- Most neuroscientists think we understand the physiology and anatomy of neuronal communication in the brain.
- In fact, we don't really know exactly which electromagnetic phenomena the brain uses to do what it does.
- Thus, "trivial" brain "epiphenomena" such as volume conduction and magnetic fields might be more important for brain function than we realize.
“What’s the weirdest, unexplained phenomenon you’ve ever seen in the lab?" I asked a famous neuroscientist during a break at a neurobiology meeting I had organized in Aspen in 2007 on behalf of my brother William’s global health foundation.
The scientist looked around before answering, as if to make sure no one else could hear. “Well,” he said, almost apologetically, “I have sometimes seen waves of excitation slowly propagate across the brain in patterns that do not correspond to any known axonal pathways.”
I paused to consider what I’d just heard. The researcher had described something that wasn’t supposed to happen, long-distance transmission of neural excitation, not through axons (the equivalent of wires in electronic circuits), but by some other process. I asked, “You mean, spread by volume conduction?”
All I got for an answer was an amused “Who knows?” shrug.
I was about to ask why he hadn’t published his strange discovery or followed up with further research, but stopped myself when I realized the answer: He didn’t want to jeopardize his career by being labeled a crank for contradicting well established neuroscience “truths,” and, in any case, would never have gotten funding to pursue the outlandish idea that long-distance communication in the brain could occur outside of axons.
The sad truth is that the researcher in question was not alone in hesitating to stray from the path of neuroscience orthodoxy. Although many neurobiologists (myself included) have stumbled across unexplainable phenomena at some point in their careers, few pursue their strange discoveries out of well-placed concern that such pursuits would end their careers.
Nevertheless, hints that the brain might work in ways not contemplated by “normal” neuroscience have emerged over the years. Here are a few examples.
Conventional wisdom has it that neurons transmit information to one another in one of two ways: release of neurotransmitters in synapses that connect one neuron to another or through ionic electrical conduction across “tight junctions” binding the membranes of different neurons together. Further, spread of this electrical excitation is believed to occur within individual neurons over short distances (e.g. within a neuronal cell body) through membrane ion currents creating “graded potentials” and over long distances (e.g. major nerve tracts such as in the spinal cord) through all-or-nothing “action potentials.”
However, the findings of my colleague in Aspen suggest that the brain may have other ways of communicating within itself that arise from viewing the brain not as a collection of individual nerve cells and non-neuronal glia (e.g. nerve insulators), but, to put it crudely, as a bucket of gelatinous saltwater. In a bucket of salty Jell-o, an electrical current source in one region of the bucket will spread to other regions of the bucket not through dendrites or axons, but through three-dimensional ionic (dissolved salt) conduction channels. Such “volume” spread of electrical currents is responsible for the appearance of the well-known medical diagnostic signals we call an EEG (electro encephalogram). Scientists have long assumed that EEG signals picked up on the scalp were not actually used by the brain to transmit or process information, but merely electrical “epiphenomena” that reflected activity of large populations of neurons near the scalp electrodes.
But what if our brains actually do extract information from volume conducted EEG-like signals? Do our brains, at least in part, act like their own EEG machines such that volume conducted signals actually mean something to the brain, rather than being trivial artifacts, as is widely assumed?
While we’re discussing neural artifacts and epiphenomena, we might as well bring up Magneto Encephalography, (MEG), a technique in which superconducting magnetic coils sense the magnetic component of brain activity (all electrical currents have associated magnetic fields).
Although MEGs offer more precise, localized representations of brain activity form the scalp than EEG’s, they too are considered epiphenomenona in the sense that the brain doesn’t actually transmit and process magnetic information in order to do what it does.
But there is mounting evidence that magnetic fields, all by themselves, do play a role in neural information processing. A wide variety of animals, such as birds, are known to use the Earth’s magnetic field for long-distance navigation, possibly through nano-crystals of iron compounds that form in some neurons. Shinsuke Shimojo and colleagues at Cal Tech have recently shown that human brains do directly respond to weak magnetic fields, even though humans are not consciously aware of these responses.
Thus, as with volume-conducted EEG signals, changes in magnetic fields, generated both inside and outside the brain, conceivably could be used by the brain to create, process, or retrieve information.
Quantum mechanical effects
Biologists have long dismissed the possibility that weird quantum mechanical effects such as superposition (an atomic particle can be in multiple places at the same time) and entanglement (changing the state of one atomic particle instantaneously alters the state of another, entangled particle, even if that other particle is billions of miles away) cannot occur in the brain, or any other biological tissue. The reason is that living tissues are far too “hot and wet” to allow ultra-fragile quantum effects to occur in anything close to a stable, useful fashion. That’s why many quantum phenomena are only observed in ultra-cold laboratory settings.
And yet, functionally significant quantum mechanical effects have been observed in some kinds of biological processes—such as in photosynthesis in plants—so it is not outside the realm of possibility that quantum effects, such as entanglement or superposition, are used by the brain to process, transmit, or recall information.
Peter Jedlicka of Goethe University in Germany points out that there is now good evidence for “non-trivial” (e.g. significant to generating usable neural information) quantum mechanical effects in generation of neural signals in the retina through photopigment response to quantal photons of light, and in the olfactory system, where quantum mechanical effects might play a role in odor discriminations.
An ultimate irony
I’m confident that, although we don't really know all of the physics the brain itself uses to do its work, most neuroscientists would dismiss volume conduction and magnetic and quantum phenomena as trivial and unimportant side effects of brain function. And, of course, such skepticism might be well placed.
But it might also be the case that those scientists, like all of us, form such opinions from cognitive biases that lead us—unconsciously—to believe only what we expect to be true and want to be true. For instance, few formally trained neurobiologists expect “side shows” (such as volume conduction) to actually be the “main event” and I believe even fewer want such untidy ideas to pollute our orderly understanding of how the brain works.
All of which is unfortunate if weird things like volume conduction and quantum effects are actually used by the brain in important ways.
The irony of all ironies here would be that the biggest obstacle standing in the way of our ultimate understanding of the brain could be the biases of the brains seeking to understand themselves.