I am a cognitive neuroscientist, and I'm trying to understand how we perceive time and how our perception of time arises from the workings of our brain. Why? Why do I want to understand that?
Well, time is the ultimate master of our lives. We are all constantly faced with its fleeting nature. Yet how we feel the passing of time can be highly malleable. When we are bored, in pain, but also when we encounter something novel or extraordinary, time feels to be passing much slower than when we are busy or simply having fun. But what does it mean to feel time? And why does the feeling of time distort depending on the situation, our level of focus, our emotional state? Do these distortions serve some function, and can we gain some level of control over how we feel time? These are very big questions, and we do not have the answer to any of them. Not just yet. But I will tell you about a surprising discovery I believe will take us a step closer to unlocking the neural basis of time. And I will show you that time is not something that is created solely by the brain, but it is also intimately shaped by what is happening inside the rest of the body.
I work in the Lab of Action and Body at Royal Holloway, University of London, and in our lab we look at the brain from an embodied point of view. What this means is that we believe we cannot fully understand the workings of the brain if we take it out of the body, because after all, the main reason for us to have a brain is to keep the body alive, so that we can act in the world. And for that, it is not enough for the brain to perceive what is happening in the world around us, but it also needs to perceive what is happening inside of our own body. It needs to understand what our body needs at any moment in time.
That additional internal sense, the perception of the body from within is called interoception. And one example of interoception is the perception of our own heart. Yes, the heart. I think all of us know that the main function of the heart is to transport oxygen-rich blood all through the body, and like other bodily functions, it is controlled by the brain. So when I’m on the move, the heart should start beating faster to provide more oxygen. When I need to slow down and focus, it will also slow down to preserve the oxygen. But what many of you may not know is that the activity of the heart itself shapes the activity of the brain.
But before I get into that, let me give you some very basic neuroscience. So the brain receives information from the outside world through our eyes, through our ears. But to make sense of that information, to perceive, it has specialized sensory areas, like the visual sensory area that allows us to see the redness of the TEDx sign, or the auditory-sensory areas that allow us to hear the sound of my voice. The information can be the same, but our perception can differ very much. But in order to act in response to what we perceive, the brain has separate movement control centers that are responsible for initiating and controlling movement. That's what makes me move my hands constantly as I'm speaking.
So how does the heart shape the brain then? Well, it turns out that there are sensory neurons in our heart that fire signals to our brain to inform it about the state of the body. But they fire only at a time when the heart contracts, and they remain silent when the heart is relaxed. So the brain and the heart are in a constant rhythmic dance. Every beat makes the brain step into an active mode, priming us for action. And between the beats, the brain steps back into perceptual mode, priming us to take in information. Now imagine what happens when the heart starts beating faster. There are more beats, so the brain is more likely to be in the active mode, whereas when the heart slows down, there are more periods of time between the beats, so the brain is more likely to be in the perceptual mode.
This got me thinking. If the heart shapes perception in such a way, will it also shape the perception of time? Is there a causal relationship between our heart and how we experience time?
Of course, we tested that in our lab. We invited 67 volunteers to participate in a study where we asked them to judge very brief durations of different stimuli. These could be sounds, images of simple shapes, images of people showing different emotions. We wanted to systematically determine whether what participants felt and sensed influenced how they perceived durations. But the key part of that study was that we hooked the volunteers to an ECG machine so we could see their heart beating in real time while they were doing this study. And this allowed us to flash the stimuli precisely at the moment when the heart squeezed tight or when it relaxed. And what we found was that stimuli that occurred during heart's contraction were perceived to last shorter than stimuli that occurred between the beats, when the heart was relaxed. What this means is that the momentary state of the heart caused time to contract and expand within each heartbeat.
Why am I so excited about this finding? Well because it shows that perception of time is an embodied experience. It might be constructed in the brain, but it is molded by the body. And I'm sure it seems intuitive, you know, that something rhythmic, like the heartbeat, would influence something rhythmic like time perception. But now we have a scientific evidence for that intuition. What's more, I can use these heart-driven time distortions to look at what is happening in the brain just before duration is distorted by each beat.
Could it be that distortions in time are connected to how each heartbeat affects the sensory and the movement centers of the brain? Remember how I told you that each beat momentarily suppressed perception, but between the beats, suppression was momentarily increased? So could it be ... And we showed that time is contracted during the beat, but expanded in between the beats. So could it be that our experience of time arises from the way in which our brain takes in sensory information that is shaped by the heart? And if that is true, could the function of our highly distorted sense of time be to shift us between an active and perceptual mode? Time could contract when we need to move, but it may expand when we want to perceive. So maybe that slowing of time you feel when you're bored is there to actually expand your perception and allow your mind to wander to something new.
I hope I've shown you that one way to shape how we experience time is to work on the internal state of our body. So the next time time becomes a little bit too fleeting, like right now for me --
(Laughter)
Let’s maybe try to take a deep breath.
(Inhales)
(Exhales)
Yeah? Feel the heart slow down, and let the brain expand the moment. And maybe that momentary expansion of time will also broaden our perception.
Thank you very much for listening. Thank you.
(Applause)
