at extreme resolution, and people struggle to shake it and its emotions.

He notes that treatments such as EMDR, exposure and cognitive behavioral therapies, and the ketamine therapies attracting interest today, do more than lower the emotion attached to a memory; they also help the person take control of the rate of its playback, speeding it up or slowing it down. By a mechanism not yet understood, this seems to help uncouple the emotional weight from the memory, which, he says, trauma survivors learn will not simply be forgotten. As for why dopamine is involved in something so unpleasant, he explains that dopamine is not only about pleasure: "It's a molecule of motivation, pursuit, and drive." It is often released alongside norepinephrine whenever arousal is high, whether the event is positive or negative.

Tools 8 and 9: Blinking and Cold Exposure

Huberman highlights a Current Biology paper by Terhune and colleagues titled Time Dilates After Spontaneous Blinking. Blinking, he says, is not just lubrication: "But it's a shutter on our experience." Higher arousal and dopamine increase spontaneous blink rate, and each blink shifts time perception toward overestimation, suggesting blink rate is tied to frame rate. In principle, blinking less would slow your perception of time and blinking more would speed it up, though you would miss more when blinking.

Cold exposure is his second example. He cites a study in the European Journal of Physiology showing cold water can raise baseline dopamine about 2.5 times in a long-lasting, apparently non-addictive way. That is why three minutes in an ice bath feels endless: rising dopamine fine-slices the discomfort. His tool is to redirect attention away from the immediate sensation, for instance to a metronome ticking every 10 seconds, a song sung in your head or out loud, or something else entirely, which separates you from both the sensation and the high-frame-rate perception of it.

Fun Feels Fast but Is Remembered as Long

Dopamine affects not just how time feels in the moment but how it is remembered, in opposite directions. A fun, varied, dopamine-rich experience, like a kid's day at an amusement park or a great vacation, flies by at the time but is later remembered as long and full of events. A boring experience, like Huberman's recent wait at the dentist, drags in the moment but is remembered as a short, empty bin. He also points back to the isolation studies, where people in boring, cue-free environments assumed much more time had passed. His image is two stopwatches: a dopaminergic one counting off fine slices, and a coarser one ticking in big intervals, with our state deciding which we use.

This extends to places and people. In a thought experiment about moving to New York City, he explains that a year spent in three apartments with three times as many people and novel experiences would feel longer than a year in one place. Likewise, sharing varied, novel settings with someone, such as a coffee shop, a sports event or time with your family, makes them feel more familiar and makes it seem you have spent more time together, even when the total hours are identical.

Tool 10: Habits as Dopamine Time Markers

The final study is a 2020 Neuron paper by Antony and colleagues, Behavioral, Physiological, and Neural Signatures of Surprise During Naturalistic Sports Viewing. People watched recorded basketball games during brain imaging, and dopamine-related activity in the nucleus accumbens and ventral tegmental area appeared both when an expected outcome happened, like their team scoring, and during surprises, even unwelcome ones. The crucial finding: whatever caused them, the frequency of these dopamine signals predicted how viewers parsed the game into time bins. In Huberman's words, dopamine release sets the frame rate on the entire perception of experience.

He applies this to his own day, noting that his first coffee, which he delays 90 to 120 minutes after waking, surely marks a new phase. The tool is to place specific habits at regular points, say one at 8 a.m. and another at 10 a.m., so that each dopamine-releasing routine opens a new epoch. He sums up the biology plainly, "dopamine is marking time", and says "habits serve as flankers or markers for the passage of your day". You don't have to be obsessive about exact timing; the regular sequence is what divides the day into functional units, which he frames as something many people would benefit from rather than a neurotic exercise.

Conclusion

Huberman's central message is that time is not experienced at a fixed speed. Slow rhythms set the foundation: seasonal light and melatonin, circadian clocks kept on track by morning and evening light, regular exercise and consistent eating windows, and 90-minute focus cycles you start on purpose. On top of them, dopamine and norepinephrine speed up the brain's frame rate, making time seem longer in the moment, while serotonin slows it. From that framework come his tools: do precise, rule-bound work early and creative work later, protect sleep so these states stay distinct, use distraction to shorten a hard cold plunge, seek novelty with the people and places you want to bond with, and use habits as dopamine markers that divide your day into deliberate units. For listeners who want to go further, he recommends Dean Buonomano's book on the neuroscience and physics of time.

This is a summary of "Time Perception & Entrainment by Dopamine, Serotonin & Hormones" from Huberman Lab, giving you the GIST so you can decide if you want the REST. Listen to the full episode.