MULTIPHOTON MICROSCOPY: Signaling of thousands of neurons imaged at 250 fps in 3-D

University of California Los Angeles (UCLA) physics professor Katsushi Arisaka thinks that he and his neuroscience colleagues have created the world's fastest two-photon excitation microscope for three-dimensional imaging in-vivo. The work grew from efforts to understand brain disorders. While it is possible to visualize damage resulting from stroke or cancer, disorders such as autism, schizophrenia and learning impairments show no physical signs—and suspicions that these disorders may result from intercellular miscommunication need confirmation. The researchers' collaboratively designed, noninvasive, ultra-high-speed optical microscope can record in real time the firing of thousands of individual neurons in the brain as they communicate, or miscommunicate, with each other.

The new approach overcomes limitations of calcium imaging, by capturing cell activity deep in the cortex at a high rate of speed. In fact, the search for speed drove Carlos Portera-Cailliau, assistant professor of neurology and neurobiology, to seek collaboration with Arisaka and graduate student Adrian Cheng. The researchers modified two-photon laser-scanning microscopes to image fluorescent calcium dyes inside the neurons, and came up with a way to split the main laser beam into four smaller beamlets. This spatio-temporal excitation-emission multiplexing (STEM) approach allowed them to record four times as many brain cells as their earlier version, or four times faster. In addition, they used a different beam to record neurons at different depths inside the brain, giving a 3-D effect, which had not been done previously. While most video cameras capture 30 frames per second (fps), the team is able to capture 250 fps and is working to achieve even greater speeds.

Their research appears in the journal Nature Methods.