Searching for the brain's quantum network

The setup for the experiment was simple. Post-mortem spinal-cord tissue from the human brain bank of the Cervo Brain Research Center in Quebec, Canada, was cut into two longitudinal slices and then illuminated from above using a fiber laser light source.

Proceeding with the experiment, researchers collected light on the underside of the spinal cord slices with a 40x objective microscope lens and recorded this with a CMOS camera. The recordings showed a patchy ring-shaped structure in the biological tissue where more light was being transmitted.

The results, published in 2020, while not the main objective of the Cervo research team, nonetheless may be the most striking. Having set out to understand the optical properties of the spinal cord for optogenetics planning, their recordings of spinal cord tissue revealed that myelin sheaths in axons could function as optical waveguides—a significant finding consistent with modeling by other researchers.

In other words, perhaps a lightbulb really does go on inside our brains. For in the blazingly complex frontiers of neuroscience, researchers from varying roosts of expertise, are beginning to see what look like tantalizing dots of hard evidence, from both theory and experiment. Together, and with much more investigation, those dots could be connected to form a new understanding of light and information processing in the human nervous system, including the brain.

One such researcher, and a theoretician behind the myelin sheath modeling effort, is Christoph Simon, a quantum physicist at the University of Calgary, in Alberta, Canada, who is also interested in theories of consciousness.

For the modeling effort, Simon wanted to find out if there is a way for quantum information to be transmitted through photons in the body. If this could be proven, it would represent a radical new way of signaling through neurons, beyond traditional voltage-gated channels.

As it happened, Simon and colleagues' modeling studies indicated that the myelin sheath surrounding axons that connect human nerve cells, has a high refractive index. What is more, even though it is interrupted by internal structures called the Nodes of Ranvier, substantial light transmission would still happen. Unlike an optic fiber, however, the guidance would predominantly be in a ring structure formed naturally by the sheath on the outer layer of the axon. The Quebec experiment confirmed the modeling and, "shows the ring sort of nicely," says Simon.

And while Simon wasn't well-versed in the hard wiring of human nervous system anatomy when he began to model light transmission there, he considered this a tractable problem. "It seemed really important to me because if I am looking for a quantum network in the brain," he says, "then clearly I need to find fiber."

He also knew that photons would be ideal candidates to transfer quantum information in the brain if they were coherently produced and entangled with the internal state of an atom or molecule.

"The closest analogy would probably be to the trapped-ion quantum computing approaches," says Simon. In such approaches, researchers are trying to realize many traps, each having a moderate number of ions, where these traps are connected through photons.

Importantly, the Quebec experiment did not prove there is a quantum network in the brain. For one to exist, there would need to be a quantum effect like spin, photons produced coherently in the same reaction, a mode of transmission for photons through the axons, as well as proteins that absorb the same photons to do biologically significant work. The experiment showed only that the axons would be viable to transmit photons.

Nonetheless, from theoretical modeling, experiments are emerging, and they are becoming increasingly concrete and relevant. "Themes are emerging and so are some connections to other interesting areas," says Simon.

For example, researchers have begun studying the role of radical pairs of electrons in neuronal signaling. What happens in this particular bit of biochemistry is that a covalent bond breaks (or an electron hops) and creates a pair of electrons whose spins are entangled. Electron and nuclear spins are part of chemical reactions that can also involve photon emissions, forming a potential interface.

Interestingly, Simon points out, the entangled state is sensitive to magnetic fields in the environment. So, as he began studying the biological relevance of spin biochemistry, a connection to another line of inquiry popped up: Recent research has suggested that those entangled spins are perturbed by magnetic fields, which may explain how birds navigate.

For sure, debate exists, including disagreement about the strength of the magnetic fields used in experiments, but the core phenomenon is real, says Simon.

Coming back to the role of light, studies of spin biochemistry suggest cryptochromes are also involved. These are light-sensitive proteins conserved and present in humans, that are connected to circadian rhythms.

Look in another direction, and one sees that circadian rhythms are connected to bipolar disorder. Indeed, in a paper he published in 2021, Simon explored mechanisms by which lithium, used to treat bipolar disorder, may interact with spins. What we have learned about the role of these radical pairs let loose in the human body, he says, is just the tip of the iceberg. Further, if such spin-crazy biochemistry is common in the human body then, potentially, so is the role of photons in neuronal signaling.

But that begs yet another question: Where do the photons that could begin this transmission chain come from? Ultraweak photon emissions have been known for decades to occur in neurons, and indeed, in all cells. Now, via technology like EM-CCD cameras, it can be seen live in animals. These emissions are quanta in the near-UV to near-IR produced in a range of oxidative metabolic processes in mitochondria.

For example, it has been suggested that phosphenes, the phenomenon of seeing light patches when rubbing our closed eyes, is caused by ultraweak photon emissions. Pressure on the eye can produce a stretch-induced mitochondrial disfunction and thus lead to overproduction of these reactive oxygen species.

The end point in these reactions, production of photons, is quantitatively clear, says Michal Cifra at the Institute of Photonics and Electronics of the Czech Academy of Sciences, the step that produces these electronically excited states is less clear.

Cifra, who trained as an electrical and biomedical engineer, is particularly interested in electromagnetic fields in biological systems. He published his first paper on ultraweak photon emission from human hands in 2007, even using his own hands for the experiments.

In more recent work, Cifra and colleagues cultured millions of yeast cells in a light-tight chamber. The signal detected using photomultiplier tubes tends to be extremely weak: A photon emitted every 15 minutes per cell. For cells larger than yeast cells that show higher biological activity, hundreds of thousands, or maybe a million cells may be required to achieve the same rate of emission.

Cifra is cautious about concluding whether these ultraweak emissions—he prefers the term "biological auto-luminescence"—play a significant role in biological signaling, or if they are simply by-products. In work done about a decade ago, he and a collaborator considered information transfer using ultraweak photon emissions.

Their conclusion: While this was glancingly possible, the task would require extremely dark environments for the signal-to-noise ratio to be high enough to work, and the bandwidth would be extremely narrow. From a theory standpoint, Cifra says, the signals are simply too low to be used for communication.

Still, whether ultraweak photon emission plays a role in information transfer in the body remains an open question, and different perspectives exist.

For one, biological photons detected in experiments are near the surface. When it comes to detecting them, it would be like measuring photons from the outer cladding of an optic fiber, which emits light several orders of magnitude lower than inside the fiber.

In other words, these are surface measurements of photons and would not capture photons guided or absorbed within the body.

Nonetheless, that light could play a functional role in signaling within the brain is becoming clearer. Simon points to a recent study in which researchers found that light-absorbing proteins called opsins lie deep in the mouse brain, and when violet light shines on them, a pathway that reduces heat production in tissue is activated. If these opsins can react to external light, then couldn't they also react to much closer ultraweak photons in the brain?

After all, the brain is a most power-hungry organ. Neurons are packed bumper-to-bumper with microtubules, protein polymers with diverse functions. Microtubules also act as tracks along which all kinds of biological transport take place within a cell. Moreover, because in neurons microtubules are situated intimately with mitochondria, they may be integral to controlling neuronal metabolism and regulating oxidative stress, which is generally higher in neurons than in other cells.

In experiments wherein neurons were excited by glutamate, a common neurotransmitter, about a billion photon emission events per second were detected from the brain. If only a tiny fraction of these were involved in the biological equivalent of quantum computing within the body, this would still represent tremendous computing power.

Even more directly, photons emitted in the UV range, including ultraweak emissions, can be absorbed by tryptophan and other aromatic amino acids, which are present in almost all proteins. Such a system could in principle allow for efficient energy transfer analogous to what happens in plants during photosynthesis, whereas its disruption could lead to signaling dysfunction.

Philip Kurian, of the Quantum Biology Laboratory at Howard University, has proposed that neurodegenerative diseases like Alzheimer's and Parkinson's may be related to such signaling problems in microtubule networks. Oxidative stress, caused by normal metabolic processes, in the form of reactive oxygen species (ROS) can produce these ultraweak photon emissions and is beneficial within a certain range. However, the pathological phenomenon of oxidative stress, when ROS thresholds exceed the capacity of the body's attempts to detoxify, is known to precipitate degradation of the microtubule network due to changes in the microtubule-associated protein tau.

While the possible mechanisms of tau dysregulation are being worked out, external light stimulation seems to show effects on these proteins. A 2019 paper in the journal Neuron entrained mice with a 40-Hz flickering LED-light and demonstrated reduction in both amyloid plaques and in tau aggregates that form in dementias like Alzheimer's.

Furthermore, modeling by Kurian and coworkers has indicated that robust quantum effects may indeed be present in microtubule networks, via an electronic phenomenon called super-radiance, which is akin to what happens when a highly symmetrical optical fiber emits light in a preferred direction.

Ordinarily, the expectation would be that the coherent energy carried by these excitations would decay as the system is bombarded by the warm, wet environment. But in super-radiance the excited states of light-matter get locked in a kind of synchrony and their combined effect is much stronger than the excitations of individual molecules. This leads to a collective emission-super-radiance.

"Contrary to conventional expectation, in which quantum effects tend to wash out in macroscopic systems," says Kurian, "we predicted ultraviolet super-radiance to grow in these tryptophan networks, precisely due to the symmetries of increasing size."

The emergent photoexcited states described by Kurian's group have been widely observed in other systems and occur at divergent timescales. Short-lived states faster than thermal noise may allow for communication with proteins that bind with microtubules. Longer-lived, so-called subradiant states may allow for synchronization across the brain where micro-tubules can extend beyond the micron scale.

Kurian says he and his colleagues are close to experimental validation of their predictions with micro-tubules, which further suggest that these collective states "may be robust in biological environments."

Meanwhile, for the scientific leap he has taken, Simon is building a bridge. First, he wants to understand the light-guiding properties of myelinated axons in more detail.

But the crucial bridge would be to show that the ultraweak photon emissions display magnetic field effects, indicating that the photons are related to the entangled radical pairs. "That will make the bridge in my mind," he says.

Once it is known that the photons come from radical pairs, then the state of the spin and the polarisation of the photons can be studied. "The details are not figured out," Simon says, "but there is a path one can explore."

VIRAT MARKANDEYA is a science writer based in Delhi, India.