Past four decades have seen a concerted push to develop regenerative treatments for incurable neurodegenerative diseases such as Parkinson's disease (PD). PD's pathophysiology is primarily characterized by dopamine deficiency caused by the progressive depletion of neurons in substantia nigra (Bernheimer et al., 1973). So, it is not very surprising that most attempts at regenerative treatment of PD focus on using pre-differentiated, dopaminergic neurons. However, PD's pathogenesis spans far beyond strictly dopamine deficiency and is still not completely known (Chaudhuri et al., 2006).