The Connectome or How I Learned to Stop Worrying and Love the Worm.

A popular aphorism from ancient Greece states: knows thyself and for a few thousand years humans could be satisfied in this by pondering the nature of self and mind. However, with the advent of modern neuroscience, we as a species have been given a chance to achieve an unprecedented new level of self-knowledge: the connectome. When fully realized, the connectome will be a representation of the human brain so detailed that it will include every neuron and every synapse between neurons. Like the human genome, the overall distribution of structures in the human brain above the synaptic level is mostly conserved, thus the complete connectome would provide incredible new insight into every niche of neuroscience.

However, creating the connectome is a task that is anything but easy. To understand the epic magnitude of this map, consider the Human Genome Project. The effort to sequence the approximately 20,000 genes that we humans call our own began in 1990 and was completed a little over a decade later. Not too shabby: that’s a rate of 2000 genes a year. Now consider the scope of the connectome: a human brain contains an estimated 100 billion (10¹¹) neurons and 1 quadrillion (10¹⁵) synaptic connections. These numbers are unbelievably daunting and current technology could hardly hope to accomplish this task, yet the magnitude of scientific progress that the connectome will make possible is motivation enough to attempt this feat.

Of course, neuroscientists would logically start by mapping specific parts of the brain to scale their work. Little by little a complete connectome will be built. This work has already begun and in fact another species’ connectome was already fully mapped more than two decades ago. Before the term connectome was even coined, the humble roundworm, C. elegans, had its entire nervous system exhaustively described.

C. elegans, like mice, fruit flies, and monkeys, has long been a popular model organism for the study of nervous systems. While this nematode cannot lay claim to a brain per se, it does have neurons and neurotransmitters that function in much the same way that ours do, making it a simple and predictable organism to study. In the mid 1980s at Cambridge, John White and colleagues published what is now considered the first connectome, describing all 302 neurons and the approximately 7000 connections between them. While scientists still do not understand how C. elegans thinks, it has become more clear how certain behaviors, like feeding for instance, are driven by specific neural activity, such as the release of the neurotransmitter dopamine at certain synapses. The precise understanding of this tiny organism’s neural mapping has been a watershed in the field of neurophysiology and a necessary predecessor of the human connectome.

White’s seminal work was the first step towards understanding the nervous systems as a sum of their parts and connections. Perhaps one day, a human connectome will help us better understand how our patterns of neural activity are manifested in the experience of consciousness. Our emotions, memories, and thoughts as well as the symptoms and signs of disease and trauma, like Alzheimer’s and stroke, will be given a new, unprecedented clarity of perspective. If you’re lucky enough to be alive when that day comes, remember that we owe much to the worms.

If you’d like to learn more about the Human Connectome Project, visit their website at http://www.humanconnectomeproject.org/