In an effort to understand the nervous system of the Caenorhabditis elegans roundworm, Dr. Cornelia Bargmann, professor and Head of the Laboratory of Neural Circuits and Behavior at Rockefeller University, engineered two roundworm neurons to glow bright green if a neuron responds when the worm is exposed to certain pheromones.

The study of its nervous system offers one of the most promising approaches for understanding the human brain, since it uses similar working parts but is around a million times less complex. It has just 302 neurons and 8,000 synapses.

Though the worm’s nervous system is routinely described as simple, that is true only in comparison with the human brain. The worm has 22,000 genes, almost as many as a person, and its brain is a highly complex piece of biological machinery.

What’s more, the worm’s connectome (nervous system wiring diagram) has two separate wiring diagrams superimposed on each other, and there is a third system that keeps rewiring the wiring diagrams. This is based on neuropeptides, hormone-like chemicals that are released by neurons to affect other neurons.