Researchers at the Salk Institute have discovered a startling feature of early brain development that helps to explain how complex neuron wiring patterns are programmed using just a handful of critical genes. The findings may help scientists develop new therapies for neurological disorders, such as amyotrophic lateral sclerosis (ALS). The Salk researchers discovered that a few proteins on the edge of a motor neuron's axon -- its outgoing electrical ‘wire’ -- and within the extracellular soup it travels through guide the nerve as it emerges from the spinal cord. "The budding neuron has to detect the local environment it is growing through and decide where it is, and whether to grow straight, move to the left or right, or stop," says the study's senior investigator, Sam Pfaff. This is one of the first studies to try and understand how a growing neuron integrates many different pieces of information in order to navigate to its eventual target and make a functional connection.