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.
So one of the mysteries in neuroscience that many people are studying is how the brain
tells time.
So in order to understand how the brain tells time it’s useful to quickly remember how
manmade clocks work.
And there’s a vast diversity of manmade clocks from pendulums to quartz watches to
atomic clocks.
And 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.
So 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.
And in the case of an atomic clock it’s a bit more complicated, but they’re related
to vacillatory cycle of an 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.
So 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 and days and months and years.
So the brain has many different clocks in order to tell the milliseconds and seconds
and to tell the time of day.
So 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 number of days that have gone by.
So the brain has different areas, different mechanisms in order to tell time.
We don’t understand, 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—And when you activate some
neurons that group of neurons can activate another group of neurons which can active
another group of neurons.
So you can have these evolving patterns of neural activity.
And in the same way that if you throw a pebble into a pond it can create this dynamical pattern.
And in a way that pattern tells you how much time has elapsed, right.
You know that looking at the pond if the diameter of those ripples is large, more time has elapsed
then if it’s a little ripple.
So any dynamical system in principle has the ability to convey information about elapsed
time.
It can be a timer.
So 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.
So this is consistent with what we all the multiple clock principle which is 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.