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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