Hameroff proposed that microtubules were suitable candidates to support quantum processing.
[24] Microtubules are made up of
tubulin protein subunits. The tubulin protein dimers of the microtubules have
hydrophobic pockets which might contain delocalized
π electrons. Tubulin has other smaller non-polar regions, for example 8
tryptophans per tubulin, which contain π electron-rich indole rings distributed throughout tubulin with separations of roughly 2 nm. Hameroff claims that this is close enough for the tubulin π electrons to become quantum entangled.
[25] Quantum entanglement is a state in which quantum particles can alter one another's quantum-mechanical state instantaneously and at a distance, in a way which would not be possible if they were macroscopic objects obeying the laws of classical physics.
In the case of the electrons in the tubulin subunits of the microtubules, Hameroff has proposed that large numbers of these electrons can become involved in a state known as a
Bose-Einstein condensate. These occur when large numbers of quantum particles become locked in phase and exist as a single quantum object. These are quantum features at a macroscopic scale, and Hameroff suggests that through a feature of this kind, quantum activity, which is usually at a very tiny scale, could be boosted to be a large scale influence in the brain.
Hameroff has proposed that condensates in microtubules in one
neuron can link with microtubule condensates in other neurons and
glial cells via
gap junctions.
[26][27] In addition to the synaptic connections between brain cells, gap junctions are a different category of connections, where the gap between the cells is sufficiently small for quantum objects to cross it by means of a process known as
quantum tunneling. Hameroff proposes that this tunneling allows a quantum object, such as the Bose-Einstein condensates mentioned above, to cross into other neurons, and thus extend across a large area of the brain as a single quantum object.
He further postulates that the action of this large-scale quantum feature is the source of the
gamma synchronization observed in the brain, and sometimes viewed as a
neural correlate of consciousness.
[28] In support of the much more limited theory that gap junctions are related to the gamma oscillation, Hameroff quotes a number of studies from recent years.
[29]