Optogenetics. Illustration of ion channels (green and pink) in a mouse brain neuron (nerve cell, centre) being controlled by light. The ion channels have been genetically engineered to become sensitive to light, a technique known as optogenetics. When light of a certain wavelength is shone on an area of the mouses brain, the channel that is sensitive to that wavelength of light opens. This precise targeting enables scientists to determine the neural circuits that underlie certain behaviours or diseases.