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Look at your hand.
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How do you know it's really yours?
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It seems obvious, unless you've experienced the rubber hand illusion.
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In this experiment, a dummy hand is placed in front of you
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and your real hand is hidden behind a screen.
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Both are simultaneously stroked with a paint brush.
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No matter how much you remind yourself the dummy hand isn't yours,
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you eventually start to feel like it is,
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and inevitably flinch when it's threatened with a knife.
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That may just be a temporary trick, but it speaks to a larger truth:
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our bodies, the physical, biological parts of us,
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and our minds, the thinking, conscious aspects,
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have a complicated, tangled relationship.
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Which one primarily defines you or your self?
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Are you a physical body that only experiences thoughts and emotions
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as a result of biochemical interactions in the brain?
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That would be a body with a mind.
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Or is there some non-physical part of you that's pulling the strings
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but could live outside of your biological body?
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That would be a mind with a body.
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That takes us to an old question
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of whether the body and mind are two separate things.
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In a famous thought experiment,
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16th-century philosopher René Descartes pointed out
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that even if all our physical sensations were just a hallucinatory dream,
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our mind and thoughts would still be there.
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That, for him, was the ultimate proof of our existence.
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And it led him to conclude that
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the conscious mind is something separate from the material body
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that forms the core of our identity.
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The notion of a non-physical consciousness
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echoes the belief of many religions in an immaterial soul
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for which the body is only a temporary shell.
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If we accept this, another problem emerges.
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How can a non-physical mind have any interaction with the physical body?
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If the mind has no shape, weight, or motion,
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how can it move your muscles?
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Or if we assume it can, why can your mind only move your body and not others?
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Some thinkers have found creative ways to get around this dilemma.
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For example, the French priest and philosopher Nicolas Malebranche
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claimed that when we think about reaching for a fork,
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it's actually god who moves our hand.
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Another priest philosopher named George Berkeley
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concluded that the material world is an illusion,
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existing only as mental perceptions.
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This question of mind versus body isn't just the domain of philosophers.
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With the development of psychology and neuroscience,
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scientists have weighed in, as well.
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Many modern scientists reject the idea
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that there's any distinction between the mind and body.
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Neuroscience suggests that our bodies, along with their physical senses,
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are deeply integrated with the activity in our brains
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to form what we call consciousness.
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From the day we're born,
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our mental development is formed through our body's interaction
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with the external world.
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Every sight, sound, and touch create new maps and representations in the brain
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that eventually become responsible for regulating our experience of self.
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And we have other senses, besides the typical five,
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such as the sense of balance
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and a sense of the relative location of our body parts.
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The rubber hand illusion, and similar virtual reality experiments,
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show that our senses can easily mislead us in our judgment of self.
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They also suggest that our bodies and external sensations
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are inseparable from our subjective consciousness.
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If this is true, then perhaps Descartes' experiment was mistaken from the start.
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After all, if we close our eyes in a silent room,
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the feeling of having a body isn't something we can just imagine away.
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This question of mind and body becomes particularly interesting
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at a time when we're considering future technologies,
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such as neural prosthetics and wearable robots
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that could become extended parts of our bodies.
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Or the slightly more radical idea of mind uploading,
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which dangles the possibility of immortal life without a body
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by transferring a human consciousness into a computer.
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If the body is deeply mapped in the brain,
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then by extending our sense of self to new wearable devices,
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our brains may eventually adapt to a restructured version
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with new sensory representations.
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Or perhaps uploading our consciousness into a computer might not even be possible
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unless we can also simulate a body capable of delivering physical sensations.
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The idea that our bodies are part of our consciousness and vice versa
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also isn't new.
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It's found extensively in Buddhist thought,
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as well as the writings of philosophers from Heidegger to Aristotle.
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But for now, we're still left with the open question
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of what exactly our self is.
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Are we a mind equipped with a physical body as Descartes suggested?
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Or a complex organism that's gained consciousness
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over millions of years of evolution
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thanks to a bigger brain and more neurons than our distant ancestors?
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Or something else entirely that no one's yet dreamt up?