Giant Neuron Found Wrapped Around the Brain Might Explain Consciousness

Digital reconstruction of three giant neurons found encircling a mammalian brain. Allen Institute for Brain Science

Consciousness is one of the great mysteries of science and philosophy. What is it? How does it work? How does the brain generate it?

Now, a potential breakthrough: scientists have discovered a huge single cell that wraps around the entire circumference of the brain. The neuron’s connections into the various regions of the outer brain are so dense that researchers suspect that it might be the link from which consciousness emerges, reports Nature.

The neuron is actually one of three newly discovered giant cells that extend across both brain hemispheres. Only the largest one wraps around the entire organ like a “crown of thorns,” but the discovery of any of the three alone would be considered significant.

Perhaps most curious about these neurons is that they each grow out of the same central brain region known as the claustrum, a thin sheet of hyper-connected grey matter that has been linked to consciousness in previous studies. All mammalian brains are suspected to possess a claustrum, and in humans it's known to communicate with almost all regions of the cortex. Many higher cognitive functions such as language, long-term planning and advanced sensory tasks like seeing and hearing have been associated with it.

It’s possible that the claustrum is where synchronization happens between the brain’s hemispheres and cortical regions — the synchronization that explains where the seamless quality of conscious experience comes from.

What took so long to find something so large?

How could researchers have missed such a huge neuron until now? The brain is a massively complex web of neurons, and the task of unweaving each of them is time-intensive and tedious. Also, researchers don’t usually have the luxury of unraveling the neural networks of live human brains (for obvious ethical reasons), so they often have to perform their experiments on animals, which has its limitations.

For instance, this study was performed on mouse brains. Christof Koch, president of the Allen Institute for Brain Science in Seattle, and his team discovered the three giant neurons by tracing them through a mouse’s brain with dye. The pathway had to be delicately followed by hand, a particularly arduous task, given how long these neurons turned out to be. In the end, it took 10,000 cross-sectional images of the mouse brain and a computer program to create a 3-D reconstruction to show just how extensive the three dyed cells were.

The existence of such all-encompassing neurons emerging from an area of the brain that's already known to be hyper-connected and linked with higher order brain processing is compelling, but more research will be needed to definitively establish this network as the seat of consciousness. Still, just the fact that this could be the string from which the mysteries of consciousness finally get unraveled is exciting to think about.

What if the wonders of the soul all hang on the thread of just these three — albeit very long and connected — brain cells? It seems impossible. But then, in many ways, so does consciousness itself.