You know the expression it's all in your head?

Well, actually with pain, it absolutely is.

The brain is your pain center, not the place where you actually injure yourself,

your stubbed toe or your broken wrist or your pulled muscle.

Pain is created when signals travel from the point of injury to the brain.

And then your brain reacts with the sensation of pain.

It's why everyone's pain is so different because everyone's brain is unique.

Two people with identical injuries on an X-ray could have completely different perceptions of pain. And it's that subjectivity that makes pain, especially chronic pain, so hard to treat.

But finding the root cause, that could be the key to unlocking our understanding of pain.

I'm Dr. Sanjay Gupta, and this is It Doesn't Have to Hurt, Part 2.

I'm about to take you on a trip inside the brain. Three and a half pounds of the most mysterious tissue in the known universe,

with more connections than stars in the sky.

And hidden in that big galaxy of stars are the connections that create pain.

It's mind-boggling, right? More than a needle in a haystack. Dr. Prasad Trevalker will be our guide. He's a neurologist, a pain doctor, a trailblazer,

and he is searching for the mystery of pain inside the brain.

So for the longest time, pain was called the fifth vital sign, right? But unlike the other four vital signs,

there's no objective measure, right? It's not like temperature or heart rate. So one of the

holy grails of pain medicine has been coming up with a biomarker for measuring how intense or

how severe somebody's pain is. This is exactly an example of the device.

So, Chavalker has made this his life's work

and has an audacious plan to try and measure pain.

To start, surgery, to stick multiple probes all over the brain.

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