Welcome to Quantum Magazine's podcast. Each episode, we bring you stories about developments in science and mathematics. I'm Susan Vallett. Every time you reach for your coffee mug, a neuroscientific mystery takes shape.

Moments before you voluntarily extend your arm, thousands of neurons in the motor regions

of your brain erupt in a pattern of electrical activity that travels to the spinal cord

and then to the muscles that power the reach. But just prior to this massively

synchronized activity, the motor regions in your brain are relatively quiet. For self-driven

movements like reaching for your coffee, the go signal that tells the neurons precisely when to act instead of the moment just before or after

has yet to be found.

What's driving the system?

That's next.

Imagine you're in a lab where you've synthesized ancient DNA sequences and spliced them into modern bacteria just to see how they'd react.

They needed each other, but they didn't want each other.

So, you know, it was like a very complicated relationship unfolding in front of me.

This isn't Jurassic Park or some sci-fi movie.

I'm Steve Strogetz, and this is The Joy of Why.

A new podcast from Quantum Magazine that takes you into some of the biggest unanswered mysteries

in science and math today.

Join me on The Joy of Why as we explore these questions.

We may not have all the answers yet,

but I'm pretty sure the curiosity to figure them out is in our DNA. Subscribe to the Joy of Why wherever you get your podcasts. New episodes drop every other Thursday. In a recent paper in E-Life, a group of neuroscientists led by John Assad at Harvard Medical School

finally reveals a key piece of the signal that tells our neurons when to act.

It comes in the form of the brain chemical known as dopamine, which carries signals from one neuron to another. It's slow ramping up

in a region lodged deep below the cortex closely predicted the moment that mice would begin a

...