How do you know it's really yours?

It seems obvious, unless you've experienced the rubber hand illusion.

In this experiment, a dummy hand is placed in front of you

and your real hand is hidden behind a screen.

Both are simultaneously stroked with a paint brush.

No matter how much you remind yourself the dummy hand isn't yours,

you eventually start to feel like it is,

and inevitably flinch when it's threatened with a knife.

That may just be a temporary trick, but it speaks to a larger truth:

our bodies, the physical, biological parts of us,

and our minds, the thinking, conscious aspects,

have a complicated, tangled relationship.

Which one primarily defines you or your self?

Are you a physical body that only experiences thoughts and emotions

as a result of biochemical interactions in the brain?

That would be a body with a mind.

Or is there some non-physical part of you that's pulling the strings

but could live outside of your biological body?

That would be a mind with a body.

That takes us to an old question

of whether the body and mind are two separate things.

In a famous thought experiment,

16th-century philosopher René Descartes pointed out

that even if all our physical sensations were just a hallucinatory dream,

our mind and thoughts would still be there.

That, for him, was the ultimate proof of our existence.

And it led him to conclude that

the conscious mind is something separate from the material body

that forms the core of our identity.

The notion of a non-physical consciousness

echoes the belief of many religions in an immaterial soul

for which the body is only a temporary shell.

If we accept this, another problem emerges.

How can a non-physical mind have any interaction with the physical body?

If the mind has no shape, weight, or motion,

how can it move your muscles?

Or if we assume it can, why can your mind only move your body and not others?

Some thinkers have found creative ways to get around this dilemma.

For example, the French priest and philosopher Nicolas Malebranche

claimed that when we think about reaching for a fork,

it's actually god who moves our hand.

Another priest philosopher named George Berkeley

concluded that the material world is an illusion,

existing only as mental perceptions.

This question of mind versus body isn't just the domain of philosophers.

With the development of psychology and neuroscience,

scientists have weighed in, as well.

Many modern scientists reject the idea

that there's any distinction between the mind and body.

Neuroscience suggests that our bodies, along with their physical senses,

are deeply integrated with the activity in our brains

to form what we call consciousness.

From the day we're born,

our mental development is formed through our body's interaction

with the external world.

Every sight, sound, and touch create new maps and representations in the brain

that eventually become responsible for regulating our experience of self.

And we have other senses, besides the typical five,

such as the sense of balance

and a sense of the relative location of our body parts.

The rubber hand illusion, and similar virtual reality experiments,

show that our senses can easily mislead us in our judgment of self.

They also suggest that our bodies and external sensations

are inseparable from our subjective consciousness.

If this is true, then perhaps Descartes' experiment was mistaken from the start.

After all, if we close our eyes in a silent room,

the feeling of having a body isn't something we can just imagine away.

This question of mind and body becomes particularly interesting

at a time when we're considering future technologies,

such as neural prosthetics and wearable robots

that could become extended parts of our bodies.

Or the slightly more radical idea of mind uploading,

which dangles the possibility of immortal life without a body

by transferring a human consciousness into a computer.

If the body is deeply mapped in the brain,

then by extending our sense of self to new wearable devices,

our brains may eventually adapt to a restructured version

with new sensory representations.

Or perhaps uploading our consciousness into a computer might not even be possible

unless we can also simulate a body capable of delivering physical sensations.

The idea that our bodies are part of our consciousness and vice versa

also isn't new.

It's found extensively in Buddhist thought,

as well as the writings of philosophers from Heidegger to Aristotle.

But for now, we're still left with the open question

of what exactly our self is.

Are we a mind equipped with a physical body as Descartes suggested?

Or a complex organism that's gained consciousness

over millions of years of evolution

thanks to a bigger brain and more neurons than our distant ancestors?

Or something else entirely that no one's yet dreamt up?