Not many people get to contemplate their brain in a jar, but if all goes to plan then Ill be in that curious position by Christmas.

Happily, Ill still have the brain Im using right now, which is how Ill be able to do the contemplating. The other one will be my second brain. About the size of a frozen pea, it will have been grown from a small lump of flesh that researchers at the Institute of Neurology of University College London recently dug from my arm.

My skin cells will be transformed into a state akin to stem cells, which can grow into any type of tissue, using Nobel Prize-winning methods devised in the mid-2000s. These so-called induced pluripotent stem cells, or IPSCs, will then be gently coaxed into becoming neurons. Following much the same program as neurons in a fetus, the cultured cells will organize themselves into brain-like structures, taking on the identities of some of the brains different varieties of neurons and even starting to form hints of the familiar folds and convolutions.

The neurons will begin to send one another signals. We cant properly call this thinking, but it constitutes the ingredients of thinking. My mini-brain wont get any larger than its pea shape, however, because it will lack a blood supply: Above a certain size, the inner neurons would be deprived of oxygen and die.

The UCL folks are growing such mini-brains to study neurodegenerative diseases. By making these so-called organoids from the IPSCs of people with genetic predispositions to dementia-causing conditions such as Alzheimers, they can investigate how those genes create problems, and perhaps eventually find treatments. My mini-brain will be used as an anonymized healthy control sample for the research.

I have no idea yet how I will respond to my own brain in a jar. But it has set me thinking about how pervasive this cultural trope is, and how much is invested in it. There is something disturbingly intimate about seeing, perhaps even touching, the brain of another person, and its not surprising that the image features in tales of transgression both real and fictional. A heart preserved in formalin is often seen as mere inert offal, but we seem to suspect that within the soft clefts of the human brain the person themselves somehow residesor at least clues to what made them who they were.

So the brain in a jar has become a potentially misleading avatar of self. Its grey folded surface represents an illusory boundary between everything we know and everything outside of that knowledge.

* * *

To find the person, then, we go delving into the brain. Albert Einsteins brain, removed by pathologist Thomas Stoltz Harvey after the great physicists death in 1955, was cut into slices and preserved. Harvey himself kept some of those fragments almost obsessively; others have now found their way into museums, where they have become macabre emblems of genius.

Rumours abound about why Einsteins brain was special, but the truth is that everyones brain is likely to show some deviations from the norm. And while some behaviors can be linked to physical features of different brain regions, the structure of the brain itself responds to experience: Were not just who we are because of the way our brain is, but vice versa. For example, UCL neurologists have found that the rear of a London taxi drivers hippocampus, a brain region associated with memory and with navigation, will enlarge during training.

Still, the notion of brain as destiny persists. Think of Dr. Frankensteins crazed assistant Fritz giving him the abnormal brain of a criminal for his monster in James Whales 1931 movie, dooming the creature to be homicidal. (Mel Brookss Young Frankenstein spoofs that scene when Marty Feldman, the boggle-eyed assistant to Gene Wilders crazed doctor, tells his master that the brain belonged to Abby Normal.)

There are deviations from the respectable tradition of preserving brains for dissection that are far more grotesque than anything you find in Gothic horror novels. In the 1970s, it became clear that shelves of little brains in jars kept for decades in the basement of the Otto Wagner Hospital in Vienna were removed from children. The kids were held in a special childrens ward and murdered as mental defectives by command of the Nazi doctor Heinrich Gross, who apparently intended to study the anatomical causes of such defects.

Today, some people want their brain to end up in a jar by choicenot for the benefit of medical research, but because they figure they might need it again. Brain freezing is big business: Many hundreds of people have paid up to $200,000 or so for their bodiesor, for less than half that cost, just their headsto be cryogenically preserved after death. The hope is that science will one day enable the brain to be revived and the person, in effect, to be brought back to lifeand perhaps then to live forever. (You wont necessarily want your original body, especially if you died from some fatal accident or illness.)

Currently there seems to be no actual prospect that a frozen brain could be revived. Experts point out that todays cryogenic techniques inevitably cause damage to tissues, and that thawing would induce still more. But brain-freezing immortalists contend that the technology offers a glimmer of hope that death can one day be cheated. If you can bridge the gap (its only a few decades), then youve got it made, writes the computer scientist Ralph Merkle. All you have to do is freeze your system state if a crash occurs and wait for the crash technology to be developed ... You can be suspended until you can be uploaded.

A crash? Uploaded? You can see where this is going: The idea is that the brain is just a kind of computer, full of data that can be stored on a hard drive in a file labeled You.

As Merkle sees it, your brain is material, governed by the laws of physics; those laws can be simulated on a computer; therefore your brain can be, too. Although the network of neural connections in the brain is astronomically complex, we can put an upper limit on how many bits should be needed to encode it. Uploading the contents of a brain will need a computer memory of about 1018 bits, performing around 1016 logic operations a second, Merkle calculates. Thats perfectly imaginable with the current rate of technological advance.

According to this transhumanist vision, we will soon be able to live on inside computer hardware. The brain in a jar becomes the brain on a chip.

* * *

Such heady visions of brain downloads ignore the fact that the brain is not the hardware of the person but an organ of the body. Several experts in both AI and cognitive science argue that embodiment is central to experience and brain function. At the immediate physiological level, the brain doesnt just control the rest of the body, but engages in many-channeled discourse with its sensory experience, for example via hormones in the bloodstream.

And embodiment is central to thought itself, according to the AI guru Murray Shanahan, who acted as a consultant on Alex Garlands 2014 AI movie Ex Machina. Shanahan, a professor of cognitive robotics at Imperial College London, writes that cognition is largely about imagining the consequences of physical actions we might make in the worlda process of inner rehearsal of future scenarios.

In this view, then, the brain in a jar is not a feasible avatar of the entire human. One could argue that the brain-on-a-chip could be coupled to a robotic body that allows physical interaction with the surroundings, or even to just a simulation of a virtual environment. But Shanahans perspective raises questions about whether there is any purely mental essence of you that can be bottled in the first place.

The embodied aspect of the brain has long exercised philosophers, who debate whether what they call a brain in a vat alone can develop any reliable notion of truth about the world. The question stems from a hypothetical scenario: How do you know youre not just a brain in a vat being presented with a simulated world? How, then, can you know that all your beliefs about the world are not false?

The question has entered popular culture via the Matrix movies, now almost an obligatory port of call for discussions around the philosophy of mind. But the predicament was grist for the philosophical mill long before the Wachowskis picked it up. The most celebrated critic of brain in a vat skepticism was the late American philosopher Hilary Putnam, who argued in 1981 that the whole notion is contradictory. Words and concepts used by a brain in a vat cant be meaningfully applied to real objects outside of the brains experience, because the ability to have causal interaction with the specific things that words name is inherently how such words acquire meaning, Putnam argued. Even if there are actual trees in the world containing the vat that are simulated for the brain, the concept tree cant be said to refer to them from the brains point of view.

The same is true for the words brain and vat, which to a brain in a vat cant refer to actual brains and vats. The philosopher Anthony Brueckner expresses Putnams argument in a seemingly Zen-like turn of phrase: If I am a Brain in a Vat, then I am not a Brain in a Vat.

Its hardly surprising that not everyone is persuaded by Putnams subtle argument against our right to be skeptical. The philosopher Thomas Nagel adds to the impression that philosophers seem here to be attempting to escape, Houdini-like, from the sealed glass jar of their own minds. So what if I cant express my skepticism by saying Perhaps I am a brain in a vat and must instead say Perhaps I cant even think the truth about what I am, because I lack the necessary concepts and my circumstances make it impossible for me to acquire them? Thats still pretty skeptical, Nagel says.

No wonder Neo just decided to shoot his way out of the problem.

* * *

The brain in a vat might sound like one of those reductio ad absurdum scenarios for which philosophers enjoy notoriety, but some think it is already a reality. The anthropologist Hlne Mialet used precisely that expression to describe the British physicist Stephen Hawking on his 71st birthday, in 2013. Hawking, who has famously been confined to a wheelchair for decades by amyotrophic lateral sclerosis, or ALS, is now unable to volitionally use just about any muscles except for slight movements of those in his cheek, which are linked to a computer system that allows him to communicate and interact with the world. Mialet argued that this essentially makes him a brain hooked up to machinery: He has become more machine now than man, like Darth Vader.

The description, intended only to highlight our own increasing dependency on machine interfaces, drew intense criticism and condemnation. But perhaps Mialet was merely articulating in a direct and confrontational fashion how many people have long viewed Hawking: as a brilliant brain trapped in a non-functioning body. His remarkable endurance in the face of a condition unimaginable to most of us fits comfortablyor uncomfortablywith our predisposition to stuff all our notions of humanity into the single organ that orchestrates our existence in the world.

It may be that my own little brain in a jar will challenge me about that. Just suppose we could give it a blood supply and let it keep growing to full size. What then would it experience? Its an artificially ghoulish idea, but one that would worry me in the way that a full-grown liver in a vat would not. I would, I think, be forced to suspect that there was someone in thereand deep down, perhaps Id suspect it was me.

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Why Philosophers Are Obsessed With Brains in Jars - The Atlantic