Parkinson's disease (PD) is a debilitating neurodegenerative disorder occurring in 7 million patients worldwide. PD is caused by progressive loss of nigro-striatal dopamine cells, which causes motor symptoms such as slowness of movement and tremor, and non-motor symptoms such as cognitive dysfunction. Converging clinical evidence indicates that PD patients are very sensitive to the effects of psychological stress. There is a high prevalence of stressrelated neuropsychiatric symptoms in PD: 30-40% of patients experience depression and 25-30% have anxiety. Furthermore, stress worsens many motor symptoms, e.g. tremor, freezing of gait, and dyskinesia. In addition to these immediate negative effects, chronic stress may also have detrimental long-term consequences, and specifically by accelerating disease progression, as suggested by animal models. However, this hypothesis remains to be confirmed in humans. Better evidence about the impact of stress on PD would have major treatment consequences: novel stress-reducing interventions may have symptomatic effects, and perhaps also disease-modifying effects. The aim of this study is to test whether a stress-reducing intervention improves clinical symptoms, slows neurodegeneration, and/or enhances neuroplasticity in PD. In a randomized controlled trial, the investigators will compare a stress-reducing mindfulness-based intervention group (MBI; one year) to a treatment as usual (TAU) group on clinical symptoms, cerebral markers of nigro-striatal dysfunction and stressor-reactivity (MRI), and inflammatory markers (serum).