Written by Brett Weiss
Consciousness has puzzled human beings since the dawn of mankind. Philosophers, biologists, physicists, and neuroscientists have all attempted to provide a definitive explanation of it, however, an accurate account is still pending. Great technological advancements in the field of neuroscience have paved the way for progress in providing an explanation, yet we still lack answers to questions such as how and from where does consciousness emerge.
In 2019, John H. Zhang from the Center of Neuroscience Research at Loma Linda University along with colleagues from Fudan University in Shanghai, China published a review in the Annals of Translational Medicine where they comprehensively described a prevailing contemporary theory of consciousness that invokes principles of quantum physics called the orchestrated objective reduction (Orch-OR) theory of consciousness. Stuart Hameroff, an anesthesiologist from the University of Arizona, and Sir Roger Penrose of the University of Oxford developed this theory in which they use principles of quantum physics to describe how neural processes facilitate consciousness. Instead of chemical interactions between neurons giving rise to consciousness through neurotransmission, Hameroff and Penrose postulate that microtubules, microscopic tubular structures in cells, transmit and store consciousness events in the brain. In fact, the duo compares microtubules in cells of the brain to transistors in computers that amplify and transmit electrical signals.
For most of the history of consciousness studies, only philosophers have examined the nature of consciousness, but more recently, neuroscientists, biologists, and physicists have begun to penetrate this field of study. These scientists have always defined consciousness as the Hard Problem due to their inability to explain how the component of experience called a qualitative experience, the “what it’s like” aspect of consciousness, comes from a physical process such as a brain. With the development of unprecedented technological advancements for research fields like physics and neuroscience, more details surrounding the Hard Problem have come to light.
Quantum mechanics deals with the tiniest components of the material world. This branch of physics supplements the theory that Isaac Newton devised when he wrote his theory of physics pertaining to larger objects, macroscopic physics. Quantum mechanics has only been around for about a hundred years, however, it could hold the capacity to resolve numerous tough, scientific problems. Examples of technological advancements from quantum physics include quantum computers, which have already fascinated physicists and information technology specialists. Quantum theory, which looks at the finer, subatomic details of consciousness, could hold the key to explanations for the majority of consciousness problems that traditional neuroscience has not provided.
Microtubules in cells, composed of large numbers of proteins bound together in structures called polymers, played an essential role in Hameroff’s and Penrose’s understanding of human consciousness that incorporates quantum mechanics. Their Orch-OR theory posits that microtubules have elaborate and dynamic structures and networks that could make them the conduits of human consciousness in the brain.
Microtubules have interesting features that make them candidates for facilitating human consciousness. Neurons have many more tubulin proteins for microtubules than cells of the body have, and the fact that neurons do not divide to generate new neurons means that signals transmitted and stored in microtubules could be uniquely stable.
Proteins that associate with microtubules to precipitate their function, called microtubule-associated proteins (MAPs), modulate the information potentially stored and propagated on microtubules. One such MAP, the tau protein, has received much attention in studies of Alzheimer’s disease.
Two types of proteins provide the building blocks of microtubules, α- and β-tubulin, and together they compose the cellular skeleton that provides structural integrity for the cell. In the Orch-OR theory, one of the most creative and crucial points states that tubulins can exist in two states at once, much like a wave in classical physics. Physicists refer to this scenario as a quantum superposition state according to the Heisenberg uncertainty principle.
A conscious event which gives rise to human consciousness occurs when information transmits between connected neurons at synapses, much like in traditional neurobiology. After the chemical signal, the neurotransmitter, binds to the receptor on the neurons receiving the signal, a molecular pore allows calcium ions to enter the cell. MAPs also then add molecular tags through a process called phosphorylation to potentially store information on microtubules.
These changes resulting from neurotransmitters could then “orchestrate” tubulin states and lead to microtubule stimulation. The tubulin quantum superpositions combine increasingly to amplify their superposed mass energy, which can meet a critical quantum gravity threshold leading to self-collapse and a consciousness event. According to Hameroff and Penrose, consciousness arises from discrete and independent self-collapse events in microtubules rather than being a continuous phenomenon.
“Microtubules’ tubulins are initially in superposed states. Synaptic inputs orchestrate these tubulins such that their state tends to be unified, and total energy increases. Then, the threshold is met, followed by Orch-OR and a conscious event,” stated Zhang and colleagues in their review. The tubulins that compose the microtubules then return to their original state, ready to process the next consciousness event.
Thinkers and academics throughout history have made various proposals and theories to explain the phenomenon of human consciousness. “Undoubtedly, the Orch-OR theory co-established by theoretical physicist Penrose and neuroscientist Hameroff is currently the most convincing theory,” wrote Zhang and his colleagues.
Li T, Tang H, Zhu J, Zhang JH. The finer scale of consciousness: quantum theory. Ann Transl Med. 2019 Oct;7(20):585. doi: 10.21037/atm.2019.09.09. PMID: 31807566; PMCID: PMC6861790.