In vivo brain imaging: fluorescence or bioluminescence, which to choose?

In the last decade, several different optical-imaging techniques have been developed to study neuronal activity, with the aim to map and decipher the neural code underlying major neurophysiologic functions, such as odor perception, learning and memory, locomotor activity, and sleep, to name a few. The first generation of these techniques was principally based on detecting either transmembrane voltage or calcium activity by using fluorescent dye markers. Recently, the development of genetically encoded probes has extended the limits, increased the accessibility of deeper structures,and more importantly, allowed investigators to precisely label and identify the desired neurons. However, several deep structures of the brain still remain refractive to these approaches, suggesting that the development of other techniques will be welcome. Recently, a new bioluminescence approach has been described, and although it is still anew technique, the first reported results, and the biological phenomena that have been revealed, make it extremely promising. This review will summarize the recent progress of these different imaging approaches, comparing the limits and constraints of each of them, and will guide the reader in choosing the most appropriate method in accordance with the desired neurons or functions under investigation.