CA2 region was found to have predominantly enriched α-synuclein accumulation in Parkinson’s disease dementia (PDD) with unknown pathological spreading routes. Here, we traced the novel neural circuit connecting the ventral tegmental area (VTA) to CA2 and identified the CA2 neuronal subtype involved in this circuit by viral tracing and tissue clearing technique. These data shed light on the potential progression route during the development of PDD.