A new twist on quantum brain theory

The new theory explains how fragile quantum states can persist for hours and even days in our warm and moist brain. Experiments are already being prepared to test it.

Matthew Fisher, who proposed a theory about the effects of quantum effects on brain function.

Just mentioning “quantum consciousness” is uncomfortable for most physicists, as this phrase seems to remind them of the muttering of some New Age guru . But if the new hypothesis is confirmed, it turns out that quantum effects do play a role in human consciousness. Matthew Fisher , a physicist at the University of California at Santa Barbara, surprised many last year by publishing in Annals of Physics a paper suggesting that the nuclear spins of phosphorus atoms can serve as rudimentary qubits of the brain - which is why it is able to work on the principle of quantum a computer.

Even 10 years ago, this hypothesis would have been rejected as nonsense. Physicists have already stepped on a similar rake, especially in 1989, when Roger Penrose suggested that the mysterious protein structures, " microtubules, " play a role in the formation of consciousness using quantum effects. Few believed in the validity of such a hypothesis. Patricia Churchland, a neurophilosopher from the University of California, spoke out on the subject, which, to explain consciousness, could just as well be talked about “fairy fairy pollen in synapses.”

The Fisher hypothesis has the same difficulties as microtubules: quantum decoherence. To build a working quantum computer, it is necessary to combine qubits - quantum bits of information - to bring them into an entangled state. But the intricate qubits are very fragile. They must be carefully protected from any noise in the environment. Only a photon colliding with a qubit will violate the coherence of the entire system, destroy entanglement, and destroy the quantum properties of the system. It is difficult to conduct quantum processing in carefully controlled laboratory conditions, not to mention the warm, moist and complex porridge of human biology, in which maintaining coherence for a fairly long time is almost impossible.

But over the past decade, there is growing evidence that some biological systems can work with quantum mechanics. For example, during photosynthesis, quantum effects help plants turn sunlight into fuel . Scientists also suggest that migratory birds have a “quantum compass” that allows them to use the earth’s magnetic field for navigation, and that the sense of smell also goes back to quantum mechanics.

Fisher's idea of ​​quantum data processing in the brain fits into a new scientific field of quantum biology. Call it quantum neuroscience. He developed a complex hypothesis, including nuclear and quantum physics, organic chemistry, neurobiology, and biology. And although his ideas encounter a high level of understandable skepticism, some researchers pay attention to them. "The people who read his work (and I hope that there will be more) cannot help but conclude that the old man is not so crazy," wrote John Preskill , a physicist at the California Institute of Technology after Fisher did there report. “He may have felt something. At the very least, it raises some very interesting questions. ”

Sentil Todadri[Senthil Todadri], a physicist at MIT, Fisher’s long-time friend and colleague, remains skeptical, but believes that Fisher has changed the main question — whether quantum computation is taking place in the brain — in such a way that this hypothesis can be thoroughly tested. “It’s generally accepted that, of course, there is no question of any quantum computing in the brain,” Todadri says. - He claims that there is exactly one loophole in this regard. So the next step will be to check the possibility of covering this loophole. " And in fact, Fisher is already recruiting a team to conduct laboratory tests that answer this question once and for all.

Looking for a back

Fisher belongs to the dynasty of physicists. His father, Michael I. Fisher, is a well-known physicist at the University of Maryland, whose work in statistical physics has earned numerous awards. His brother, Daniel Fisher , is an applied physicist at Stanford University specializing in evolutionary dynamics. Matthew Fisher followed in their footsteps, building a very successful career as a physicist. In 2015, he received the prestigious Oliver I. Buckley Award for his study of quantum phase transitions.

So what made him move away from conventional physics toward a contradictory and confusing mess of biology, chemistry, neurobiology, and quantum physics? His struggle with clinical depression.

Fisher remembers that day in February 1986, when he woke up, feeling poorly about his body, and with the feeling that he had not slept for a week. “It seemed to me that they pumped me up with drugs,” he said. Sleep did not help. Changing the diet and exercise yielded nothing, and blood tests did not reveal any pathologies. But such a state of his remained for two whole years. “It was like a headache all over my body, every moment of wakefulness,” he says. He even tried to commit suicide, but the birth of his first daughter gave meaning to his further struggle with the fog of depression.

In the end, he found a psychiatrist who prescribed a tricyclic antidepressant, and after three weeks his condition began to improve. “The metaphorical fog that surrounded me and obscured the sun began to thin out, and I saw that there was light behind it,” says Fisher. Five months later, he felt like he was reborn, despite serious side effects from the medication, including excessive blood pressure. He later switched to fluoxetine and has since been constantly monitoring and fine-tuning his medication.

His experience convinced him that the drugs were working. But Fisher was surprised at how little neuroscientists knew about the exact mechanisms of their work. This fueled his curiosity, and thanks to his experience in quantum mechanics, he began to consider the possibility of quantum data processing in the brain. Five years ago, he began an in-depth study of the issue, based on his own experience with antidepressants.

Since almost all drugs used in psychiatry usually turn out to be complex molecules, he concentrated on one of the simplest, lithium, single atom - a spherical horse, so to speak, which is much easier to study than fluoxetine. By the way, this analogy, according to Fisher, is quite suitable for this case, since the lithium atom is a sphere of electrons surrounding the nucleus. He focused on the fact that with a prescription in a pharmacy you can usually buy the common lithium-7 isotope. But will the use of a rarer isotope, lithium-6, lead to the same result? In theory, it should, because chemically these isotopes are identical. They differ only in the number of neutrons in the nucleus.

Having rummaged in the literature, Fisher found that experiments on the comparison of lithium-6 and lithium-7 have already been carried out. In 1986, scientists from Cornell University studied what effect these two isotopes have on rat behavior. Pregnant rats were divided into three groups - one was given lithium-7, one was lithium-6, and the third served as a control group. After the birth of offspring in rats treated with lithium-6, the maternal instinct, expressed in the care, care and construction of nests, was much more developed than in the other two groups.

It hit Fisher. Chemically, the two isotopes must be identical, and even more so in the moisture-filled environment of the human body, they should not show any differences. So what could have caused the differences in behavior observed by the researchers?

Fisher believes that the secret can be hidden in the back of the nucleus, in a quantum property that affects how long each of the atoms can remain coherent - isolated from the environment. The smaller the spin, the less the core interacts with electric and magnetic fields, and the slower the coherence is lost.

Since lithium-7 and lithium-6 have different numbers of neutrons, their spins also differ. As a result, lithium-7 loses coherence too quickly for quantum consciousness to work, and lithium-6 can remain confused longer.

Fisher discovered two substances that are similar in everything except the quantum spin, and ours that they have different effects on behavior. For him, it was a tantalizing hint that quantum data processing plays some kind of functional role in the mind.

Quantum defense circuit

However, the task of moving from an interesting hypothesis to a real demonstration that quantum processes play a role in the functioning of the brain looks depressing. The brain needs some mechanism for the long-term storage of quantum information in qubits. Many qubits need to be entangled, and this entanglement, in some chemical way, must affect how neurons work. There must also be a mechanism for transmitting quantum information stored in qubits throughout the brain.

This is a very difficult task. For five years of searching, Fisher has identified only one suitable candidate for storing quantum information in the brain: phosphorus atoms, the only common biological element besides hydrogen, with a half spin small enough to increase the coherence time. Phosphorus cannot itself create stable qubits, but its coherence time can be extended if it is bound to calcium ions to form clusters.

In 1975, Aaron Posner, a scientist at Cornell University, discoveredincomprehensible clustering of calcium and phosphorus in the study of bone x-rays. He drew the structure of these clusters - nine calcium atoms and six phosphorus atoms, and later they began to call them "Posner molecules" in his honor. These clusters reappeared in the 2000s, when scientists, simulating bone growth in artificial fluid, noticed them floating in it. Subsequent experiments found evidence of their presence in the body. Fisher believes that Posner molecules can serve as a natural qubit of the brain.

This is the big picture, but the devil is in the little things that Fisher has been studying for the past few years. The process begins in a cell with a chemical called pyrophosphate. It consists of two bound phosphates, each of which consists of a phosphorus atom surrounded by several zero-spin oxygen atoms. The interaction between the backs of phosphates entangles them. They can create pairs in four different ways: three configurations give a total spin of 1 (loosely coupled triplet), and the fourth gives a zero spin, or “singlet,” a state of maximum entanglement, critical for quantum mechanics.

The enzymes then separate the entangled phosphates into three free ions. They remain confused even after separation. This process, according to Fisher, is faster for singles. These ions, in turn, can be combined with calcium ions and oxygen atoms and converted into Posner molecules. Calcium and oxygen have no nuclear spin; therefore, the general half-integer spin, critical for long-term coherence, is preserved. These clusters protect entangled pairs from external influences so that they can maintain coherence for as long as possible. Fisher estimates that it can be hours, days, or even weeks.

Thus, confusion can spread over fairly large distances inside the brain, affecting the output of neurotransmitters and the work of synapses between neurons - a frightening long-range action in the version of the brain at work.

Theory check

Researchers in quantum biology are intrigued by Fisher's assumption. Alexandra Olaya-Castro , a physicist at University College London who worked on quantum photosynthesis, calls this a “well-conceived hypothesis. It does not give answers, but only opens questions that can lead us to checks of individual steps of the hypothesis. "

With her agreement, and the University of Oxford chemist Peter Hoar [Peter Hore], exploring quantum effects when applied to the navigation of migrating birds. “The theoretical physicist offers us certain molecules, mechanisms, and all the technology of how they can affect the functioning of the brain,” he says. “This opens up opportunities for experimental testing.”

Fisher is now trying to conduct experimental checks. He spent time off at Stanford, working with researchers to reproduce a 1986 study with pregnant rats. He admitted that the preliminary results were disappointing, the data did not provide enough information. But he believes that if it is better to reproduce the 1986 experiment, the results may be more convincing.

Fisher has applied for a grant for more in-depth experiments in quantum chemistry. He gathered a small group of scientists of various specialties at his university and attracted scientists from the University of California at San Francisco. First, he wants to figure out whether calcium phosphate forms stable Posner molecules, and whether the nuclear spins of phosphorus from these molecules can become entangled for long periods of time.

Even Houre and Olaya Castro are skeptical of this, especially Fischer’s estimates regarding the time frame - a day or more. “Honestly, I think this is highly unlikely,” Olaya Castro says. “The longest time intervals related to biochemistry and occurring in the brain are no more than a second.” (In neurons, information is stored for microseconds). Hour calls this possibility “distant,” saying a maximum of seconds. “This does not reject the whole idea, but it seems to me that other molecules will be needed for long entanglement,” he says. “I don't think these are Posner molecules.” But I wonder how the idea will develop. ”

Some people believe that no quantum processes are needed at all for the brain to function. “There is evidence that anything interesting about consciousness can be explained by the interaction of neurons,” said Paul Thagard, a neurophilosopher at the University of Ontario, with New Scientist.

Many other aspects of the Fisher hypothesis also need to be properly verified. He hopes that he will be able to put in the necessary experiments for this. Is the structure of the Posner molecule symmetrical? How isolated are nuclear backs?

More importantly, what if these experiments prove that the hypothesis is wrong? Then, you may have to completely abandon the idea of ​​quantum consciousness. “I believe that if the nuclear spin of phosphorus is not used in quantum data processing, then quantum mechanics does not play a role in the work of consciousness at long intervals,” says Fisher. - From a scientific point of view, it is very important to exclude it. It will be useful for science to know this. ”