A tiny juvenile fish. That’s what’s at the center of a big effort to image the brain of a vertebrate organism like never before. Spencer Smith, PhD, assistant professor in the Department of Cell Biology and Physiology and the UNC Neuroscience Center at the UNC School of Medicine, is part of an international team that hopes to create a new imaging system to study individual neurons in high resolution throughout the entire brain of a freely moving vertebrate.
This sort of technological feat has never been accomplished.
“We will image neural activity in high resolution, enough to see individual neurons, as if we’re reading the zebrafish’s mind while it’s completely unrestrained and performing natural movements and behaviors,” Smith said. “There will be no surgery, nothing tethered to the animals.”
“This is basic science, for sure, but if we’re successful, we hope our work will allow us and other scientists to gain insights that will have broader applicability to human health down the road.”
Smith, who is also a member of the Carolina Institute for Developmental Disabilities, added, “This is basic science, for sure, but if we’re successful, we hope our work will allow us and other scientists to gain insights that will have broader applicability to human health down the road.”
To bring this unique project to life, the team received a $900,000 grant from the Human Frontier Science Program (HSFP), an organization that funds basic scientific research through the financial support of 15 countries, including the United States.
A New Imaging Frontier
We all know about MRIs, PET scans, and CT scans. These important diagnostic tools can provide images that tell us a lot about human biology, disease, and to an extent what’s happening in the human brain. But they can’t be used to study what specific kinds of neurons are doing, what roles these neurons play in various neurological conditions, or even which neurons are important for typical behaviors and where the cells are located. For that, scientists need technology that can focus in on individual neurons, and it would be best if scientists could focus on individual neurons throughout the brain while the animals are freely moving about. That kind of microscope doesn’t exist.
Smith and his colleagues – German scientist Benjamin Judkewitz, PhD, of Charité Berlin & Humboldt University, and Spain’s Ruben Portugues, PhD, at the Max Planck Institute of Neurobiology – are taking on this challenge. They’re building a new kind of microscope with a wide enough field of view to image nearly the entire brain of a juvenile zebrafish while the fish is living its life. That is, the researchers hope to create real-time high-resolution visualizations of individual neurons firing throughout the brain of the transparent fish while it’s hunting for prey, swimming back and forth, darting here and there.
“That’s the high bar,” Smith said. “The low bar would be to track neuronal activity throughout most of the brain while the fish is stationary or moving slowly. Both are difficult challenges, but tracking the fish during fast motion will be quite a trick and will require the expertise of the entire team. That’s why this grant is a good fit for the HFSP, which funds high-risk, high-reward international and interdisciplinary projects that are, frankly, difficult to get funded otherwise.”
Smith’s lab at UNC is building the optics – the microscope they hope is capable of capturing images of individual neurons firing throughout the juvenile zebrafish’s brain while it navigates its world. One fish is four millimeters long. Therefore, it can live in a small dish, swim freely, and hunt for even tinier critters. Still, optics large enough for this sort of experiment have never been made before, which is why Smith’s lab is custom-designing the optics and having the parts custom-made. He is also creating a new kind of scanning engine to rapidly image the moving fish.
The other scientists are working on the fast-tracking system so that the microscope can capture high resolution images of individual neurons across the brain even while the fish moves quickly through three dimensions. Smith’s European colleagues will also conduct the actual experiments on the zebrafish.
A New Imaging Future
The grant is for three years. By the end, the scientists hope to have a new piece of technology that they and other scientists can use to gain insights into how vertebrates process visual information while moving to achieve a goal, such as hunting prey. Down the line, it’s conceivable that Smith and his colleagues could extend this kind of technology to other organisms and answer various questions about brain functions of other model animals, including other complex vertebrate organisms.
“Scientists have developed computer models of neural activity related to visual processing and motor activity.”
This work builds upon Smith’s other projects – the creation of imaging systems that can image multiple brain areas of a mouse. The limitation of this innovation is that the mouse must be stationary. Therefore, there are a limited number of experiments related to visual processing that Smith and others can perform.
“Scientists have developed computer models of neural activity related to visual processing and motor activity,” Smith said. “But if we can’t measure neural activity during an animal’s natural behavior, then we can’t completely validate those models.”
He added, “This won’t happen soon, but we’re already thinking about optically monitoring individual neural activity throughout the brains of freely moving rodents without any instrumentation on their heads or tethers,” Smith said. “From a physics standpoint, there’s no reason why we couldn’t do that. If we can, then we could learn a lot about brain function related to behaviors and even neurological conditions. This zebrafish research is a big, complicated first step in that direction.”