quantum physics
Some approaches apply current quantum theory to develop causal models linking specific biological microstructures to the physiological and psychological mechanisms of consciousness. For example, in the 1990s, Beck and Eccles suggested that the probabilistic nature of the release of neurotransmitters from the synaptic vesicles into the synaptic gap was of quantum origin. According to these authors, the extremely small size of the sites where the exocytosis of the synaptic vesicles occurs enables quantum uncertainty to play a role in this process.

Eccles describes structures called “dendrons” composed of groups of about 100 dendrites of pyramidal neurons in the cortex. He theorizes that consciousness operates by reciprocally linking each dendron with its associated unit of mental experience, or “psychon”. The effect of the psychon on the dendron would then increase the probability of the synaptic vesicles’ releasing neurotransmitters into the excitatory synapses of this dendron’s dendrites.

Eccles thus offers a dualist hypothesis,one that posits two distinct worlds. In this hypothesis, quantum physics at the level of the synaptic vesicles plays a role somewhat like the role of the pineal gland in the philosophy of Descartes: the site where the two worlds interact. Such dualism is intriguingly consistent with Eccles’s religious background: though he received the Nobel Prize for Medicine in 1963 for his important discoveries regarding synaptic mechanisms, he was a practicing Catholic who never disguised his faith in a human soul of divine origin.

Of all the theories of consciousness that draw directly on quantum physics, the one with the longest history was proposed by John von Neumann in the 1930s, developed further by Eugene Wigner in the 1960s, and refined a bit further by Henry Stapp starting in the 1980s.

In his 1955 monograph on the mathematical bases of quantum physics, von Neumann addressed the thorny issue of measurement in the context of quantum physics—the famous Heisenberg uncertainty principle. According to this principle, the more closely we approach the infinitely small, the more we realize that what we call reality tends toward a state that is more potential than real. This suggests that the only thing that can be considered fixed at this level arises from the act of observation itself, which in a sense determines one particular state at the expense of others.

From this came Von Neumann’s idea that what we call the “observer”of a measurement can be regarded as the measuring instrument just as much as it can be regarded as the human brain that takes note of this measurement. Other authors go even further and state that it is human consciousness that actually completes the quantum measurement, thus ascribing to this consciousness a critical role in taking this quantum measurement