Achieved for the first time! Congratulations to Chinese scientists

Chinese scientists develop "miniaturized three-photon microscope" to achieve "deep brain imaging" of mice for the first time

The human brain contains tens of billions of neurons and trillions of synapses. Its extremely complex and precise connections and interactions in structure and function are the material basis for the emergence of consciousness and thought. Developing research tools for analyzing brain connection maps and functional dynamic maps is a core direction of brain science programs in various countries. On the 24th, the research team of Cheng Heping and Wang Aimin of Peking University published a latest research result online in the journal Nature Methods: a miniaturized three-photon microscope weighing only 2.17 grams can directly penetrate the cerebral cortex and corpus callosum, and for the first time realize the functional imaging of the entire cerebral cortex and hippocampal neurons of freely behaving mice, opening up a new research paradigm for revealing the neural mechanisms in the deep structures of the brain.

The picture shows a mouse wearing a miniaturized three-photon microscope (provided by the research team)

Zhao Chunzhu, a member of the research team and a postdoctoral fellow at Peking University's School of Future Technology, said that the hippocampus is located below the cerebral cortex and corpus callosum, and plays an important role in memory consolidation, spatial memory, and emotional encoding. However, since brain tissue, especially the corpus callosum, has high scattering properties for propagating light beams, breaking through the corpus callosum to achieve direct imaging of the deep brain has long been a great challenge for neuroscientists. Previously, the internationally known miniaturized multiphoton microscopes were unable to penetrate the entire cortex and directly image the hippocampus without loss.

It is reported that the newly developed miniaturized three-photon microscope has broken through the previous imaging depth limit in one fell swoop: the microscope's excitation light path can penetrate the mouse cerebral cortex and corpus callosum, enabling direct observation and recording of the mouse hippocampal CA1 subregion, and the maximum imaging depth of neuronal calcium signals can reach 1.2 mm, and the vascular imaging depth can reach 1.4 mm.

This breakthrough in imaging depth is due to the microscope's new optical configuration design, which has doubled the efficiency of collecting scattered fluorescence. In addition, the microscope can also observe neuronal functional activities for a long time without obvious photobleaching and photodamage.

The picture shows the use of a miniaturized three-photon microscope to image the structure of the mouse cerebral cortex and hippocampal CA1 subregion (provided by the research team)

Academician Cheng Heping, director of the National Center for Biomedical Imaging Sciences at Peking University, said that using the microscope, the team studied the coding mechanism of neurons in the sixth layer of the parietal cortex of mice during the process of grasping jelly beans and found that about 37% of the neurons became active before the grasping action and were most active during the grasping action, and about 5.6% of the neurons became active after the grasping action.

"This shows that different neurons are involved in encoding at different stages, and also preliminarily demonstrates the application potential of miniaturized three-photon microscopes in brain science research." Cheng Heping said that this imaging technology provides an important tool for humans to explore the mysteries of the brain more deeply and reveal the brain's functional connection map.

In 2017, Cheng Heping's team successfully developed the first generation of miniaturized two-photon microscopes, which captured dynamic images of the activity of neurons and synapses in the cerebral cortex of mice during free behavior. In 2021, the team developed a second-generation miniaturized two-photon microscope that expanded the imaging field of view by 7.8 times and has the ability to obtain three-dimensional imaging of functional signals of thousands of neurons in the cerebral cortex.