BDNF and Parkinson disease: A reduction in BDNF signaling has been documented during normal aging and decreased BDNF levels are associated with vulnerable neuronal populations in several neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases, demonstrating the need for further therapeutic research on components of the BDNF signaling pathway (Tapia‐Arancibia, Aliaga, Silhol, & Arancibia, 2008).