This PDF file contains the front matter associated with SPIE Proceedings Volume 12829, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Infrared neural stimulation is an optical stimulation methodology which delivers brief trains of small heat pulses leading to neuronal response modulation. In the past several years, we have tailored this method for stimulation of focal activation of single cortical columns in ultrahigh field MRI in the monkey brain, revealing functional networks of mesoscale sites at brainwide scale. The network activations, which span sensory , motor, cognitive, and limbic areas of the brain, offer novel understanding of network architecture in the primate brain. These findings have important implications for precision medicine, brain machine interface design, and the organization of primate intelligence.

The talk will guide the audience through the experimental validation of an implantable stimulation microdevice that is able to record single unit activity and stimulate neurons by infrared light. Recent results aiming to characterize the cell-specific cortical response to continuous-wave and pulsed-wave infrared light in rodents will also be presented in detail.

Infrared neural stimulation (INS) is an optical method, label-free, not cell-type specific, that can modulate neural activity with a high spatial resolution. Recent studies have shown that it can also trigger calcium signaling in non-excitable cells such as astrocytes. Astrocytes participate in neural communication, and play a key role in many neurodegenerative diseases in a calcium-dependent way. As infrared triggers calcium signaling in both astrocytes and neurons, it appears as a good technique to explore the influence of astrocytes in neuronal communication and pathology. However, questions remain on how the same infrared paradigm affect both astrocytes and neurons, and how their respective infrared-induced activities are affecting each other. In this work, we show infrared-induced calcium signals in both astrocytes and neurons simultaneously in mice spinal cord slices using two different genetically encoded calcium indicators. Preliminary results tend to demonstrate that infrared exposure induces intercellular calcium waves in the astrocytic network. The influence of astrocytic signaling on neuronal activity is also investigated.

Infrared neural stimulation (INS) is a label-free optical neurostimulation technique that offers increased spatial specificity over traditional neurostimulation techniques. Initial studies on calcium signaling in the rat cortex demonstrated a multipart response indicating INS induces signaling in both neurons and astrocytes. We further characterized this response in cortical astrocytes in vitro, showing that different INS pulse structures induce varying levels of calcium signaling in these cells. Here we evaluate the effects of varying laser pulse parameters in cultured cortical neurons. We hypothesize that reducing the pulse duration will lead to lower stimulation thresholds. We show that INS induces a calcium response in vitro cortical neurons dependent on the total radiation exposure and time, indicating that the peak power of the infrared pulse influences INS efficacy. In conclusion, INS efficacy in vitro depends on the laser pulse width parameters.

Neuromodulation serves as a cornerstone for brain sciences and clinical applications. Recent research indicates that midinfrared stimulation (MIRS) causes non-thermal modulation of brain functions. Current understanding of its mechanism hampers the routine application of MIRS. In this study, we examined how MIRS with 34.88THz modulated the sensorimotor transformation from neuronal signals to behavior performances in awaking-behaving pigeons. We applied MIRS and electrical stimulation to the pretectal nucleus lentiformis mesencephali (nLM), an essential retinorecipient structure in the pretectum, and compared their effects on the visual-guided eye movement optokinetic nystagmus. We found that MIRS altered eye movements by modulating a specific gain depending on the strength of visual inputs, in a manner different than the effect of ES. Simultaneous extracellular recordings and stimulation showed that MIRS could either excite and inhibit the neuronal activity in the same pretectal neuron depending on its ongoing sensory responsiveness levels in awake-behaving animals. These modulations increased with the size of MIRS output powers. Computational simulations suggest a potential mechanism underlying these effects in which MIRS preferentially enhances the resonance of a carbonyl group of the potassium channel, which critical to the action potential generation, thereby altering neuronal responses to sensory inputs and as a result guiding behavior. Our findings suggest that MIRS could be a promising approach for modulating neuronal functions for brain research and treating neurological diseases.

Photovoltaic arrays implanted under the degenerated retina can convert light into pulsed electric current to stimulate the second-order retinal neurons for restoration of sight. Images captured by a camera are projected onto the retina from augmented-reality glasses using pulsed near-infrared light. Patients with such implants demonstrated consistent form perception with a letter acuity closely matching the 100um pixel size. Using current steering and 3-dimensional electrodes, pixels as small as 20um can stimulate the inner retina, providing grating acuity matching the pixel pitch, up to the natural resolution limit of 28um in rats. Optimization of these implants for human retina is in progress.

The cochlear implant uses electrical stimulation to activate spiral ganglion neurons to restore hearing. Despite its efficiency, electrical stimulation activates a broad region of the cochlea, thereby reducing cochlear implant performance. Optogenetic stimulation, which uses light to stimulate neurons, has the potential for precise neural activation. In this study, we compared the spread of activation and channel interaction arising from multi-channel electrical or optogenetic stimulation in the mouse cochlea. Our findings revealed that optogenetic stimulation resulted in a 2-fold narrower spread of activation. Also, optogenetics stimulation resulted in significantly lower channel interaction with adjacent channels and had a 13-fold less relative influence on threshold compared to simultaneous electrical stimulation (P<0.05), demonstrating the potential advantages of optogenetic stimulation in cochlear implant technology.

Retina prosthesis are implantable devices stimulating diseased retina of individuals to restore vision. New technologies are needed for precise and non-genetic retinal stimulation. Here we report the development of different photoacoustic platforms for retina stimulation. First, we demonstrated that a tapered fiber based photoacoustic emitter consistently evokes action potentials with response patterns that are sensitive to the stimulus waveform using patch clamp recordings in a retinal explant. Second, toward the implantable retinal prothesis, we confirmed successful blind retina stimulation through a PDMS-based photoacoustic film safely. These results show the potential of using optoacoustic signal to drive activity in photoreceptor-damaged retinas.

Traditional visual cortical prosthetics based on electrical stimulation have induced percepts low in spatial resolution and devoid of rich visual features. Here, using pulsed infrared neural stimulation (INS), a method that evokes perceived phosphenes in alert monkeys, we have developed an approach with the submillimeter spatial precision needed for interfacing with cortical columns. We delivered INS through a linear optic fiber array in anesthetized cat visual cortex and monitored effects by optical imaging in contralateral visual cortex. INS modulation of response to ongoing visual oriented gratings produced enhanced responses in orientation-matched domains and reduced response in non-matched domains. This oriented response is a higher order, integrated effect. Controls included dynamically applied speeds, directions and patterns of multipoint stimulation. This provides groundwork for a conceptually and technologically new generation of BMI, one based in the columnar code of visual featural perception.

Cortical surface stimulators are an application of µLEDs allowing spatiotemporal stimulation of genetically targeted populations of neurons in the cerebral cortex. To address challenges with the spatial resolution and density of stimulation sites, a high-precision 100-pixel µLED device was developed. The device consists of a 10 x 10 matrix addressed array of GaN µLEDs with 200 µm spacing, which emit blue light at 450 nm through a sapphire substrate. In-vivo experiments in the auditory cortex of ChR2-expressing transgenic mice have shown consistent multi-unit activity with low µLED drive current and low lateral spread of activation.

Remote and minimally invasive neuromodulation is a promising approach in the advent of clinical applications. Ultrasound-triggered mechanoluminescent technology offers a promising approach for achieving remote brain modulation. However, its application has thus far been limited to shallow brain depths due to challenges related to low sonochemical reaction efficiency and restricted photon yields. Here we report a self-amplifying mechanoluminescent nanotransducer based on cascade reactions in liposomes to achieve efficient light emission upon ultrasound stimulation. As a result, blue light was generated under ultrasound stimulation with subsecond response latency. Leveraging the high energy transfer efficiency of focused ultrasound in brain tissue and the high sensitivity to ultrasound of these mechanoluminescent nanotransducers, we are able to show efficient photon delivery and activation of ChR2 expressing neurons in both the superficial motor cortex and deep ventral tegmental area (VTA). Our novel liposome nanotransducers enable minimally invasive deep brain stimulation for behavioral control in animals via a flexible, mechanoluminescent sono-optogenetic system.

For photovoltaic biointerfaces AgBiS2 quantum dots (QDs) offer favorable properties such as two-orders of magnitude higher absorption coefficient at near-infrared (NIR) in comparison with silicon for ultra-thin and flexible device formation and non-toxic material content. We demonstrate AgBiS2 QD based photovoltaic biointerface that stimulates cells within the spectral tissue transparency window by using NIR light (λ = 780 nm). The biointerface converts light energy below the ocular safety limit of light exposure to safe capacitive photocurrents that leads to reproducible action potentials on primary hippocampal neurons with high success rates.

Neural circuitry and information transfer in the brain are poorly understood, necessitating new technologies for studying brain function and treating neurological disorders. Photoacoustic stimulation, using fiber-based optoacoustic emitters (FOE), allows precise neural stimulation. We investigated the role of the photothermal effect and found that pure photothermal neuromodulation requires significantly higher energy dosage compared to photoacoustic stimulation. Pharmacological inhibition revealed the importance of elastic modulus and ruled out a significant thermal effect from FOE. We also identified the involvement of Piezo1, TRPC1, and voltage-gated T-type calcium channels. These findings improve our understanding of photoacoustic neuromodulation and its potential clinical applications.

The striatum is a critical brain area in the control and initiation of movement. Recently, the activity in striatal spiny projection neurons (SPNs) has also been shown to be different for different gross body movements, suggesting that activity in striatum is movement-specific and can bias which movements animals will perform. However, these larger actions were performed with different body parts, and may reflect somatotopy more than action specificity, and therefore it is unclear how fine the granularity of movement-specificity is. To probe this, we have developed an isometric force task that requires no overt movement, and imaged and analyzed the activity in striatum during learning and execution. From the optically recorded neural activity combined with simultaneous behavior, we trained classifiers that could predict action from activity across days, revealing stable ensembles encoded specific actions. Finally, using targeted two-photon stimulation, we perturbed small sub-populations of these ensembles in closed-loop during behavior, seemingly leading to small, but perceptible, changes in action.

Modulation of brain arteriole diameter is critical for maintaining cerebral blood pressure and controlling regional hyperemia during neural activity. However, studies of hemodynamic function in health and disease have lacked a method to control arteriole diameter independently with high spatiotemporal resolution. Here, we describe an all-optical approach to manipulate and monitor brain arteriole contractility in 3-dimensions using combined in vivo two-photon optogenetics and imaging. The expression of the red-shifted excitatory opsin, ReaChR, in vascular smooth muscle cells enabled rapid and repeated vasoconstriction controlled by brief light pulses. Two-photon activation of ReaChR using a spatial light modulator produced highly localized constrictions when targeted to individual arterioles within the neocortex. Wide-field photoactivation with an LED constricted all arteries in the imaging field leading to widespread reductions in blood flow. We demonstrate the utility of this method for examining arteriole contractile dynamics and creating transient focal blood flow reductions. Additionally, we show that optogenetic constriction can be used to reshape vasodilatory responses to sensory stimulation, providing a valuable tool to dissociate blood flow changes from neural activity. We also demonstrate the confound in fluorescence imaging caused by changes in vessel diameter and discuss potential remedies.

Cardiomyocytes form an electrically coupled syncytium, enabling synchronized action potential wavefronts. Optogenetics facilitates the study of cardiac excitation wavefronts in vivo and in vitro. We demonstrate a laser-optical system utilizing computer-generated holograms to stimulate and inhibit light-sensitive human stem-cell-derived cardiomyocytes, allowing e.g. non-destructive modeling of myocardial scarring and exctiation wavefront control. With rapid frame rates upt to 1.7 kHz, our system spatially positions multiple foci or complex illumination patterns, achieving defined 3D-distributed excitation wavefronts for quickly changing stimulation protocols. High-speed video microscopy assesses contractions in samples. We show successful coupling of cardiomyocyte contraction to optical stimulation and stimulation-wavefront shape-dependencies, paving the way for patient-specific disease modeling using multi-photong holographic light shaping and red-shifted opsins in 3D cardiac organoids.

Recent studies have highlighted the importance of understanding the architecture and function of microvasculature, and dysfunctions of these microvessels may underlie neurodegenerative disease. Here, we utilized a highly precision ultrafast laser-induced photothrombosis (PLP) method to occlude single capillaries and then quantitatively studied effects on vasodynamics and surrounding neurons. Analysis of the microvascular architecture and hemodynamics after single-capillary occlusion reveals distinct changes upstream vs downstream branches, which shows rapid regional flow redistribution and local downstream BBB leakage. Focal ischemia via capillary occlusions surrounding labeled target neuron induced dramatic and rapid lamina-specific changes in neuronal dendritic architecture. The adaptive changes in neuronal function networks were correlated to the degree of ischemia core. Further, we find that micro-occlusion at two different depths within the same vascular arbor results in distinct effects on flow profiles in layerin layer 2/3 vs layer 4. The current results raised the possibility that relatively greater impacts on microvascular function contribute to neuronal network function.

Photoacoustic (PA) neural modulation has gained attention for its non-genetic, precise, and minimally damaging properties. Existing PA methods relay on thermal expansion of the absorber/ elastomer matrix. Usually, a visible or near-infrared (NIR) laser is used to excite the electronic transition of the absorber. Here, we present a mid-infrared photoacoustic (MIPA) emitter through vibrational excitation in polydimethylsiloxane (PDMS). A transparent film with 37.5 times enhancement of PA performance compared to carbon nanotube based PA emitter is obtained due to bypass the thermal conduction process. Both wide-field (100μm) and single cell MIPA neural stimulation were achieved and validated through calcium imaging.