Here's an article by Anne Eisenberg for the NY Times that explains why the latest results of Brown University's rhesus macaque monkey experiments are particularly significant:
Don't Point, Just Think: The Brain Wave as Joystick.

In the experiment, performed on three monkeys, the team implanted a tiny set of 100 miniature electrodes in the motor cortex, the part of the brain just under the skull that commands how the arms will move. Then they threaded the wires from the electrodes through a hole in the skull and connected them to a computer.

When the monkeys played the pinball game, their brains made characteristic signals that were recorded as the neurons fired near the electrodes. The team wrote a program that paired the spiky patterns the neurons made as they fired with the related trajectories of the monkeys' arms as they moved the cursor.

Then they were able to substitute a signal that translated brain-wave data into joystick output, so that when the monkey thought about a move, the cursor actually made that move.

Dr. Donoghue said that the electrodes tapped up to 30 neurons, and that only three or so minutes of data were needed to create a model that could interpret the brain signals as specific movements.

In the experiment, the pinball game was switched intermittently by the researchers from hand to brain control. It took slightly longer for the monkey to succeed in hitting the red dot with brain control, but the difference was negligible, he said.

Related experiments by other researchers, Dr. Donoghue said, have required extensive training for the monkeys to bring a cursor under their mental control. "In our work, we had immediate substitution of the program for hand control," he said.

The experiment demonstrates the plasticity of the brain in adapting itself to new jobs, said Dr. William Heetderks, director of the neural prosthesis program at the National Institute of Neurological Disorders and Stroke, one of the agencies financing the work at Brown.

Dr. Heetderks said he expected the animals to learn to control the cursor mentally. "But the speed and quality with which the monkey learned to control the movement of the cursor was a surprise," he said. "It was minutes, not weeks."