This conference presentation was prepared for the Optogenetics and Optical Manipulation conference at SPIE BiOS, 2023.

Functional Magnetic Resonance Imaging (fMRI) with optogenetic neural manipulation is a powerful tool that enables brain-wide mapping of functional networks. To achieve flexible manipulation of neural excitation throughout the mouse cortex, we incorporated spatiotemporal programmable optogenetic stimuli generated by a digital micromirror device into an MR scanner via an optical fiber bundle. This approach offered versatility in space and time in planning the photostimulation pattern, combined with in situ optical imaging and cell-type or circuit-specific genetic targeting in individual mice. Brain-wide functional connectivity was successfully obtained by fMRI with optogenetic stimulation of atlas-based cortical regions. fMRI combined with flexible optogenetics opens a new path to investigate dynamic changes in functional brain states in the same animal.

Our perception of the environment relies on the efficient propagation of neural signals across cortical networks. During the time course of a day, neural responses fluctuate dramatically as the state of the brain changes to possibly influence how electrical signals propagate across neural circuits. Here, we used multielectrode laminar arrays to reveal that brain state strongly modulates the propagation of neural activity across the layers of early visual cortex (V1). We optogenetically induced synchronized state transitions within a group of neurons and found that although optogenetic stimulation elicits stronger neural responses during wakefulness relative to rest, signals propagate only weakly across the cortical column during wakefulness. In contrast, the light-induced population activity vigorously propagates throughout the entire cortical column during rest even when neurons are in a desynchronized wake-like state prior to light stimulation.

Recent developments in optogenetics allow for quick and minimally invasive methods of mapping functional brain circuits in animal models. DeepLabCut (DLC), a toolbox for markerless pose estimation, offers the ability to track features in three-dimensions. We demonstrate a hybrid method utilizing DLC and light-based, optogenetic motor mapping to concurrently localize motor representations of multiple limbs in mice. Our results suggest that behaviorally-relevant, motor movements involving multiple limbs reside in overlapping cortical representations of each limb. Applications of this technique include characterizing recovery of finer, articulated movements of affected limbs after stroke, or mapping brain network activity during naturalistic behavior.

Parvalbumin interneurons (PV-INs) are the largest subpopulation of GABAergic neurons. Recent evidence suggests transcallosal projections of PV-INs within primary motor, visual and auditory cortices. Whether transcallosal PV-INs feature prominently, and the extent to which their local influence affects global excitatory activity is unknown. We created a novel imaging system and mouse line for all-optical neuronal probing and readout to map local and global interactions between excitatory neurons and PV-INs over the cortex in awake mice. PV-INs extend inhibitory influences spanning several mm over the cortex and into more distant, ipsilateral regions. Further, we show region-specific interhemispheric inhibitory influences of PV-INs.

Optogenetics has become a ubiquitous tool for studying and controlling the electrical activity in cardiac cells. In this work, we demonstrate optogenetics stimulation using a microLED array. A microLED array with 256 individually addressable switchable pixels (Qubedot GmbH) is integrated in a widefield imaging setup. Localized and patterned stimulation are both demonstrated showing that intensity is sufficient to pace cardiac bodies and bioartificial cardiac tissues. Dynamic control of each individual microLED pixel permits wave steering of calcium waves in a cardiomyocyte syncytium. Our system provides a compact and easy to use platform for optogenetic stimulation of various cardiac models.

In conventional electrical visual prostheses, current spread produces diffuse patches of response, whereas optical stimulation of gold nanorods bound to genetically modified photoreceptors has recently shown great promise. Here we demonstrate that Retinal Ganglion Cells (RGCs) can be optically stimulated directly via gold nanorods without the need for genetic modification. Single-cell responses from explanted rat retinae exposed to gold nanorods were recorded by patch clamping. Near infrared laser pulses of 100 and 500 µs evoked robust stimulation, whilst longer 200 ms pulses were biased towards OFF-type inhibition. Differential modulation of ON- and OFF-type RGCs is essential for future high-acuity prostheses.

We have developed dual-color Drosophila melanogaster (fruit fly) optogenetic system, based on transgenic line containing two opsins, ChR2 and NpHR2.0, and a customized Optical Coherence Microscopy (OCM) hardware. The initial experiments demonstrated feasibility of increasing the heart rate following the designed blue light pulses and inducing the restorable heart arrest caused by prolonged red light illumination in the same animal. The heart function control was achieved non-invasively. We have optimized the OCT system parameters to minimize the detrimental effects on live animals to ensure longitudinal studies on Drosophila models of human heart arrhythmia disorders.

High precision neuromodulation is a powerful tool for fundamental studies in neuroscience and potential treatments for neurological disorders. Recently photoacoustic stimulation has been showed as a non-genetic high precision method in vitro and in vivo. Here we report new insights on cellular mechanism of photoacoustic stimulation. Specifically, we showed the direct involvement of mechanosensitive ion channels during fiber based photoacoustic stimulation using sonogenetics. In addition, we also report the development of a miniaturized fiber stimulator integrating with electrodes for simultaneous stimulation and recording. Such devices are used for closed-loop stimulation in deep brain stimulation as a potential clinical application.

Brain stimulation using electrical, magnetic, and ultrasound offer different spatiotemporal specificities for treating neurological and neuropsychiatric disorders. Towards developing a precision method of targeting specific functional circuits in humans, we have applied infrared neural stimulation to human cerebral cortex intra-operatively. Brief pulse trains of infrared laser light, applied with a fine fiber optic, excites neural activity at submillimeter scale as assessed by intrinsic signal optical imaging. The response is intensity-dependent, non-damaging below threshhold, and activates local cortical networks similar to that in nonhuman primates (NHP). We suggest INS is a promising tool for precision medicine.

Conventional electrically-stimulating retinal prostheses exhibit low stimulus resolution due to current spread, which precludes high-acuity vision. Optogenetic neuromodulation techniques offer a high stimulus resolution, and are uniquely well-suited to exploit the optical accessibility of the retina. However, such techniques often exhibit a low stimulus response rate, and may risk phototoxic damage during chronic applications. The present study uses combined optogenetic and electrical co-stimulation to reduce the current threshold requirements, thereby limiting current spread. A time delay in the electrical stimulus was found to improve stimulation efficacy, and response probability was increased during co-stimulation at higher pulse train frequencies.

This conference presentation was prepared for the Optogenetics and Optical Manipulation conference at SPIE BiOS, 2023.

Sensory, motor, and cognitive operations involve the coordinated action of large neuronal populations. To facilitate the study of how neural circuits are formed, function and evolve, there is a pressing need for tools that allow the measurement and manipulation of neuronal firing patterns from large populations of neurons. Imaging and stimulating neurons optically, rather than electrically, holds tremendous promise due to the cellular selectivity and high spatial and temporal resolutions of the technique. However, available technologies still fail to provide holistic insight into how patterns of electrical activity in the brain give rise to thought, sensation, and action. The most capable all-optical systems incorporate Computer-Generated Holography (CGH) using Spatial Light Modulators (SLMs) that sculpt light to address ensembles of neurons simultaneously and with single-cell precision. A primary bottleneck of holographic tools is the slow switching speed (~3ms) of commercially available SLMs based on liquid crystal technology, which constrains the bandwidth and throughput of the optical neural interface. We propose high-speed Microelectromechanical Systems (MEMS) based SLMs capable of switching faster than 100 μs, enabling a significant increase in throughput, and opening the door to optical neural interfaces with the temporal precision to mimic naturally occurring neuronal signaling.

We demonstrate the monolithic integration of both orange and blue Organic Light-Emitting Diodes (OLEDs) on Complementary Metal–Oxide–Semiconductor (CMOS) chips featuring four shanks (length 8 mm, width 150 μm) and a total of 1024 OLED pixels each 20x20 µm2. Pixel yield and device brightness were maximized through systematic optimization of the aluminum contact pad. These improvements enable the first in vivo single-OLED / single-neuron optogenetic stimulation with CMOS-based brain implants, thus bridging a current technology gap for controlled and specific optical excitation at the cellular level.

This conference presentation was prepared for the Optogenetics and Optical Manipulation 2023 conference at SPIE BiOS, SPIE Photonics West 2023.