The image shows a section through the midbrain of a mouse, highlighting in light blue the dopamine-containing neurons that die in Parkinson’s disease. Neuronal fibers labeled in red form tight connections to a cluster of the dopamine-containing neurons- we recently discovered this unusual structure and named it the ‘striosome-dendron bouquet.’ We have engineered the red fibers to contain an optogenetic molecule so that we can use light to control these inputs to the dopamine-containing cells. Cell nuclei are labeled in dark blue.