Most of what we know about how a body's organs coordinate comes from looking at one system at a time — record the brain, then separately study the gut, then the heart, and try to stitch the story back together afterward. A new technique out of HHMI's Janelia Research Campus skips the stitching. Developed by postdoctoral researcher Virginie Ruetten in Misha Ahrens's lab and published this week in Nature, the method, called WHOLISTIC, records real-time activity from nearly every cell in a living vertebrate at the same time — nervous system, digestive system, and cardiovascular system, all captured together as they actually happen, not reconstructed afterward from separate experiments.
The trick is tracking calcium signals, which is essentially the shared language cells across the body use to communicate with their neighbors. The Ahrens Lab spent more than a decade building tools to image those signals across an entire zebrafish brain — genuinely difficult work on its own. WHOLISTIC takes that same foundation and extends it past the brain to the whole organism, combining high-speed volumetric fluorescence imaging with computational tools built to track and line up signals across completely different tissue types at once. That last part is the harder engineering problem than it sounds: a heart cell and a gut cell and a neuron don't behave the same way or sit still the same way, and getting a single system to follow all of them simultaneously, in a living animal, is most of what took years to build.
The findings that have already come out of it are the kind you don't get by studying one organ in isolation. The team found the brainstem is what redirects blood flow away from the gut and toward the brain and muscles when oxygen runs low — a whole-body decision that only shows up if you're watching the whole body. They also caught traveling waves of activity moving along the spinal cord, coming from cells called ependymal cells, specifically during quiet periods with no motor activity — a pattern that looks like it could be tied to sleep, though that's still an open thread rather than a settled answer. Separately, they found that ketamine doesn't just act on neurons the way it's usually described — it also activates the meninges, the membranes wrapping the brain and spinal cord. And cartilage cells, of all things, turned out to respond directly to cold. None of these were the headline result WHOLISTIC set out to prove; they're the kind of finding you only stumble into when you're recording everything at once instead of testing one hypothesis at a time.
The scope, for now, is a larval zebrafish — small and naturally transparent, which is exactly what makes this kind of whole-body optical recording possible in the first place. The team, working with collaborators at University College London, Virginia Tech, and Tsinghua University, is already adapting the approach for Danionella, a fish that stays transparent into adulthood, which would open the door to studying more complex, adult-level behavior with the same whole-body view. It's also worth noting what this isn't yet: a tool for mammals, or humans, whose bodies aren't optically transparent in the same way. What makes WHOLISTIC likely to spread quickly through other labs regardless is that it doesn't require exotic hardware — the microscope involved is a common type many biology labs already have, and the computational side of the method is open source. The ambition behind it is bigger than one fish: understanding a nervous system by only ever measuring the brain, when the body clearly makes plenty of its own decisions outside it, may have always been missing more than researchers realized.