Fluorescent indicators for functional optical imaging

Optical imaging is developing towards the method of choice for monitoring the activities of large numbers of cells in the cortex of living rodents. During the last decade this approach was fueled by methodological progress in both optical instrumentation and fluorescent indicators of neuronal activities. In the first part of this chapter, we provide information required to reach an informed decision regarding the most suitable fluorescent indicators for the different imaging modalities and the experimental approaches for imaging cortical circuit dynamics in vivo. In particular, an overview is given of the available palettes of synthetic and genetically encoded calcium- and voltage-sensitive indicators. In the second half of the chapter we describe the status of voltage imaging of cortical activity using genetically encoded voltage-sensitive fluorescent proteins.