Why does knowing every connection of the worm not predict what it does? · Grey Matter

The wiring of C.

Why does knowing every connection of the worm not predict what it does?

The wiring of C. elegans has been known since 1986, but a diagram lists possible paths and says little about which ones are in use. Neuromodulators such as serotonin, dopamine and neuropeptides change how excitable neurons are and how strongly synapses transmit, often acting on cells they have no synapse with, so the same wiring can run as different functional circuits depending on hunger, stress or what the animal has just sensed. Studies in crustaceans, worms, flies and the retina have shown such switches repeatedly. A connectome fixes the hardware, and the modulators choose the program running on it.