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Here’s why we’ll never be able to build a brain in a computer

It’s easy to equate brains and computers – they’re both thinking machines, after all. But the comparison doesn’t really stand up to closer inspection, as Dr Lisa Feldman Barrett reveals.

People often describe the brain as a computer, as if neurons are like hardware and the mind is software. But this metaphor is deeply flawed.

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A computer is built from static parts, whereas your brain constantly rewires itself as you age and learn. A computer stores information in files that are retrieved exactly, but brains don’t store information in any literal sense. Your memory is a constant construction of electrical pulses and swirling chemicals, and the same remembrance can be reassembled in different ways at different times.

Brains also do something critical that computers today can’t. A computer can be trained with thousands of photographs to recognise a dandelion as a plant with green leaves and yellow petals. You, however, can look at a dandelion and understand that in different situations, it belongs to different categories. A dandelion in your vegetable garden is a weed, but in a bouquet from your child, it’s a delightful flower. A dandelion in a salad is food, but people also consume dandelions as herbal medicine.

In other words, your brain effortlessly categorises objects by their function, not just their physical form. Some scientists believe that this incredible ability of the brain, called ad-hoc category construction, may be fundamental to the way brains work.

Also, unlike a computer, your brain isn’t a bunch of parts in an empty case. Your brain inhabits a body, a complex web of systems that include over 600 muscles in motion, internal organs, a heart that pumps 7,500 litres of blood per day, and dozens of hormones and other chemicals, all of which must be coordinated, continually, to digest food, excrete waste, provide energy and fight illness.

Your brain’s most important job is to regulate the systems of your body so you stay alive and maybe even thrive. That’s probably a major reason that brains evolved in the first place. Over hundreds of millions of years, animal bodies became complicated, with dozens of systems to balance, and they needed a central controller to shuttle around blood, water, salt, oxygen and other bodily resources for survival.

A brain needs a body

Your brain’s control of your body is at the core of your mental activity. Every thought you’ve ever had, every concept you’ve ever learned, every emotion you’ve ever experienced and everything you’ve ever seen, heard, smelled, tasted or touched includes data about the state of your body. You don’t experience your mental life in this way, but that’s what is happening ‘under the hood’.

If we want a computer that thinks, feels, sees or acts like us, it must regulate a body – or something like a body – with a complex collection of systems that it must keep in balance to continue operating, and with sensations to keep that regulation in check. Today’s computers don’t work this way, but perhaps some engineers can come up with something that’s enough like a body to provide this necessary ingredient.

For now, ‘brain as computer’ remains just a metaphor. Metaphors can be wonderful for explaining complex topics in simple terms, but they fail when people treat the metaphor as an explanation. Metaphors provide the illusion of knowledge.

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