Alzheimer's disease (AD) and Parkinson's disease (PD) are currently the leading neurodegenerative disorders. Despite some therapeutic benefits from the medications targeting at cholinergic and dopaminergic pathways in AD and PD respectively, it remains far away from a satisfied treatment goal. DAAOI-P is a D-amino acid oxidase (DAAO) inhibitor and an agent specific to facilitate NMDA receptor subunit 1 (NR1). The investigators have demonstrated that NMDA-enhancement can help PD-D patients. The aim of this project is to examine the effectiveness and safety of DAAOI-P treatment for PD with dementia. In addition to evaluating clinical treatment response, multidisciplinary examinations, including electroencephalography, transcranial magnetic stimulation, magnetic resonance imaging (MRI), and psychophysical methods to analyze the changes in perceptual sensitivity to faces, emotion expressions, and biological motion recognition will be arranged to elucidate the underlying mechanism of NMDA modulation in neurodegenerative disorder.