New research conducted at The Scripps Research Institute shows that the connectome (the road atlas of the brain) undergoes constant revisions as the brain of a young animal develops, with new routes forming and others dropping away in a matter of hours.

Up until now, researchers had focused their work primarily on determining how new connections form and on finding ways to enhance such formation. But Cline’s findings that so many immature connections are removed during development puts greater emphasis on the process of elimination, she says.

“It is possible that some genetic diseases are caused by the inefficient elimination of synapses,” says Cline. For example, individuals with a disease known as fragile X, a leading cause of mental retardation, are thought to have too many synapses, suggesting elimination did not occur properly.