Fiberoptic Microscopy For Optical Imaging Of Brain Function And Neural Photostimulation

For the last30years, optical imaging of brain function has been developing rapidly and is playing an important role in the field of bran research. Optical imaging of brain function has formed a rich and various research field and attracts more interests. Because of the advantages of multimodal combination and high spatial-temporal resolution, optical imaging becomes an irreplaceable brain research technology.Cortical optical imaging on awake and freely moving animals is one of the key development tendency in brain functional imaging. For a long time, one of the aims in brain research is to address the advanced nervous activity such as perception, motor control, learning and memory, and the underlying neuroscience mechanism. Therefore, researcher need a new technology that supports brain functional optical imaging on freely moving animals which can be combined with behavioral study.In this study, facing the technical challenges of brain functional optical imaging on freely moving animals, we proposed an idea of an extendable fiberoptic microscopy system that can perform brain functional optical imaging and neural photonstimulation. We developed a fiberoptic microscopy which can detect the change of hemoglobin concentration, blood flow and neuron membrane potential of the cortex on freely moving animals and simultaneously activate the targeted cortical neural network by photonstimulation. The main results of this thesis are as follows:Fiberoptic microscopy for optical imaging of brain function. We designed the extendable optical framework based on imaging fiber bundle. A multi-channel image acquisition module based on liquid crystal tunable filter and fiber-coupled multi-spectrum illuminating module is implemented. We also developed a head-mounted microscopy which can support adjustable field of view (FOV) and high resolution. The spatial resolution is up to5μm and the FOV is up to5mm in diameter. The aberrations of the GRIN lens are analyzed in ZEMAX and further improvement is proposed to reduce the field curvature. Based on fast Fourier transform we designed an band-stop filter to remove the cellular structure of the fiber bundle. We also designed the normalized laser speckle contrast analysis for the speckle images of fiber bundle. Finally, we tested the stability of this system during the animals’freely movements. Self-built spatial light modulation system for neural photonstimulation based on digital micromirror devices (DMD). To sufficiently modulate the pixels of the imaging fiber bundle we designed the projection optical path from the DMD to the surface of fiber bundle. The output beam from the GRIN lens is tested. We analyzed the major parameters of the output beam. The power of the beam is up to13.3mW/mm2in the centre and about5mW/mm2in average, which could reach the threshold of photonstimulation. The area that the DMD can modulate basically matches the FOV. Finally we analyzed the light intensity attenuated of the output beam during the propagation in the brain tissue.Voltage sensitive dye (VSD) imaging on the bilateral cortical hemisphere in vivo. According to the VSD imaging, we designed the dual-fiber-bundle-based microscopy and improved the fiberoptic system. The system can perform VSD imaging of the bilateral cortex and photonstimulation on freely moving animals. We also observed the bilateral sensory responses activated by hindlimb electric stimulation in mice and found that cortical spreading depression (CSD) could modulate the bilateral response balance. Further more, we discussed the possible underlying mechanism.Testing and application of the fiberoptic microscopy system.1) We performed multi-spectrum optical intrinsic signal (OIS) imaging and laser speckle blood flow imaging on this system and monitored the cortical hemodynamic parameters during CSD in freely moving rat. We analyzed the changes of hemoglobin concentration and blood flow and observed significant differences between anesthesia and freely moving states.2) We tested photonstimulation function of the system to activate the cortex of freely moving mice and detected the response by OIS imaging after stimulation.3) By using VSD imaging of the system, we recorded the bilateral neural activities in awake mice during resting state. We analyzed the correlation of bilateral sensory areas of the cortex and observed significant differences in the correlation of the two hemisphere between awake and anesthesia states.