Researchers at Cornell Medical College have found a gene that can cause symptoms of major depression, and might be able to use this information to help treat it, Reuters reports. The researchers are testing a gene therapy technique in the brains of patients with Parkinson’s disease, which could perhaps be adapted to treat depression. The causes of depression are complex and different patients respond to different treatments. The gene is called p11, which is in a part of the brain tied to reward satisfaction. It helps regulate serotonin, a chemical tied to mood, sleep and memory that’s often targeted by antidepressants.