The animals were able to feed themselves using prosthetic arms, which were controlled by brain activity.
Small probes, the width of a human hair, were inserted into the monkeys' primary motor cortex - the region of the brain that controls movement.
Writing in Nature journal, the authors said their work could eventually help amputees and people who are paralysed.
Lead researcher Dr Andrew Schwartz, who is based at the University of Pittsburgh School of Medicine, said: "We are beginning to understand how the brain works using brain-machine interface technology.
"The more we understand about the brain, the better we'll be able to treat a wide range of brain disorders, everything from Parkinson's disease and paralysis to, eventually, Alzheimer's disease and perhaps even mental illness."