What looks like a time-lapse video of city lights at night turns out to be active neurons within the brain of a zebrafish embryo. This is the result of groundbreaking brain imaging research published in Nature Methods by Misha Ahrens and Philip Keller at Howard Hughes Medical Institute in Virginia this past March. The video shows distinct hubs of light and flashes bursting from one region to another throughout the brain.
The two researchers, microscopists and neurobiologists by trade, developed a modified light-sheet microscopy technique that allowed the activation of almost all neurons in the brain to be recorded as flashes of light. Prior to this, brain-imaging technology could measure activity in regions of the brain or a handful of individual neurons, but never at the same time. “We see the big picture without losing resolution,” said Keller, in an interview with Nature News & Comment.
Using genetically engineered neurons that fluoresce upon activation, images of the whole brain were taken once every second for an hour. The activity of 80,000 neurons, 80 per cent of the total, were recorded simultaneously.
Not only do the images show the overall complexity of a brain, but they also elucidate functional neural connections that span the entire brain. These circuits were discovered by correlating patterns of activity in separate brain regions.
This is the first time that whole brain activity has been imaged at the level of individual neurons. However, it will take some time before this new technique can be applied to the human brain, which has 85,000 times more neurons than a zebrafish brain.

With files from Nature News & Comment

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