How Your Amazing Brain Tells Time: Circadian Watch, Pattern Pendulum, & Tempo Timer | Dean Buonomano

So human beings have been building clocks for millennium, and it’s been a long endeavor of our species from sundials to hour glasses to pendulum clocks to quartz watches to car and atomic clocks. Yet the brain has been telling time since the dawn of animal species, right? So even plants have the ability to tell time in terms of circadian clock.

One of the mysteries in neuroscience that many people are studying is how the brain tells time. In order to understand how the brain tells time, it’s useful to quickly remember how manmade clocks work. There’s a vast diversity of manmade clocks, from pendulums to quartz watches to atomic clocks. As diverse as these things are, they share a common principle—an almost embarrassingly simple principle—which is just counting the ticks of an oscillator.

With the pendulum, you just count the ticks of the pendulum going back and forth. In the quartz watch, you’re just counting the mechanical vibrations of a quartz crystal. In the case of an atomic clock, it’s a bit more complicated, but they’re related to the vacillatory cycle of electromagnetic waves.

So it’s reasonable to ask, “Well, is that how the brain tells time? Does the brain have some oscillator that’s ticking away and some circuit that’s counting those ticks and tocks?” The answer is no. The brain seems to have fundamentally different ways of telling time.

The first thing to notice is that while the mechanical clocks that we make—even your quartz watch—can tell time across a vast range of scales, from tens of milliseconds to hours, minutes, days, months, and years, the brain has many different clocks in order to tell the milliseconds and seconds and the time of day.

One way to think about it is the circadian clock—the clock that tells you what time of day it is and when to arise and when to go to sleep. That doesn’t have a minute hand, much less a second hand. In contrast, the clock that tells you—the timing device in your brain that tells you, “Hmm, this red light is taking a bit too long to turn,” “This traffic light is taking a bit long to turn,” or “I think the waiter forgot my coffee”—that clock doesn’t have an hour hand, much less the number of days that have gone by.

So the brain has different areas and different mechanisms in order to tell time. We don’t fully understand how the brain tells you what the tempo of a song is or when the red light is going to change. But it doesn’t seem to have to do with any oscillator-counter mechanisms.

It seems to do with neural dynamics, which is the fact that patterns of neurons—neurons are coupled to each other; neurons are connected to each other. When you activate some neurons, that group of neurons can activate another group of neurons, which can activate another group of neurons. So you can have these evolving patterns of neural activity.

In the same way that if you throw a pebble into a pond, it can create this dynamical pattern. That pattern tells you how much time has elapsed, right? You know that by looking at the pond; if the diameter of those ripples is large, more time has elapsed than if it’s a little ripple.

Any dynamical system, in principle, has the ability to convey information about elapsed time. It can be a timer. As far as we know, it seems that one of the mechanisms that the brain uses to tell time on the scale of hundreds of milliseconds to seconds is through neural dynamics and changing patterns of neural activity. Neuron A activates neuron B, which activates neuron C, and you have these complex evolving patterns.

This is consistent with what we call the multiple clock principle, which is that the brain doesn’t have any master clock. It has many different circuits, each specialized or that focuses on processing time on one scale or another.