A major goal of neuroscience is understanding how neuronal circuits produce cognition. The growing field of connectomics promises to revolutionize this pursuit by providing comprehensive wiring diagrams of the brain, but faces significant conceptual and technical challenges. First, wiring diagrams give only a static view of brain connectivity, making it difficult to relate to brain function, which is dynamic. Second, volume electron microscopy (vEM) techniques capable of resolving neuronal connectivity are limited to circuit volumes orders of magnitude smaller than even a mouse brain. Finally, EM images do not reveal crucial molecular information related to function, such as synaptic proteins.
In my research, I have developed new imaging approaches to address these challenges and investigate how neuronal connectivity underlies brain function. I will describe experiments combining real-time recordings of animal behavior and neuronal activity with high-throughput vEM. We discovered connectivity patterns that specifically link neurons associated with left or right-turn decisions, providing an example of how connectivity underlies complex cognitive processes. However, this detailed approach does not include long-range connections between brain regions, which traverse distances too large to encompass in EM datasets. I will demonstrate how synchrotron-based X-ray tomography can be used to map brain wiring over large distances, combined with EM on the same tissue samples to obtain multiscale wiring diagrams. Lastly, I will show an expansion microscopy technique that makes it possible to map synaptic connectivity with diffraction-limited optical microscopy. Crucially, this is compatible with multicolor immunostaining, making it possible to reveal how the subcellular distribution of synaptic proteins underlies circuit function.