Ahrens, Keller and others have previously used light-sheet microscopy to image developing embryos over days; for the latest study, they modified light detectors and other aspects of the system to increase the rate of imaging tenfold. In a series of hour-long experiments, each of which generated 1 terabyte (1 million megabytes) of data, the researchers were able to see populations of neurons in distinct regions that correlated to their activity (see video above).
The technique does have its limitations. For one thing, it works best in zebrafish embryos, which are transparent. Ahrens and Keller think that it could work in intact mammal brains, but it would require surgery and would cover only a small fraction of the brain.
Another limitation is that neither the protein sensor nor the imaging system yet works fast enough to distinguish whether a neuron has fired once or several times in quick succession. But Fetcho says that it is fast enough to start to understand how activity flows through the brain. “No one is anywhere in the ball park of this for any other animal model.”