WASHINGTON -- Researchers have developed an endoscope as thin as a human hair that can image the activity of neurons in the brains of living mice. Because it is so thin, the endoscope can reach deep into the brain, giving researchers access to areas that cannot be seen with microscopes or other types of endoscopes.
"In addition to being used in animal studies to help us understand how the brain works, this new endoscope might one day be useful for certain applications in people," said Shay Ohayon, who developed the device as a postdoctoral researcher in James DiCarlo's lab at the Massachusetts Institute of Technology. "It could offer a smaller, and thus more comfortable, instrument for imaging within the nasal cavity, for example."
The new endoscope is based on an optical fiber just 125 microns thick. Because the device is five to ten times thinner than the smallest commercially available microendoscopes, it can be pushed deeper into the brain tissue without causing significant damage.
In The Optical Society (OSA) journal Biomedical Optics Express, the researchers report that the endoscope can capture micron-scale resolution images of neurons firing. This is the first time that imaging with such a thin endoscope has been demonstrated in a living animal.
"With further development, the new microendoscope could be used to image neuron activity in previously inaccessible parts of the brain such as the visual cortex of primate animal models," said Ohayon. "It might also be used to study how neurons from different regions of the brain communicate with each other."
Acquiring images from a fiber
The new microendoscope is based on a multimode optical fiber, which can carry different multiple beams of light at the same time. When light enters the fiber, it can be manipulated to generate a tiny spot at the other end, and can be moved to different positions on the tissue without moving the fiber. Scanning the tiny spot across the sample allows it to excite fluorescent molecules used to label neuron activity. As the fluorescence from each spot travels back through the fiber, an image of neuron activity is formed.
"To achieve scanning fast enough to image neurons firing, we used an optical component known as a digital mirror device (DMD) to quickly move the light spot," said Ohayon. "We developed a technique that allowed us to use the DMD to scan light at speeds up to 20 kilohertz, which is fast enough to see fluorescence from active neurons."
