A next-generation spatial light modulator for mapping of neural networks

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Boulder Nonlinear Systems (BNS) and Prof. Edward Boyden’s Synthetic Neurobiology Group at the Massachusetts Institute of Technology (MIT) Media Lab propose to develop a new liquid crystal spatial light modulator (SLM) capable generating high resolution holograms to overcome the “imaging gap” that currently divides cellular-level optogenetic techniques and whole brain techniques to improve functional mapping/dissection of complex brain networks. This effort builds upon the successful Phase I effort, in which new modeling techniques were developed to guide this Phase II hardware development. Whole brain imaging techniques, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), are powerful tools for visualizing neural activity and connections, respectively, across regions of the brain, however their spatial resolution is limited to the millimeter scale and therefore they cannot resolve individual neurons. Meanwhile, optical imaging and photostimulation provide complimentary tools that allow not only direct imaging of neurons and their action potentials, but also the ability to directly stimulate action potentials, all with single cell resolution over small sub-millimeter volumes. This disconnect between the length-scales of whole brain imaging and optical techniques, the so-called “imaging gap”, is one of the critical barriers to understanding how coherent states arise from the activity of neuronal ensembles. In Phase I, BNS and MIT worked with Zemax, Inc. to develop a new optical modeling capability able to simulate holographic microscopy with pixelated phase-modulating SLMs. Using this new modeling capability, BNS identified the barriers to closing the imaging gap by holographically addressing a 1×1×0.5 mm3 volume of tissue. Specifically, we identified the need for a new SLM that optimally balances the trade-offs between addressable field of view, resolution, and switching speed and for corrective optics that undo the lateral chromatic dispersion experienced by the ultrashort laser pulses used for deep tissue microscopy. In Phase II, BNS will develop a next-generation SLM consisting of a 12 V 1280×1280 pixel backplane designed to achieve or exceed 1 ms switching speed. This device will be delivered via custom corrective optics into a commercial microscope at MIT for demonstration of holographic interrogation of neuronal ensembles over a 1×1×0.5 mm3 volume of tissue.