“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.
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.”