From the brain's point of view, what is the self? How do you put together 36 trillion cells and have it feel like one thing? Does the self of a blind person include the tip of the walking stick? How flexible is our sense of self?

And what does any of this have to do with psychedelics or trauma or synchronized swimmers or religious

rituals or cheerleaders or wise soldiers across time and place love to march in unison in lockstep.

Welcome to Inner Cosmos with me David Eagleman.

I'm a neuroscientist and an author at Stanford,

and I've spent my career at the intersection

between how the brain works and how we experience life.

So I'm going to begin today's episode with a question that I've wondered about since I was a kid.

Something I've always found

amazing is watching armies. Thousands of soldiers march in perfect lockstep. And even as a kid,

I noticed that across the world, all armies did this. And this goes back to the earliest days of armies.

And I know this, because when I was younger,

I read about how the Romans discovered a problem

where if they marched in lockstep over a bridge,

it would sometimes hit the resonance frequency of the bridge

and then it would collapse.

So they learned from their mistakes,

and whenever they came to a bridge,

they would purposely go out of sync with one another and they would cross the bridge that way.

But the point is that they normally marched in lockstep. They, like all modern armies,

loved acting as a mega organism. So why do armies love to synchronize? I mean,

why not just have all the soldiers walk asynchronously however they want to as long as they keep up?

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