Video-assisted motion tracking allows the quantitative analysis of fruit fly behavior. Shown on the left are normal flies in their arenas during a one-minute recording. On the right are flies in which parts of the central complex are defective. These flies exhibit Parkinsonism, as they have problems with initiating and maintaining movement. This video relates to a paper that appeared in the April 12, 2013, issue of Science, published by AAAS. The paper, by Nicholas Strausfeld at University of Arizona in Tucson, Ariz., and colleagues was titled, "Deep Homology of Arthropod Central Complex and Vertebrate Basal Ganglia."