Ebina, T. et al. PNAS 116, 22844–22850 (2019)

Optogenetics is now widely used for investigating the neural underpinnings of behavior. However, optogenetic stimulation has yet failed to induce or modulate any limb movements in nonhuman primates. A new study published in PNAS describes an improved method of optogenetic cortical stimulation in marmosets using adeno-associated viruses with a tetracycline-inducible gene expression system carrying CaMKII promoter and a Channelrhodopsin-2 variant with fast kinetics. Forelimb movements could be induced when Channelrhodopsin-2-expressing neurons in the motor cortex were illuminated by blue laser light through a cranial window. This method could be used to gain a better understanding of the motor circuits that are involved in learning or affected after brain injury.