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It is clear that with time, most people can and do psychologically recover from even devastating losses, like the death of a spouse; but reactions to the same blow vary widely, and no one can reliably predict who will move on quickly and who will lapse into longer-term despair.

The role of genes is likewise uncertain. In a paper published online Monday in The Archives of General Psychiatry, researchers at the University of Michigan who analyzed more than 50 studies concluded that variations in a single gene determine people’s susceptibility to depression following stressful events. But an earlier analysis, of fewer but similar studies, concluded that the evidence was not convincing. New research suggests that resilience may have at least as much to do with how often people have faced adversity in past as it does with who they are — their personality, their genes, for example — or what they’re facing now. That is, the number of life blows a person has taken may affect his or her mental toughness more than any other factor.

The scientists, including several at MIT, are working on technologies needed to accelerate the slow and laborious process that the C. elegans researchers originally applied to worms. With these technologies, they intend to map the connectomes of our animal cousins, and eventually perhaps even those of humans. Their results could fundamentally alter our understanding of the brain. Mapping the millions of miles of neuronal “wires” in the brain could help researchers understand how those neurons give rise to intelligence, personality and memory, says Sebastian Seung, professor of computational neuroscience at MIT. For the past three years, Seung and his students have been building tools that they hope will allow researchers to unravel some of those connections. To find connectomes, researchers will need to employ vast computing power to process images of the brain. But first, they need to teach the computers what to look for.

“Instead of specifying the details of how the computer does something, you give it an example of what you want it to do and an algorithm that tries to figure out how to do what you want,” says Jain. After the computer is trained on the human tracings, it is applied to electron micrographs that have not been traced by humans. This new technique represents the first time that computers have been effectively taught to segment any kind of images, not just neurons.

“Doing such a microscopic level of resolution seemed to be infeasible at the time,” he says. “But now I’m coming around to the idea that something like that may well be possible.” The machine learning technology that Seung and his students are developing could be “a big leap forward” in making that kind of diagram a reality, Sporns adds.

is called connectomics, and the neuroscientists pursuing it compare their work to early efforts in genetics. What they are doing, these scientists say, is akin to trying to crack the human genome — only this time around, they want to find how memories, personality traits and skills are stored.

“You are born with your genes, and they don’t change afterward,” said H. Sebastian Seung, a professor of computational neuroscience at the Massachusetts Institute of Technology who is working on the computer side of connectomics. “The connectome is a product of your genes and your experiences. It’s where nature meets nurture.”

New research conducted at The Scripps Research Institute shows that this road atlas undergoes constant revisions as the brain of a young animal develops, with new routes forming and others dropping away in a matter of hours. "We have shown that the connectome is dynamic during development, but we expect it will also change according to an individual's experience and in response to disease,"

Cline's group has been studying how experience—the different sights and sounds and other environmental cues picked up by neurons—change connections and activities in the brain through a process known as plasticity. "Based on our prior research we expected that the connectome would be dynamic," says Cline. To start to document how the connectome changes and test current models of how the map is laid out, Cline and colleagues turned to the frog Xenopus laevis. They combined two new techniques to map in great detail all the connections that form during tadpole development in an area of the brain that receives and interprets signals from the eyes. In the nervous system, information is handed from one nerve cell to another through two arms, called dendrites and axons, stretching out from opposite sides of each cell. The axon carries information away from a nerve cell, or neuron, and passes it to the dendrite of another; dendrites receive the information, which travels through the cell to the axon. The region where information is transferred from one neuron to another (and where axons and dendrites connect) is called the synapse.

Cline's study shows instead the process is not as selective. Each growing dendrite samples not one but many possible partners before selecting one with which to maintain contact. As new branches grow from dendrites, they form many immature synapses on axons. Then, as each new dendrite branch matures, most immature synapses are eliminated; the ones not eliminated mature into stable synapses. "We did not know that dendrites make so many connections that are then removed," says Cline. "It is always fun in science when you see that what was expected is not what actually happens."