Our ability to perceive time both a gift and a curse – neuroscientist

SS: So Dean, let's start with looking at how we perceive time. If you look at the traditional depictions of time, be it Dali’s melting clock, or Heraclitus’s concept of time being the river that you cannot step twice into, where did we get this idea that time is fluid? Is there any scientific explanation to that?

DB: Yeah, that's an interesting question. I think for most humans, there's few things that are as dominant as the notion that time is flowing, that the past is evaporating into this unaccessible experience and opening the doors to the future. So this flow of time, this fluid motion of time is one of our most profound, subjective experiences, no doubt. We feel like we're losing – the past is no longer under our control, and we're opening new doors to the future. So that's tightly coupled to consciousness. So consciousness creates this narrative of things changing, things flowing in time. And that's probably shared with many other animals, but it's a bit of an illusion. So if you feel we all feel that time is flowing linearly, like a, b, c, d, e and that we're sort of creating this percept as one continuous flow. But that's a bit of an illusion. Because in reality, we process the world in a bit of chunks and jumps and edit the past and edit the future. Let me give you an example of that. If I say the sentence, ‘The mouse was broken,’ or if I say the sentence, ‘The mouse was hungry,’ the mouse has two different meanings there. One is the computer mouse, and one is a rodent. But you only know what mouse I meant by what came after. So you only know the meaning of the word mouse by the next word, but your brain didn't stop and say, ‘Oh, we added that, that was mouse the rodent or mouse the computer.’ So your brain is sort of waiting a certain specific amount of time, and then creating a narrative that it sends to consciousness that creates your conscious awareness. So consciousness in a way is a creation, a narrative, a construct of our unconscious brain that’s sent to our conscious brain.

SS: How does our brain calculate time? I mean, where's this timer in our braincase that tells us, ‘okay, seven minutes must have passed, spaghetti must be just the right condition of al dente’ or ‘it must be noon already’, like ‘it's time to go to bed.’ Where does it happen?

DB: So human beings have been inventing clocks since the dawn of civilisation. But really, the first clocks, of course, were in our brain. And we're very good at sort of determining speech, sound of speech, music, knowing when we're hungry, knowing when we should get up, knowing when the food might be ready. Unlike the clocks that we've built, – it's amazing, right? One of the biggest technological achievements that we have is that same clock, the clock on your smartphone, for example, can tell milliseconds, seconds, days, hours, weeks, minutes, and so forth. But the brain can also tell those times, but it doesn't have a master clock as many, many, many different clocks. So you have one clock, that's your circadian clock that helps you with the hours when you should get up when you're hungry. And that clock doesn't have a second hand, doesn't know how many seconds have gone by. You have other clocks or timers that are in other parts of your brain that know how many seconds have gone by that help you play the piano or help you determine the prosody of my speech. And those are different types of mechanisms. So the brain has many, many different clocks unlike our technological, manmade clocks, and each one is a bit different. And you think of something like the circadian clock. You don't even need a brain to have a circadian clock, plants have a circadian clock, bacteria have circadian clocks. So that's a very relatively well understood biochemical mechanism that involves the DNA and proteins and feedback loop that happens to oscillate every 24 hours. 

SS: So do we have neuron cells that are responsible for telling us microsecond time, like we're playing in a band, and then other cells are responsible for telling macro time, like, I don't know, planning for retirement?

DB: We have clocks that tell us the beat of music, as well as the time of the day. Now, humans are very unique in that we also have the ability to conceptualise time. So that's the planning for retirement that you mentioned. So we don't really have good clocks that operate at that. But humans are very unique in our ability to conceptualise time, to plan for the future. There's this great quote by Jorge Luis Borges, saying that man is the only animal that is not immortal because all other animals are ignorant of death. So we have the curse of seeing the future, as well as the gift of seeing the future. And we have the gift of seeing the future because that allows us to plan for the long-term, to plan for retirement, to invent things that take a long time to build, build the pyramids, travel to the moon. But the curse there is that we get to see that we're ephemeral, that we will die. So it's both a gift and a curse.

SS: Is it possible to train your brain in a way that it can tell time with clock-like accuracy? 

DB: We can certainly improve our ability to tell time, and musicians do that, athletes do that. But it's very specific to scale. So if you have a really good clock, an atomic clock, it's very good at telling microseconds, milliseconds, seconds, hours and days, but that's because it's one clock. Humans have many different clocks. So if you get much better, as a musician, the ability to time seconds, that doesn't mean you're going to be better at knowing when your pasta al dente is ready. So you do this wonderful interview, and you probably have a good feeling of time on the scale of 20 minutes, 30 minutes, which might be your general duration of a show, approximately, I don't know. So that means you've probably become good at determining those periods of time that are the duration of your show. But that doesn't mean you're very good at or necessarily much better than other people at determining the beat of a song or whether it's a half note or a full note. So yes, the brain improves the ability to tell time, but it's very specific to the task at hand.

SS: Does every person see time differently? I mean, let's say, you and I are talking real-time right now, right? Does time flow differently for you than for me? Or let me give you another suggestion: if we arrange to meet in two hours, and neither of us has a watch, does that mean that we won't meet in time because your two hours will be different from my two hours?

DB: So for that task, our subjective sense of time, absolutely, it can be very different, it can feel – I might be excited to meet you so time might be going very slowly. And maybe you're very busy so time might be flying by. But it's more than that, Sophie. So it's not only time is different for me and for you. It's different for you at different points of your life. So depending on what you're doing, if you're engaged in a task time might be flying by, if you're having fun with friends, or if you're in the hospital undergoing a procedure, time might seem to be going very slowly. So time is not only individual for each of us have, a subjective feeling of time, of course, objectively time is determined by external events. But for each of us, time flows differently depending on context, or you can take psychoactive drugs that will shape your feeling of the flow of time.

SS: Why is it that time speeds up as we get older? I mean, it's a philosophical question on one hand, but on the other hand, it's objective reality, it does speed up.

DB: You mean, it feels like it speeds up? Is that what you mean?

SS: Yeah, I mean, when you're younger, it’s just, you know, one slow flow of a piece of time. And then when you get older, it's like, years turn to months and months turn to weeks and weeks turn to days and days turn into one hour and then minutes. It's really like that, it's almost like you're always running out of time.

DB: “Where did it all go?” 

SS: Yeah.

DB: So in that context, it's important to make a distinction between two types of subjective feeling of time. One is prospective timing, sort of where we feel time flowing right now, as we're having this conversation. And the other is retrospective timing. So that's when you look back at the past. A lot of people notice this during the pandemic, particularly when they're in lockdown. They look back in last year, maybe the month of April seemed to disappear, because nothing was happening. So that's retrospective time. So retrospective time is closely coupled to memory. So if you have many, many experiences during the last month, new memories were formed, then it seems that it lasted a long time. But if you don't have many memories formed, if you didn't do anything interesting, you didn't meet many new people, you didn't do many of your interviews, it probably feels like it flew by. So part of the question, one of the hypotheses that answers your question is that as we become older, we have lived more and we form less memories. So we feel that time has been going retrospectively more quickly, because we're forming less memories. So here's an extreme example, imagine somebody, you've heard of both people with a lesion to their temporal lobes in the brain, the hippocampus, and they've lost the ability to form new memories. In the extreme case, that person is living in the present. They don't know what they did yesterday, they don't know what they did the day before. So they're continuously living in the present and think that time is always flying by because they don't have any memories of the past. So memory and retrospective timing are closely related. And I think that's one of the reasons for this impression that we all have that time seems to be accelerating, if you will, retrospectively as we get older.

SS: What happens with time when we dream? I mean, you can dream a wonderful weekend in Venice during a two-hour nap after lunch, right? Or, like in Nolan's Inception movie, asleep for five hours real-time, the characters spent 50 years in a dream world.

DB: Yeah. Subjective experience is very flexible. We can taste a million different flavours, we can see different forms of arts. Our conscious experience is incredibly flexible and that includes our feeling of the flow of time. So even consciously, you can play a song in your head very quickly or very slowly. If I asked you, what are the last words of your favourite song, of the lyric of your favourite song, you might have to start at the beginning of the song to reach the end. But you can do that probably very quickly to reach the end. So subjective time can be dilated, or contracted or compressed as a result of the neural mechanisms, as a result of the brain processes that underlie timing. So in dreams, presumably, the brain has these ways to accelerate or de-accelerate the passage of time, it can run things quickly and slowly. We don't understand exactly how that happens, Sophie, we don't understand the nature of the subjective feeling of time. But it is clear that the brain can, just like you can accelerate a piece on the piano that you're playing, you can play it quickly, or you can pay it slowly, you can compress or accelerate time. And there's interesting parallels here with the physics of time.

SS: You know, it's easy to say why evolution has taught us to perceive space in the old days. It would help us locate predators, look for a safe hideout for ourselves or our offsprings. But is there an evolutionary purpose for the sense of time?

DB: Yeah. So there's certainly a very profound evolutionary purpose for why we need to tell time and why we need to conceptualise time. And in many ways, the brain’s main function is temporal in nature, right? Because we store information about the past in order to predict the future. In many ways, that's your brain's main job is to predict and prepare for the future. So the animal that's capable of predicting where the predators will be, where the food will be, where the prey will be, where its mates will be, is obviously more likely to survive and reproduce. So the ability to predict the future is, in my opinion, probably the main evolutionary drive for the evolution of the brain and for a relationship with time. Now, to feel that time, to have a subjective sense of time – that's a much harder question. And why we have to feel that going, feel it flowing, is an open question. But what's clear, is that humans, unlike most animals have the ability to conceptualise time long-term. So most of what we do is aimed not for the next minutes but for the next days, weeks, months and years. We go to school because we want to become a doctor or we want to become a lawyer or a journalist, and that takes time. We need to dedicate ourselves to an activity for the next year, in order to achieve something in 10 years. If you look at what was probably one of the most significant technological advances in humankind was the invention of agriculture. So in agriculture, you plant a seed and a year from now, you reap the fruits of that seed, you have food to eat to survive. That simple act is beyond the cognitive ability of most animals, most animals are unable to see the connection between cause and effect, separated by long periods of time. So this ability to conceptualise time gave humans a very, very unique power. Rather than just trying to predict the future, we were able to create it. Rather than look for food, we were able to create food by planting it. Rather than looking for shelter, we were able to create shelter by building houses and building habitats and so forth. So evolutionarily it's one of our best weapons, the ability to conceptualise time, and without that ability, homo sapiens would not be very sapient or wise.

SS: You know, when we study the phenomenon of the brain and of time in the brain, we are concerned about the present moment, right? But with time passing, is there even such a thing as a present moment? I mean, you react to my words, which have already been said and they're already in the past like starlight. Can we, therefore, say that the present moment is an illusion, like, you know, the Buddhists would have us believe, I think?

DB: Yes, absolutely. In a sense, we live slightly in the past. So my brain takes some time to process the words that you are speaking. So there's certainly a delay there. But it's a very short delay. And it's a delay that doesn't seem to have significant impact on how we interact with the environment. But absolutely, we're we have this processing delay, just like a computer has a delay, or in a Zoom meeting, there can be a delay because the signal is going up to a satellite and back down so sometimes you can feel that delay or perceive that delay. But generally speaking, the present is thought of as a bounded amount of time, maybe a half a second, maybe a second and we sort of process information that's happening within that period of time, all at once. So I think our sense of time is absolutely focused on the present and that's what we mean when we say we have a sense of the flow of time. But most of our time – we can also be thinking about the future in the present or thinking about the past while we are in the present.

SS: How does our brain differentiate between various degrees of the past? What I mean is where does that marker come from in our memory that says, ‘Well, this happened yesterday,’ and about another bit of knowledge, - ‘this happened five centuries ago?’ 

DB: When we're talking about our memory of the past, there's an interesting distinction between semantic memory and that's factual knowledge about history. I know that there were the Olympic Games in 1980 in the United States [Editor’s note: 1980 Summer Olympics took place in USSR], but that's historical, that's something I didn't necessarily experience. But then when I talk about my birthday or my meetings with my family, then I have an autobiographical memory, I have knowledge of that. So you have experiences that you know from history, and you have experiences that you know from your own autobiographical experiences. So those, your autobiographical experiences seem to be stored in order, they seem to be sort of you know what happened first, your college graduation or your meeting your first boyfriend, you have some order of that, and that things are stored in some sort of temporal sequence. But the other information is really just knowledge, we don't know what it means that the Americas were discovered in the 1500s. It’s just a fact, it's just a piece of information, it's just a number that we have that’s not too different from saying the speed of light is 300,000 kilometres per second, it’s just knowledge. So I don't think we have a good subjective feeling of historical time.

SS: So does understanding more about the subjective sense of time move us any closer to understanding what consciousness in general really is?

DB: This is a very deep question and it's fascinating. In many ways, time is one of the deepest questions that humans deal with because it relates to consciousness, it relates to free will, it relates to this question of ‘Can I make a decision? The decisions that I make – are they predetermined? Could they possibly be predicted? Or is the future truly open?’ And it also relates to physics. Is our perception that time is flowing, that time is changing, real? Or, as some people believing in physics, is it the case that in some ways, we live in a universe in which everything has already played out, the past still sort of exists, in some sense, and the future exists in one sense, but we just happen to be here, in the present? So it's a very deep question of what our perception of time tells us about the reality and about consciousness. So regarding consciousness, I think consciousness tells us more about time than time tells us more about consciousness. So I think that consciousness is the real mystery here. And we have evolved ways to perceive our environment. And that allows us to create these subjective experiences. Unlike taste, or sight, or hearing, the brain doesn't have an organ for time. We have no organ for time, nor could we, because time isn't a material, physical substance, like matter or light. So the brain has to create the perception of time. And how it does that is tightly coupled to consciousness, and we don't really understand the nature of consciousness yet.

SS: Why is this connection so important, the connection between the perception of time and consciousness? Can't someone just be conscious and have a totally messed up perception of time, like in a case of amnesia or something?

DB: Yeah… And one wonders... So humans are unique in our ability to perceive time on long timescales, but maybe animals, maybe our fellow mammals, have very different perception of time in that they're very locked into the present. So yes, you're absolutely correct. If you had very severe amnesia, or maybe my dog perceives time just as an amnesic patient, that it just worried about the present. It's just feeling the present: whether I'm hungry, whether I'm sleepy, and so forth. So I think the question of consciousness is a very deep one in that allows us to try to understand how the brain creates any perception, whether it's conscious, whether it's temporal or not, whether it's space, you can have a feeling of if you're in a big space or a small space, if you’re claustrophobic or agoraphobic. So consciousness is the real mystery here, and then how that gives us different attributes such as the flow of time is, I think, something that we’ll truly understand once we understand consciousness, hopefully.

SS: If that ever happens.

DB: If that ever happens, Sophie. The question is can the brain understand itself, you know. Are we smart enough? Is the brain smart enough to understand itself? And that's an open question. Maybe we're not.

SS: Dean, it's been such a pleasure talking to you and discussing the concept of time and how it relates to the brain. And I hope we get to do this again. Good luck with everything.

DB: Thank you so much, Sophie, and thank you for your time.

SS: Thank you and have a great day. 

DB: Thank you.