“In the way fluorescence works, you shine light beams at something, and you get a different wavelength of light beams back,” said Moore, who leads the Bioluminescence Hub. “You can make that process calcium-sensitive so you can get proteins that will shift back a different amount or different color of light, depending on whether or not calcium is present, with a bright signal.”

While fluorescent probes are useful in many contexts, he said, there are significant limitations to using them to monitor brain activity. First, bombarding the brain with high amounts of external light for a prolonged amount of time can damage cells. Second, high-intensity illumination can cause the molecule involved in fluorescence to change its structure so that it can no longer give off adequate light — this is called photobleaching, and it limits the amount of time fluorescence can be used. Finally, shining light at the brain involves hardware, such as lasers and fibers, that require a more invasive approach.

In contrast, bioluminescent light production, where light is produced when an enzyme breaks down a specific small molecule, has several advantages. Because bioluminescence probes do not involve bright external light, there’s no risk of photobleaching, and they also don’t have a phototoxic effect, so they’re safer for brain health.

The light also makes it easier to see.

"Brain tissue already glows faintly on its own when hit by external light, creating background noise,” Shaner said. “On top of that, brain tissue scatters light, blurring both the light going in and the signal coming back out. This makes images dimmer, fuzzier, and harder to see deep inside the brain. The brain does not naturally produce bioluminescence, so when engineered neurons glow on their own, they stand out against a dark background with almost no interference. And with bioluminescence, the brain cells act like their own headlights: You only have to watch the light coming out, which is much easier to see even when scattered through tissue.”

The idea of measuring brain activity with bioluminescence has been around for decades, Moore said, but no one had figured out how to make bioluminescent light bright enough to allow detailed imaging of brain cell activity — until now.

The insights that ignited CaBLAM

“The current paper is exciting for a lot of reasons,” Moore said. “These new molecules have provided, for the first time, the ability to see single cells independently activated, almost as if you’re using a very special, sensitive movie camera to record brain activity while it’s happening.”

The new tool can capture the behavior of a single neuron in a living lab animal, even down to the activity within sub-compartments of cells. In the study, the team showed data from a recording session that lasted for five continuous hours — which would have been impossible using the time-limited fluorescence method.

“For studying complex behavior or learning, bioluminescence allows one to capture the entire process, with less hardware involved,” Moore said.

This work is part of a broader push by the hub to create new ways of controlling and observing brain activity. One project uses a living cell to send a burst of light that is detected by a neighboring cell, effectively allowing neurons to communicate through light (what Moore calls, “rewiring the brain with light”). The team is also engineering new methods that use calcium to control cellular activity. As these ideas took shape, it became clear that all of them depended on brighter, better calcium sensors. That has become a key focus, Moore said.

“We made sure that as a center that's trying to push the field forward, we created the necessary component pieces,” Moore said.

Moore hopes that CaBLAM can eventually be used to study areas of the body beyond the brain.

“This advance allows a whole new range of options for seeing how the brain and body work,” Moore said, “including tracking activity in multiple parts of the body at once.”

He added that the tool is a testament to the power of team science. At least 34 researchers contributed to the project from Bioluminescence Hub partners including Brown, Central Michigan University, U.C. San Diego, the University of California Los Angeles and New York University. Funding for the research came from the National Institutes of Health, the National Science Foundation and the Paul G. Allen Family Foundation.