For as long as humans have wondered how thought arises from matter, the brain's wiring has remained one of nature's most guarded secrets — knowable only in fragments, one painstaking connection at a time. Researchers at the Francis Crick Institute have now introduced BRISC, a method that uses molecularly barcoded rabies viruses to map thousands of synaptic connections across hundreds of neurons simultaneously in the mouse visual cortex, preserving not just which cells speak to which, but where in the tissue those conversations take place. The achievement does not complete the map of the mind,