During development, our brain goes through an amazing process of making and destroying connections between nerve cells. What connections remain in adulthood determine how we function and influence many both simple and complex functions of the brain. It is when those connections falter that we realize their importance being it in psychiatric disorders or in epilepsy. To date, the studies on brain connectivity has been limited to either crude assessment on the multi-millimeter scale of the entire human brain using brain imaging techniques or using labor intensive electron-microscopy techniques mapping each connection one by one. The goal of our research is to develop a novel technology that could fill the gap in between so that we can understand how complete circuits in the brain function and connect before we have the entire map of the brain completed. To reach this goal we have chosen to develop synthetic viruses and utilize the genetic code as address labels. These viruses can infect nerve cells at their connectivity points (the synapses) and transport the information in their genome back to the connected nerve cells where we then can map this information using modern sequencing techniques. In the end, this technology would help us to understand what goes wrong in the brain in many complex disorders such as Parkinson’s disease and Schizophrenia but the newly developed viruses could also help us to develop new treatments as they could target specific connections in the brain, leaving the rest untouched.