Neuroscientists aim to understand how the brain works and to advance treatments for diseases and disorders of the nervous system. This type of research requires investigating complex functions at all levels of the living nervous system. Because it is impossible to use humans for this work, neuroscientists turn to animals. Acting under regulations put forth by governmental agencies, scientists use animals to discover how diseases and their potential therapies affect the entire body — experimental procedures that are often difficult, if not impossible, to replicate with alternative methods.