A second approach to charting brain activity is to make use of “activity tracers,” which integrate neuronal activity over time. The challenge of recording activity from thousands of neurons in parallel during activity presents a unique obstacle that is difficult to overcome with current imaging technologies. One solution is to use an integrating, rather than sensing, approach, in which neuronal activity is “recorded” or “captured” by the integrating molecule, independent of observation by the experimentalist. An integrating approach leaves a permanent record of biochemical events, enabling high-fidelity spatial reconstruction of neuronal activity. The Miller Lab is developing activity integrators to trace neuronal activity at multiple scales—from sub-cellular to circuits—using a variety of modalities, including fluorescence imaging, super-resolution optical microscopy, and electron microscopy.