SNCA and Parkinson disease: Moreover, the gadolinium-based contrast agent spread further in a forward direction, suggesting that glymphatic activity varied among patients and brain regions.28 Braak proposed a typical progression pattern of ɑ-synuclein accumulation in Parkinson's disease, which propagates initially through the brainstem, then enters limbic structures, and ultimately spreads to the neocortex.29 This theory highlights the spatially and temporally heterogeneous nature of ɑ-synuclein distribution.