Examining Braak's hypothesis by imaging Parkinson's disease.

In this review, in vivo patterns of structural, metabolic, and neurotransmitter binding changes revealed by imaging in both symptomatic Parkinson's disease (PD) and at-risk subjects are compared with those predicted at different Braak stages. It is concluded that the dysfunction revealed by imaging in PD is only partially in line with the sequential ascending topography of Lewy body pathology reported by Braak, suggesting that neurons in different brain regions are likely to be selectively vulnerable to the presence of intracellular synuclein aggregates.