Nature reports on the discovery of a single, brain-encircling “crown of thorns” neuron that might be the seat of consciousness:
Christof Koch, president of the Allen Institute for Brain Science in Seattle, Washington, explained his group’s new technique at a 15 February meeting of the Brain Research through Advancing Innovative Neurotechnologies initiative in Bethesda, Maryland. He showed how the team traced three neurons from a small, thin sheet of cells called the claustrum — an area that Koch believes acts as the seat of consciousness in mice and humans.
Koch and his colleagues engineered a line of mice so that a certain drug activated specific genes in claustrum neurons. When the researchers fed the mice a small amount of the drug, only a handful of neurons received enough of it to switch on these genes. That resulted in production of a green fluorescent protein that spread throughout the entire neuron. The team then took 10,000 cross-sectional images of the mouse brain and used a computer program to create a 3D reconstruction of just three glowing cells.
The three neurons stretched across both brain hemispheres, and one of the three wrapped around the organ’s circumference like a “crown of thorns”, Koch says. He has never seen neurons extend so far across brain regions. The mouse body contains other long neurons, such as a nerve projection in the leg and neurons from the brainstem that thread through the brain to release signalling molecules. But these claustrum neurons seem to connect to most or all of the outer parts of the brain that take in sensory information and drive behaviour.
Koch sees this as evidence that the claustrum could be coordinating inputs and outputs across the brain to create consciousness.