Eventually that could help scientists develop devices paralysed people could control, such as robotic arms.
Researchers had thought because the part of the brain that controls movement contains so many cells, an individual cell would not have much impact, said Michael Brecht, author of the study that appeared in Thursday's issue of the journal Nature.
"This changes our view on what a single cell does," said Brecht, a researcher at the Max Planck Institute for Medical Research in Heidelberg, Germany.
Brecht said the findings, which he described as a surprise, could help scientists develop brain-controlled devices.
"This will help us to understand how we would have to read the activities of these cells," Brecht said.
Jon H Kaas, a neurology professor at Vanderbilt University, called the results encouraging.
"This changes our view on what a single cell does"
The researchers used tiny electrodes to excite individual brain cells in the motor cortex of anaesthetised rats.
The brain's motor cortex, which controls movement, does not directly activate muscles, but signals a pattern generator that sends more detailed commands to the muscles, Kaas said.
"Those pattern generators are not very complicated and could easily be generated by a small computer" to control a robot arm, for example, Kaas said.
Sandro Mussa-Ivaldi, a neurologist at Northwestern University, said it was not clear whether the findings would apply to brain-controlled devices.
Scientists differ on how many brain cells will have to be involved to control such devices, he said.
The new work does not shed much light on the debate because so many rat brain cells are devoted to whisker movement.