More than a decade ago, Erik Sorto, 34, was paralyzed after a gunshot wound to the neck. Now, using a robotic arm that he controls with his brain, he can pick up a drink and bring it to his lips in one smooth motion.

But unlike other experimental robotic arms, this one relies on signals sent from a device implanted in Mr. Sorto’s posterior parietal cortex — a part of the brain that plans and imagines activities.

Neural prosthetic devices are generally implanted in the motor cortex, the part of the brain responsible for executing movements. The robotic arms work, but in delayed, jerky movements.

The new device results in motion that is more natural and fluid, researchers reported on Thursday in the journal Science.