Scientists have discovered a giant neuron that wraps around the entire outer layer of the brain like “a crown of thorns.” This giant neuron—along with two others that branch out over a large area of the brain—may be the reason why you’re aware of your surroundings. In other words, this trio of neurons may be the origin of consciousness itself.
Scientists have long wondered how the brain creates consciousness. These new findings may offer an explanation.
The research was presented by Christof Koch, president of the Allen Institute for Brain Science in Seattle, Washington, at a meeting of the Brain Research through Advancing Innovative Neurotechnologies initiative in Bethesda, Maryland. The results were achieved using a new technique because past methods were more invasive and time consuming. Previously, researchers had to inject cells with a dye, slice the brain into thin sections, and then trace the dyed neuron’s path by hand. Using this old method, few scientists could follow a neuron’s path through the entire organ.
With the new technique, Koch and his associates used a certain drug to activate specific genes in neurons in an engineered line of mice. After the mice received a low dose of the drug, genes in entire neurons lit up with a green fluorescent protein. The scientists used 10,000 cross-sectional images of the brains of the mice and a computer program to develop a 3D reconstruction.
Using this new method, researchers identified three neurons located in a small, thin region of cells called the claustrum. The claustrum are made up of two claustra—one on each side of the brain—located underneath the temples, just above the ears. Scientists consider the claustrum to be the seat of consciousness in mice and humans.
The three neurons took up considerable real estate in the brain. They stretched across both brain hemispheres. One of them encircled the brain’s entire circumference in what Koch described to the journal Nature as a “crown of thorns.” Koch said he has never observed neurons extend so far across areas of the brain.
The researchers observed other long claustrum neurons in the mice, such as a nerve projection in the leg and brainstem neurons that extend through the brain and generate signaling molecules. These neurons appear to be connected to most or all of the brain’s outer regions and are responsible for analyzing sensory information and influencing behavior. Koch believes this indicates that the claustrum could be in charge of creating inputs and outputs by communicating with other regions of the brain to produce consciousness.
Other scientists have pointed out that this study does not prove without a doubt that a giant neuron controls consciousness. But they believe it will be useful for mapping out different cell types in the brain, which is important for understanding how the brain works.
Source: Sara Reardon. Nature. A giant neuron found wrapped around entire mouse brain. February 24, 2017;543(7643):14-15. doi:10.1038/nature.2017.21539