One of the fundamental challenges in monitoring and modulating central nervous system activity is the lack of tools for non-
invasive interrogation of local neuronal ensembles simultaneously in different regions of the brain. Despite recent advances in
neural modulation techniques, including a rapidly expanding optogenetic and imaging toolset, still we lack a robust, minimally-
invasive optogenetic stimulation platform. The ability to independently deliver light to multiple, highly- localized regions of the
brain would drastically improve in vivo optogenetic experiments. Illuminating a large volume of brain using light sources above the
brain surface does not provide the requisite spatial resolution, and since the intensity diminishes rapidly, only a small fraction of
target neurons in the vicinity of the light source (~200 Ám) will be excited. Increasing the light source power, on the other hand,
results in the generation of excessive heat in the brain and the potential for tissue damage. In this project, we use specially
designed up converting nanocrystal particles (UCNP) to deliver light locally to neurons. We use an acoustic-optics modality to
deliver and steer light in the brain from outside without causing damage to the brain tissue.