Comparison of photobleaching rate measured at different imaging depths. Excitation power density at the brain surface was kept constant at 80 mW mm-2. The reduction in photobleaching rate with increasing imaging depth is caused by the reduction in excitation power received by the targeted neurons due to tissue scattering. Box plot same as Fig. 2e. Wilcoxon rank sum test, P = 2.21 10-1 for 130199 versus 200249, P = 8.60 10-2 for 130199 versus 250300 and P = 3.86 10-2 for 200249 versus 250300.
