Kristen Harris is one of the world’s leading neuroscientists investigating synapse structure and function. She has been a professor of neuroscience at Harvard, Boston University, Georgia Health Sciences University, and since 2006 in the Center for Learning and Memory at the University of Texas at Austin. She is the author of numerous publications and recipient of the prestigious Sloan Fellowship and Javits Neuroscience Investigator Awards, and she serves as a reviewer for the National Institutes of Health. Her research uses 3D reconstructions from electron microscopy to decode the cell biology of learning and memory. Recent findings show that mature neurons sustain a maximum synaptic capacity, exactly balancing the strengthening of some synapses by eliminating weak neighbors during long-term potentiation, a cellular mechanism of learning. These novel findings provide the basis for new understanding of structural and molecular mechanisms of synapse growth and elimination in the mature brain, a crucial step in developing treatments to mend the mind.