Tag Archives: Optics

Injectable optoelectronics with wireless control

The ability to wirelessly control neural circuitry has been a long-standing goal in neuroscience. Recent advances have put this goal in site using optogenetic approaches. In 2011, multiple groups presented the first attempts at making wireless light delivery application for optogenetics (Iwai et al., 2011; Wentz et al., 2011). These advances, however, were constrained to particular environments or apparatuses to power the devices. The radiofrequency power scavenging approach presented in Kim et al., 2013 frees the experimenter from these constraints. In the recent report, the Bruchas (Washington University at St. Louis) and Rogers (University of Illinois at Urbana-Champaign) labs present ultrathin, microscale optoelectronics and sensors that can be used for the optogenetic manipulations. Unlike other wireless approaches this system can be used with any behavioral apparatus or paradigm, which should allow researchers to explore more complex behaviors while perturbing neural circuitry.

The wireless µILED devices can incorporate wired cellular-scale components that can all be inserted into the brain using a combination of a silk-based biodissolvable adhesive (Kim et al., 2010) and an injection needle similar in concept to electrode delivery presented previously (Kozai and Kipke, 2009). These components include, but are presumably not limited to, temperature sensors, electrodes for … Continue reading

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Combining up to 16 individually adjustable electrodes with optical stimulation in mice

Simultaneously recording and perturbing neural circuits with millisecond-scale temporal precision is a cornerstone of optogenetics research, but the methods for doing so are not always easily accessible. A variety of labs have come up with ad hoc ways to incorpoate fiber optic cables into existing multielectrode implant designs. Very few of these solutions have been documented or published, even though this is becoming an increasingly popular technique. Fortunately, the Moore Lab at Brown University recently published a manuscript on their “flexDrive,” a lightweight implant that can hold multiple fiber optic cables and 16 electrodes (Voigts et al., 2013).

The basic concept is similar to the designs from Matt Wilson’s lab involving a ring of electrodes, each driven by its own screw (Kloosterman et al., 2009). But it introduces a novel spring-based drive mechanism that significantly reduces both the weight of the implant and the time it takes to build. In contrast to previously published designs (Anikeeva et al., 2011), each of the electrodes on the flexDrive can be moved independently—a feature that is essential for maximizing the number of well-isolated single units that can be recorded.

The authors have put a lot of effort into making their designs as accessible … Continue reading

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Thermal and optical characterization of a micro-LED probe

Over the last few years, there has been a significant drive to improve light sources for in vivo optogenetic control of neuronal activity. In particular, recent work has focused on the design and microfabrication of compact devices that exhibit multiple optical stimulation sites in order to gain control over closely spaced regions within the brain (see here a list of posts related to this). In a recent Optics Letters paper, McAlinden, Massoubre and colleagues presented a novel microprobe device with integrated light sources. The probe produces sufficient light for optogenetic stimulation without causing significant heating in local brain tissue. The device (see figure below) consists of a 100 µm wide, 50-100 µm thick probe with 5 individually addressable microLEDs. Each LED has a diameter of 40 µm, but can be reduced to 10 µm if higher density probes are required. The LED probes are p-n diodes made from quantum well structures using GaN on Sapphire material. The spacing between LEDs is fixed to allow 1mm of neural tissue to be addressed.

The light output from the LEDs was measured, with scattering and absorption accounted for by experimentally measuring the light transmitted through varying thicknesses of brain tissue. The recorded light … Continue reading

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Holographic optogenetic control of retinal neural activity

Sensory information is typically represented in distributed patterns of activity across large populations of neurons. Therefore, many emerging neuro-photonic applications, such as optogenetic retinal prostheses require systems capable of delivering intense, parallel and dynamic light patterns. Such a system will ideally allow photo-control with single-cell selectivity of large neural populations expressing optogenetic probes, rather than nonspecific flashed illumination of the whole population (as provided by many current optogenetic light delivery systems). In a recent Nature Communications report, Reutsky-Gefen, Shoham and colleagues demonstrate holographic optogenetic control of retinal neural activity which is shown to provide rapid cellular-resolution, massively parallel excitation across macroscopic (millimeter-scale) coverage areas. The study illustrates that diffractive wavefront shaping (holographic) tools offer a powerful modality for dynamic patterned photo-stimulation as they naturally combine the high intensity, efficiency and resolution that are characteristic of sequential laser deflectors (like acousto-optical deflectors) with the simultaneous scan-less parallel illumination of multiple locations of microdisplay array projectors, but without their respective limitations. Holographic tools were previously shown to allow structured excitation of dendritic arbors and neurons using neurotransmitter photolysis, as well as two-photon optogenetic stimulation of proximal neurons in brain slices.

The study’s main goal was to develop a prosthetic system that would … Continue reading

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A multimodal micro-optrode

Microelectrodes are powerful tools for in vivo functional studies. However they are limited in the number of information they provide. In January 2011, LeChasseur and colleagues (Nature Methods 8(4), 319-325, 2011) developed a glass microelectrode which was integrating an optical micro-channel for light delivery and fluorescence collection. The probe serves for specific cellular fluorescence optical detection and activation/inhibition. In a recent issue of PLOS ONE, Dufour et al. extended the multimodal aspect of this micro-optrode. They introduce a, aluminum-coated, fibre optic-based glass microprobe (diameter ≤ 10 μm) with multiple electrical and optical detection capabilities. The probe enables optical separation from individual cells in transgenic mice expressing multiple fluorescent proteins in distinct populations of neurons within the same deep brain nucleus. It also enables color conversion of photoswitchable fluorescent proteins, which can be used for post-hoc identification of the recorded cells and finally it enables dual electrical recordings. Figure 1 shows a representation of the microp-optrode and the modalities described in this paper.

These modalities are in addition to the calcium monitoring and optogenetic cellular activation previously reported (Nature Methods 8(4), 319-325, 2011). In this study, two different excitation sources and detection pathways were used simultaneously to differentiate two different populations … Continue reading

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The optopatcher: an electrode holder allowing the insertion of an optical fiber into a patch pipette

In order to perform simultaneous intracellular recording and light stimulation of a single neuron, two separate positioning systems are often needed (one to position the recording electrode, one to position a waveguide near the recorded neuron). More sophisticated solutions for single neuron photostimulation involve light patterning techniques which are not suited for deep in vivo recordings. Katz et al. came up with a simple and affordable solution for this problem, by designing a patch pipette holder containing an additional port for the insertion of an optical fiber into the pipette.

This device, which they called “OptoPatcher” allows whole cell patch-clamp recording simultaneously with direct projection of light from the recording pipette. The holder spares the use of an additional manipulator and, importantly, enables accurate, stable and reproducible illumination. Moreover, the presence of the bare fiber within an aqueous solution instead of the brain can prevent tissue damage due to heating of the brain. In addition, replacement of standard pipettes is done as easily as with the available commercial holders.

The OptoPatcher was used successfully in vivo for intracellular recordings from different cortical layers in the motor cortex of transgenic mice expressing channelrhodopsin-2 under the Thy1 promoter and it was also … Continue reading

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Micro-electrocorticogram electrodes for simultaneous recording and optical stimulation

Wen Li’s group at Michigan State University recently presented preliminary results on the development of an epidural micro-electrocorticogram (μECoG) array combining microelectrodes and light emitting diodes (LEDs) for optical neural stimulation. This work follows-up on a new line of research aiming at providing μECoG arrays with versatile optical stimulation capabilities (see for example the work of Ledochowitsch et al). The “Opto-μECoG” arrays developped in Wen Li’s group were especially designed to address three major limitations of current designs, in particular the limited cortical area and spatial resolution available for optical stimulation. The key features of these Opto-μECoG arrays are the following:

Untethered system: integration of surface mounted μ-LED light sources (220 × 270 ×50 μm3, wavelength peak at 460nm, Cree® TR2227TM) on the Opto-μECoG array allows the possibility to achieve a truly untethered system. Maximized target cortical area available for optical stimulation: optically transparent indium tin oxide (ITO) [2] epidural electrodes of the Opto-μECoG array allow maximum exposure of the target cortical area for optical stimulation. Maximized spatial resolution of optical stimulation: the embedded light sources, placed on top of the ITO electrodes, were preciously arranged based on a recent study of the optimal spacing of subdural, epidural, and scalp … Continue reading

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A multimodal microimplant for combined light/liquid delivery and multi-site electrical recording

As optogenetic neuronal control strategies develop and get widely adopted in neurobiology labs, the demand for devices allowing combined light delivery and electrophysiological recording is growing. These devices, commonly called opto-electrodes or optrodes, already exist under a wide variety of forms, from the simple home made single optical fiber + single electrode to more complex microfabricated multi-fiber/multi-electrode systems. In the past years, Zhang et al. integrated an optical fibre in a Utah Array, and NeuroNexus assembled an optical fiber on their standard silicon shaft. Other groups implemented waveguides directly into the optrode fabrication process: Cho et al. integrated a microstructured SU-8 waveguide on the shaft of a Michigan Probe and the group of Ed Boyden integrated 12 silicon oxynitride waveguides on silicon shafts (paper1, paper2). Royer et al. in the Buszaki lab managed to establish silicon based shaft arrays with integrated optical fibers.

In a recent paper published in “Lab on a Chip”, the Stieglitz and Lüthi labs introduced a novel optrode which also comprises a microfluidic channel for liquid delivery at the tip of the probe. This channel can be used for example to inject a solution containing a virus right under the waveguide tip and around the electrical … Continue reading

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A 3D multiwaveguide array for delivering light to multiple brain circuits

The ability to deliver light into the brain for the purpose of controlling neural activity or other biological processes, optogenetics, has opened up new frontiers in both basic neuroscience and neuroengineering. One arena of great activity is in the use of microbial opsins such as channelrhodopsins, halorhodopsins, and archaerhodopsins to make neurons activatable or silenceable by light, thus enabling assessment of the causal contribution of specific neurons, brain regions, and neural pathways to normal and abnormal behaviors and neural computations. To date, numerous in vivo studies have used optical fibers, and fiber-electrode hybrids, to deliver visible light into brain targets in which neurons express opsins, but an optical fiber can target just a single region. An implantable probe capable of delivering light to arbitrary points in a 3-dimensional volume would enable more versatile optical control, opening up the ability to deliver patterned light to manipulate neural activity in distributed brain circuits.

The Boyden lab recently developed a linear probe comprising a set of integrated microwaveguides running in parallel to each other, microfabricated on a single substrate and capable of delivering light independently to multiple brain targets along the probe axis. In a paper published in Optics Letters, they now extend … Continue reading

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3D waveguide array for optogenetic neuronal stimulation

Numerous applications enabled by optogenetic tools require the delivery of different light profiles within tissue. In some instances, wide-field illumination is needed to blanket a region of a specific brain layer, while cell body-size beams are necessary in other cases to achieve highly-selective localized stimulation; in addition, spatiotemporal patterning or multi-level access of light may be incorporated. In a recent paper published in Biomedical Optics Express, Abaya, et al. presented a novel device structure that facilitates three-dimensional deep-tissue light penetration with capabilities for simultaneous spatiotemporal modulation with different wavelengths. This device consists of > 1 mm length needle-shaped waveguides that circumvent intrinsic tissue absorption and scattering. This array can be adapted to a wide variety of illumination systems (e.g., microscope, μLED arrays, optical fibers, collimated beams, spatial light modulators) and can potentially facilitate the advancement of a broad range of applications utilizing optical neural stimulation.

The waveguide array is micromachined from fused silica/quartz wafers, which are transparent to visible and near-infrared wavelengths. First, bevel blades are used with a dicing saw to create arrays of pyramids as tips for the array. Next, the shanks are formed by dicing down material in between the pyramids to produce waveguides having a pyramidal … Continue reading

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