Periodic optogenetic stimulation enhances neuronal regeneration in vivo. A, B, Representative images of 24 h regeneration in nonstimulated (ChR2, ATR) and photo-stimulated neurons (ChR2, ATR, Light). Red arrows indicate position of laser damage. Scale bars, 20 μm. C, D, The average 24 and 7 h regenerative outgrowth in optogenetically stimulated ALM neurons exposed to repeating blue light (10 s on 50 s off, 175 μW/mm2) compared with nonstimulated controls. E, Average 24 h regenerative outgrowth in control and optogenetically stimulated PLM neurons. C, E, *p < 0.05 (multiple comparison in one-way ANOVA using a Tukey Adjustment). D, *p < 0.05 (t test). F, The behavioral response to a 3 s, 1 mW/mm2 flash of blue light for animals exposed to the repeating photo-stimulation pattern used in the regeneration assays for the indicated time periods. Animals raised without ATR serve as controls. G, H, Average 24 h ALM regeneration with different light intensities (G) and temporal patterns of photo-stimulation (H).