- [Heather] To keep us alive, the brain has evolved to look for signals of potential danger.

One of the most important is pain.

And as neuroscientist Theanne Griffith is about to show me, sometimes that can be a kind of illusion as well.

So what is this?

- [Theanne] This is a thermal grill.

- [Heather] Okay.

- This is a machine that could give us some insight as to how pain works in your brain.

- All right.

This is making me nervous already as I'm getting strapped in.

(Theanne laughing) - [Theanne] Don't worry.

It's all an illusion, actually.

- Okay.

- And it's comprised of these different metal bars that are either set to a cold or warm temperature.

So why don't you go ahead and touch that first bar.

It's warm, right?

And then the next bar.

Cold.

(Heather humming) And then the next one, warm.

You see?

So they're alternating cold, warm, cold, warm.

(Heather humming) Now you wanna see what happens when you put your hand down.

- Not necessarily.

(Theanne and Heather laughing) - Go ahead.

- Okay.

Okay, here we go.

Ow!

- [Theanne] Right?

Isn't that interesting?

- Whoa.

Yeah.

What is going on there?

It sort of feels cold at first, but then- - Then it gets this kind of burning sensation, right?

- Yes, very much so.

It feels super hot, like I'm getting burnt.

- So it's not a hundred percent clear exactly how this is happening, but what we think might be going on is that basically your brain is getting a little bit confused, - Okay.

- It's feeling cold, and it's also feeling warmth.

And somehow it's interpreting these two signals as pain.

(curious music) - [Heather] Here's what neuroscientists think is going on.

In your hands, you have separate sensors for heat, cold, and pain.

Normally when you touch something slightly cold, both your cold and pain sensors are activated, but the cold ones override the signals from the pain sensors, telling your brain there's nothing to worry about.

Unless, in this very unnatural scenario with the thermal grill, you happen to be touching something warm at the same time.

Here, the heat signals cancel out the cold ones, leaving you with just the pain ones activated, telling your brain, ouch!

So in that respect, is pain real or is it just an illusion or a construct of the brain?

- That's a really good question.

So noxious stimuli is a real thing, right?

If you stick your hand in boiling water, that's an aversive stimulus.

The perception of a noxious stimuli is real.

Pain is more of a construct, right?

And it can vary from individual to individual.

(curious music) - Pain is a construct of the brain.

How do we know that?

You touch a needle, right, and prick your finger, we can draw the anatomy of what just happened.

We have very well-defined pathways saying this is pain information.

We don't interpret it as pain until it hits your brain.

- [Heather] Pain, not unlike the experience of color, is a construct of the mind.

(toddler babbling) But just because pain is in your brain doesn't make it any less critical for survival.

- [Theanne] Pain is a very important learning mechanism for children.

They learn what behaviors they can engage in that are safe, and what behaviors will they should not engage in because they could cause them bodily harm.

And there's different mutations that people can have in certain proteins that make them completely insensitive to pain.

And so kids do things like bite on their lips or on their fingers when they're very young, and as they get older, can engage in risky behavior.

So pain is extremely important for us to feel.