These include infection at the surgical site and cognitive decline, the study of 225 advanced Parkinson's patients at seven U.S. Veterans Affairs hospitals and six university medical centers found.

The study, published in Wednesday's Journal of the American Medical Association, also found benefits to the procedure, in which electrodes are implanted in specific parts of the brain to ease involuntary movements.

"Patients had significant improvement in their motor function and quality of life after surgery," lead author Frances Weaver, director of the Center for Management of Complex Chronic Care at the Hines Veterans Administration Hospital near Chicago, told USA Today.

Most adverse events cleared up within six months, said study co-author Claudia Moy, program director at the National Institute of Neurological Disorders and Stroke.

One in 100 people over age 60 live with Parkinson's, the Michael J. Fox Foundation for Parkinson's Research says.

The degenerative disorder occurs when the dopamine-producing cells in the brain that normally help muscles move become impaired or destroyed, damaging a person's motor skills, speech and other functions.