Parkinson's disease can lead to changes in the chemical composition and structure of the brain, which can impair thinking and memory. This is because the Parkinson's disease-related protein alpha-synuclein forms sticky clusters known as Lewy bodies, which can impair cognitive function and cause dementia. Parkinson's disease initially manifests as physical symptoms, but as the condition worsens, almost 4 out of 5 patients experience dementia, which can lead to severe memory loss and make it difficult to maintain connections. Additionally, cognitive issues, such as difficulty concentrating and forgetting things, may appear later.