Our Entire Brains Resolutions Show Health Level

How Resolutions Show Health Level Our Entire Brains

Brains Resolutions Show Health Level

Making detailed maps of the brain requires charting its activity and wiring -- in humans, the thousands of connections made by each of more than 80 billion neurons. Such maps could help scientists spot where brain disease begins, build better artificial intelligence, or even explain behavior. "That's like the holy grail for neuroscience," Boyden says.

Years ago, his group had an idea to figure out how everything was organized: What if they could actually make the brain bigger -- big enough to look inside? By infusing samples with swellable gels -- like the stuff in baby diapers -- the team invented a way to expand tissues, making the molecules inside less crowded and easier to see under the microscope. Molecules lock into a gel scaffold, keeping the same relative positions even after expansion.

But it wasn't easy to image large tissue volumes. The thicker a specimen gets, the harder it is to illuminate only the parts you want to see. Shining too much light on samples can photobleach them, burning out the fluorescent "bulbs" scientists use to light up cells.

Expanding a sample just four-fold increases its volume 64-fold, so imaging speed also becomes paramount, Gao says. "We needed something that was fast and didn't have much photobleaching, and we knew there was a fantastic microscope at Janelia."

The lattice light-sheet microscope sweeps an ultrathin sheet of light through a specimen, illuminating only that part in the microscope's plane of focus. That helps out-of-focus areas stay dark, keeping a specimen's fluorescence from being extinguished.

When Gao and Asano first tested their expanded mouse tissues on the lattice scope, they saw a thicket of glowing nubs protruding from neurons' branches. These nubs, called dendritic spines, often look like mushrooms, with bulbous heads on skinny necks that can be hard to measure. But the scientists were able to see even "the smallest necks possible," Asano says, while simultaneously imaging synaptic proteins nearby.

"It was incredibly impressive," says Betzig. The team was convinced that they should explore the combined technique further. "And that's what we've been doing ever since," he says.

The brain and beyond

Over the last two years, Gao and Asano have spent months at Janelia, teaming up with biologists, microscopists, physicists, and computer scientists across the campus to capture and analyze images. "This is like an Avengers-level collaboration," Gao says, referring to the crew of comic book superheroes.

Yoshinori Aso and the FlyLight team provided high-quality fly brain specimens, which Gao and Asano expanded and used to collect some 50,000 cubes of data across each brain -- forming a kind of 3-D jigsaw puzzle. Those images required complicated computational stitching to put the pieces back together, work led by Stephan Saalfeld and Igor Pisarev. "Stephen and Igor saved our bacon," Betzig says. "They dealt with all the horrible little details of image processing and made it work on each multi-terabyte data set."

Next, Srigokul Upadhyayula from Harvard Medical School, a co-first author of the report, analyzed the combined 200 terabytes of data and created the stunning movies that showcase the brain's intricacies in vivid color. He and his co-authors investigated more than 1,500 dendritic spines, imaged fatty sheaths that insulate mouse nerve cells, highlighted all of the dopaminergic neurons, and counted all the synapses across the entire fly brain.

The nuances of Boyden's team expansion technique make it well suited for the lattice scope; the technique produces nearly transparent samples. For the microscope, it's almost like looking through water, rather than a turbid sea of molecular gunk. "The result is that we get crystal clear images at blazingly fast speeds over very large volumes compared to earlier microscopy techniques," Boyden says.

Still, challenges remain. As with any kind of super-resolution fluorescence microscopy, Betzig says, it can be hard to decorate proteins with enough fluorescent bulbs to see them clearly at high resolution. And since expansion microscopy requires many processing steps, there's still the potential for artifacts to be introduced. Because of this, he says, "we worked very hard to validate what we've done, and others would be well advised to do the same."

Now, Gao and the Janelia team are building a new lattice light-sheet microscope, which they plan to move to Boyden's lab at MIT. "Our hope is to rapidly make maps of entire nervous systems," Boyden says.

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Materials provided by Howard Hughes Medical Institute. Note: Content may be edited for style and length.

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