Fiber-optic technology revolutionized the telecommunications industry and may soon do the same for brain research.
A group of researchers from Washington University in St. Louis in both the McKelvey School of Engineering and WashU Medicine have created a new kind of fiber-optic device to manipulate neural activity deep in the brain. The device, called PRIME (Panoramically Reconfigurable IlluMinativE) fiber, delivers multi-site, reconfigurable optical stimulation through a single, hair-thin implant.
“By combining fiber-based techniques with optogenetics, we can achieve deep-brain stimulation at unprecedented scale,” said Song Hu, a professor of biomedical engineering at McKelvey Engineering, who collaborated with the laboratory of Adam Kepecs, a professor of neuroscience and of psychiatry at WashU Medicine.
Optical fibers power the field of optogenetics by using light-sensitive ion channels to control neurons in the deep brain, turning the cells on or off. But conventional fibers have limits: a single fiber can deliver light to only one destination.
In order to understand complex brain circuits, researchers need to deliver light to hundreds, if not thousands, of different points in the brain, and it’s far too invasive to add a thousand optical fibers to handle that task.
But what if that single fiber could direct light into a thousand different directions, like a controllable disco ball in the brain?
That’s precisely what the group set out to achieve. Hu’s team, including postdoctoral researcher and first author Shuo Yang, who led the development of the PRIME technology, used ultrafast-laser 3D microfabrication to inscribe thousands of grating light emitters (acting as mirrors) into a fiber the width of a human hair. Meanwhile, Kepecs’ team, including graduate student and co-first author Keran Yang and postdoctoral senior scientist Quentin Chevy, validated the technology by studying its neural modulation technique in freely behaving animal models.
These results, published in Nature Neuroscience, represent both a neurotechnology innovation and a fabrication breakthrough.
“We’re carving very small light emitters into very small pieces,” Shuo Yang said. “Very small meaning tiny mirrors that are 1/100th the size of a human hair.”
The PRIME fiber connects light to neurons across different brain regions. In proof-of-concept studies in animal models, Keran Yang used PRIME to drive activity in subregions of the superior colliculus, a hub for sensorimotor transformation, and systematically induced freezing or escape behavior, depending on the reconfigurable light pattern.
“This kind of tool lets us ask questions that were impossible before,” Keran Yang said. “By precisely shaping light in both space and time, we can start to see how neighboring circuits interact and how patterns of activity across the brain give rise to behavior.”
“This device significantly expands what’s possible in experimentally linking distributed neural activity to perception and action,” Kepecs added. “It brings a new level of access to probe neural circuit function.”
Looking ahead, the group aims to extend PRIME into a bidirectional interface by combining optogenetics with photometry to allow researchers to stimulate and record brain activity at the same time.
“This is just the start of an exciting journey,” Hu said. “Our ultimate goal is to make PRIME wireless and wearable. The less cumbersome the tool, the more natural the data they can get from freely behaving subjects that are not bogged down in wires.”
---------------
Yang S, Yang K, Chevy Q, Kepecs A, Hu S. Laser-engineered PRIME fiber for panoramic reconfigurable control of neural activity. Nat Neurosci (2025). DOI: https://doi.org/10.1038/s41593-025-02106-x
This research was supported by funds provided by the McDonnell Center for Systems Neuroscience at Washington University in St. Louis (to S.Y.), discretionary research funds from Washington University in St. Louis (to S.H.), and the NIH Director’s Pioneer Award (DP1MH140021 to A.K.).
Journal
Nature Neuroscience