Are we quantum computers, or merely clever robots?
Below, in brief, I describe the motivation behind my foray into "quantum neuroscience" - a field that I have been attempting to start (or revive?) in recent years.
My sojourn from "conventional" condensed matter physics started in Spring 2013 when I set out to try and understand how lithium can be such an effective drug in tempering mania and taming bipolar disorder. The "drug" lithium is just one atom - a "spherical cow" of psychiatric medications, suitable for study by a physicist (indeed, the Li+ ion is quite literally spherical, the same shape, albeit smaller, than the neutral helium atom) - altogether different than every other medication, such as Prozac, which are large molecules
Together with my collaborators, Wikipedia and Google, I thought of a simple yet intriguing question: Would the effects of lithium be modified if one were to replace the common isotope lithium-7 (92% natural abundance) present in the pharmacy medication by the much rarer isotope lithium-6 (8% natural abundance)? Reluctant to switch out the lithium-7 by lithium-6 in my own prescription, I suggested - to Wikipedia and Google - that we give the different isotopes of lithium to rats, and look for any differential manifestations in behavior. Google's reply: You're a bit late, since this was already done in 1986! (Abberant Parenting and Delayed Offspring Development in Rats Exposed to Lithium, J.A. Sechzer et.al., 1986). Remarkably, this paper reported that mother rats receiveing lithium-6 showed much stronger maternal behaviors, such as grooming, nursing and nest-building, than the rats in either the lithium-7 or control groups.
How could that possibly be, I exclaimed loudly and emphatically to my mute collaborators. Bio-chemistry depends on the number of electrons in an atom/ion, and is largely insensitive to the number of neutrons in the atomic nucleus (3 or 4, for the lithium-6 and lithium-7 isotopes, respectively). But when Google told me that the quantum coherence time of the nuclear spin of a lithium-6 ion when solvated in water is a whopping 5 minutes (!) - roughly the same as my memory, and much longer than lithium-7's coherence time of 10 seconds - the remarkable possibility that quantum processing with nuclear spins might be operational in the brain was placed firmly in my own brain! (Conceivably accounting for consciousness, if I might.) Not to be dislodged. Yet, at least.
But lithium is a trace element, largely absent in people that do not imbibe lithium pharmaceutically, yet I do (vaguely) recall being conscious before I started taking lithium! So I decided to step back, and open my mind - quite considerably - to approach science in a new way (for me, at least), employing a "reverse engineering" stategy. I proceeded to list isome necessary - but surely not sufficient - requirements that must be satisfied by biology, chemistry and neuroscience in order that quantum processing with nuclear spins could conceivably be present in the brain, for example,
(i) the existence of a common biological element with a very isolated nuclear spin to serve as a putative "neural qubit",
(ii) a mechanism for entangling pairs of such nuclear spins,
(iii) a mechanism for quantum processing with neural qubits
(iv) a mechanism for transducing quantum entanglement into neurotransmitter release...
(v)....
Guided by these requirements, my collaborators and I set out to see if the natural world of biology, chemistry, neuroscience and physics could satisfy such requirements - necessary for the (presumed) existence of the quantum brain - seeking to identify the bio-chemical ``substrate" and mechanisms hosting such putative quantum processing. Remarkably, we have since identified a specific neural qubit and a unique collection of ions, molecules, enzymes and neurotransmitters, illuminating an apparently single path towards nuclear spin quantum processing in the brain.
Some of this can be found in our papers, Quantum Cognition: The possibility of processing with nuclear spins in the brain, M.P.A. Fisher, Annals of Physics 362, p. 593-602 (2015) and A new spin on neural processing: Quantum cognition, by C.P. Weingarten, P.M. Doraiswamy and M.P.A. Fisher, Frontiers in Human Neuroscience 10, 541 (2016). Also see a paper that I wrote, based on a talk I gave at a conference in Singapore in January 2017, entitled: Are we quantum computers, or merely clever robots?
See also the following articles in the "popular press"
Neural qubits: Quantum Cognition based on synaptic nuclear spins, by John Hewitt, 2015 https://phys.org/news/2015-08-neural-qubits-quantum-cognition-based.html
Your Quantum Brain: Does weird physics control our thoughts?, by Michael Brooks in the New Scientist, 2015
Is Quantum Processing Operative in the Brain?, by Tenille Bonoguore, Permimeter Institute glossy, 2016
A New Spin on the Quantum Brain by Jennifer Oullette, Quanta Magazine, 2016
The strange link between the human mind and quantum physics by Philip Ball, BBC online, 2017 http://www.bbc.com/earth/story/20170215-the-strange-link-between-the-hum...