English: "Figure 1. Bi-directional interaction between gastrointestinal (GI) tract and central nervous system (CNS). Schematic representation summarizes Braak's model of Parkinson's disease (PD) progression initiated from the GI tract. Changes in GI mucosal immunity, environmental toxins, infection, sleep quality, diet, and genetics modify the gut microflora and induce inflammation, mitochondrial dysfunction, and abnormal protein accumulation. Accumulation of α-syn in the GI tract spread via the vagus nerve to the CNS and leads to dopaminergic neuron degeneration."(Chao Yin-Xia, Gulam Muhammad Yaaseen, Chia Nicholas Shyh Jenn, Feng Lei, Rotzschke Olaf, Tan Eng-King 2020)