Parkinson's disease (PD) affects more than 100,000 Canadians and results in symptoms affecting both motor and cognitive (thinking and memory) functions. Parkinson's disease with Mild Cognitive Impairment (MCI) frequently results in development of dementia for which few treatment options exist. Transcranial Magnetic Stimulation (TMS) is used to alter activity in the outer regions of the brain and has been shown in previous studies to increase cognitive performance in patients with different disorders. This study will investigate the effectiveness of TMS as a clinical treatment for the cognitive deficits associated with Parkinson's disease. 64 male and female participants between the ages of 50 and 90 will attend eight study visits over a period of 63 to 66 days. This study is a double-blind randomized clinical trial meaning the participant will be assigned by chance to either the TMS-treatment group or the Sham-treatment group. Additionally, a combination of memory and thinking tests and Magnetic Resonance Imaging (MRI) will be used to see if there are structural and functional changes within the brain. Genotyping and blood analysis before and after treatment for different biomarkers will also be performed and these data will be compared to the TMS data. Initially, this research will increase knowledge about the effects of TMS on various brain regions. Ultimately, we will be able to determine if TMS can be used as a complementary therapy for PD to improve cognitive performance and to reduce progression into dementia.