For the first time ever, scientists have imaged the entire central nervous system (CNS) of a non-transparent organism, watching it perform specific actions. The incredible footage reveals the dance of light and color from the mind of a developing fruit fly larva.

The research, reported in Nature Communications, was carried out by scientists from the Janelia Research Campus at the Howard Hughes Medical Institute in Ashburn, Virginia. They removed the CNS from the larva and observed its subsequent activity with the new method, the first time anything on this scale and level of precision has been done.

Imaging an entire CNS had remained almost impossible until now, but advances in imaging technology such as light-sheet microscopy – which involves illuminating a thin slice of a sample using laser light – have made it much more accessible. Using the technique, the scientists showed they are able to image neural tissue at high speed in 3D, with resolution increased 25-fold over other methods. Previously, the biggest nervous system that could be imaged in detail was that of the microscopic nematode Caenorhabditis elegans, but with this method that has been increased to 0.5 millimetres (0.02 inches) and at a much higher level of detail.

^{Above is a video of neural activity throughout the larva's CNS. Keller et al./Nature Communications.}

In the research, the CNS of a Drosophila melanogaster fly larva was removed and its neural activity imaged up to five times per second for an hour. In their paper, the researchers said they had demonstrated “for the first time, to our knowledge, functional imaging of neural activity in the entire, non-transparent CNS of a higher invertebrate.” The team has also been using live samples, specifically zebrafish, in the research.

In the video above, the orange flashes are the result of something called a genetically encoded calcium indicator (GECI) being inserted into the larva's CNS. The changing concentration of the calcium in the cells shows as flashes as it moves around. This particular activity shows the CNS attempting to get the larva to crawl forwards or backwards by sending signals to its muscles, which have been removed. The next step will be to see what's going on in the brain exactly.

Speaking to IFLScience, Bill Lemon from the Howard Hughes Medical Institute said that the process was essentially the "holy grail" of neuroscience research. At the moment, it's impossible to scale up any further than 0.5 mm, but Lemon said that if someone could take the idea further and apply it to a human brain, the impications could be huge. "If some day we can do this with a human brain, then all our neuroscience questions would be answered," he said.

Exciting times, indeed.