Ask a simple question, get a simple answer: When Abraham Lincoln was asked how long a man's legs should be, he absurdly replied, "Long enough to reach the ground." Now, by using a new microscopy technique to watch the growth of individual neurons in the microscopic roundworm Caenorhabditis elegans, Rockefeller University researchers are turning another deceptively simple question on its head. They asked, "How long should a worm's neurons be?" And the worms fired back, "Long enough to reach their targets."

The researchers' surprising result: Rather than growing like the branches of a tree - extending outward - certain neurons work backward from their destination, dropping anchor and stretching their dendrites behind them as they crawl away. The work, led by Shai Shaham, head of the Laboratory of Developmental Genetics, and Maxwell Heiman, a research associate in the lab, not only addresses an age-old question of how neurons get their shape, but is also changing the way scientists think about the genetic program that wires the brain and allows it to grow throughout development…