A tool developed by researchers at Brown University provides a way to use bioluminescent light to visualize brain activity. The work is the result of 10 years of development, realized by the Bioluminescence Hub at Brown’s Carney Institute for Brain Science. The researchers have developed a tool called the Ca2+ BioLuminescence Activity Monitor — or “CaBLAM,” for short. It captures single-cell and subcellular activity at high speeds and has proven effective in mice and zebrafish, allowing multi-hour recordings while removing the need for external light. According to Christopher Moore, a professor of brain science at Brown University, the work began with the question: “What if we could light up the brain from the inside?” “Shining light on the brain is used to measure activity — usually through a process called fluorescence — or to drive activity in cells to test what role they play,” he said. “But shooting lasers at the brain has down sides when it comes to experiments, often requiring fancy hardware and a lower rate of success. We figured we could use bioluminescence instead.” This image shows the cortical neurons of a lab mouse bioluminescing while the mouse runs on a wheel. The large, dark tube-like structures are blood vessels. Courtesy of Brown University/Jeremy Murphy. Measuring ongoing activity of living brain cells is essential to understanding the functions of biological organisms, Moore said. The most common current approach uses imaging with fluorescence-based genetically encoded calcium-ion indicators. “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,” said Nathan Shaner of UC San Diego. “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 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 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. 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. 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, including tracking activity in multiple parts of the body at once,” Moore said. The research was published in Nature Methods (www.doi.org/10.1038/s41592-025-02972-0).