Next year, medical researchers will test in patients a one-of-a-kind brain implant that can sense electrical activity in the brain while simultaneously emitting electric pulses, says device developer Medtronic.

Deep-brain stimulators are mainly used to regulate the movement problems associated with Parkinson's and other diseases, but they are also used in Europe and Canada to treat epilepsy and are being used experimentally to treat severe depression and obsessive-compulsive disorder. But doctors must use trial and error to determine the best parameters for the electrical stimulation programmed into each patient's chip.

The smarter brain stimulator is an improved version of Medtronic's existing deep-brain stimulator device, which has already been implanted in more than 80,000 people around the world. Medtronic has added an extra chip so that it can detect electrical activity and respond automatically to changes in the brain.

"If you are in the brain already, you might as well take advantage of the fact that you can listen in," says Lothar Krinke, who manages the Deep Brain Stimulation division at Medtronic. This means the device could respond automatically when a patient's symptoms grow stronger, or could turn itself off when the patient is asleep. "We really only want to deliver the electricity when it is needed," says Krinke. The company has tested the device in lab animals and says that next year outside teams of researchers will test it in patients with diseases such as Parkinson's and epilepsy.