However, rotigotine, which has a much weaker effect on D1 dopamine receptor compared with D2, D3, D4, and D5 receptors [44], presents an improving effect on both letter fluency and semantic fluency [20], suggesting that dopamine receptors other than the D1 receptor may play a role in verbal fluency impairment in PD patients [46]. Here, DRD1 is linked to Parkinson disease.