202 research outputs found
Holographic Photolysis for Multiple Cell Stimulation in Mouse Hippocampal Slices
Background: Advanced light microscopy offers sensitive and non-invasive means to image neural activity and to control signaling with photolysable molecules and, recently, light-gated channels. These approaches require precise and yet flexible light excitation patterns. For synchronous stimulation of subsets of cells, they also require large excitation areas with millisecond and micrometric resolution. We have recently developed a new method for such optical control using a phase holographic modulation of optical wave-fronts, which minimizes power loss, enables rapid switching between excitation patterns, and allows a true 3D sculpting of the excitation volumes. In previous studies we have used holographic photololysis to control glutamate uncaging on single neuronal cells. Here, we extend the use of holographic photolysis for the excitation of multiple neurons and of glial cells. Methods/Principal Findings: The system combines a liquid crystal device for holographic patterned photostimulation, high-resolution optical imaging, the HiLo microscopy, to define the stimulated regions and a conventional Ca 2+ imaging system to detect neural activity. By means of electrophysiological recordings and calcium imaging in acute hippocampal slices, we show that the use of excitation patterns precisely tailored to the shape of multiple neuronal somata represents a very efficient way for the simultaneous excitation of a group of neurons. In addition, we demonstrate that fast shaped illumination patterns also induce reliable responses in single glial cells
Multimodal wide-field two-photon excitation imaging: characterization of the technique for in vivo applications
We report fast, non-scanning, wide-field two-photon fluorescence excitation with spectral and lifetime detection for in vivo biomedical applications. We determined the optical characteristics of the technique, developed a Gaussian flat-field correction method to reduce artifacts resulting from non-uniform excitation such that contrast is enhanced, and showed that it can be used for ex vivo and in vivo cellular-level imaging. Two applications were demonstrated: (i) ex vivo measurements of beta-amyloid plaques in retinas of transgenic mice, and (ii) in vivo imaging of sulfonated gallium(III) corroles injected into tumors. We demonstrate that wide-field two photon fluorescence excitation with flat-field correction provides more penetration depth as well as better contrast and axial resolution than the corresponding one-photon wide field excitation for the same dye. Importantly, when this technique is used together with spectral and fluorescence lifetime detection modules, it offers improved discrimination between fluorescence from molecules of interest and autofluorescence, with higher sensitivity and specificity for in vivo applications
Comparison of nematic liquid-crystal and DMD based spatial light modulation in complex photonics
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial
light modulators (SLMs) for applications in photonics, primarily due to their modulation rates,
which exceed by several orders of magnitude those of the already well-established nematic liquid
crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and
diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when
applied to light control in complex environments, including an aberrated optical system, a highly
scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only
modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all
considered regime
Spatial and Spectral Coherent Control with Frequency Combs
Quantum coherent control (1-3) is a powerful tool for steering the outcome of
quantum processes towards a desired final state, by accurate manipulation of
quantum interference between multiple pathways. Although coherent control
techniques have found applications in many fields of science (4-9), the
possibilities for spatial and high-resolution frequency control have remained
limited. Here, we show that the use of counter-propagating broadband pulses
enables the generation of fully controlled spatial excitation patterns. This
spatial control approach also provides decoherence reduction, which allows the
use of the high frequency resolution of an optical frequency comb (10,11). We
exploit the counter-propagating geometry to perform spatially selective
excitation of individual species in a multi-component gas mixture, as well as
frequency determination of hyperfine constants of atomic rubidium with
unprecedented accuracy. The combination of spectral and spatial coherent
control adds a new dimension to coherent control with applications in e.g
nonlinear spectroscopy, microscopy and high-precision frequency metrology.Comment: 12 page
Mapping nonlinear receptive field structure in primate retina at single cone resolution
The function of a neural circuit is shaped by the computations performed by its interneurons, which in many cases are not easily accessible to experimental investigation. Here, we elucidate the transformation of visual signals flowing from the input to the output of the primate retina, using a combination of large-scale multi-electrode recordings from an identified ganglion cell type, visual stimulation targeted at individual cone photoreceptors, and a hierarchical computational model. The results reveal nonlinear subunits in the circuity of OFF midget ganglion cells, which subserve high-resolution vision. The model explains light responses to a variety of stimuli more accurately than a linear model, including stimuli targeted to cones within and across subunits. The recovered model components are consistent with known anatomical organization of midget bipolar interneurons. These results reveal the spatial structure of linear and nonlinear encoding, at the resolution of single cells and at the scale of complete circuits
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