CHAT and infection: To simultaneously follow the activity of dozens of CINs within striatal microcircuits of histological dimensions, we combined adenoviral infection of FLEX-tdTomato in ChAT-Cre mice to label CINs (ChAT-positive cells; Figure 3A, first frame from left to right) and have a reference photomicrograph, with Syn-GCaMP6f expressed in neurons of different classes inside the infection area (Figure 3A, second frame from left to right).