Category: Science

This afternoon, I saw a few posts on twitter on the topic of mind uploading, particularly via a link to this blog post by Athena Andreadis. Not sure why a 2011 post appeared on Twitter today, but it got me thinking. As a neuroscientist and SFF writer, I wanted to give my expert(?) opinion.

First off, do go read Athena’s post — it’s very well-written and reasoned. But one part of it concludes that (to paraphrase) “moving the brain into another container is intrinsically impossible,” and I disagree.

Here’s the key paragraph:

Recall that a particular mind is an emergent property (an artifact, if you prefer the term) of its specific brain – nothing more, but also nothing less. Unless the transfer of a mind retains the brain, there will be no continuity of consciousness. Regardless of what the post-transfer identity may think, the original mind with its associated brain and body will still die – and be aware of the death process. Furthermore, the newly minted person/ality will start diverging from the original the moment it gains consciousness. This is an excellent way to leave a clone-like descendant, but not to become immortal.

Absolutely true. Mind uploading is a vastly harder concept than 1970s computer scientists could have possibly imagined. Consciousness is a property of what the brain is doing. (Most likely for the evolutionary goals of error-checking and causality-determining, but that’s another blog post.) If you somehow copied a mind into a computer, it’d be just that: a copy. This has plenty of interesting implications, but it’s not really a consciousness transfer, and it’s certainly not going to make you immortal — at least, not the current “you.”

But wait…

Let’s now discuss the possible: in situ replacement [of brain cells].

Here’s the fun part. Do brain cells¹ regrow during adult life? Generally no, except for a few narrow parts of the brain. There’s no turnover in our brain cells. But I think that a brain could function if the cells did get replaced. After all, we lose brain cells throughout adulthood, yet that doesn’t impinge on our identity. Those cells form new connections, new ways of accomplishing the same things. Some people with strokes or other localized brain damage can relearn the lost skills — for instance, my aunt lost her ability to speak due to a stoke in her 40s, but over the following couple of years she relearned it. She finds herself at a loss for words more often than most people, but you’d never know she had the stroke. The dead cells did not grow back, but the existing ones learned to pick up the slack. What if we put an artificial chunk of brain in there instead, over where the old stuff died?

We could do this at the single-cell level too. What if we could use microsurgery to replace a damaged nerve cell? Put in an artificial cell that has the same connections, responds to inputs in the same ways, etc.² It’s not a natural neuron, but its functional role is the same: it does the same things. (We are nowhere near the tech level to build such artificial cells, let alone install them, but it’s certainly possible.) If there are any hiccups during the surgery process, it doesn’t matter: the new cell doesn’t have to exactly copy the current state of the old one. The networks will learn to incorporate that replacement cell, and make it a part of the ever-changing symphony of activity in the brain.³

Replace a cell or a small part of the brain. Then another. And another.⁴ Each replacement part is functionally equivalent to the old one, remember. Eventually, you get a whole brain made out of the new components. Wait, what are the new components made out of? It doesn’t matter. Maybe they’re culture-grown artificial neurons. Maybe they’re 24th-century biopolymers. Maybe they’re silicon.

And now that mind is running on an artificial device, without any interruption in conscious experience.⁵

As Athena notes, you certainly don’t want to cut the brain off from sensory and motor experience. The brain evolved to help us act adaptively, after all; a brain in a jar is a nonfunctional brain. But that just means you should put your computerized brain in an android body, or in a vat-grown human body, or — if you really want to call it “uploading” — in a software simulation of human sensory and motor feedback. These are all beyond modern science, but probably easier than getting the brain into silicon in the first place.

Therefore: while the “hardware”⁶ of the brain is critical to our consciousness, it may be possible to replace that hardware with the electronic.

In a couple centuries, anyways!

By popular request, an explanation for why tryptophan in turkey does not actually make you sleepy. Neuroscientist Approved(tm)!

The wikipedia article on this is pretty good, and has nice references, but it’s not exactly in layman’s language. Let me try to explain it in my own words:

What is tryptophan?

Tryptophan is an amino acid, a building block of protein. Your brain uses it to produce serotonin, a neurotransmitter that plays an important role in sleep. So if you eat a food with lots of tryptophan, you should produce more serotonin, and thus get sleepy, right? Well…

Tryptophan in food ≠ tryptophan in brain 

Most things cannot move easily between your blood and your brain. It’s a delicate environment in there! Tryptophan (like all amino acids) needs another molecule to drag it bodily across that blood-brain barrier. However, that transport molecule is already working at full speed, hauling a full load of various amino acids. Unless you’re starving, your blood already has plenty of tryptophan, so a little extra from the turkey will make no difference. When the ferry is moving at full speed, and there’s already a backlog, adding more cars to the waiting list doesn’t get any more cars across the water.

So why do we get sleepy after Thanksgiving dinner?

Part of it’s just meal size — after a big meal your body diverts resources to digestion. But let’s focus on Thanksgiving dinner. It does contain something special, but not the turkey. When you eat lots of carbohydrates, your body produces insulin to pull sugar out of the blood, into storage. Insulin also makes your body pull some amino acids into storage… but not tryptophan. So after a lot of carbs, more of the amino acids in your blood are tryptophan. When a bunch of non-tryptophan cars bail out of the ferry line, you do end up with more tryptophan cars across the water.

In other words, tryptophan in your brain can make you sleepier — but you get more tryptophan in your brain from eating the potatoes and the stuffing, not the turkey.

On top of all that, turkey doesn’t even contain more tryptophan than chicken, pork, or cheese. Anyone know where the heck this urban legend comes from?