http://www.braincampaign.org/Common/Docs/Files/2766/chchap2.pdf
Richard Restak in his book Brainscapes. Now this book is 14 years old, and is meant to by concise/ not highly technical but he seems to be pretty clear on this.
From pages 91 and 92 of the book:
One of the reasons that [the operation of the brain] remains so mysterious is that it is governed by both mechanical and quantum principles. As a result the brain is inherently indeterminant, unpredictable, and uncertain. For instance, at the cellular level the "firing' of a neuron is dependent on the ratio of excitatory influences (via excitatory neurotransmitters) to inhibitory ones (via inhibitory neurotransmitters). At the molecular layer this translates into whether or not a synaptic vesicle will discharge its contents into the synaptic space. But this action cannot be predicted, since the synaptic vesicles are so small they are governed by quantum rules and are inherently indeterminate. Thus we can only speak of the "probability" that the vesicle will discharge its contents - no one can predict for certain - which does away with the possibility of predicting brain activity on the molecular scale.
There's also this paper: Quantum physics in neuroscience and psychology:a neurophysical model of mind–brain interaction, which I have not even come close to reading in its entirety and which probably gets more technical on both topics of quantum physics and neuroscience that I can currenltly understand, that seems to state the same info as given by Restak. I know nothing of the paper's authors except what's listed at the beginning of the paper, and I can't say at this point I completely understand (much less agree or disagree with) all their conclusions, but they appear to be saying that quantum physics is relevant to the synaptic vesicles releasing their contents.
From pages 11 and 12 of the paper under the heading "(b) Nerve terminals, ion channels and the need to use quantum theory in the study of the mind–brain connection"
Nerve terminals are essential connecting links between nerve cells. The general way they work is reasonably well understood. When an action potential travelling along a nerve fibre reaches a nerve terminal, a host of ion channels open. Calcium ions enter through these channels into the interior of the terminal. These ions migrate from the channel exits to release sites on vesicles containing neurotransmitter molecules. A triggering effect of the calcium ions causes these contents to be dumped into the synaptic cleft that separates this terminal from a neighbouring neuron, and these neurotransmitter molecules influence the tendencies of that neighbouring neuron to ‘fire’.
At their narrowest points, calcium ion channels are less than a nanometre in diameter (Cataldi et al. 2002). This extreme smallness of the opening in the calcium ion channels has profound quantum mechanical implications. The narrowness of the channel restricts the lateral spatial dimension. Consequently, the lateral velocity is forced by the quantum uncertainty principle to become large. This causes the quantum cloud of possibilities associated with the calcium ion to fan out over an increasing area as it moves away from the tiny channel to the target region where the ion will be absorbed as a whole, or not absorbed at all, on some small triggering site.
This spreading of this ion wave packet means that the ion may or may not be absorbed on the small triggering site. Accordingly, the contents of the vesicle may or may not be released.
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Re: Neurology and quantum physics
by Lincoln on September 25th, 2009, 9:36 pm
OK, so ask yourself...what electrical current is embodied by a single electron? Then ask yourself how many electrons are necessary to conduct any neurochemical reaction. Is one electron sufficient to set off an entire neuron? Or is it the case that you need some small amount of charge to actually do something. Even a femtocoulomb of charge requires 6,000 electrons. And these electrons are not produced in a quantum state.
Further, even if a single neuron firing were governed by quantum principles (and I hope that the question above, with a bit of googling will convince you that they aren't), how many neurons must fire to have a significant effect in the brain? Will one neuron cause a decision, retrieve a memory, etc.?
It is 100% clear that at the very tiniest size scales that quantum principles hold. After all, the brain is made of neurons, which are cells, made of matter, which consists of atoms, which are governed by quantum principles. But what that is uniquely quantum translates to the macro-realm of coherent neural states?
Further, while we have free will in some sense, it is also true that there is a huge aspect to which we are culturally and/or psychologically programmed. Were quantum principles governing our behavior, we'd have totally random behaviors, as which neuron fired when would have not be predictable. But this just isn't the case.
The case for a uniquely-quantum source of consciousness and free will is only compelling inasmuch as they are not understood and seem to be somehow different from traditional physical determinism. The linkage is natural for those who want to think of the mind as really somehow actually different from the neurochemistry. This is a thinly-disguised scientific quest for the origin of the soul.
But the causal linkage doesn't survive an inspection of the two distinct phenomena (of which I am admittedly far more expert in one than the other.)
Further, even if a single neuron firing were governed by quantum principles (and I hope that the question above, with a bit of googling will convince you that they aren't), how many neurons must fire to have a significant effect in the brain? Will one neuron cause a decision, retrieve a memory, etc.?
It is 100% clear that at the very tiniest size scales that quantum principles hold. After all, the brain is made of neurons, which are cells, made of matter, which consists of atoms, which are governed by quantum principles. But what that is uniquely quantum translates to the macro-realm of coherent neural states?
Further, while we have free will in some sense, it is also true that there is a huge aspect to which we are culturally and/or psychologically programmed. Were quantum principles governing our behavior, we'd have totally random behaviors, as which neuron fired when would have not be predictable. But this just isn't the case.
The case for a uniquely-quantum source of consciousness and free will is only compelling inasmuch as they are not understood and seem to be somehow different from traditional physical determinism. The linkage is natural for those who want to think of the mind as really somehow actually different from the neurochemistry. This is a thinly-disguised scientific quest for the origin of the soul.
But the causal linkage doesn't survive an inspection of the two distinct phenomena (of which I am admittedly far more expert in one than the other.)
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