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Huberman Lab

Essentials: Time Perception, Memory & Focus

Published October 9, 2025
View Show Notes

About This Episode

Andrew Huberman explains how different biological timing systems-from yearly and daily rhythms to 90-minute ultradian cycles-shape our perception of time, mood, energy, and performance. He describes how neuromodulators like dopamine, norepinephrine, and serotonin alter how fast or slow time feels in the moment and how we remember events later. He then connects these mechanisms to trauma, novelty, and habits, showing how deliberate routines and environmental variation can structure our days, influence memory, and support better focus.

Topics Covered

Time perception Circadian rhythms Ultradian rhythms Dopamine Serotonin Sleep Trauma Habits Memory improvement Personal Development

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Quick Takeaways

  • Biological clocks operate at yearly, daily, and ~90-minute scales, and these rhythms strongly influence energy, mood, health, and capacity for focused work.
  • Precise circadian entrainment-mainly through light exposure and consistent activity-supports accurate short-interval time perception and overall performance.
  • Dopamine and norepinephrine tend to make us overestimate how much time has passed, while serotonin makes us underestimate it, and their levels vary across the day.
  • Highly exciting or varied experiences feel short while they are happening but are remembered as long and rich; boring or unpleasant experiences feel long in the moment but seem brief in memory.
  • Extreme arousal during trauma can "overclock" perception, creating slow-motion experiences that are encoded very densely in memory and can be hard to shake.
  • Using 90-minute ultradian cycles for deep work aligns with how focus-related neurochemicals are released and can significantly improve productivity.
  • Regular habits placed at specific times of day leverage dopamine to segment your day into functional units and shape how you experience and remember time.
  • Moving through multiple novel environments with a place or a person increases the sense of familiarity and the feeling that more time has passed.

Podcast Notes

Introduction and framing of time perception

Purpose of Huberman Lab Essentials segment

Revisiting past episodes for actionable science-based tools[0:04]
• Series focuses on tools for mental health, physical health, and performance drawn from earlier full-length episodes

Host background

Andrew Huberman introduces himself[0:09]
• States he is a professor of neurobiology and ophthalmology at Stanford School of Medicine

Why time perception matters

Time perception as central to how we gauge our life[0:23]
• Links time perception directly to neurochemical states that control mood, stress, happiness, and excitement
Time perception frames past, present, and future[0:41]
• It shapes how we evaluate our past, whether we feel on-track or off-track in the present, and how we view our future

Entrainment and circannual rhythms

Definition of entrainment

Entrainment as linking internal processes to external events[0:54]
• Describes entrainment as how biology and psychology are matched to something outside us, such as light-dark cycles

Circannual rhythms as fundamental entrainment

Neurons track passage of time across the year[1:21]
• We have nerve cells in eye, brain, and body that effectively create a yearly calendar system

Role of light and melatonin in circannual rhythms

Light inhibits melatonin release[1:31]
• Explains that light seen by the eyes reduces melatonin levels in the brain
Two major functions of melatonin[1:42]
• Melatonin makes you sleepy at night
• It also regulates other hormones, especially testosterone and estrogen

Day length, melatonin, and seasonal changes in mood and energy

Day length varies throughout the year, changing light exposure[1:52]
• With longer days, less melatonin is released; with shorter days, more melatonin is released and for longer duration
Brain averages light exposure over days[2:38]
• There is a process that averages light from both artificial and sunlight, marking off yearly time very precisely
Seasonal effects on mood and energy[3:45]
• In spring with increasing day length and decreasing melatonin, most people feel more energy
• In winter with decreasing day length and increasing melatonin, most people feel less energy and slightly lower mood

Melatonin as entrainment to Earth's rotation around the sun

Melatonin links internal state to annual light cycle[3:45]
• Mood, energy, and appetite are entrained to the Earth's rotation around the sun via melatonin signaling

Seasonal variation in sex hormones

Testosterone and estrogen vary across the calendar year[4:07]
• On longer days, humans tend to make more testosterone and estrogen than on shorter days

Circadian rhythms and health impacts

Circadian clock basics

24-hour circadian time cycle[4:28]
• Describes circadian rhythm as a 24-hour oscillation we cannot escape
Location and behavior of the circadian clock[4:40]
• States that the circadian clock resides over the roof of the mouth and its cells fire on a regular rhythm
• These oscillations correspond to periods of alertness and sleep each 24 hours

Cellular oscillations and light-dark entrainment

Every cell has a 24-hour gene expression oscillation[5:08]
• These cellular oscillations are entrained to the outside light-dark cycle via morning light, evening light, and darkness at night

Why precise circadian entrainment is critical

Health problems from circadian disruption[5:43]
• Disruptions in circadian entrainment increase cancer risk, obesity, and mental health issues
• They also decrease wound healing and physical and mental performance, and disrupt hormones
Goal: link cellular clocks to external light-dark cycle[5:33]
• Emphasizes that you want your cells' oscillations matched to when there is sunlight and when there is not

Simple behavioral protocols for circadian entrainment

Morning light viewing[5:17]
• Recommends 10-30 minutes of bright light, ideally sunlight, within an hour of waking, especially if waking early
Afternoon and evening light[6:17]
• Suggests another 10-30 minutes of outdoor light in the afternoon or around evening, depending on brightness
Limit bright light at night[6:30]
• Advises minimizing bright light entering the eyes in the evening to support circadian alignment
Exercise timing as an entrainment tool[6:51]
• Engaging in physical activity at fairly regular times of day helps entrain circadian rhythms
• You do not need to exercise every day, but should aim for consistent timing on days you do exercise

Circadian disruption and short-interval time perception

Aschoff isolation study on time perception

Experimental setup without external time cues[7:00]
• People were placed in environments without clocks, windows, or watches, sometimes in constant dark or constant light
Underestimation of longer intervals[7:56]
• After around 42 days, subjects tended to report shorter durations such as 28 or 36 days, underestimating how long they had been inside
Disruption of shorter-interval timing[7:56]
• Normally, people can estimate two minutes within about 5-15 seconds, but in circadian-disrupted conditions, their estimates were greatly off

Why accurate time perception matters for performance

Circadian entrainment supports precise short-interval perception[7:56]
• States that accurate perception of task-relevant time intervals is a fundamental predictor of how well one performs tasks

Ultradian rhythms and 90-minute focus cycles

Definition of ultradian rhythms

Ultradian rhythms are about 90-minute cycles[10:32]
• All of existence is broken into ~90-minute ultradian cycles, including sleep cycles and waking activities

Ultradian structure of sleep and wake

Sleep composed of repeated 90-minute cycles[10:49]
• Regardless of whether one sleeps 4, 6, 8, or 10 hours, sleep is organized into these 90-minute cycles
Ultradian patterns in focused work[10:55]
• The brain can typically sustain intense focus for about 90 minutes before performance drops

Using 90-minute cycles for productivity

Popularization in self-help and business literature[11:17]
• Many sources advocate limiting difficult focused work to 90 minutes or less to align with ultradian cycles
Andrew Huberman's personal use of 90-minute work blocks[11:35]
• He uses 90-minute work cycles himself and finds them extremely powerful for focus

Neurochemical basis of 90-minute focus limits

Acetylcholine, dopamine, and norepinephrine in focused work[11:51]
• These neuromodulators support narrow focus, motivation, and drive, and their release follows ultradian patterns
Finite capacity of focus-related circuits[11:51]
• After about 90 minutes, neurons that release these chemicals are far less willing to engage, making high-level focus harder

Starting and spacing ultradian focus bouts

You can initiate a 90-minute cycle deliberately[12:09]
• The cycle does not have to begin immediately upon waking; you can decide when a focused 90-minute work bout starts
Limits on consecutive focus cycles[12:24]
• You cannot effectively stack one intense 90-minute bout directly onto another; circuits need recovery
Recommended number and spacing of cycles[13:01]
• Suggests spacing focus blocks by 2-4 hours and notes most people can handle one or two such cycles per day
• Defines this work as very focused, hard problem-solving, as opposed to checking email or social media

Forms of time perception

Distinguishing entrainment from time perception

Previous discussion focused on subconscious oscillatory rhythms[14:13]
• Circannual, circadian, and ultradian rhythms govern background biological timing but are not the same as conscious time perception

Three types of time perception

Perception of current passage of time (interval timing)[14:43]
• Describes this as an internal ticking-either fine-sliced (many small ticks) or coarse (larger ticks)-governing how fast or slow the present feels
Prospective timing (future intervals)[15:04]
• Like a stopwatch: you are asked to measure off an interval into the future (e.g., two or five minutes) without external clocks
• For longer intervals, you must internally decide how to set and count the tick marks to estimate time
Retrospective timing (past intervals)[15:44]
• Relies on memory to reconstruct events and their relative ordering, such as inferring time between lunch and dinner from remembered clock times

Neuromodulators and subjective speed of time

Key neuromodulators involved in time perception

Dopamine, norepinephrine, and serotonin[16:40]
• These neuromodulators change whether we fine-slice time into small segments or batch it into larger bins

Effects of dopamine and norepinephrine on interval timing

More dopamine leads to overestimation of elapsed time[16:56]
• When given drugs that increase dopamine, people asked to estimate one minute tend to report that the minute is up too early (e.g., at ~38 seconds)
Norepinephrine has a similar effect to dopamine[18:16]
• Norepinephrine (noradrenaline) also biases people toward overestimating how much time has passed

Serotonin's opposing effect

Serotonin causes underestimation of elapsed time[18:48]
• When serotonin levels are higher, people tend to think less time has passed than actually has

Circadian modulation of neuromodulators and daily time perception

Time-of-day changes in dopamine, norepinephrine, and serotonin

Morning bias toward dopamine and norepinephrine[19:00]
• Evidence suggests that in the approximate first half of the day, dopamine and norepinephrine are relatively elevated compared to serotonin
Evening and night bias toward serotonin[19:10]
• In the second half of the day and especially toward evening and night, serotonin levels tend to increase

Implications for structuring the day and productivity

Different time perception profiles across the day[19:16]
• Because neuromodulator levels vary across the circadian cycle, our experience of how fast or slow time passes differs in morning vs. evening
Advice to do hardest tasks early in the day[19:27]
• Notes that most productivity literature recommends tackling the most important or least appealing tasks early in the day and endorses this

Sleep disruption and neuromodulator dysregulation

Impact of poor sleep on dopamine, norepinephrine, and serotonin[20:43]
• When sleep is too short, fragmented, or low quality across days, one of the first consequences is dysregulation of these neuromodulatory states throughout the day

Trauma, overclocking, and memory encoding

Overclocking during traumatic events

Definition of overclocking[21:05]
• Overclocking refers to extremely increased frame rate of perception, often experienced as events unfolding in ultra slow motion during trauma
Role of dopamine and norepinephrine in overclocking[20:43]
• During highly arousing events such as car accidents, dopaminergic and noradrenergic activity can increase dramatically, fine-slicing time

Memory system as a space-time recorder

Involvement of hippocampus and neocortex[21:17]
• These brain regions record which neurons fired (space code) and when (rate/timing code) during experiences
Example of encoding a car accident[22:04]
• Neurons representing visual motion, sounds, and emotional reactions fire in specific sequences and rates, and these patterns are replayed into hippocampus for storage
Importance of rate coding for memory capacity[22:54]
• Using different firing rates of overlapping neuron sets allows many more memories to be stored without requiring an enormous hippocampus

Why overclocked trauma memories are hard to shake

Dense encoding leads to persistent replay[23:18]
• When events are encoded at a very high frame rate, the resulting memory can be extremely vivid and repeatedly intrude into awareness
Goal of trauma treatment[23:47]
• Trauma therapy aims not to erase the memory but to separate or reduce the emotional weight attached to the stored memory

Clarifying dopamine's role in aversive events

Dopamine is not just a reward molecule[24:04]
• He emphasizes dopamine is more accurately a molecule of motivation, pursuit, and drive, not simply pleasure
Co-release of dopamine and norepinephrine in arousal[24:41]
• Any heightened arousal state-positive or negative-typically involves increases in both dopamine and norepinephrine

Dopamine, retrospective time, and paradoxes of fun vs. boredom

Neuromodulators and retrospective time perception

Dopamine changes how we remember timing of past events[26:36]
• Different dopamine states alter not only present experience but also the remembered rate at which events unfolded

Paradox of exciting vs. boring experiences

Exciting, varied events feel fast but are remembered as long[27:21]
• Example: a child's day at an amusement park or an amazing vacation day seems to fly by in the moment but is later recalled as a long, rich sequence of events
Boring or disliked events feel long but are remembered as short[27:30]
• Tasks that are tedious or unpleasant drag in real time, yet in memory later they occupy a relatively small space

Two internal "stopwatches" governed by neuromodulators

Dopaminergic stopwatch for fine slicing[27:41]
• He likens high-dopamine states to a stopwatch capturing high-frame-rate movies of experience
Serotonergic or low-dopamine stopwatch for coarse bins[28:48]
• In lower-dopamine or higher-serotonin states, the internal hand moves in larger steps, batching time into bigger intervals

Novelty, place, social relationships, and perceived duration

Novel experiences and feeling of time spent in a place

More novelty makes a place feel more familiar and time-rich[29:39]
• Research shows that the more novel experiences one has in a given location, the more one feels they know that place and the longer they feel they have been there

Thought experiment of living in New York City

Same calendar time, different perceived duration[29:13]
• Living in one apartment for a year with about 100 exciting experiences leads to one sense of that year
• Living in three different places, meeting three times as many people, and having three times the novel experiences makes that same year feel much longer in hindsight

Novel environments and social bonding

Changing settings with another person accelerates felt familiarity[30:39]
• Moving through several novel environments with someone else tends to increase the feeling that you know each other well and that they know you

Dopamine as a flexible currency and the role of habits

Dopamine release sets experiential frame rate

Dopamine responds to hoped-for and surprising events[31:21]
• Dopamine is released when something we expect or want happens and also when surprising events occur, even if negative
Global influence of dopamine on time perception[31:39]
• How often and when dopamine is released effectively sets the frame rate for perception across all experiences, not just those directly tied to reward or punishment

Habits as tools to structure time and dopamine

Placing habits at specific daily intervals[31:45]
• He recommends using specific, repeated routines at particular times of day to harness dopamine and create functional segments of the day
Morning habit as a time-bin marker[32:35]
• Example: waking up and immediately engaging in a consistent habit that triggers dopamine, marking the start of a distinct time block
Subsequent habits further partition the day[33:02]
• Another routine, such as around breakfast, can serve as another regular marker that segments the day into functional units
Regular sequencing vs. obsessive precision[32:40]
• He notes that these routines need not be timed to the minute but should occur in a regular sequence to effectively shape perception of the day
Dual effect of dopamine-linked habits[33:02]
• Such habits both provide dopamine-related feelings of motivation and reward and form the scaffolding for how one experiences and remembers the day's passage

Closing summary and recommended reading

Recap of key topics

Coverage of entrainment, dopamine, habits, and routines[35:02]
• Summarizes that the episode addressed entrainment (circannual, circadian, ultradian), the role of dopamine, and how habits and routines can adjust one's sense of time for specific goals

Book recommendation on time

Your Brain is a Time Machine by Dean Buonomano[35:26]
• Recommends the book "Your Brain is a Time Machine: The Neuroscience and Physics of Time" by Professor Dean Buonomano of UCLA as an excellent resource on time

Closing thanks

Expresses gratitude[35:38]
• Thanks listeners for their time, attention, and interest in science

Lessons Learned

Actionable insights and wisdom you can apply to your business, career, and personal life.

1

Aligning your behavior with circadian and ultradian rhythms-especially light exposure, sleep, and 90-minute focus blocks-can significantly improve mood, health, and performance by matching internal biology to the external day.

Reflection Questions:

  • • How consistently do I expose myself to morning and evening daylight, and how might adjusting that improve my sleep and daytime alertness?
  • • In what parts of my day could I carve out one 60-90 minute block for truly focused work that respects my natural energy peaks?
  • • What specific change to my sleep or light routine will I implement this week to better align with my circadian rhythm?
2

Your perception of how fast or slow time moves is heavily shaped by neuromodulators like dopamine, norepinephrine, and serotonin, so choosing when to do stimulating versus calming activities can strategically alter how you experience and remember your day.

Reflection Questions:

  • • When during the day do I naturally feel most alert and engaged, and how does that map onto the tasks I currently schedule then?
  • • How could I rearrange demanding, exciting, or tedious tasks to better match the times when my brain is naturally more dopaminergic versus more serotonergic?
  • • What is one task I can move to a different time of day over the next week to experiment with its impact on my time perception and productivity?
3

Novelty dramatically expands the felt length and richness of experiences, so deliberately seeking varied environments and activities can make time feel fuller and deepen your sense of connection to places and people.

Reflection Questions:

  • • Which areas of my life currently feel monotonous, and where could I introduce small but meaningful forms of novelty (new routes, settings, or activities)?
  • • How might planning experiences with others in multiple different environments change the depth of those relationships over the next few months?
  • • What is one new environment or experience I can schedule in the coming week to test how it affects my sense of time and engagement?
4

Highly arousing events, including traumas, are encoded at a very high perceptual "frame rate," which explains why they feel vivid and persistent; effective coping focuses on changing the emotional weight of these memories rather than trying to erase them.

Reflection Questions:

  • • What intense past experiences still feel unusually vivid to me, and how do they influence my current reactions or decisions?
  • • How could acknowledging that my brain overclocked during those events change the way I interpret intrusive memories or emotional responses?
  • • What supportive practice or professional resource could I engage with to help decouple the emotional charge from a difficult memory I'm carrying?
5

Regular habits placed at consistent points in your day act as dopamine-linked anchors that segment time into functional units, making your days more structured, predictable, and easier to manage mentally.

Reflection Questions:

  • • What are the first three things I typically do after waking, and are they consistent enough to serve as reliable anchors for my day?
  • • How might adding a simple, rewarding habit at the start of a key time block (morning, midday, or evening) change how coherent and productive that block feels?
  • • Which single new habit can I place at a fixed time over the next two weeks to help carve out a clearer segment of my day?

Episode Summary - Notes by Quinn

Essentials: Time Perception, Memory & Focus
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