A new study probing quantum phenomena in neurons as they transmit messages in the brain could provide fresh insight into how our brains function.
In this project, described in the Computational and Structural Biotechnology Journal, theoretical physicist Partha Ghose from the Tagore Centre for Natural Sciences and Philosophy in India, together with theoretical neuroscientist Dimitris Pinotsis from City St George’s, University of London and the MillerLab of MIT, proved that established equations describing the classical physics of brain responses are mathematically equivalent to equations describing quantum mechanics. Ghose and Pinotsis then derived a Schrödinger-like equation specifically for neurons.
Our brains process information via a vast network containing many millions of neurons, which can each send and receive chemical and electrical signals. Information is transmitted by nerve impulses that pass from one neuron to the next, thanks to a flow of ions across the neuron’s cell membrane. This results in an experimentally detectable change in electrical potential difference across the membrane known as the “action potential” or “spike”.
When this potential passes a threshold value, the impulse is passed on. But below the threshold for a spike, a neuron’s action potential randomly fluctuates in a similar way to classical Brownian motion – the continuous random motion of tiny particles suspended in a fluid – due to interactions with its surroundings. This creates the so-called “neuronal noise” that the researchers investigated in this study.
Previously, “both physicists and neuroscientists have largely dismissed the relevance of standard quantum mechanics to neuronal processes, as quantum effects are thought to disappear at the large scale of neurons,” says Pinotsis. But some researchers studying quantum cognition hold an alternative to this prevailing view, explains Ghose.
“They have argued that quantum probability theory better explains certain cognitive effects observed in the social sciences than classical probability theory,” Ghose tells Physics World. “[But] most researchers in this field treat quantum formalism [the mathematical framework describing quantum behaviour] as a purely mathematical tool, without assuming any physical basis in quantum mechanics. I found this perspective rather perplexing and unsatisfactory, prompting me to explore a more rigorous foundation for quantum cognition – one that might be physically grounded.”
As such, Ghose and Pinotsis began their work by taking ideas from American mathematician Edward Nelson, who in 1966 derived the Schrödinger equation – which predicts the position and motion of particles in terms of a probability wave known as a wavefunction – using classical Brownian motion.
Firstly they proved that the variables in the classical equations for Brownian motion that describe the random neuronal noise seen in brain activity also obey quantum mechanical equations, deriving a Schrödinger-like equation for a single neuron. This equation describes neuronal noise by revealing the probability of a neuron having a particular value of membrane potential at a specific instant. Next, the researchers showed how the FitzHugh-Nagumo equations, which are widely used for modelling neuronal dynamics, could be re-written as a Schrödinger equation. Finally, they introduced a neuronal constant in these Schrödinger-like equations that is analogous to Planck’s constant (which defines the amount of energy in a quantum).
“I got excited when the mathematical proof showed that the FitzHugh-Nagumo equations are connected to quantum mechanics and the Schrödinger equation,” enthuses Pinotsis. “This suggested that quantum phenomena, including quantum entanglement, might survive at larger scales.”
“Penrose and Hameroff have suggested that quantum entanglement might be related to lack of consciousness, so this study could shed light on how anaesthetics work,” he explains, adding that their work might also connect oscillations seen in recordings of brain activity to quantum phenomena. “This is important because oscillations are considered to be markers of diseases: the brain oscillates differently in patients and controls and by measuring these oscillations we can tell whether a person is sick or not.”
Going forward, Ghose hopes that “neuroscientists will get interested in our work and help us design critical neuroscience experiments to test our theory”. Measuring the energy levels for neurons predicted in this study, and ultimately confirming the existence of a neuronal constant along with quantum effects including entanglement would, he says, “represent a big step forward in our understanding of brain function”.
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