Time Perception, Memory & Focus | Huberman Lab Essentials

Welcome to Huberman Lab Essentials,

where we revisit past episodes for the

most potent and actionable science-based

tools for mental health, physical

health, and performance.

I'm Andrew Huberman and I'm a professor

of neurobiology and opthalmology at

Stanford School of Medicine. Today we

are talking about time perception. Our

perception of time is perhaps the most

important factor in how we gauge our

life. And the reason for that is that

our perception of time is directly

linked to the neurochemical states that

control mood, stress, happiness,

excitement. And of course, it frames the

way in which we evaluate our past. It

frames our present, whether or not we

think we are on track or off track. And

it frames our sense of the future. So

let's talk about time perception. And

the most fundamental aspect of time

perception is something called

entrainment. Entrainment is the way in

which your internal processes, your

biology and your psychology are linked

to some external thing. And the most

basic form of entrainment that we are

all a slave to all year round for our

entire life are so-called circanial

rhythms. We have neurons, nerve cells in

our eye, in our brain, and in our body

that are marking off the passage of time

throughout the year. Literally a

calendar system in your brain and body.

And the way this works is beautifully

simple.

Light seen by your eyes inhibits,

meaning it reduces the amount of a

hormone released in your brain called

melatonin. Melatonin has two major

functions. One function is to make you

sleepy at night and the other is to

regulate some of the other hormones of

the body in particular testosterone and

estrogen. Throughout the year, depending

on where you live, day length varies.

And as a consequence, the amount of

light from the sun that is available to

you varies. So when days are long, the

amount of melatonin in your brain and

body that's released tends to be less.

When days are very short, the amount of

melatonin that's released and the

duration that that melatonin exists in

your brain and body tends to be much

longer. So melatonin correlates with

daylength.

And if we are viewing more light, we

have less melatonin. We view less light,

we have more melatonin.

You see different amounts of light each

day. But we have a process in our brain

and body that averages the amount of

light that you're seeing both from

artificial sources and from sunlight and

measures that off. And it's so

exquisitly precise that for a given say

8hour day in the spring because spring

in the northern hemisphere or elsewhere

you know days are getting longer.

That means that the amount of melatonin

is getting progressively less and less.

And that signal is conveyed to all the

systems of your brain and body. And this

is why most people, not all, but most

people feel like they have more energy

in the spring. Conversely, when you have

an 8-hour day in the winter, the amount

of melatonin that corresponds to that 8

hour day is getting progressively

greater and greater because why? Days

are getting shorter. So melatonin is

increasing from day to day to day. Every

cell and system of your body pays

attention to this and as a consequence

most people not all but most people feel

they have a little less or sometimes a

lot less energy and a slightly lower

mood in the winter months. Now there are

exceptions to this of course but the

melatonin signal is the way in which

your internal state your mood your sense

of energy even your appetite is

entrained is matched to some external

event. In this case the event is the

rotation of the earth around the sun.

There are other forms of entrainment

meaning the matching of your brain and

body to things that are happening in

your external environment across the

calendar year. The amount of

testosterone and estrogen that human

beings make varies such that in longer

days they tend to make more testosterone

and estrogen than in shorter days. The

next level of time or bin of time as we

say that we are all entrained or matched

to is the so-called circadian time cycle

which is 24-hour rhythm. This is perhaps

the most powerful rhythm that we all

contain and that none of us can escape

from.

We all have this circadian clock that

resides over the roof of our mouth. The

cells in that circadian clock fire,

meaning they release chemicals into our

brain and body on a very regular rhythm.

Not surprisingly, there are periods of

every 24-hour cycle when we are very

active and we tend to be alert and

others when we are asleep. We have this

circadian clock. It oscillates. It goes

up and down once every 24 hours and then

repeats. Every cell of our body has a

24-hour oscillation in the expression of

various genes. They are entrained as we

say to the outside light dark cycle

because morning sunlight, evening

sunlight and the lack of light in the

middle of the night make sure that the

changes these oscillations that are

occurring within the cells of our brain

and body are matched to the outside

light dark cycle. And I cannot emphasize

enough how important it is that your

circadian entrainment be precise.

Why? Because disruptions in circadian

entrainment cause huge health problems.

They increase cancer risk. They increase

obesity. They increase mental health

issues. They decrease wound healing.

They decrease physical and mental

performance. They disrupt hormones. You

want your cells to be linked to the

circadian cycle that's outside you. And

the circadian cycle outside you mainly

consists of when there's sunlight and

when there is not. And that's why the

simple protocols to fall out of this

whole discussion about circadian

entrainment are the following. View 10

to 30 minutes of bright light, ideally

sunlight within an hour of waking,

assuming that you're waking early in the

day. Especially you wake up early in the

day, get outside, see sunlight. Do that

again in the afternoon or around evening

10 to 30 minutes depending on how bright

it is outside. Basically, you want as

much bright light ideally from sunlight

in coming in through your eyes

throughout the day. And then in the

evening, you want as little bright light

coming in through your eyes. There are

other ways to so-called entrain your

circadian clock. One of the best ways to

do that is to engage in physical

activity at fairly regular times of day.

You don't have to do it every day, but

if you're going to exercise, try and

exercise at a fairly consistent time of

day. What happens when this circadian

clock starts getting disrupted? I mean,

this is after all an episode about time

perception. It's not an episode about

circadian rhythms and entrainment. Well,

there's a classic study by Ashoff done

in 1985 that's now been repeated many

times where they had people go into

environments where they didn't have

clocks and they didn't have windows and

they didn't have watches and they were

sometimes even in constant dark or

constant light. And they evaluated how

well people perceive the passage of time

on shorter time scales. And what they

found was really interesting. And what

they found is that people underestimate

how long they were in these isolated

environments. So after 42 days or so,

they'd ask people, "How long do you

think you've been in here?" And people

would say, "8 days or 36 days." They

generally underestimated how long they

had been in this very odd environment

with no clocks or watches or exposure to

sunlight or regular rhythms of

artificial light. In addition, they

found that their perception of shorter

time intervals was also really

disrupted. So if they asked them to

measure off 2 minutes, normally people

are pretty good at measuring off 2

minutes, people come within, you know, 5

to 15 seconds uh at most. Well, when

people's circadian clocks or circadian

entrainment, I should say, was

disrupted, their perception of time

measurement on shorter time scales of

minutes or even seconds was greatly

disrupted. And as we'll see in a couple

of minutes, that actually causes great

problems for how you contend with work,

how you contend with challenges of

different kinds. You want your circadian

entrainment to be pretty locked in or

pretty entrained to the outside light

dark cycle so that your perception of

time on shorter time intervals can be

precise because the ability to perceive

time accurately for the given task or

given thing that you're involved in

turns out to be one of the most

fundamental ways that predicts how well

or poorly you perform that thing or

task. Next, I'd like to talk about

so-called altradian entrainment.

Altradian rhythms are rhythms of about

90 minutes or so. And all of our

existence is broken up into these

90minute altradian cycles. When you go

to sleep at night, whether or not you

sleep 6 hours or 4 hours or 8 hours or

10 hours, that entire period of sleep is

broken up into these 90-minute altradian

cycles. However, when you wake up in the

morning, many of the things that you do

are governed by these altradian rhythms.

For instance, the 90inut time block

seems to be the one in which the brain

can enter a state of focus and alertness

and do hard work and focus, focus,

focus. And then at about 90 minutes,

there's a significant drop in your

ability to engage in this mental or

physical work. Now, everybody

from, you know, the self-help literature

to the business literature to the pop

psychology literature has tried to

leverage these altradian cycles by

saying if you're going to do something

hard and you want to focus on it, limit

it to 90 minutes or less. And I am one

of those people who's also joined that

conversation and indeed I use 90-minute

work cycles and I think uh they are

extremely powerful. While this isn't

time perception per se, it is again an

example of entrainment. What are we in

training to? Well, what you're in

training to is the release of particular

neurochemicals, in this case

acetylcholine and dopamine that allow

your brain to focus for particular

periods of time, 90 minutes or so. And

after about 90 minutes or so, the amount

of those chemicals that can be released

tends to drop very low, which is why

your ability to focus becomes

diminished. I always get the question,

how do you know when the 90-minut cycle

begins? In other words, let's say you

wake up at 8:00 a.m. and you just

finished a 90-minute sleep cycle. Does

that mean that your next 90-minute cycle

where you could do work begins right at

8:01? No. The interesting thing about

these basic rest activity cycles, these

altranian rhythms, is that you can

initiate them whenever you want. You can

set a clock and decide, okay, now the

focus begins. Now the work begins. And

this 90minut cycle is the period in

which I'm going to do work. What you

can't negotiate, however, is that at

about 100 minutes or 120 minutes, no

matter who you are, you're going to see

a diminishment in performance. You're

not going to focus as well. And that's

again because of the way that these

90-minute cycles are linked to the

ability of the neurons that release

acetylcholine and dopamine and to some

extent norepinephrine, the things that

give us narrow focus, motivation, and

drive. the way that these 90-minute

cycles are involved in those circuits.

After about 90 minutes, those circuits

are far less willing to engage, and

therefore, it's much harder to continue

to focus to a high degree. Some people

like to do multiple 90-minute cycles per

day of focus. In that case, you need to

separate them out. You can't do one

90minut cycle, then go right into

another 90-minut cycle, then another

90-minut cycle. You can't cheat these uh

circuits related to acetylcholine and

dopamine and norepinephrine.

Unfortunately for me, I can do one midm

morning. I can probably do another one

in the afternoon. This is not the kind

of work that's like checking email or

text messaging or social media. This is

very focused, hard work. It's working on

hard problems of various kinds. And this

will be differ for everybody. So I

recommend that they be spaced by at

least 2 to four hours. And most people

probably won't be able to handle more

than two per day. There are probably

some mutants out there that could do

three or four, but that's exceedingly

rare. I think even one a day is going to

feel like a significant mental

investment and afterwards you're going

to feel pretty taxed. So now we've

talked about circanial, circadian, and

ultradian rhythms, but we haven't really

talked about time perception per se.

We've mainly talked about the

subconscious slow oscilly ways in which

we are entrained or matched to the year

or to the day and these altranian cycles

that we can impose on our work and that

we can leverage toward more focus if we

like. But what about the actual

perception of time? What actually

controls how fast or how slowly we

perceive time going by? There are

basically three forms of time perception

that we should all be aware of. One is

our perception of the passage of time in

the present. How quickly or slowly

things seem to be happening for us. This

is kind of like an interval timer.

Ticking off time. Tick tick tick tick

tick tick. It's either fine slicing like

that or tick

tick tick. We have interval timers. I'll

discuss the basis of those interval

timers. We also engage in what's called

prospective timing, which is like a

stopwatch, measuring off things as they

go forward. That might sound a little

bit like what I just described, but it's

actually uh a little bit different. For

instance, if I told you to start

measuring off a twominut time interval

into the future, you could do that

pretty well. But if I told you you had

to measure a five minute timer interval

into the future and you couldn't use any

clocks or watches or your phone or

anything like that, you would have to

set the tick marks. You'd have to decide

how many times you were going to count

off during that five minute time block.

There's also retrospective time, which

is how you measure off time in the past.

So, if I say, you know, last week I know

you went to the park, you did some

things with friends, you know, you went

out in the evening. Um, how long was it

between lunch and when you went to

dinner with friends? You probably think,

okay, well, I remember I went to dinner

at 7:00 and we had lunch right around 2.

You're using memory to reconstruct

certain sets of events in the past and

get a sense of their relative

positioning within time. Okay, so we

have retrospective current time interval

measurements and then prospective time

measurement into the future.

The beauty of time perception in the

human nervous system is that it boils

down to a couple of simple molecules

that govern whether or not we are fine

slicing time or whether or not we are

batching time in larger bins. Those

molecules go by names that maybe you've

heard. Things like dopamine and

norepinephrine. Neurom modulators called

neurom modulators because they modulate.

They change the way the other neural

circuits work. Also things like

serotonin.

Serotonin is released from a different

site in the brain than dopamine and

norepinephrine is and has a different

effect on time perception. So just to

give you an example of how things like

dopamine and serotonin can modulate our

perception of time, I want to focus on a

little bit of literature that now has

been done fortunately in animals and

humans and which essentially shows that

the more dopamine that's released into

our brain, the more we tend to

overestimate the amount of time that has

just passed. Let me repeat that. The

more dopamine that is released into our

brain, the more we tend to overestimate

how much time has passed. These

experiments are very straight

straightforward, excuse me, and they're

very objective, which is really nice,

which is you can give people or an

animal a drug that increases the amount

of dopamine and then ask them to measure

off without any measurement device like

a watch or a clock when one minute has

passed. As dopamine levels rise in the

brain, people tend to think that the

minute is up before a minute. So they at

the 38 second mark, they'll say, "Okay,

I think a minute is up." So they've

overestimated how much time has passed.

Okay? The higher the level of dopamine,

the more people tend to overestimate.

Now, it's also true that norepinephrine,

also called noradrenaline, plays a role,

and its role is very similar to that of

dopamine. Conversely, the neurom

modulator serotonin causes people to

underestimate the amount of time that's

passed. So, this is very interesting.

It's interesting in terms of how

pharmarmacology can be used to adjust

time perception, but it's also

interesting in the context of that

circadian rhythm. There's some emerging

evidence that throughout the 24-hour

cycle, there are robust changes in the

amount of dopamine, norepinephrine, and

serotonin that are present in the brain

and bloodstream and body depending on

time of day within the circadian cycle.

So

much of the evidence points to the fact

that in the first half of the day,

approximate first half of the day,

dopamine and norepinephrine are elevated

in the brain, body and bloodstream much

more than is serotonin. And that in the

second half of the day and in particular

towards evening and nighttime, serotonin

levels are going up. What that means is

that our perception of the passage of

time will be very different in the early

part of the day and in the latter half

of the day. Now this is important in

terms of how one thinks about

structuring their day because I know

many people are thinking about the

various tasks that they need to do

throughout their day.

Many or I should say all of the

literature at least that I can find on

productivity and things of that sort

point to the idea that we should be

doing the hardest task, the thing that

we want to do the least or the most

important task early in the day as a

kind of a psychological tool for getting

it done and feeling as if we

accomplished something. And I think

that's an excellent protocol frankly.

And as an aside to support what I said,

but also to take us back to this

critical role of the circadian rhythm,

there is a lot of evidence that when

one's sleep is disrupted, when sleep is

either too short or is fragmented or is

not of high enough quality for enough

days, one of the first things to happen

is that there is a disregulation of

these dopamineergic, neurogeneric and

serotonin states throughout the day.

Now, there is a version of how dopamine

and norepinephrine can impact our

perception of the passage of time in

ways that can be very disruptive or even

maladaptive.

And the best example that I'm aware of

is trauma. Many people who have been in

car accidents or who have experienced

some other form of major trauma

do what's called overclocking.

Overclocking

is when levels of dopamine and

norepinephrine increased so much during

a particular event that we fine slice.

In other words, the frame rate is

increased so much so that we perceive

things as happening in ultra slow

motion. Now that might not seem like a

bad thing overall, but the problem with

overclocking is the way in which that

information gets stamped down into the

memory system. So the memory system

which involves areas of the brain like

the hippocampus but also the neoortex is

basically a space-time recorder. What do

I mean by space-time recorder? Well,

your nervous system of course is housed

in the uh darkness of your skull. It

doesn't have a whole lot of information

about the outside world except light

coming in through the eyes and whatever

happens to hit our ears and in terms of

sound waves and and skin and and so

forth. So it has to take all those

neural signals and it has to create a

record of what happened. Now it doesn't

create a record of everything that

happened but car accidents and trauma

and things of that sort oftentimes are

stamped down into our record of what

happened. And what gets stamped down,

what we actually mean by the phrase

stamped down is that the precise firing

of the sequence of neurons that

reflected some event. So let's say I'm

in a car accident. Certain neurons are

firing because of the flipping of the

car or there screams or there's blood or

you know things of that sort. All of

that neural activity gets repeated in

the hippocampus and then the sequence of

the firing of those neurons is also

remembered. So it's not just that neuron

1 2 3 4 fired in that sequence. It's

also that neuron 1 2 3 4 fired at a

particular rate. So it would be 1 2 3 4

during the actual event and then the

memory is stored as firing of those

neurons as 1 2 3 4. Right? If it if

during the event it was 1 2 3 4 at that

rate the storage of the memory is not

going to be one two 34. Okay. In other

words there's both a space code as we

say meaning the particular neurons that

fire is important and there's a rate

code how quickly those neurons fire or

the relative firing the timing of the

firing of those neurons is also part of

the memory. This affords our memory

system tremendous flexibility. What it

means is that you can take the same set

of neurons in the hippocampus and stamp

down many many more memories because all

you have to do is use a match of the

different rates of the different neurons

that were firing in order to set that

code right you don't otherwise if you

needed a different set of neurons for

every memory you need an enormous

hypocampus you need an enormous head so

I think I think you get the basic idea

overclocking is a case in which the

frame rate is so high that a memory gets

stamped down and people have a very hard

time shaking that memory and the

emotions associated with that memory. In

fact, you know, one of the first things

that trauma victims learn is that they

aren't going to forget what happened.

What's eventually going to happen

ideally with good treatment is that the

emotional weight of the experience will

eventually be divorced from the memory

of the experience. Some of you are

probably saying, why dopamine during

trauma? I thought dopamine was the

feel-good molecule. Well, uh, in

reality, dopamine is not necessarily a

molecule of reward. It's a molecule of

motivation, pursuit, and drive. And

because of the close relationship

between dopamine and norepinephrine,

often times they are co-released. So

whether or not dopamine is released

during car crashes or other forms of

trauma, we don't know. But what we do

know is that both the dopamine system

and neurageneric system, when we say

norineric, we mean norepinephrine. Those

systems are greatly increased anytime

there's a heightened state of arousal.

And arousal can have negative veilance

like a meaning associated with an event

that we really hate that we would prefer

not to be involved in or it can have

positive veilance. But dopamine and

norepinephrine are kind of the common

hallmark of all things of elevated

arousal. And so that's why we see

evidence for dopamine being associated

with these changes in time perception

both for positive events and for

negative events. Now, up until now, I've

been talking about how dopamine and to

some extent serotonin can differentially

impact your perception of how fast or

how slowly things are happening in the

moment. But remember, we have

prospective time, we have our experience

of time in the moment, and we have

retrospective time. And there are

beautiful studies that have showed that

the dopamineergic state changes the way

not just that we experience things now

but that it changes the way in which we

remember things in the past and the rate

at which those things occurred and those

are in opposite direction. So to make

this very simple, if something that you

experience is fun or varied, meaning it

has a lot of different components in it

and is in other words is associated with

an increase in dopamine in your brain.

You will experiencing experience that as

going by very fast. Imagine an amazing

day for a kid in amusement park. They

can do a ton of things. It's all new.

They're very excited and they'll feel

like it goes by very fast, but later

they will remember that experience as

being very long, that it was a long day

full of many, many events. And so

there's this paradoxical relationship

between how we perceive fun, exciting,

varied events in the present and how we

remember them in the past. For those of

you that have gone on vacation, if

you've had an amazing day on vacation,

it'll seem like or an amazing vacation

overall, it will seem like it goes by

very fast. The last day of vacation, you

sort of go, whoa, it went by so fast

because there's so much happening. But

in memory, 6 to 8 months later, you'll

remember, wow, that that just went, you

know, that was a long long thing. We had

this, then we had that, then we did

this, then we had that. It tends to

spool out in a longer memory than the

actual experience. Conversely, if you're

bored with something or it's something

you really don't like, it's going to

seem like it takes a long time to go

through that experience in the moment.

But retroactively looking back, it will

seem like that moment was very short.

And so, the reason I bring this up is we

aren't just driven by these circadian

clocks and these circanial clocks and

these altradian clocks. We are driven by

these timers that vary depending on our

level of excitement and they vary on

depending on our level of excitement

because of these neurom modulators

dopamine and serotonin. So the way I

like to think about it is that you have

two clocks, two stopwatches. One is a

dopamineergic stopwatch that fine slices

really closely. It's like counts off

milliseconds and it's grabbing a movie

of your experience at very high

resolution. And in the other hand, you

have a a stopwatch that's gathering big

time bins, big ticks along the the uh

you know that the hand is moving at

bigger intervals. You know, marking off

time and depending on whether or not

you're excited or whether or not you're

bored, you're using different

stopwatches on time and therefore you're

perceiving your experience differently.

One very interesting aspect to the way

that neurom modulators like dopamine and

novelty interact with time perception

and memory is how we perceive our

relationship to places and people.

So really interesting literature showing

that the more novel experiences we have

in a place,

the more we feel we know that place

obviously, but the longer we feel we've

been there. So here's the kind of

gdunkan or thought experiment that

illustrates uh what's in the literature.

Let's say I were to move to New York

City. I happen to really like New York

City. I've never lived there, but let's

say I live there. Uh I lived in a given

apartment uh for a year and I would have

a number of different uh experiences.

And this mental experiment, let's say uh

I had a hundred uh different exciting

and new experiences.

I would at the end of that year feel as

if I lived there a certain period of

time, one year. I would actually know I

lived there one year. If however I lived

in three different places in New York

City and I met three times as many

people and I had three times as many

novel experiences, I would actually feel

as if I had been there much longer than

had I only lived in one location. This

is also true for social interactions.

When we move to multiple or several

novel environments with somebody else,

we tend to feel as if we know that

person much better and that they know us

much better. Now, that's all very

interesting and speaks to the fact that

dopamine is a kind of flexible currency

in the brain. It's doled out, if you

will, or released when something that

one hopes will happen happens. And it's

released when there's a surprise, even

if it's a kind of a negative surprise.

It's not something that the subject

wanted to happen.

But the more interesting thing is how

that relates to time perception. What I

mean is how often and when you release

dopamine is actually setting the frame

rate on the entire perception of

everything not just of for positive

events or negative events. This

governance over our perception of time

that dopamine has points to a very clear

very actionable and very powerful tool

and that is a tool that many people have

talked about before which are habits.

People have discussed habits in a

variety of contexts, but in the context

of dopamine reward and time perception,

what this means is that placing specific

habitual routines at particular

intervals throughout your day is a very

not just convenient, but a very good way

to incorporate the dopamine system so

that you divide your day into a series

of what I would call functional units.

What would this look like? It would mean

waking up and having one specific habit

that you always engage in that causes a

release of dopamine. You could say,

"Well, great. That'll make me feel

good." And I would would agree dopamine

release generally makes us feel

motivated, but it would have an

additional effect of marking that time

of day as the beginning of a particular

time bin. then inserting another habit

perhaps the beginning of I don't know

your breakfast or something but

recognizing that that's a habit and

being fairly habitual. You don't have to

be you know obsessively precise about

the timing but that the that regular

sequencing of things is going to lead

not just to dopamine release as it

relates to reward and motivation and

feeling good but it actually becomes the

way in which we carve up our entire

experience of our day. Today we covered

a lot about time perception. We

certainly didn't cover everything about

time perception, but we covered things

like entrainment, the role of dopamine,

habits, and various routines that can

adjust your sense of time for sake of

particular goals. If you're interested

in learning more about time perception,

I'd like to point you to a really

excellent book called Your Brain is a

Time Machine, the neuroscience and

physics of time. The book was written by

Professor Dr. Dean Bornemano, who's a

professor at UCLA and a world expert in

the neuroscience and physics of time.

Thank you for your time and attention

today. And last, but certainly not

least, thank you for your interest in

science.

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