A First Look Through the Cortical Layers of the Awake Brain
Three-dimensional rendering of a sequence of 450 lateral three-photon images acquired with 2-μm increment from the visual cortex (layer 1 on the left to the subplate on the right). Green color represents GCaMP6s signal, and magenta color represents label free THG signal generated in the blood vessels and myelin fibers in the white matter. Scale bar, 100 μm. Credit: Murat Yildirim et. al.
Just like doctors seek to scan deeper into the body with sonograms, CT and MRI, and astronomers seek to look farther out into the universe with space-based telescopes, adaptive optics and different wavelengths of light, neuroscientists pursue new ways to watch brain cells at work deep inside the brain. Three-photon microscopy recently emerged to give them a deeper look at brain cells than ever before. Now, based on a substantial refinement of the technology, scientists at MIT have conducted the first-ever study of stimulated neural activity in an awake mouse through every visual cortex layer and notably the mysterious “subplate” below.
“By optimizing the optical design and other features for parameters for making measurements in the live brain, we were able to actually make novel discoveries that were not possible before,” said co-corresponding author Mriganka Sur, Newton Professor of Neuroscience in the Picower Institute for Learning and Memory. The paper’s co-lead authors are postdocs Murat Yildirim and Hiroki Sugihara. The other corresponding author is Peter So, professor of mechanical engineering and biological engineering.
“The concept has existed, but the question was how do you make it work,” Sur said.
Plunge all the way through the visual cortex from the surface to the subplate beneath in this movie made using a new three-photon microscope developed at the Picower Institute for Learning and Memory. Green indicates neural activity while magenta labels blood vessels and white matter fibers. Credit: Murat Yildirim et. al.
In the study, published in Nature Communications, the team showed that as mice watched visual stimuli, their human observers could measure patterns of activity among neurons in all six layers of visual cortex and the subplate, providing new data about their role in how mammals process vision. Moreover, through a series of careful experiments, the researchers were able to show that the light they sent in, as well as the light that came back out, neither damaged, nor even altered, the cells they measured.
In all, the paper describes a new three-photon microscope optimized to deliver rapid, short, low-power pulses of light capable of reaching deep targets without causing any functional disturbance or physical damage, and then to detect the resulting fluorescence emitted by cells with high efficiency to produce images with sharp resolution and a fast frame rate.
“We were motivated to show what we could do with three-photon microscope technology for an animal in an awake condition so we could ask important questions of neuroscience,” Yildirim said. “You could think you have the best microscope in the world, but until you ask those questions you don’t know what results you are going to get.”
This article has been republished from materials provided by the Picower Institute for Learning and Memory. Note: material may have been edited for length and content. For further information, please contact the cited source.
Reference: Yildirim, M., Sugihara, H., So, P. T. C., & Sur, M. (2019). Functional imaging of visual cortical layers and subplate in awake mice with optimized three-photon microscopy. Nature Communications, 10(1), 177. https://doi.org/10.1038/s41467-018-08179-6