The brain of a mouse consists of almost 100 million nerve cells that are densely packed together with supporting cells. To study these cells, individual cells are specifically labelled with fluorescent dyes. After appropriate excitation with light, such fluorescent dyes emit light themselves that can be detected microscopically. Of particular interest are synapses, the contact sides between two nerve cells where information is transferred from cell to cell and which form the basis of our memory and all neuronal activity. Synapses are only a few tens to a few hundreds of nanometers in size and can be localized using conventional light microscopy. Their exact shape and size, however, can only be imaged in living organisms using super-resolution light microscopy such as STED microscopy. A research group at the Max Planck Institute of Experimental Medicine in Göttingen, led by Katrin Willig, has now developed a method to simultaneously image three different protein structures using STED microscopy in the brain of a living mouse. The study, published in the Journal Cell Reports shows that this method can be used, for example, to observe pre- and postsynaptic protein structures with super-resolution in the brain.