This PDF file contains the front matter associated with SPIE Proceedings Volume 12366, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Combining functional Magnetic Resonance Imaging (fMRI) with cell-type selective optogenetic stimulation offers a unique chance to dissect brain functional networks and probe causal connections. Our team employed opto-fMRI and opto-electrophysiology to map the brain circuits of the secondary somatosensory cortex (S2) in nonhuman primate brains after unilateral transfection with AAV5 and AAV9 constructs of blue light opsin ChR2 with CaMKIIa promoter, largely specific to excitatory neurons. Our results revealed that blue light stimulation of varying intensities (1, 2, 4, 8, 16, and 24 mW) in the transfected S2 hand region elicited robust Local Field Potentials (LFPs) and spiking activity. Blue laser evoked LFP power increases peaked at 16 mW. Delivery of blue laser to transfected S2 evoked robust BOLD signal changes locally and in distant cortical and subcortical brain regions, including bilateral MCC, posterior insula, thalamus, bilateral area 3b/1, and contralateral S2 cortices. As expected, green light stimulation did not produce detectable spiking and LFP activity, but it did lead to robust BOLD signal changes in both local and distant brain regions. To monitor possible heating effects from laser stimulation, we developed an MRI method that measures temperature by computing the phase information of fMRI images. We measured small temperature increases at high laser power (e.g., 24 mW delivered through a 200 μm diameter optical fiber) but not at low laser powers (1,2, 4, and 8 mW). The low power green light-associated BOLD signal changes require further elucidation but suggest some opto-fMRI findings should be interpreted with caution.

Infrared neural stimulation (INS, 1875 nm) is an emerging neuromodulation technology that holds promise for clinical application. However, little is known about its effect on excitatory and inhibitory cell types in the cerebral cortex. Here, using two-photon calcium imaging in the awake mouse somatosensory cortex, we have examined the effect of INS pulse train application on non-GABAergic (hSyn) excitatory neurons and GABAergic (mDlx) inhibitory neurons tagged with GCaMP6s. We find that each INS pulse train reliably induces a robust response in both excitatory and inhibitory neurons characterized by an initial decrease in intracellular calcium signal followed by a positive rebound; cessation of the several pulse trains leads to a large positive rebound, most prominently seen in non-GABAergic neurons. Quantification using indices of correlation, oscillation amplitude, and size of post-stimulation rebound illustrates responses are intensity-dependent and distance-dependent. Estimates of summed population response timecourses provide a potential basis for neural and hemodynamic signals described in other studies.

Implantable optical fibers have been widely used for optical neuromodulation in deep brain regions. Polymer fiber-based neural devices have natural advantages over silica fibers since their high flexibility would lead to a less inflammatory response in chronic in vivo experiments. Using three kinds of polymer materials: polycarbonate (PC), polysulfone (PSU), and fluorinated ethylene propylene (FEP), we present multifunctional soft polymer fiber (POF)-based brain implants with an Ultra-High Numerical Aperture (UHNA) and integrated Microfluidic Channels (MCs) for wide illumination and drug delivery, respectively. The flexibility of the proposed fiber devices has been found to be 100-fold reduced compared to their commercially available counterparts. Biofluids delivery can be controllably achieved over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min by the structured MCs in the fiber cladding. The illumination area of the UHNA POFs in brain phantom has been increased significantly compared with the commercially available silica fibers. A fluorescent light recording experiment has been conducted to demonstrate the proposed UHNA POFs can be used as optical waveguides in fiber photometry. The limited illumination angle of the optical fiber imposed by current technology has been enlarged by the proposed UHNA POFs and we anticipate our work to pave the way toward more efficient multifunctional neural probes for neuroscience.

Infrared neurostimulation has emerged in recent years as a promising technique for controlling neuronal activity without genetic manipulation. Having high absorption of the employed wavelengths as its fundamental mechanism, it requires implantable platforms to deliver light in brain regions deeper than the first cortical layers. Due to the spatial confinement of the stimulation, electrodes integrated in close proximity to the illumination spot are desirable to verify the effects of the stimulation by extracellular electrophysiology. Here we developed and validated in vivo a multifunctional neural interface based on a soft, biocompatible polymer optical fiber that allows simultaneous infrared neurostimulation and electrophysiology.

Cochlear Implants (CIs) are considered one of the most successful neural prostheses. Today, more than 500,000 severely-to-profoundly deaf individuals have received a CI to restore some of their hearing. However, the performance of individual users varies largely. While some patients experience a notable improvement in functional hearing, others receive little benefit from CIs. Some situations, such as noisy listening environments, tonal languages, and music perception, remain challenging for all users. Reducing interaction between neighboring CI electrode contacts and more independent stimulation channels can improve CI performance. While reducing the interaction of adjacent channels during electrical stimulation is challenging, neural stimulation with light might be a novel approach to address the problem since it can evoke responses from small populations of neurons. Optical radiation can be delivered more selectively to groups of target neurons. It is anticipated that neural prostheses with enhanced neural fidelity can be developed by using optical stimulation. Two methods for optical stimulation are currently under investigation, optogenetics and Infrared Neural Stimulation (INS). With the presentation, the efforts and advances leading to a novel cochlear implant incorporating electrical and optical stimulation are shown and discussed, including designing parameter considerations, device development, and testing prototypes.

Flexible polymer neural probes enable minimally invasive interfacing with biological tissue. The smaller mechanical mismatch between soft polymer materials and the tissue reduces inflammation response and scarring in the tissue during chronic implantation of flexible neural probes compared to those made of rigid substrates, including Silicon, Silicon Dioxide, and Silicon Nitride. We have previously demonstrated a fully flexible Parylene photonic waveguide array platform for high-resolution targeted light delivery in tissue. Parylene photonics is a novel integrated photonic platform composed of flexible, biocompatible materials with a large refractive index contrast. The core of the photonic layer is Parylene C (n = 1.639) and the cladding is PDMS (n = 1.4), both two orders of magnitude more flexible than traditional Silicon substrates. Here, we perform optogenetic stimulation experiments using Parylene photonic waveguide arrays to deliver light to the brain in a transgenic mouse line expressing ReaChr; a red-shifted opsin. In this paper, we discuss, for the first time, the application of Parylene photonic waveguides for in vivo optogenetic stimulation of neurons in rodent models, evidenced by increased neural firing following light delivery. Spike sorting was performed to isolate neural units in the vicinity of the recording electrodes, demonstrating selective neural stimulation. Parylene photonic waveguide arrays were packaged with commercially-available single mode optical fibers and laser light sources operating at 𝜆=633 nm. Implantation of the flexible waveguide arrays was achieved via attachment to a rigid shuttle using bioresorbable polyethylene glycol (PEG) coating. Post implantation, Nissl staining was used to characterize neuronal damage following insertion. Neuroinflammation was also assessed using immunofluorescence.

Optogenetics allows non-invasive control of cardiac function by inducing physiological heart distress. The main challenge for optogenetic pacing is relatively shallow light penetration into biological tissue. Recently, ChRmine was reported as an excitatory opsin that can respond to much lower light power which induces a larger cellular membrane electrical current than the previously characterized opsins. It has been shown that ChRmine expressed deep inside the mouse brain (~7 mm) sensed the external illumination leading to mouse behavior change. However, the ChRmine application for optogenetic cardiac function control has not been optimized yet. This study demonstrates the feasibility of ChRmine-mediated restorable tachycardiac pacing in Drosophila (fruit fly) hearts non-invasively and discusses the influence of different parameters of both optical settings and gene expression levels to achieve its optimal performance. custom optical coherence microscopy (OCM) was synchronized with the illumination module to monitor the dynamics of the fly heart while light pulses were applied. The quantification of cardiac function was performed by lab-developed software FlyNet 2.0+. The results demonstrate successful pacing at designed frequencies higher than the resting heart rate in ChRmine flies. Irradiance power density and pulse width were tested for minimal light power input. Illumination protocols were set up to provide pacing control. Different transcriptional activator strains were crossed in to enhance transgenic ChRmine expression. Opsin ligand concentration in Drosophila media was adjusted for saturating opsin membrane channel opening. Red light wavelengths (617 or 656 nm) were considered to promote penetration depth for optogenetic activation. This study will serve as practical guidance for performing optogenetic pacing using ChRmine opsin.

In this proceeding we discuss the recent work involving our developed optogenetic tool, where we use digital light processor (DLP) as a light-stimulation source of neuronal culture and microelectrode array (MEA) system as the sampling unit. In this work we aim at developing an integrated experimental platform which should assist in the study of the structure and the function of neuronal networks. In particular, the setup proposed in this work should serve as an optogenetic tool for in-vitro experiments, controlled by a feedback from electrophysiological signals from the network to address specific neuronal circuits. In this manuscript some of the recent results from experiments involving optical stimulation and electrophysiological recording of neuronal cultures are shown. Additionally, we have developed an AI-based model which is trained according the recorded electrophysiological signals and reproduces the functionality and the macro-structure of the culture under test. The description and some preliminary results of this model are also discussed in this proceeding.