Kyle Fischer is a graduate student in neuroscience at UC San Diego and a member of Dr. Ed Callaway’s lab at the Salk Institute. Kyle is developing viral tracing tools for unraveling the “neural knot” that characterizes our nervous system, which is made up of trillions of neurons that fall into distinct morphological, molecular, and physiological classes. These cells form synaptic connections with specific partners both within their local neighborhood and across the brain. This complex network forms the circuitry that defines the flow of information underlying sensation and behavior. Over millennia several species of viruses, such as rabies, have developed neurotropic characteristics that can be co-opted to map neural networks. For instance, by deleting or replacing a small region of the rabies genome essential for transsynaptic spread we can limit the spread of rabies to only those cells in which we have resupplied this missing component, thereby mapping the inputs a single neural population receives. Kyle is working to improve upon this technique and apply it to better our understanding of visual processing.