Ed Boyden, inventor of optogenetics and expansion microscopy at MIT and HHMI, presents cutting-edge techniques for mapping and manipulating brain circuits at nanoscale resolution. He covers how expansion microscopy — swelling brain tissue with superabsorbent polymers to physically magnify it — enables imaging of individual synapses and molecular complexes. He also discusses optogenetic tools for controlling specific neuron populations, and how these technologies together open paths toward whole-brain circuit mapping and the understanding of neural computation.