Nicolas Pégard

Compressive light-field microscopy for 3D neural activity recording

Understanding the mechanisms of perception, cognition, and behavior requires instruments that are capable of recording and controlling the electrical activity of many neurons simultaneously and at high speeds. All-optical approaches are particularly promising since they are minimally invasive and potentially scalable to experiments interrogating thousands or millions of neurons. Conventional light-field microscopy provides a single-shot 3D fluorescence capture method with good light efficiency and fast speed, but suffers from low spatial resolution and significant image degradation due to scattering in deep layers of brain tissue. Here, we propose a new compressive light-field microscopy method to address both problems, offering a path toward measurement of individual neuron activity across large volumes of tissue. The technique relies on spatial and temporal sparsity of fluorescence signals, allowing one to identify and localize each neuron in a 3D volume, with scattering and aberration effects naturally included and without ever reconstructing a volume image. Experimental results on live zebrafish track the activity of an estimated 800+ neural structures at 100xa0Hz sampling rate.

Precise multimodal optical control of neural ensemble activity

Understanding brain function requires technologies that can control the activity of large populations of neurons with high fidelity in space and time. We developed a multiphoton holographic approach to activate or suppress the activity of ensembles of cortical neurons with cellular resolution and sub-millisecond precision. Since existing opsins were inadequate, we engineered new soma-targeted (ST) optogenetic tools, ST-ChroME and IRES-ST-eGtACR1, optimized for multiphoton activation and suppression. Employing a three-dimensional all-optical read–write interface, we demonstrate the ability to simultaneously photostimulate up to 50 neurons distributed in three dimensions in a 550u2009×u2009550u2009×u2009100-µm3 volume of brain tissue. This approach allows the synthesis and editing of complex neural activity patterns needed to gain insight into the principles of neural codes.The authors present a new approach to create and edit custom spatiotemporal neural activity patterns in awake, behaving animals with extremely high spatial and temporal precision. They present novel opsins optimized for multiphoton optogenetics.

Three-dimensional scanless holographic optogenetics with temporal focusing (3D-SHOT)

Optical methods capable of manipulating neural activity with cellular resolution and millisecond precision in three dimensions will accelerate the pace of neuroscience research. Existing approaches for targeting individual neurons, however, fall short of these requirements. Here we present a new multiphoton photo-excitation method, termed three-dimensional scanless holographic optogenetics with temporal focusing (3D-SHOT), which allows precise, simultaneous photo-activation of arbitrary sets of neurons anywhere within the addressable volume of a microscope. This technique uses point-cloud holography to place multiple copies of a temporally focused disc matching the dimensions of a neuron’s cell body. Experiments in cultured cells, brain slices, and in living mice demonstrate single-neuron spatial resolution even when optically targeting randomly distributed groups of neurons in 3D. This approach opens new avenues for mapping and manipulating neural circuits, allowing a real-time, cellular resolution interface to the brain.Optogenetics, the optical stimulation of neurons, suffers from many technical challenges that limit the number of neurons that can be excited as well as their relative positions. Here, Pégard et al. develop a method to simultaneously stimulate an arbitrary number of neurons in 3D space with single neuron resolution.

3D computer-generated holography by non-convex optimization

3D computer-generated holography uses a digital phase mask to shape the wavefront of a laser beam into a user-specified 3D intensity pattern. Algorithms take the target 3D intensity as input and compute the hologram that generates it. However, arbitrary patterns are generally infeasible, so solutions are approximate and often sub-optimal. Here, we propose a new non-convex optimization algorithm that computes holograms by minimizing a custom cost function that is tailored to particular applications (e.g.,xa0lithography, neural photostimulation) or leverages additional information like sample shape and nonlinearity. Our method is robust and accurate, and it out-performs existing algorithms.

All-Silicon Broadband Ultraviolet Metasurfaces

Featuring high photon energy and short wavelength, ultraviolet (UV) light enables numerous applications such as high-resolution imaging, photolithography, and sensing. In order to manipulate UV light, bulky optics are usually required, and hence do not meet the fast-growing requirements of integration in compact systems. Recently, metasurfaces have shown unprecedented control of light, enabling substantial miniaturization of photonic devices from terahertz to visible regions. However, material challenges have hampered the realization of such functionalities at shorter wavelengths. Herein, it is experimentally demonstrated that all-silicon (Si) metasurfaces with thicknesses of only one-tenth of the working wavelength can be designed and fabricated to manipulate broadband UV light with efficiencies comparable to plasmonic metasurface performance in infrared (IR). Also, for the first time, photolithography enabled by metasurface-generated UV holograms is shown. Such performance enhancement is attributed to increased scattering cross sections of Si antennas in the UV range, which is adequately modeled via a circuit. The new platform introduced here will deepen the understanding of light-matter interactions and introduce even more material options to broadband metaphotonic applications, including those in integrated photonics and holographic lithography technologies.

Special Section Guest Editorial: UC Berkeley Sculpted Light in the Brain 2017 debates future technologies to communicate with the brain

This article summarizes presentations at Sculpted Light in the Brain 2017.

High-speed 3D brain activity quantification with Compressive Light-Field Microscopy

We present a non-imaging light-field microscopy method for volume quantification of neural activity in scattering brain tissue. Individual neuron fluorescence is computed directly by independent component identification in the phase-space time domain, without deconvolution.