बेबादि थै रोदानि सबस्टेनसिया नाइग्रा मुंनि बाहागोआव डोपामिन दिहुनथाया बेजेफोरनि अराइ खहा जानायनि जाहोन ।
This happens because of continual damage of dopamine producing fibers in a part named substantia nigra of nervous system .