Over the last 10 years optogenetics gave us a new way to address neuroscientific questions. Ideally, optogenetics enables a non-invasively control of neuronal activity of a genetically-targeted subpopulation of neuron in a behaving animal at high temporal and spatial resolution. But under most experimental settings, animals are attached to a light guide, brain tissue is destroyed from chronically implanting an optical fiber and social as well as long-term experiments are not easily feasible. Those major limitations all arise from the low penetration depth of visible light into the brain which is necessary to activate most light-sensitive probes. Here I am proposing a universal method in which nanocrystals are injected together with a virus, carry an ultra-light sensitive channelrhodopsin gene, into the same location in the brain. Upconverting nanocrystals are excited with infrared light, which can penetrate through brain tissue as well as skull. Excited nanocrystals are then emitting visible light which will stimulate nearby neurons expressing channelrhodopsin. This method has therefore the potential to control neuronal activity in a contact-free manner.