Optogenetics, the intersection between physics and neuroscience: light stimulation of neurons in physiological conditions.

Neuronal stimulation by light is a novel approach in the emerging field of optogenetics, where genetic engineering is used to introduce light-activated chan-nels. However, light is also capable of stimulating neurons even in the absence of genetic modifications through a range of physical and biological mechanisms. As a result, rigorous design of optogenetic experiments needs to take note of alterna-tive and parallel effects of light illumination of neuronal tissues. Thus all matters relating to light penetration are critical to the development of studies using light-activated proteins. This paper discusses ways to quantify light, light penetra-tion in tissue, as well as light stimulation of neurons in physiological conditions. We also describe the direct effect of light on neurons investigated at different sites. [ABSTRACT FROM AUTHOR]