Final answer:
Parkinson's disease is a neurodegenerative disorder that causes motor symptoms followed by cognitive impairment, typically noted as Parkinson's disease dementia (PDD) when it occurs within one year after motor symptoms begin.
Step-by-step explanation:
Parkinson's Disease and Cognitive Impairment
Parkinson's disease (PD) is a neurodegenerative disease known for its impact on motor function due to the loss of dopamine neurons in the substantia nigra, part of the midbrain. Along with the well-documented motor symptoms such as tremor, rigidity, slowed movement, and postural instability, PD can also lead to cognitive impairment. When cognitive decline occurs within one year of the onset of motor symptoms, it's indicative of Parkinson's disease dementia (PDD). PDD is characterized by disruptive memory loss, confusion, impaired planning and execution of tasks, poor judgment, and sometimes personality changes. This progression to dementia is distinct from Alzheimer's disease, which typically starts with cognitive symptoms before the appearance of motor symptoms.