Single-molecule switchable FRET

Two-photon microscopy offers unique advantages for excitation of channelrhodopsin-2 (ChR2)-expressing neurons, but previous attempts had limitations in terms of the axial and temporal resolution. Emiliani and colleagues now use a scanless approach that combines generalized phase contrast and temporal focusing to shape two-photon excitation patterns and trigger single action potentials or trains of action potentials in cultured neurons and in mouse cortical slices. These patterns of light can be used to selectively and flexibly activate single neuronal processes as well as simultaneously excite multiple neurons or multiple dendrites of one cell. article p848, news and Views p798