The worm connectome

Scientists have mapped the entire nervous system of the microscopic round worm C. elegans...

Owing to the complexity of the nervous system, previous work had focused on drawing the network of nerve cells, or neurons, in just specific parts of the worm's body. This new study marks the first time that scientists have traced and plotted the complete neural network of the organism.

Network maps like this, known as connectomes, also detail the different types of neuron involved. For example, sensory neurons and motor neurons are documented. “They play a central role in basic neuroscience research, which informs us of the human nervous system, just like every other nervous system,” says Albert Einstein College of Medicine, New York, research Scott Emmons, who led the new study.

C. elegans measures just 1 mm in length, and is barely visible with the naked eye. Therefore, to obtain images that are able to resolve the cellular structure in these worms, an electron microscope was required.

Thousands of images were taken along the length of the worm and the positions of the individuals neurons were painstakingly marked by hand on each of the images.

The marked-up images were then fed into a computer to link them together and draw up the connectome.

The team are now turning their attention to something larger than a worm. According to Emmons, “the next one that will come along will be fruit flies! But where C. elegans have 300 neurons, fruit flies have a hundred thousand!”

But is the work relevant to humans? The answer is yes: “We know that these basic functions of the nervous system are conserved from worms to mice to humans,” Emmons explains.

This means that, if the nervous system of a worm can be mapped and understood, scientists are one step closer to understanding the complexity of the human nervous system, although with 100 billion nerve cells each making an average of 5000 connections to other neurones in the average person's brain, there's still a long way to go...