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09

2024

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Voltage imaging new tool! The Wang Kai team of the Chinese Academy of Sciences has developed a new three-dimensional voltage imaging technology, which greatly improves the throughput of voltage imaging!

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Voltage imaging measures neuronal activity directly, promising the understanding of information processing between individual neurons and populations. However, due to the simultaneous requirements of high imaging speed and signal-to-noise ratio, large volume coverage and low photobleaching rate, imaging voltage on large neuron populations has always been a challenge.

On October 8, 2024, the Wang Kai team of the Center for Excellence and Innovation in Brain Science and Intelligent Technology of the Chinese Academy of SciencesNature Methods（IF=36）Published online entitled“Volumetric voltage imaging of neuronal populations in the mouse brain by confocal light-field microscopy”The research paper,The studyA confocal light field microscope was developed that exceeds traditional speed and noise performance limitations by combining a speed-enhanced camera, a fast and powerful scanning mechanism, laser speckle noise cancellation, and optimized light efficiency.

In this way, the study simultaneously recorded more than 300 spike neurons with a diameter of 800 µm and a thickness of 180 µm in the mouse cortex for more than 20 minutes. By integrating spatial and voltage activity profiles, the researchers mapped the three-dimensional neural coordination patterns of the brains of awake mice. The method is robust for regular applications of volume voltage imaging.

Optical imaging can non-invasively monitor the activity of dense and large neuronal populations, with cell-type specificity and broad molecular sensitivity, through a variety of functional indicators. However, the temporal resolution of light recordings is often limited by indicator dynamics and physiological dynamics. Voltage imaging, designed to accurately report the membrane potential of neurons, has the potential to preserve many of the advantages of optical recording while breaking its traditional speed limit. It offers hope for a better understanding of information processing in neural circuits. Despite the promise and advantages of voltage imaging, voltage imaging faces challenges due to the requirements for imaging speed one to two orders of magnitude higher than calcium imaging.

Two-photon microscopy can penetrate deep into brain tissue and volumetric calcium imaging has been demonstrated in large neuronal populations. However, the imaging speed is too slow to be directly extended to voltage imaging. In order to improve the imaging speed and throughput, the space-time multiplexing technology of two-photon excitation focus is introduced; however, synchronous recording is currently realized on one plane, which limits them to further improve throughput compared with volume imaging.Two-photon microscopy is also optimized for longitudinal voltage imaging, by enlarging the volume to reduce photobleaching. However, due to its serial scanning scheme, the high imaging speed required compromises the number of neurons that can be recorded simultaneously.

In order to improve imaging throughput, a multi-planar confocal microscope has been developed, which can simultaneously image densely labeled neurons on four different planes. However, its relatively small field of view (FOV) limits the number of neurons that can be recorded simultaneously. In addition, although the thin section microscope has been developed to perform high-throughput voltage imaging in zebrafish brains, it is not suitable for imaging in mouse brains. Despite these advances, high-throughput recording of voltage signals from bulk populations of neurons in the mouse brain remains a huge challenge, hindering their application to the study of larger, more complex neural networks.

In this work, the author developed a confocal light field microscope that can image a volume with a diameter of 800 μm and a depth of 180 μm at 400Hz, and the noise performance is close to the theoretical limit. This allowed the Voltron to simultaneously perform voltage imaging of approximately 1000 neurons in the mouse primary visual cortex.In this imaged population, more than 300 neurons exhibited sufficient signal-to-noise ratio to record their peak activity. Approximately 1/3 of these neurons responded to visual stimuli, exhibiting typical directional and directional selectivity, indicating successful optical recording of sensory evoked spikes at the population level.This high-throughput volume voltage imaging lasts for tens of minutes. It can analyze rapid temporal coordination between 3D distributed neuron populations and identify different spatial patterns of positively and negatively correlated neuron populations.Overall, confocal light field microscopy represents a valuable advance in meeting the increasing demand for in vivo voltage recording within larger neuronal populations and 3D volumes.

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