Where is the brain defect located that causes Parkinson's disease?

Parkinson's disease is primarily associated with a defect in a specific area of the brain known as the substantia nigra, which is part of the basal ganglia. This region is critical for the production of dopamine, a neurotransmitter that plays a key role in regulating movement. In Parkinson’s disease, the neurons in the substantia nigra degenerate and die, leading to a significant reduction in dopamine levels. This deficiency causes the hallmark symptoms of Parkinson's, such as tremors, rigidity, and bradykinesia (slowness of movement).

The other regions mentioned, while important for various brain functions, are not directly involved in the pathology of Parkinson's disease. The hippocampus is primarily associated with memory and learning, the frontal lobe plays a role in higher cognitive functions and personality, and the cerebellum is responsible for balance and coordination. None of these areas are the primary locations where the disease process occurs in Parkinson's, which is why the substantia nigra is recognized as the critical site of the defect.