Projectome of the mammalian navigation system

Neuroscientists have long studied the representation of space in the brain, discovering place and grid cells in the hippocampus (HC) and medial entorhinal cortex (MEC), which are highly interconnected. Despite extensive experiments, the circuitry between those cell types remain unresolved. Using synchrotron radiation-based X-ray imaging of these regions in the Etruscan shrew, we will be able to obtain the complete HC-MEC projectome: all interrelated axons, with high-resolution determination of their source and target layers. Preliminary experiments have shown that myelinated axons are exquisitely visible and can be easily reconstructed from current stage X-ray data. In just 6 days of imaging, we can map the complete mammalian HC-MEC projectome. This will allow us to search for sparse and so far unknown connectivity quantifying source-target projections. This data will be a key resource for analyzing the spatial navigation system and advancing towards a complete synaptic-level map.