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A gene therapy treatment for Parkinson’s disease appears to relieve symptoms by rewiring the brain circuits involved in movement.

People with Parkinson’s disease have tremors and muscle stiffness that are caused by overstimulation of a brain area called the subthalamic nucleus, which is responsible for coordinating the brain’s motor regions.

In a trial published in 2011, researchers at the Feinstein Institute for Medical Research in New York found that a gene therapy designed to turn down the activity of the subthalamic nucleus .

Though the treatment reduced Parkinson’s symptoms for at least a year, it was unclear how. To find out, the researchers have since used PET scans to compare the brains of 15 people who received the gene therapy with 20 who received a placebo.

Reshaping the brain

One year after treatment, the people in the gene therapy group were found to have new brain connections that weren’t seen in the placebo group. Shutting down the disease-causing pathways between the subthalamic nucleus and the brain’s motor regions appeared to encourage alternative pathways to develop instead, says  at the Feinstein Institute, who led the study.

These alternative pathways are not found in healthy people. This suggests that gene therapy lets people with Parkinson’s form novel, compensatory brain circuits for controlling movement, says Eidelberg. “We call it adaptive rewiring.”

Another treatment for Parkinson’s disease – called deep brain stimulation – involves sticking electrodes into the subthalamic nucleus and suppressing its activity using electrical pulses. However, Eidelberg and his colleagues found that this did not lead to the same adaptive rewiring.

The team is now planning a larger trial of gene therapy for Parkinson’s disease that is due to start at the end of 2019.