Development of fast multi-photon microscope for kHz-imaging of in vivo neuronal network activity

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Two-Photon microscopy (TPM) enables high-resolution, 3-D imaging of the brain. TPM is already widely used for the study of degenerative diseases like Alzheimer´s and dementia. However, in order to study neural activity and disease-related modifications of whole neural networks, the images must be obtained at high frame rates. The synaptic information transport occurs at the millisecond and sub-millisecond timescale, so kHz frame-rates are desired. This was already achieved with one-photon microscopy (FIRE microscope) in the group of Prof. Bahram Jalali at the University of California Los Angeles (UCLA). The aim of this DFG research proposal is the development of a fast TPM system, thus enabling much higher imaging depth in tissue at high resolution. By employing fast lasers in combination with a time-encoded imaging technique, pixel rates of 100 MHz and frame rates of 1.5 kHz at 256x256 pixels shall be reached. In order to accomplish this, the signals will be generated using advanced modulation techniques paired with the detection of the two-photon signals by highly sensitive photomultiplier tubes (PMT). PMTs have time-resolutions of sub-ns and are thus also suited for fluorescence lifetime imaging (FLIM) in parallel. This would also lead to a dramatic increase of FLIM imaging speeds by the proposed system. Over all, the envisaged multi-modal microscope would yield a speed enhancement of more than a factor of 10 as compared to conventional TPM systems and is thus suited for application in imaging of neural networks in vivo at time-resolutions intrinsic to axon potential spiking events.