Neuronal signals can vary on millisecond timescales, with communicating neurons often separated by hundreds of microns. Imaging such fast dynamics over extended volumes presents a challenge for standard fluorescence microscopes. For example, a new generation of genetically encoded voltage indicators are becoming available whose response times are on the order of milliseconds. To address this challenge, we propose to develop a new type of microscope that can perform near- 1kHz-rate high resolution volumetric imaging over 1mm x 1mm x 0.2mm scales. Our proposed solution, called Multi-Z confocal microscopy, is based on two key ideas. First, it combines high-NA detection with low-NA illumination. The former leads to high signal collection efficiency; the latter leads to axially extended illumination over an extended range of Z depths. Second, it detects multiple signals from this extended depth range using multiple confocal pinholes that are axially distributed. The pinholes are reflecting, so that signal rejected by one pinhole is sent to the next pinhole, and so forth. In this manner, no signal is lost, and signal collection efficiency remains high. Two versions of our microscope will be developed, based on line-scan and sheet-scan illumination. The former provides better optical sectioning and will be designed for calcium imaging. The latter provides much higher speed (near kHz-rate) and will be designed for voltage imaging. In contrast to conventional line-scan or light-sheet microscopes, our lines and sheets are oriented parallel to the optical axis rather than perpendicular to the axis. The versatility of both versions of our microscope will be augmented with the addition of optogenetic stimulation and combined confocal reflectance contrast. We have enlisted the help of Drs. Alberto Cruz-Martin (BU, Biology) and Xue Han (BU, BME), who both specialize in in-vivo mouse imaging and have expertise in the genetic or viral delivery of novel probes, animal preparation, head fixation, behavior protocols, etc.. For voltage imaging, we will test a state-of-the-art indicator called SomArchon1 (provided by the Dr. Ed Boyden lab). The ability to image large sample volumes at 1kHz rates is of general applicability and can be broadly impactful. Our goal will be to demonstrate the effectiveness of our Multi-Z microscopy technique by performing calcium and voltage imaging over entire populations of neurons in behaving mice.
We propose to develop a new light efficient microscope that can perform large-scale volumetric imaging at near-1kHz rates with high contrast. We will apply this to demonstrate voltage sensing of neuronal ensembles across large scales in behaving mice with a new genetically encoded indicator.
