The controversial idea that quantum effects in the brain can explain consciousness has passed a key test. Experiments show that anaesthetic drugs reduce how long tiny structures found in brain cells can sustain suspected quantum excitations. As anaesthetic switches consciousness on and off, the results may implicate these structures, called microtubules, as a nexus of our conscious experience.
According to some interpretations of quantum mechanics, a system can exist in multiple states simultaneously until the act of observing it distils the cloud of possibilities into a definite reality. Orchestrated objective reduction (Orch OR) theory postulates that brain microtubules are the place where gravitational instabilities in the structure of space-time break the delicate quantum superposition between particles, and this gives rise to consciousness.
Physicist Roger Penrose and anaesthesiologist Stuart Hameroff proposed Orch OR in the 1990s, but a lack of experimental evidence consigned it to the fringes of consciousness science. Some scientists regarded the theory as untestable, while others noted that the brain was too wet and warm to ever harbour these fragile quantum states.
Now Jack Tuszynski at the University of Alberta in Canada and his colleagues have presented work at the Science of Consciousness conference in Tucson, Arizona, on 18 April, to challenge these convictions – showing that anaesthetic drugs shorten the time it takes for microtubules to re-emit trapped light. “It’s a major step in the right direction,” says Tuszynski.
“It is interesting,” says Vlatko Vedral, a quantum physicist at the University of Oxford. “But this connection with consciousness is a really long shot.”
“It’s fascinating,” says Steven Laureys, a neuroscientist at the University of Liège in Belgium. “I don’t think we can just a priori claim that there is no role whatsoever for quantum principles in the workings of the mind and brain.”Microtubules are hollow tubes made up of the tubulin protein that form part of the “skeletons” of plant and animal cells. Tuszynski and his colleagues shone blue light on microtubules and tubulin proteins. Over several minutes, they watched as light was caught in an energy trap inside the molecules and then re-emitted in a process called delayed luminescence – which Tuszynski suspects has a quantum origin.
It took hundreds of milliseconds for tubulin units to emit half of the light, and more than a second for full microtubules. This is comparable to the timescales that the human brain takes to process information, implying that whatever is responsible for this delayed luminescence could also be invoked to explain the fundamental workings of the brain. “It’s quite mind boggling,” says Tuszynski.
The team then repeated the experiment in the presence of anaesthetics and also an anticonvulsant drug for comparison. Only anaesthetic quenched the delayed luminescence, decreasing the time it takes by about a fifth. Tuszynski suspects that this might be all that is needed to switch consciousness off in the brain. If the brain exists at the threshold between the quantum and classical worlds, even a small quenching could prevent the brain from processing information.
In a second experiment, led by Gregory Scholes and Aarat Kalra at Princeton University, laser beams excited even smaller building blocks within tubulin in microtubules. The excitation diffused through microtubules far further than expected.
When Scholes and Kalra added anaesthetic into the mix, they also found that the unusual microtubule behaviour was quenched. “The anaesthetic does interact with the microtubules and changes what happens. That is surprising,” says Scholes. While this lends weight to the idea that microtubules control consciousness at the level of individual brain cells, Scholes stresses that further research is needed before conclusions about quantum effects are drawn.
The phenomena seen in the experiments could also be described by classical physics rather than quantum mechanics, says Vedral. “In these complex systems, it’s very hard to pin quantum effects down properly and to have a conclusive piece of evidence.”The successes of the classical mechanical view in neuroscience do not preclude quantum mechanics playing an important role, says Laureys. “It would be dogmatic to say this is not worth looking at,” he says. “But, of course, the devil is in the details, and it’s up to the community to take a look at this.”
One possibility being investigated by Tuszynski’s team to explain delayed luminescence is a quantum process called superradiance, in which collectively excited atoms suddenly emit light in a chain reaction akin to a nuclear bomb. “We’re scratching our heads and trying to come up with a model,” says Tuszynski.
“We still have a ways to go,” says Hameroff, who is at the University of Arizona and was also part of Tuszynski’s study. The group now plans to repeat the experiments with a variety of anaesthetics of different potencies in humans to see if the microtubule response matches.
To sustain the theory, similar effects must also be demonstrated in living neurons and at temperatures found in the human body. “We’re not at the level of interpreting this physiologically, saying ‘Yeah, this is where consciousness begins’, but it may,” says Tuszynski.
Vedral says demonstrating quantum transport in cells would be a “big deal”, whether or not it has anything to say about consciousness. “It’s certainly worth investigating. Even if you could claim that cell division is somehow underpinned by some quantum effects, this would be a huge thing for biology,” he says.
The remarkable characteristics of microtubules revealed in these latest experiments show that they are far more than just the scaffold of cells, says Scholes. “Nature is full of surprises. And if nature has some kind of structural framework, why not utilise it in more sophisticated ways than we’d think?”
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