Hello,
I am cross posting this here from another philosophy forum.


A typical philosophical question is whether the Universe is deterministic or random. Modern physics tells that the second option is more likely. However, even if the universe is random, it could contain mechanisms that are deterministic for all practical purposes; mechanisms on whose operations randomness has only a negligible effect. So, is the brain one of such mechanisms?

If the workings of the brain are deterministic, then the behaviour of the brain is completely determined by:
1) received sensory data (a posteriori)
2) the "built-in software" and hardware (a priori)
(Assume physicalism for the sake of this discussion.)

On the other hand, if brains are not deterministic, there must be some random inputs to brain "algorithms". What could be the possible sources of such indeterminism? I can think of:
1) Quantum effects.
2) External random impacts, for example cosmic rays and radiation. They theoretically can create random errors in the operation of the brain.
3) Something like "uninitialized memory". I don't know if something similar to this concept exists in neuroscience, but I think that there should be some regions is brain that are like filled with random data - like computer memory contains random data after the computer has just been is turned on. Of course, the contents of the memory are in some way determined by the physical universe (at least probabilistically), but the determination is so complex, untraceable, and unrelated to the workings of the computer (or brain) that these data can be treated as random from the computer's point of view.

So I am interested what the modern science has to say about all that. I have heard that it's considered unlikely that quantum effects play significant role in the brain. Brain is a warm and chaotic environment, so quantum decoherence is expected to happen almost immediately. But can cosmic rays have an effect of our consciousness? And are the "algorithms" of the brain deterministic, or do they contain some truly random elements, like "reading from an uninitialized memory"? Are scientists working on these questions? To what extent they are answered at the present moment?

The bottom line: I am interested whether the brain can be simulated using a computer with a pseudo-random number generator or a truly random elements are required.

While random effects may be present in the brain, I don't think they dominate or even have a significant effect. Freud was so very wrong in so many things, but he may have been right when he said that there are no accidents. I.e., the unconscious mind is behind all behavior.

Including reasoning?

'Are brains deterministic? '.... some are!

Yes, of course. If reasoning weren't involved, one would never wake up with a good idea.

my words determines your reply.... does action, in fact, cause a reaction

But if you can't predict my reply, how can you say you determine it?

.... but can we ascertain the finite reactive potentialities?

Or, does one wake up 'to' a good idea?

the permutations are as infinite ....

there's 1.... shall we start counting!

.... those potentialities can thus be narrowed down based on the capacity at hand, case in hand!

... dependent upon the size of the case!

If every neuron in the brain acted randomly as in the case of particle decay how could any thought be logical or directed.

Nevertheless there are some fluid mechanics that could be said to be non-deterministic in nature in the brain and they may contribute slightly to the decision making process visa vi butterfly effect.

So if you really want to believe the brain is non-deterministic you could say it is by the gust of a butterfly's wing but we all know that the brain really must work as a system.

So what I guess I am saying is the question lends itself to the answer that one wants to hear.

I mean you could believe like Marvin Minsky that the mind is just a collection of independent autonomous problem solving circuits that form in the brain.

Or like John Searle-- that the mind and the process of thinking is something more that might give a wink to quantum mechanics.


yes, a brain can be simulated without a random number generator no less. The mind however-- the question remains does a virtual car really drive?

Most neuroscientists I know (who have an opinion) believe that:

1) The brain cannot be 100% deterministic because there is too much irregularity in the random brownian motion of the molecules involved in intracellular signaling.

2) Whatever nondeterminism may exist in the brain is not important for understanding how it works. The brain is a (mostly!) reliable system built out of unreliable components.

3) Even if the brain was "completely determined" by the sensory input and internal state, the variety in the sensory input is essentially infinite and the controllability of internal state is near zero. No two moments are ever the same. Unlike digital computers, which are designed to replay precisely controlled sequences with zero variance, the brain exploits variance. The brain is better viewed through the lens of chaos theory. Like the weather, the brain's state is so sensitive to the uncontrollable "initial conditions" of life that its behavior could never be perfectly predicted, even if it was "100% deterministic".


Intelligent minds disagree.

I think the most common view among theoretical neuroscientists is "sure, why not" with the caveat that the paradigm of information processing in the brain is entirely different from a digital computer. Since this paradigm is not fully understood yet, it is an open question whether the architecture of a digital computer could ever be adequately adapted to simulate the brain. However most neuroscientists believe that the brain is essentially a biological machine governed by mechanisms. Whether the functioning of this machine will ever be fully "solved" or successfully emulated with technology is an open question.

Biology has a way of providing endless surprises. So just because neuroscientists assume the brain is just a bunch of mechanisms doesn't mean that the mechanistic approach will ever fully explain it.

Blue Brain is a giant project by IBM and neuroscientists to attempt to fully simulate a cubic millimeter of cerebral cortex on the world's fastest parallel supercomputer.

As far as the question of "free will", I think most neuroscientists would say that free will is a psychological belief held by humans that is not very relevant to understanding how the brain works. Let the philosophers tackle that one!