Imagine if we could unlock the secrets of the brain's intricate wiring, revealing the very essence of what makes us human. But here's the catch: the brain's complexity has long been a puzzle too difficult to solve with existing technology. Now, a groundbreaking technique is changing the game in 3D brain imaging, and it’s nothing short of revolutionary.
Scientists at the Swiss Light Source (SLS) have achieved something remarkable: they’ve mapped a piece of brain tissue in 3D with unprecedented clarity using X-rays—all without damaging the sample. This breakthrough shatters a long-standing technological barrier that has hindered the use of X-rays in such studies. And this is the part most people miss: with the recent SLS upgrade, researchers can now image much larger brain tissue samples at high resolution, opening doors to a deeper understanding of the brain’s intricate architecture. The study, a collaboration between the Paul Scherrer Institute (PSI) and the Francis Crick Institute in the UK, is published in Nature Methods.
The brain is often hailed as the most complex biological system on Earth. Adrian Wanner, Group Leader of the Structural Neurobiology Research Group at PSI, puts it this way: “Take the liver—we know its 40 cell types, their arrangement, and their functions. But the brain? We’re still in the dark. The real difference isn’t in the cells themselves, but in how they’re organized and connected.” Wanner’s team is tackling this mystery through connectomics—the study of how neurons are wired together.
Consider this: in just one cubic millimeter of brain tissue, there are roughly 100,000 neurons connected by about 700 million synapses and 4 kilometers of ‘cabling.’ But here’s where it gets controversial: understanding this wiring is crucial for diseases like Alzheimer’s, yet its 3D complexity has been nearly impossible to study. “If you take a neural network with 17 neurons, there are more ways to connect them than atoms in the universe,” Wanner explains. “We can’t just model it—we need to measure it.”
Enter the game-changing advance by Wanner and his colleagues at SLS, in partnership with the Francis Crick Institute. Their solution? X-rays, which can penetrate millimeters or even centimeters of tissue, eliminating the need for slicing samples into thousands of thin sections—a process prone to errors and information loss in traditional volume electron microscopy.
However, X-rays come with their own challenges. The problem? Contrast. Biological tissues lack the natural contrast of, say, computer chips, where copper wires stand out against their surroundings. “When you’re dealing with proteins and lipids in a water-dominated matrix, the X-ray interaction is weak, making high resolution difficult,” explains Ana Diaz, a scientist at SLS’s cSAXS beamline.
To tackle this, researchers typically stain brain tissue with heavy metals. But here’s the kicker: these metals absorb X-rays, causing the sample to deform. Embedding materials can stabilize the tissue, but they too warp under X-ray exposure, destroying the delicate ultrastructure.
And this is where the real innovation lies: Wanner, Diaz, and their team introduced a new approach. They developed an epoxy resin—typically used in aerospace and nuclear industries—that infiltrates biological tissue while withstanding radiation. Paired with a custom stage that cools samples to -178°C using liquid nitrogen and a reconstruction algorithm to correct minor deformations, this method has achieved remarkable results.
Using this technique, the researchers studied mouse brain tissue up to 10 microns thick, achieving a 3D resolution of 38 nanometers. “This is a record for X-ray imaging of extended biological tissue,” Diaz notes. At this resolution, they could clearly identify synapses, axons, dendrites, and other neural features—matching the gold standard of volume electron microscopy but with far greater potential for scaling up.
With the SLS upgrade, the future looks even brighter. The facility now operates as a 4th-generation synchrotron, boasting up to 100 times more coherent X-ray flux. “This means we can image samples faster or tackle larger volumes,” Diaz explains. “The possibilities are immense.”
The study’s publication coincides with a major milestone: in July 2025, the first X-rays post-upgrade were seen at the cSAXS beamline. Now that technical barriers have been overcome, the stage is set to explore larger brain tissue samples in 3D at high resolution.
But here’s a thought-provoking question for you: As we unlock the brain’s secrets, how will this knowledge reshape our understanding of consciousness, disease, and even what it means to be human? Share your thoughts in the comments—let’s spark a conversation!
