Human perception, thought, learning, and memory are all made possible by the activity and connections between the 100 billion neurons in the brain. These complex functions are thought to arise from a combination of (1) the strength of synapses that connect neurons together, (2) the ability of individual neurons to fire electrically, and (3) the speed at which electrical signals propagate through neuronal axons. Neuroscientists have long focused on understanding how synapses and electrical excitability contribute to higher-order brain functions. However, far less is known about whether the speed of electrical signals through axons is also dynamically tuned to regulate brain function. We aim to determine how myelin—the electrical insulator around neuronal axons that speeds nerve signaling—contributes to the plasticity of neuronal circuits. We will leverage our team’s complementary scientific strengths in myelin biology, bioengineering, and neurobiology to develop novel tools for perturbing myelin in the brain. These tools will enable us to dissect how myelin contributes to specific brain circuits and types of neurons, bringing us closer to a holistic understanding of how cells in the brain collaborate to build a functional nervous system.