The concept that the brain has a structure is not obvious. While it’s been a long time since Aristotle argued the heart was the thought center of the body, it wasn’t until the 1700s that scientists hypothesized and began to gather evidence that the brain has distinct regions with specialized functions. Phineas Gage, the man whose personality changed drastically after an accident where an iron spike was driven through his head, is a famous early example of the link between brain regions and behavior. Also around that time, French scientists Marc Dax and Paul Broca independently discovered the speech production center of the brain when autopsies of speech-impaired patients revealed lesions in a particular brain region, later named the Broca’s area. In this post I’ll describe a new virus with retrograde function and how it’s enabling scientists to access neurons in a powerful way. Keep reading to find out what retrograde function is and how it gives us better access and ultimately a better understanding of the brain.