Figure 1. Identifying ChR2-tagged neurons in vivo.

Photostimulation-assisted identification of neuronal populations: general method for identifying neuronal populations during in vivo electrophysiological recordings. (A) ChR2 expression is restricted to distinct neuronal populations using methods that allow targeting of genetically identifiable populations of neurons (more detail in text). (B) Spikes from ChR2-positive (green) and ChR2-negative (black) single units are recorded extracellularly during a normal in vivo experiment, for example in response to sound stimulation. (C) ChR2-positive units are identified on the basis of their response to a flash of blue light.