Marshall, J.D. et al. Cell 167, 1650–1662 (2016).

Voltage sensors have been steadily improving, but they are still difficult to record with current optical technologies. Marshall et al. provide an optimized approach for optical recording of membrane voltage dynamics in freely moving mice. To remove motion artifacts, the researchers coexpressed and recorded a red fluorescent protein together with a green fluorescent voltage sensor. They sinusoidally modulated excitation of the two fluorescent proteins in order to deal with optical crosstalk between the fluorophores. Furthermore, they optimized a multimode optical fiber for their experimental setup, and used it for two-color illumination and recording. And finally, the researchers developed a custom unmixing algorithm to separate the fluorescent channels. They used this approach to analyze the contribution of two classes of dopamine-responsive neurons to local field potentials in the mouse striatum.