Quantum Hypothesis of Synaptic Transmission

James P. Isaacs, John C. Lamb

N. S. Khan

Sylvia Pulmannová

Steven J. Burden, Ronald D.G. McKay

John Carew Eccles

If non-material mental events, such as the intention to carry out an action, are to have an effective action on neural events in the brain, it has to be at the most subtle and plastic level of these events. In the first stage of our enquiry an introduction to conventional synaptic theory leads on to an account of the manner of operation of the ultimate synaptic units. These units are the synaptic boutons that, when excited by an all-or-nothing nerve impulse, deliver the total contents of a single synaptic vesicle, not regularly, but probabilistically. This quantal emission of the synaptic transmitter molecules (about 5000-10 000) is the elementary unit of the transmission process from one neuron to another. In the second stage this refined physiological analysis leads on to an account of the ultrastructure of the synapse, which gives clues as to the manner of its unitary probabilistic operation. The essential feature is that the effective structure of each bouton is a paracrystalline presynaptic vesicular grid with about 50 vesicles, which acts probabilistically in vesicular (quantal) release. In the third stage it is considered how a non-material mental event, such as an intention to move, could influence the subtle probabilistic operations of synaptic boutons. On the biological side, attention is focused on the paracrystalline presynaptic vesicular grids as the targets for non-material mental events. On the physical side, attention is focused on the probabilistic fields of quantum mechanics which carry neither mass nor energy, but which nevertheless can exert effective action at microsites. The new light on the mind-brain problem came from the hypothesis that the non-material mental events, the 'World 2' of Popper, relate to the neural events of the brain (the 'World 1' of matter and energy) by actions in conformity with quantum theory. This hypothesis that mental events act on probabilistic synaptic events in a manner analogous to the probability fields of quantum mechanics seems to open up an immense field of scientific investigation both in quantum physics and in neuroscience.

Julian Collados

We propose that thermally assisted proton tunneling in presynaptic enzymes contributes measurably to synaptic variability, producing a kinetic isotope effect (KIE) distinguishable from classical thermal noise. H→D isotope substitution in neuronal cultures should reduce the interspike interval coefficient of variation (ISI CV) by a KIE_network factor in the range of 1.5–3.5×, with a modal estimate of ~2.5×, under conditions where pure thermal noise predicts KIE ≈ 1. The prediction rests on: (1) documented proton tunneling in enzymes with KIE up to 100×; (2) a PCET-mediated vesicular fusion model; and (3) experimental evidence that heavy water modulates hippocampal synaptic transmission. The hypothesis does not require macroscopic quantum coherence or novel physics. The falsification threshold is explicit: KIE_red < 1.5× under controlled conditions with sufficient statistical power would refute the hypothesis in its current formulation.