Rex received undergraduate degrees in math, physics, and molecular and cell biology from the University of California at Berkeley.  During his Ph.D. in Biology with William Schafer at the University of California at San Diego, he performed the first studies of neural activity in C. elegans using genetically encoded calcium indicators.  As a postdoctoral fellow in biophysics, Rex worked on stochastic reaction-diffusion modeling to enable simulations of molecular interactions in small compartments such as synapses--with Terrence Sejnowski at the Salk Institute and in collaboration with Herbert Levine and Wouter Jan-Rappel at the Center for Theoretical Biologial Physics at UCSD. Rex came to Janelia as a Fellow in order to study how small circuits of neurons in C. elegans function to give rise to the animal's behavior.