This study evaluates the efficacy of an eight-week online cognitive training program on objective and subjective cognitive functions in Parkinson's disease. Moreover, we intend to map the effect on brain network function, and if cognitive training can prevent the development of PD-MCI/PD-D after one- and two-year follow-up. In this study, two training groups will be compared (N: 70 vs 70). In half of the participants MRI and magnetoencephalography (MEG) will be assessed (N: 40 vs. 40). We expect cognitive training to improve cognitive functions, and to improve the efficiency of brain network function. Moreover, we expect that cognitive training can decrease the risk of PD-MCI/PD-D at one- and two-year follow-up.