Like many neuroscientists, my experience with the brain is centred mostly around blood, how blood feeds the neurons. fMRI, while an amazing tool, works to understand changing blood flow which we argue is affected by neurons but our understanding of how blood flow works in the brain is imperfect. To better understand the blood, and then the neurons, we need to study the architecture by which the brain is supplied with new blood. You will have seen photos of the brain's arteries at some point in your life but today we are talking about capillaries that are smaller than a millimetre and neurons are never more than a few microns away from a capillary. The trickest with studying something that small is normal microscopes don't cut it, and the usual techniques of electron microscopy involve killing the animal we study. Today's episode is about 2-photon microscopy, a relatively new technique that doesn't require the animal to die and instead lets us study calm, usually peacefully sleeping rodents to understand how their neurons are supplied with blood at the smallest levels.