In labs around the world, mice learn to navigate complex mazes, locate chocolaty rewards, and after an interval, run the mazes again with maximum efficiency, swiftly collecting all the sweets. But in Susumu Tonegawa’s lab, the mutant mice he has created cannot perform these tasks. Tonegawa “ knocks out” a gene that impairs a specific part of the mouse hippocampus, the area of the brain responsible for spatial memory, among other things. Mutant mice struggle to acquire and recall information about their surroundings. Tonegawa’s work involves manipulating genes to explore memory and learning from the most basic biochemical and cellular levels, up to the most complex behaviors. One of Tonegawa’s goals in designing defective mice is to simulate profound human disorders, like schizophrenia.