A single neuron has somewhere on the order of 5x10^16 atoms in it. There's no rule that says it couldn't potentially use a large fraction of those atoms for its functionality. That's your upper bound on computational complexity.
> There's no rule that says it couldn't potentially use a large fraction of those atoms for its functionality
There is no question that a neuron uses a large fraction of its atoms for its functionality, as is every other cell. What I think you're postulating is that these atoms form a functionally uber-complex network with mind-boggling combinatorics - but that position does not align well with current science. Single neurons are not that smart. For starters, they don't have the I/O address space or bandwidth to be, nor do they have the energy budget to behave like a block of Computronium.
Neurons have not been opaque black boxes to us for a long time now. We understand a lot of the biochemical processes going on in there. We may not have a complete picture in many areas regarding many neuron types, but there is not enough unexplored space in there to allow for a cell-sized quantum supercomputer or anything like that.
The upper bound on a neuron's computational complexity is dictated by the intricacies of its protein machinery, which is many many orders of magnitude lower than the number of atoms making up the whole.
While that's true, you need to consider that neurons don't act alone in a real system. Not only must one simulate the dozens of types of ligands and receptors in a typical neuron, but also how those ligands are modulated not only by neighbors, but also at a macro-scale (for example, if an organism increases serotonin levels due to some external stimuli, that will have significant effects across the nervous system, even parts that ostensibly have nothing to do with responding to that stimuli.)
So given ~20 types of receptors, ~8 response types ranging from inverse agonist to full agonist, and conservatively, 20 relevant concentrations per ligand, we have over 3000 states dictated both by macro and local conditions.
Forgive me if I misunderstood your intent, but this feels a little like moving the goal posts on me. In my comment, I was addressing the specific claim that we know little enough about neuronal complexity so the number of atoms in a cell could be seen as a reasonable upper bound on the complexity of the neuron. When you say I "need to consider" the complexities of response modulation and the combinatorics of the entire neuron population acting together, I disagree (purely in the context of the original claim, because that was specifically about the capabilities of a single neuron).
I don't see much discussion of quantum mechanics as being leveraged inside of neurons.
But I'm just not convinced chemistry is fast enough for thought to happen any other way than quantum.
Life has been far ahead of human state of the art for a long time.
Often, we don't even know what to look for until we learn basic physics ourselves.
For example, barely 100 years ago, we figured out that light is energy delivered in photon packets. Only then could we understand processes like photosynthesis. Something life figured out billions of years ago.
As we learn more about quantum mechanics, we discover that photosynthesis seems to harness quantum effects to improve conversion efficiency.
I'm convinced the brain is using advanced physics we don't fully understand yet.
Yet, that the brain and neurons are quantum is something I haven't seen much of in literature.
Once we figure out room temperature quantum computing, I wouldn't be surprised if we find that the brain has been doing it all along.
We just don't know what to look for, until we learn enough about physics ourselves.
Chemistry is extremely fast, and it's all based on quantum mechanics. Each atom/molecule is colliding at least billions of times per second at standard pressure and human body temperatures. Example calculation: [0]
Doesn't every interaction between particles involve quantum mechanics? Meaning every chemical reaction? Even simple things like heating water on your stove is a quantum process. Thought isn't something special here. Unless I completely misunderstand quantum mechanics.
If you are proposing that quantum processes aren't really random, that somehow human thought affects how they work, I doubt we have any evidence of that one way or the other. I would call that a fringe theory, but I can't say you are wrong.
I've recently being seeing more about a theory that consciousness is inherent in matter, and that particles choose which quantum path they take. This is way beyond anything we currently know about physics though.
> But I'm just not convinced chemistry is fast enough for thought to happen any other way than quantum.
How fast do you think? I know my reaction time to unexpected external stimulus is up in the 200ms+ range, and sometimes even basic things can take multiple seconds to think through with my conscious mind. This is an enormous amount of time chemically speaking.
I mean, there are some rules, actually. The structure of a neuron is not a black box about which we know nothing. There will be many atoms used to construct the cell wall, for example.
Your analogy is like saying my computer has X number of atoms, so they might all be used for computation! Instead, we know that, for example, the case is not used for computation. The power supply is not used for computation, etc.
Read the article. They accurately modeled the biological neuron's behavior with about 1000 'neurons'. They didn't need quintillions of neurons. So clearly the computational complexity is vastly lower than the number of atoms or molecules.
But that model represented the input/output behavior of the neuron. Of course it doesn't represent the behavior of every single atom of the neuron itself, but that isn't relevant to its computational behavior.
