Bundles of microelectrode wires fan out over a small area of a human brain. These electrodes were placed by neurosurgeons at the University of Utah to see if they could detect precise brain activity associated with motor movements. To their surprise, the hair's-width microelectrodes, originally designed to study epilepsy, picked up the firings of small groups of neurons despite being merely set on the surface of the brain. Previously, this fine tracking was possible only by inserting wire probes directly into brain tissue, a potentially risky maneuver because, though thin, the probes can still damage nerve cells during insertion. Now the researchers are testing designs that cover more of the brain's surface. "Our goal is to develop something [that sends signals to a robotic arm] that will be implanted into paralyzed patients and give them some control to interact with their environment," says Bradley Greger, a professor of bioengineering who oversaw the work.