For decades, neuroscientists have destroyed nerves to study how well they can regenerate. Recently a team led by Stanford University physicist Mehmet Fatih Yanik (shown) brought new exactitude to this art by using a femtosecond laser to cut the outstretched arms, or axons, of individual nerve cells in the tiny worm Caenorhabditis elegans. The laser fires 40-nanojoule bursts that last only 200 quadrillionths of a second. It cut 0.3-micron gaps in motor neuron axons (inset) with so little surrounding damage that the axons regenerated within a day. Yanik says he is the first to slice lone neurons with a laser.