Additional Study Information: We are looking for participants for a study on the role of immune response in Parkinson's disease (PD) and Alzheimer's disease (AD). We are inviting people WITH PD, WITH AD, WITH amnestic Mild Cognitive Impairment, or WITHOUT PD or AD to come and participate. We will be doing several questionnaires, a motor exam, and a short cognitive assessment, in addition to a blood draw of up to 250cc. This study will involve one to two visits for a total of up to 3 hours, and you will be compensated with $50.00 to $200 accordingly and a parking voucher.