Photostimulation

(a) Photosensitive proteins can be inserted into neural membranes by means of genetically modified viruses. Blue light causes ChR2 ion channels to depolarize the membrane, and yellow light causes NpHR ion transporters to hyperpolarize it. (b) The graph shows the effects on the membrane potential of different wavelengths of light acting on ChR2 or NpHR proteins. (c) The graph shows action potentials elicited by pulses of blue light (blue arrows) and the inhibitory effects of the hyperpolarization caused by yellow light.  (Part (a) adapted from Hausser, M., and Smith, S. L. Nature, 2007, 446, 617–619, and parts (b) and (c) adapted from Zhang, F., Wang, L. P., Brauner, M., et al. Nature, 2007, 446, 633–639.)