How does the brain measure time?
How do we actually have a notion of time? What makes the brain tick? And why does something exciting seem to take no time at all, yet boring things seem to drag. And why does time seem to go into slow motion when something frightening happens? That’s what SISSA scientist Domenica Bueti works on. Her work suggests that the brain uses how much information we have stored about an event to decide how long something took to happen…
Domenica - Your perception of time depends on the amount of input, of sensory input, that your senses get. So the brighter, for example, a visual image is, the longer you perceive or the faster something moves, the longer is your perception of time.
Chris - So if I was suddenly galvanized into paying attention to something, I would be storing huge amounts of information. My brain would say, Well, there's lots of information corresponding to that event, therefore it must have happened over a long period of time. But equally we know it didn't. So therefore I'm going to assume time slowed down.
Domenica - Yeah, this is it. So it's just that your brain interprets this amount of information as if there are multiple events happening in that time lapse basically. And this is what we hypothesize based on these experiments that we run.
Chris - Tell us about those.
Domenica - Okay. For example, in this case, we ask this healthy individuals to put their hands in a water tank and the water tank could be filled of ice or of water at room temperature. And we measure actually the perceptual capacity. So how good they were in perceiving a simple visual image. And also we asked them to judge for how long this visual image was presented on screen. And what we saw is that their visual acuity was higher, so was much better. So they really were better under the stress. So when the hand was in ice compared to when the hand was in warm water. This was interpreted as okay, the fact that your visual system incorporates more information and this corresponds to your expansion of time, because of course the judgment was that the visual image was displayed for longer than it physically was.
Chris - It's really interesting that it transfers across senses then. So you put in a sensory stimulus, but it affects your perception of a visual one.
Domenica - Yeah, indeed. What we hypothesized was to change the physiological state of the subject. Indeed we measure some physiological illnesses like cortisol reactivity or some neuro-adrenaline
Chris - So these are little stress signals then.
Domenica - Exactly. We were stressing those people. So your physiological, your general, we call it arousal. So your physiological state was aroused compared to having your hands in warm water and this has caused this better visual perception and time expansion.
Chris - How does my brain know what happened last year versus the year before that? How is time coded for memories? How do we attach a timeline or a calendar to memory? Because it's one thing for me to have a concept of how long something took, but to then store when it occurred relative to everything else that's happened in my life, which we all do really well. How on earth do we do that?
Domenica - This has to do with the capacity of putting things in sequence, right? And again has been associated with the neural circuitry that deals with your memory capacity. So this hippocampus structure in the temporal lobes. It looks like that really it depends on the memory, and this memory is not just the memory of the past, it's your capacity of putting yourself into this timeline and imagining yourself in the future. There is a debate whether this is something that exclusively is a capacity that belongs to humans or also other animals have.
Chris - Do we know in the brain where that sort of metronome is? Do we know how the brain generates a clock sequence or a clock signature that gives us our concept of time?
Domenica - We don't know. Actually, this is the easy and quick answer. We don't know yet if there is a single clock or multiple clocks. Actually now based on our experiments, we seem more inclined to believe that there is no single clock, no single metronome in the brain. But actually there are multiple brain areas, multiple circuits that enable you to keep track of time. And most of those circuits are circuits that deal with movement.
Chris - I was just going to say, because I could see you tapping your foot. So am I as you are talking and that motor movement can happen just like a pendulum on a clock, can't it? So it is our brain generating a movement, even in the imaginary, one to then superimpose a sensation of time.
Domenica - I think this has to do with how we learn about time. You can sense it, but you cannot touch it. You cannot see it or smell it. But time is everywhere. And the way you learn time is through change. And the most prominent way we experience change is through motion. Our own movement, body movements or the movement we see and indeed the neural circuits that are related to this capacity of keeping track of time are areas that deal with motion. With visual motion like this area, V5 we call MT or the areas that are responsible for our own movement. Body movements like the premotor areas or motor cortex.