Optogenetics is a field of bioengineering research that centers on the development and use of tools that enable the use of light to control specific biological processes in order to understand how those processes causally contribute to complex cellular and organismal functions. By turning off a specific biological process, it is possible to understand what complex or emergent functions that process is necessary for. On the other hand, by stimulating a specific biological process, it may be possible to see what complex functions that process is sufficient to initiate. As might be inferred from the name, the most common optogenetic strategy is to express specific foreign genes that encode for light-receptive proteins in cells, in vitro or in vivo, and then to illuminate the cells to activate the resulting light-receptive protein, thus driving the specific signaling pathway that is downstream of the protein. These genes are taken from cells of other organisms and introduced using transgenic vectors, such as viruses.