Anyway, neurons are a convenient example because they're so well known, but there are many other factors that lead me to believe the brain itself can in no way be construed as a Turing machine. Namely, the contribution of glial cells to neurophysiology, which is largely ignored by most people who espouse their ideas on the deterministic nature of the brain (which, if the brain is a Turing machine, it certainly is deterministic). However, we need look no further than the tripartite synapse to see that the behavior of many neural mechanisms is often stochastic. The tripartite synapse is so named because there are three essential components: the axon terminal (pre-synaptic terminal); the post-synaptic terminal; and a psuedopod of an astrocyte. The role of the astrocyte is to provide neurotransmitters and other bio-molecules that can vastly alter long term depression and potentiation. This makes a non-neuronal cell, that does not fire an action potential, integrally important to the normal firing of action potentials. I don' believe there is any such analog in computers.

Furthermore, there is biomolecule sharing between oligodendrocytes and axons that drastically alter the properties of the axon, such as the ability of the axon to produce neurotransmitters, to grow and to conduct current. These, and many other, properties are stochastic, not deterministic, and cannot be ignored when developing a complete picture of the brain, but they often are by those who are trying to model the brain and those who are writing about the deterministic quality of the brain (John Searle comes to mind).

I believe this is history's influence on neurobiology. It was thought for many years that astrocytes provide structure and nutrients and oligodendrocytes provide myelin; end of story. This is as far from the truth as claiming the world is flat, but is still ignored in so many arguments.

I will need to brush up on the Tractatus to have a meaningful discussion about it. I take PI to be divine words, but I've always read that LW himself rejected a lot of the Tractaus later in life, so I haven't paid nearly as much attention as it probably deserves. I appreciate the free link though; definitely going to bookmark.