Time Perception, Memory & Focus | Huberman Lab Essentials

00:00:00.200 | - Welcome to Huberman Lab Essentials,

00:00:02.360 | where we revisit past episodes

00:00:04.420 | for the most potent and actionable science-based tools

00:00:07.600 | for mental health, physical health, and performance.

00:00:10.360 | I'm Andrew Huberman,

00:00:12.760 | and I'm a professor of neurobiology and ophthalmology

00:00:15.600 | at Stanford School of Medicine.

00:00:17.560 | Today, we are talking about time perception.

00:00:20.680 | Our perception of time is perhaps the most important factor

00:00:24.560 | in how we gauge our life.

00:00:26.680 | And the reason for that is that our perception of time

00:00:29.880 | is directly linked to the neurochemical states

00:00:32.660 | that control mood, stress, happiness, excitement.

00:00:36.860 | And of course, it frames the way

00:00:38.920 | in which we evaluate our past.

00:00:41.560 | It frames our present,

00:00:42.760 | whether or not we think we are on track or off track,

00:00:45.500 | and it frames our sense of the future.

00:00:48.180 | So let's talk about time perception.

00:00:50.080 | And the most fundamental aspect of time perception

00:00:52.620 | is something called entrainment.

00:00:54.780 | Entrainment is the way in which your internal processes,

00:00:58.680 | your biology and your psychology are linked

00:01:01.460 | to some external thing.

00:01:03.400 | And the most basic form of entrainment

00:01:05.660 | that we are all a slave to all year round

00:01:10.360 | for our entire life are so-called circanial rhythms.

00:01:14.900 | We have neurons, nerve cells in our eye, in our brain,

00:01:19.660 | and in our body that are marking off the passage of time

00:01:24.700 | throughout the year.

00:01:26.440 | Literally, a calendar system in your brain and body.

00:01:29.180 | And the way this works is beautifully simple.

00:01:32.040 | Light, seen by your eyes, inhibits,

00:01:37.440 | meaning it reduces the amount of a hormone released

00:01:40.440 | in your brain called melatonin.

00:01:43.440 | Melatonin has two major functions.

00:01:45.340 | One function is to make you sleepy at night.

00:01:48.120 | And the other is to regulate some of the other hormones

00:01:51.280 | of the body, in particular, testosterone and estrogen.

00:01:54.160 | Throughout the year, depending on where you live,

00:01:56.820 | day length varies.

00:01:58.640 | And as a consequence, the amount of light from the sun

00:02:02.620 | that is available to you varies.

00:02:05.060 | So when days are long, the amount of melatonin

00:02:08.220 | in your brain and body that's released tends to be less.

00:02:11.600 | When days are very short,

00:02:13.440 | the amount of melatonin that's released

00:02:15.520 | and the duration that that melatonin exists

00:02:17.720 | in your brain and body tends to be much longer.

00:02:20.440 | So melatonin correlates with day length.

00:02:23.920 | And if we are viewing more light, we have less melatonin,

00:02:28.420 | we view less light, we have more melatonin.

00:02:33.780 | You see different amounts of light each day,

00:02:36.560 | but we have a process in our brain and body

00:02:40.020 | that averages the amount of light that you're seeing,

00:02:42.380 | both from artificial sources and from sunlight,

00:02:44.920 | and measures that off.

00:02:46.780 | And it's so exquisitely precise

00:02:49.760 | that for a given, say, eight-hour day in the spring,

00:02:54.320 | because spring in the Northern Hemisphere or elsewhere,

00:02:57.000 | days are getting longer,

00:02:59.820 | that means that the amount of melatonin

00:03:02.260 | is getting progressively less and less,

00:03:04.500 | and that signal is conveyed to all the systems

00:03:06.780 | of your brain and body.

00:03:08.160 | And this is why most people, not all,

00:03:09.980 | but most people feel like they have more energy in the spring.

00:03:13.560 | Conversely, when you have an eight-hour day in the winter,

00:03:18.400 | the amount of melatonin that corresponds to that eight-hour day

00:03:22.360 | is getting progressively greater and greater,

00:03:25.140 | because why?

00:03:26.140 | Days are getting shorter,

00:03:27.280 | so melatonin is increasing from day to day to day.

00:03:31.180 | Every cell and system of your body pays attention to this,

00:03:33.580 | and as a consequence, most people, not all,

00:03:35.340 | but most people feel they have a little less,

00:03:37.640 | or sometimes a lot less energy,

00:03:39.280 | and a slightly lower mood in the winter months.

00:03:42.180 | Now, there are exceptions to this, of course,

00:03:44.480 | but the melatonin signal is the way in which

00:03:48.080 | your internal state, your mood, your sense of energy,

00:03:52.660 | even your appetite is entrained,

00:03:55.560 | is matched to some external event.

00:03:57.860 | In this case, the event is the rotation of the earth

00:04:00.680 | around the sun.

00:04:02.040 | There are other forms of entrainment,

00:04:04.240 | meaning the matching of your brain and body

00:04:06.720 | to things that are happening in your external environment.

00:04:09.180 | across the calendar year,

00:04:11.180 | the amount of testosterone and estrogen

00:04:13.720 | that human beings make varies,

00:04:16.180 | such that in longer days,

00:04:18.280 | they tend to make more testosterone and estrogen

00:04:20.720 | than in shorter days.

00:04:21.940 | The next level of time, or bin of time, as we say,

00:04:26.080 | that we are all entrained or matched to

00:04:30.420 | is the so-called circadian time cycle,

00:04:33.100 | which is 24-hour rhythm.

00:04:35.540 | This is perhaps the most powerful rhythm

00:04:39.060 | that we all contain and that none of us can escape from.

00:04:42.340 | We all have this circadian clock

00:04:46.400 | that resides over the roof of our mouth.

00:04:48.260 | The cells in that circadian clock fire,

00:04:51.120 | meaning they release chemicals into our brain and body

00:04:55.440 | on a very regular rhythm.

00:04:57.080 | Not surprisingly, there are periods of every 24-hour cycle

00:05:00.220 | when we are very active and we tend to be alert,

00:05:02.860 | and others when we are asleep.

00:05:04.820 | We have this circadian clock.

00:05:06.580 | It oscillates.

00:05:07.420 | It goes up and down once every 24 hours and then repeats.

00:05:11.220 | Every cell of our body has a 24-hour oscillation

00:05:14.260 | in the expression of various genes.

00:05:16.120 | They are entrained, as we say,

00:05:17.940 | to the outside light-dark cycle

00:05:19.560 | because morning sunlight, evening sunlight,

00:05:24.660 | and the lack of light in the middle of the night

00:05:28.620 | make sure that the changes, these oscillations that are occurring

00:05:33.340 | within the cells of our brain and body are matched to the outside light-dark cycle.

00:05:38.060 | I cannot emphasize enough how important it is that your circadian entrainment be precise.

00:05:43.260 | Why? Because disruptions in circadian entrainment cause huge health problems.

00:05:49.660 | Because they increase cancer risk, they increase obesity, they increase mental health issues,

00:05:54.940 | they decrease wound healing, they decrease physical and mental performance, they disrupt hormones.

00:06:01.100 | You want your cells to be linked to the circadian cycle that's outside you.

00:06:05.420 | And the circadian cycle outside you mainly consists of when there's sunlight and when there is not.

00:06:11.100 | And that's why the simple protocols to fall out of this whole discussion about circadian entrainment

00:06:16.700 | are the following: view 10 to 30 minutes of bright light, ideally sunlight, within an hour of waking,

00:06:22.540 | assuming that you're waking early in the day, especially you wake up early in the day,

00:06:25.820 | get outside, see sunlight.

00:06:27.020 | Do that again in the afternoon or around evening, 10 to 30 minutes, depending on how bright it is outside.

00:06:33.020 | Basically, you want as much bright light, ideally from sunlight,

00:06:36.220 | coming in through your eyes throughout the day.

00:06:38.300 | And then in the evening, you want as little bright light coming in through your eyes.

00:06:42.940 | There are other ways to so-called entrain your circadian clock.

00:06:45.980 | One of the best ways to do that is to engage in physical activity at fairly regular times of day.

00:06:52.220 | You don't have to do it every day, but if you're going to exercise,

00:06:55.020 | try and exercise at a fairly consistent time of day.

00:06:57.420 | What happens when this circadian clock starts getting disrupted?

00:07:01.980 | I mean, this is after all an episode about time perception.

00:07:04.780 | It's not an episode about circadian rhythms and entrainment.

00:07:07.420 | Well, there's a classic study by Ashoff done in 1985 that's now been repeated many times where

00:07:15.420 | they had people go into environments where they didn't have clocks and they didn't have windows

00:07:20.060 | and they didn't have watches, and they were sometimes even in constant dark or constant light.

00:07:24.220 | And they evaluated how well people perceive the passage of time on shorter timescales.

00:07:31.260 | And what they found was really interesting.

00:07:33.340 | What they found is that people underestimate how long they were in these isolated environments.

00:07:37.820 | So after 42 days or so, they'd ask people, "How long do you think you've been in here?"

00:07:42.140 | and people would say 28 days or 36 days.

00:07:45.820 | They generally underestimated how long they had been in this very odd environment with no clocks

00:07:51.020 | or watches or exposure to sunlight or regular rhythms of artificial light.

00:07:55.980 | In addition, they found that their perception of shorter time intervals was also really disrupted.

00:08:03.100 | So if they asked them to measure off two minutes, normally people are pretty good at measuring off two minutes.

00:08:08.140 | People will come within, you know, five to 15 seconds at most.

00:08:12.220 | Well, when people's circadian clocks or circadian entrainment, I should say, was disrupted,

00:08:17.660 | their perception of time measurement on shorter timescales of minutes or even seconds was greatly disrupted.

00:08:25.740 | And as we'll see in a couple of minutes, that actually causes great problems for how you contend with work,

00:08:31.900 | how you contend with challenges of different kinds.

00:08:34.700 | You want your circadian entrainment to be pretty locked in or pretty entrained to the outside light dark cycle

00:08:42.620 | so that your perception of time on shorter time intervals can be precise.

00:08:47.820 | Because the ability to perceive time accurately for the given task or given thing that you're involved in

00:08:53.980 | turns out to be one of the most fundamental ways that predicts how well or poorly you perform that thing or task.

00:09:01.260 | Next, I'd like to talk about so-called ultradian entrainment.

00:09:05.100 | Ultradian rhythms are rhythms of about 90 minutes or so.

00:09:09.180 | And all of our existence is broken up into these 90-minute ultradian cycles.

00:09:14.380 | When you go to sleep at night, whether or not you sleep six hours or four hours or eight hours or 10 hours,

00:09:18.620 | that entire period of sleep is broken up into these 90-minute ultradian cycles.

00:09:23.980 | However, when you wake up in the morning, many of the things that you do are governed by these ultradian rhythms.

00:09:31.900 | For instance, the 90-minute 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.

00:09:41.820 | And then at about 90 minutes, there's a significant drop in your ability to engage in this mental or physical work.

00:09:49.740 | Now, everybody from, you know, the self-help literature to the business literature to the pop psychology literature has tried to leverage these ultradian cycles by saying,

00:10:00.380 | if you're going to do something hard and you want to focus on it, limit it to 90 minutes or less.

00:10:04.860 | And I am one of those people who's also joined that conversation.

00:10:07.740 | And indeed, I use 90-minute work cycles.

00:10:09.900 | And I think they are extremely powerful.

00:10:12.540 | While this isn't time perception per se, it is, again, an example of entrainment.

00:10:18.380 | What are we entraining to?

00:10:19.820 | Well, what you're entraining to is the release of particular neurochemicals.

00:10:23.500 | In this case, acetylcholine and dopamine that allow your brain to focus for particular periods of time,

00:10:29.260 | 90 minutes or so, and after about 90 minutes or so, the amount of those chemicals that can be released

00:10:36.300 | tends to drop very low, which is why your ability to focus becomes diminished.

00:10:40.860 | I always get the question, how do you know when the 90-minute cycle begins?

00:10:44.220 | In other words, let's say you wake up at 8:00 a.m. and you just finished a 90-minute sleep cycle.

00:10:49.420 | Does that mean that your next 90-minute cycle where you could do work begins right at 8:01?

00:10:54.860 | No.

00:10:55.820 | The interesting thing about these basic rest activity cycles,

00:10:58.780 | these ultradian rhythms is that you can initiate them whenever you want.

00:11:02.620 | You can set a clock and decide, okay, now the focus begins.

00:11:07.420 | Now the work begins.

00:11:08.540 | And this 90-minute cycle is the period in which I'm going to do work.

00:11:11.820 | What you can't negotiate, however, is that at about 100 minutes or 120 minutes,

00:11:16.940 | no matter who you are, you're going to see a diminishment in performance.

00:11:20.940 | You're not going to focus as well.

00:11:23.180 | And that's, again, because of the way that these 90-minute cycles are linked to the ability of the neurons

00:11:27.900 | that release acetylcholine and dopamine and, to some extent, norepinephrine, the things that give us

00:11:31.740 | that give us narrow focus, motivation, and drive, the way that these 90-minute cycles are involved in those circuits.

00:11:38.380 | 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.

00:11:47.580 | Some people like to do multiple 90-minute cycles per day of focus.

00:11:51.180 | In that case, you need to separate them out.

00:11:52.860 | You can't do one 90-minute cycle, then go right into another 90-minute cycle, then another 90-minute cycle.

00:11:57.500 | You can't cheat these circuits related to acetylcholine and dopamine and norepinephrine, unfortunately.

00:12:03.420 | For me, I can do one mid-morning.

00:12:05.260 | I can probably do another one in the afternoon.

00:12:07.420 | This is not the kind of work that's like checking email or text messaging or social media.

00:12:11.100 | This is very focused, hard work.

00:12:13.020 | It's working on hard problems of various kinds, and this will be different for everybody.

00:12:17.900 | So I recommend that they be spaced by at least two to four hours.

00:12:21.820 | And most people probably won't be able to handle more than two per day.

00:12:26.060 | There are probably some mutants out there that could do three or four, but that's exceedingly rare.

00:12:30.460 | I think even one a day is going to feel like a significant mental investment.

00:12:34.780 | And afterwards, you're going to feel pretty taxed.

00:12:37.180 | So now we've talked about circanual, circadian, and ultradian rhythms.

00:12:41.420 | But we haven't really talked about time perception per se.

00:12:45.740 | We've mainly talked about the subconscious, slow, oscillatory ways in which we are entrained

00:12:51.660 | or matched to the year or to the day, and these ultradian cycles that we can impose on our work

00:12:58.780 | and that we can leverage toward more focus if we like.

00:13:02.220 | But what about the actual perception of time?

00:13:05.340 | What actually controls how fast or how slowly we perceive time going by?

00:13:10.700 | There are basically three forms of time perception that we should all be aware of.

00:13:15.580 | One is our perception of the passage of time in the present.

00:13:19.100 | How quickly or slowly things seem to be happening for us.

00:13:22.780 | This is kind of like an interval timer, ticking off time.

00:13:25.980 | Tick, tick, tick, tick, tick.

00:13:27.740 | It's either fine slicing like that or tick, tick, tick.

00:13:33.180 | We have interval timers.

00:13:34.700 | I'll discuss the basis of those interval timers.

00:13:37.100 | We also engage in what's called prospective timing, which is like a stopwatch,

00:13:41.100 | measuring off things as they go forward.

00:13:43.500 | That might sound a little bit like what I just described, but it's actually a little bit

00:13:46.940 | different.

00:13:47.660 | For instance, if I told you to start measuring off a two-minute time interval into the future,

00:13:55.260 | you could do that pretty well.

00:13:58.060 | But if I told you you had to measure a five-minute time interval into the future

00:14:01.820 | and you couldn't use any clocks or watches or your phone or anything like that,

00:14:05.020 | you would have to set the tick marks.

00:14:08.700 | You would have to decide how many times you were going to count off during that five-minute time block.

00:14:14.380 | There's also retrospective time, which is how you measure off time in the past.

00:14:21.100 | So if I say, you know, last week, I know you went to the park, you did some things with friends,

00:14:26.380 | you know, you went out in the evening.

00:14:27.660 | How long was it between lunch and when you went to dinner with friends?

00:14:32.620 | You probably think, okay, well, I remember I went to dinner at seven and we had lunch right around two.

00:14:36.620 | You're using memory to reconstruct certain sets of events in the past and get a sense of their

00:14:43.180 | relative positioning within time, okay?

00:14:45.660 | So we have retrospective, current time interval measurements, and then prospective time measurement

00:14:50.780 | into the future.

00:14:53.500 | The beauty of time perception in the human nervous system is that it boils down to a couple of simple

00:15:01.260 | molecules that govern whether or not we are fine slicing time or whether or not we are batching

00:15:07.980 | time in larger bins.

00:15:10.700 | Those molecules go by names that maybe you've heard, things like dopamine and norepinephrine.

00:15:15.580 | Neuromodulators, called neuromodulators because they modulate, they change the way that other neural

00:15:20.140 | circuits work.

00:15:20.860 | Also things like serotonin.

00:15:23.740 | Serotonin is released from a different site in the brain than dopamine and norepinephrine is and has a

00:15:29.740 | different effect on time perception.

00:15:32.460 | So just to give you an example of how things like dopamine and serotonin can modulate our

00:15:37.980 | perception of time, I want to focus on a little bit of literature that now has been done, fortunately,

00:15:43.820 | in animals and humans, and which essentially shows that the more dopamine that's released into our brain,

00:15:52.780 | the more we tend to overestimate the amount of time that has just passed.

00:15:56.940 | Let me repeat that.

00:15:58.460 | The more dopamine that is released into our brain, the more we tend to overestimate how much time has passed.

00:16:05.340 | These experiments are very straightforward, excuse me, and they're very objective, which is really nice,

00:16:10.380 | which is you can give people or an animal a drug that increases the amount of dopamine

00:16:16.140 | and then ask them to measure off without any measurement device, like a watch or a clock,

00:16:20.940 | when one minute has passed.

00:16:23.420 | As dopamine levels will rise in the brain, people tend to think that the minute is up

00:16:29.980 | before a minute.

00:16:32.060 | So they, at the 38 second mark, they'll say, "Okay, I think a minute is up."

00:16:35.500 | So they've overestimated how much time has passed.

00:16:37.900 | The higher the level of dopamine, the more people tend to overestimate.

00:16:43.020 | Now it's also true that norepinephrine, also called noradrenaline, plays a role

00:16:48.780 | and its role is very similar to that of dopamine.

00:16:51.580 | Conversely, the neuromodulator serotonin causes people to underestimate the amount of time that's

00:16:58.620 | passed.

00:16:59.340 | So this is very interesting.

00:17:01.180 | It's interesting in terms of how pharmacology can be used to adjust time perception,

00:17:06.700 | but it's also interesting in the context of that circadian rhythm.

00:17:11.260 | There's some emerging evidence that throughout the 24-hour cycle,

00:17:14.780 | there are robust changes in the amount of dopamine, norepinephrine and serotonin that are present

00:17:20.700 | in the brain and bloodstream and body, depending on time of day within the circadian cycle.

00:17:26.700 | So much of the evidence points to the fact that in the first half of the day, approximate first half

00:17:33.260 | of the day, dopamine and norepinephrine are elevated in the brain, body and bloodstream

00:17:37.980 | much more than is serotonin and that in the second half of the day and in particular towards evening

00:17:43.820 | and nighttime, serotonin levels are going up.

00:17:45.980 | What that means is that our perception of the passage of time will be very different in the early part of

00:17:52.300 | the day and in the latter half of the day.

00:17:54.700 | Now, this is important in terms of how one thinks about structuring their day, because I know many

00:17:59.260 | people are thinking about the various tasks that they need to do throughout their day.

00:18:03.260 | Many, or I should say all of the literature, at least that I can find on productivity and things of

00:18:10.460 | that sort point to the idea that we should be doing the hardest task, the thing that we want to do the

00:18:15.580 | least or the most important task early in the day as a kind of a psychological tool for getting it done

00:18:22.060 | and feeling as if we accomplish something. And I think that's an excellent protocol, frankly.

00:18:26.540 | And as an aside to support what I said, but also to take us back to this critical role of the circadian

00:18:32.780 | rhythm, there is a lot of evidence that when one's sleep is disrupted, when sleep is either too short or

00:18:39.580 | is fragmented or is not of high enough quality for enough days, one of the first things to happen

00:18:45.980 | is that there is a dysregulation of these dopaminergic, noradrenergic and serotonergic

00:18:51.820 | states throughout the day. Now, there is a version of how dopamine and norepinephrine can impact our

00:18:56.540 | perception of the passage of time in ways that can be very disruptive or even maladaptive.

00:19:02.220 | And the best example that I'm aware of is trauma.

00:19:06.940 | Many people who have been in car accidents or who have experienced some other form of

00:19:11.900 | major trauma do what's called overclocking. Overclocking is when levels of dopamine and

00:19:20.220 | norepinephrine increase so much during a particular event that we fine slice, in other words, the frame

00:19:28.060 | rate is increased so much so that we perceive things as happening in ultra slow motion.

00:19:34.780 | Now, that might not seem like a bad thing overall, but the problem with overclocking

00:19:41.900 | is the way in which that information gets stamped down into the memory system.

00:19:46.460 | So the memory system, which involves areas of the brain like the hippocampus, but also the neocortex,

00:19:51.740 | is basically a space-time recorder. What do I mean by space-time recorder? Well,

00:19:57.900 | your nervous system, of course, is housed in the darkness of your skull. It doesn't have a whole

00:20:02.460 | lot of information about the outside world except light coming in through the eyes and whatever

00:20:06.300 | happens to hit our ears and in terms of sound waves and skin and so forth. So it has to take all those

00:20:11.980 | neural signals and it has to create a record of what happened. Now, it doesn't create a record of everything

00:20:17.580 | that happened, but car accidents and trauma and things of that sort oftentimes are stamped down

00:20:23.340 | into our record of what happened. And what gets stamped down, what we actually mean by the phrase

00:20:29.980 | stamped down, is that the precise firing of the sequence of neurons that reflected some events.

00:20:36.700 | So let's say I'm in a car accident, certain neurons are firing because of the flipping of the car or

00:20:42.380 | there's screams or there's blood or things of that sort. All of that neural activity gets repeated

00:20:50.380 | in the hippocampus and then the sequence of the firing of those neurons is also remembered. So it's

00:20:56.940 | not just that neuron one, two, three, four fired in that sequence, it's also that neuron one, two, three,

00:21:02.460 | four fired at a particular rate. So it would be one, two, three, four during the actual event,

00:21:06.780 | and then the memory is stored as firing of those neurons as one, two, three, four, right? If it,

00:21:11.820 | if during the event, it was one, two, three, four at that rate, the storage of the memory is not going

00:21:17.340 | to be one, two, three, four. Okay. In other words, there's both a space code, as we say, meaning the

00:21:25.100 | particular neurons that fire is important. And there's a rate code, how quickly those neurons fire or the

00:21:31.580 | relative firing, the timing of the firing of those neurons is also part of the memory. This affords our

00:21:36.300 | memory system, tremendous flexibility. What it means is that you can take the same set of neurons in the

00:21:40.620 | hippocampus and stamp down many, many more memories, because all you have to do is use a match of the

00:21:48.540 | different rates of the different neurons that were firing in order to set that code, right? You don't,

00:21:53.660 | otherwise, if you needed a different set of neurons for every memory, you need an enormous

00:21:57.180 | hippocampus, you need an enormous head. So I think, I think you get the basic idea.

00:22:00.700 | Overclocking is a case in which the frame rate is so high that a memory gets stamped down and

00:22:08.060 | people have a very hard time shaking that memory and the emotions associated with that memory.

00:22:12.620 | In fact, you know, one of the first things that trauma victims learn is that they aren't going to

00:22:17.660 | forget what happened. What's eventually going to happen ideally with good treatment is that the emotional

00:22:23.740 | weight of the experience will eventually be divorced from the memory of the experience.

00:22:29.660 | Some of you are probably saying, why dopamine during trauma? I thought dopamine was the feel-good

00:22:34.540 | molecule. Well, in reality, dopamine is not necessarily a molecule of reward. It's a molecule of

00:22:41.260 | motivation, pursuit, and drive. And because of the close relationship between dopamine and norepinephrine,

00:22:46.700 | oftentimes they are co-released. So whether or not dopamine is released during car crashes or other

00:22:52.380 | forms of trauma, we don't know. But what we do know is that both the dopamine system and the

00:22:56.860 | noradrenergic system, when we say noradrenergic, we mean norepinephrine, those systems are greatly

00:23:01.900 | increased anytime there's a heightened state of arousal. And arousal can have negative valence,

00:23:07.020 | like a meaning associated with an event that we really hate, that we would prefer not to be involved in,

00:23:12.140 | or can have positive valence. But dopamine and norepinephrine are kind of the common hallmark of

00:23:18.060 | all things of elevated arousal. And so that's why we see evidence for dopamine being associated with

00:23:24.940 | these changes in time perception, both for positive events and for negative events. Now, up until now,

00:23:30.940 | I've been talking about how dopamine and to some extent serotonin can differentially impact your

00:23:37.260 | perception of how fast or how slowly things are happening in the moment. But remember,

00:23:44.060 | we have prospective time, we have our experience of time in the moment, and we have retrospective time.

00:23:49.660 | And there are beautiful studies that have showed that the dopaminergic state

00:23:56.540 | changes the way not just that we experience things now, but that it changes the way in which we remember

00:24:03.980 | things in the past and the rate at which those things occurred. And those are in opposite direction.

00:24:09.980 | So to make this very simple, if something that you experience is fun or varied, meaning it has a lot of

00:24:18.460 | different components in it, and is, in other words, is associated with an increase in dopamine in your brain,

00:24:24.780 | you will experience that as going by very fast. Imagine an amazing day for a kid at an amusement park.

00:24:34.700 | 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.

00:24:40.860 | But later, they will remember that experience as being very long, that it was a long day full of many,

00:24:49.180 | many events. And so there's this paradoxical relationship between how we perceive fun, exciting,

00:24:55.180 | varied events in the present, and how we remember them in the past.

00:24:57.900 | For those of you who have gone on vacation, if you've had an amazing day on vacation, it'll seem like,

00:25:03.260 | or an amazing vacation overall, it will seem like it goes by very fast. The last day of vacation,

00:25:07.580 | you sort of go, "Whoa, it went by so fast, because there's so much happening." But in memory,

00:25:11.980 | six to eight months later, you remember, "Wow, that just went, you know, that was a long,

00:25:18.540 | long thing. We had this, then we had that, then we did this, then we had that." It tends to spool out

00:25:23.820 | in a longer memory than the actual experience. Conversely, if you're bored with something,

00:25:29.100 | or it's something you really don't like, it's going to seem like it takes a long time to go through

00:25:35.500 | that experience in the moment. But retroactively looking back, it will seem like that moment was

00:25:40.300 | very short. And so the reason I bring this up is we aren't just driven by these circadian clocks,

00:25:45.900 | and these circanual clocks, and these ultradian clocks. We are driven by these timers that vary

00:25:53.100 | depending on our level of excitement. And they vary depending on our level of excitement because of

00:25:59.420 | these neuromodulators, dopamine and serotonin. So the way I like to think about it is that you have

00:26:04.060 | two clocks, two stopwatches. One is a dopaminergic stopwatch that fine slices really closely. It's

00:26:10.700 | like counts off milliseconds, and it's grabbing a movie of your experience at very high resolution.

00:26:15.660 | And on the other hand, you have a stopwatch that's gathering big time bins, big ticks along

00:26:21.500 | that the hand is moving at bigger intervals, marking off time. And depending on whether or

00:26:29.020 | not you're excited or whether or not you're bored, you're using different stopwatches on time, and

00:26:34.300 | therefore you're perceiving your experience differently. One very interesting aspect to the way that

00:26:39.740 | neuromodulators like dopamine and novelty interact with time perception and memory is how we perceive

00:26:47.820 | our relationship to places and people. So really interesting literature showing that the more novel

00:26:54.940 | experiences we have in a place, the more we feel we know that place obviously, but the longer we feel we've

00:27:04.140 | been there. So here's the kind of gedanken or thought experiment that illustrates what's in the

00:27:08.620 | literature. Let's say I were to move to New York City. I happen to really like New York City. I've

00:27:12.700 | never lived there, but let's say I lived there. I lived in a given apartment for a year and I would have

00:27:18.140 | a number of different experiences in this mental experiment. Let's say I had a hundred different exciting

00:27:25.420 | and new experiences. I would, at the end of that year, feel as if I lived there a certain period of time,

00:27:31.820 | one year, I would actually know I lived there one year. If, however, I lived in three different places

00:27:35.900 | in New York City and I met three times as many people and I had three times as many novel experiences,

00:27:41.660 | I would actually feel as if I had been there much longer than had I only lived in one location. This is

00:27:47.660 | also true for social interactions. When we move to multiple or several novel environments with somebody

00:27:56.220 | else, we tend to feel as if we know that person much better and that they know us much better.

00:28:00.380 | Now that's all very interesting and speaks to the fact that dopamine is a kind of flexible

00:28:05.260 | currency in the brain. It's doled out, if you will, or released when something that one hopes will happen,

00:28:12.540 | happens. And it's released when there's a surprise, even if it's a kind of a negative surprise. It's not

00:28:18.540 | something that the subject wanted to happen. But the more interesting thing is how that relates to time

00:28:25.260 | perception. What I mean is how often and when you release dopamine is actually setting the frame rate

00:28:32.060 | the entire perception of everything, not just for positive events or negative events. This governance

00:28:38.860 | over our perception of time that dopamine has points to a very clear, very actionable and very powerful tool.

00:28:47.740 | And that is a tool that many people have talked about before, which are habits. People have discussed

00:28:54.540 | habits in a variety of contexts, but in the context of dopamine reward and time perception, what this means

00:29:04.380 | is that placing specific habitual routines at particular intervals throughout your day

00:29:11.340 | is a very, not just convenient, but a very good way to incorporate the dopamine system so that you divide

00:29:19.740 | your day into a series of what I would call functional units. What would this look like?

00:29:23.980 | It would mean waking up and having one specific habit that you always engage in that causes a release of

00:29:30.700 | dopamine. You could say, well, great, that'll make me feel good. And I would agree, dopamine release

00:29:37.180 | generally makes us feel motivated, but it would have an additional effect of marking that time of day

00:29:42.940 | as the beginning of a particular time bin. Then inserting another habit, perhaps the beginning of,

00:29:48.780 | I don't know, your breakfast or something, but recognizing that that's a habit and being fairly

00:29:53.340 | habitual, you don't have to be obsessively precise about the timing, but that regular

00:30:00.380 | sequencing of things is going to lead, not just to dopamine release as it relates to reward and

00:30:06.140 | motivation and feeling good, but it actually becomes the way in which we carve up our entire experience of

00:30:12.300 | our day. Today, we covered a lot about time perception. We certainly didn't cover everything about time

00:30:17.020 | perception, but we covered things like entrainment, the role of dopamine habits and various routines that can

00:30:22.940 | adjust your sense of time for the sake of particular goals. If you're interested in learning more about time

00:30:27.980 | perception, I'd like to point you to a really excellent book called Your Brain is a Time Machine:

00:30:34.060 | The Neuroscience and Physics of Time. The book was written by professor Dr. Dean Buonamano,

00:30:39.260 | who's a professor at UCLA and a world expert in the neuroscience and physics of time. Thank you for

00:30:45.020 | your time and attention today. And last but certainly not least, thank you for your interest in science.

Time Perception, Memory & Focus | Huberman Lab Essentials

Chapters