Optogenetics in neural systems

Chemical imaging for biological systems: techniques, AI-driven processing, and applications

Visualizing the chemical compositions of biological samples is pivotal to advancing biological sciences, with the past two decades witnessing the emergence of innovative chemical imaging platforms such as single-molecule imaging, coherent Raman scattering microscopy, transient absorption microscopy, photothermal microscopy, ambient ionization mass spectrometry, electrochemical microscopy, and advanced chemical probes. These technologies have enabled significant breakthroughs in diagnosing pathological transitions, designing targeted therapies, and understanding drug resistance mechanisms. Recent advancements in resolution, contrast, sensitivity, and speed have transformed the field, with techniques like fluorescence, infrared absorption, and Raman scattering being widely applied across diverse biological domains. This review provides a comprehensive overview of the evolution and current state of chemical imaging technologies, coupled with systematic analyses of data processing workflows, including pre-processing, machine learning-assisted pattern extraction, and neural network-based predictions. Artificial intelligence (AI) and machine learning-assisted imaging are transforming chemical imaging through key advancements such as improved resolution and sensitivity via noise reduction techniques, enhanced data analysis (e.g., spectral unmixing, pattern recognition), automated feature extraction using neural networks, real-time processing via high-performance cluster, and data fusion across optical platforms. These innovations are significantly advancing both current applications and the future development of chemical imaging techniques in biomedical research. However, several critical challenges remain, including the scarcity of high-quality training datasets, limited generalizability across different instruments and experimental conditions, high computational costs, challenges in output interpretability and trust, and the lack of standardized validation protocols across different approaches. Looking ahead, the integration of bioimaging into cell biology, lipid research, tumor studies, microbiology, neurobiology, and developmental biology is anticipated to expand its impact, aided by interdisciplinary expertise in biochemistry, physics, and optical engineering. These developments promise unprecedented resolution and speed, facilitating high-speed, high-resolution imaging of living systems, with applications leading to discoveries such as biomarkers for cancer aggressiveness and drug resistance. Moreover, the miniaturization and commercialization of imaging platforms are broadening accessibility, enabling on-site clinical investigations and in vivo measurements, underscoring the transformative potential of chemical imaging in advancing biological science and medical research.

Flexible modeling of large-scale neural network stimulation: Electrical and optical extensions to The Virtual Electrode Recording Tool for EXtracellular Potentials (VERTEX)

BACKGROUND

Computational models that predict effects of neural stimulation can serve as a preliminary tool to inform in-vivo research, reducing costs, time, and ethical considerations. However, current models do not support the diverse neural stimulation techniques used in-vivo, including the expanding selection of electrodes, stimulation modalities, and stimulation protocols.

NEW METHOD

We developed several extensions to The Virtual Electrode Recording Tool for EXtracellular Potentials (VERTEX), the MATLAB-based neural stimulation tool. VERTEX simulates input currents in a large population of multi-compartment neurons within a small cortical slice to model electric field stimulation, while recording local field potentials (LFPs) and spiking activity. Our extensions enhance this framework with support for multiple pairs of parametrically defined electrodes and biphasic, bipolar stimulation delivered at programmable delays. To support the growing use of optogenetic approaches for targeted neural stimulation, we introduced a feature that models optogenetic stimulation through an additional VERTEX input function that converts irradiance to currents at optogenetically responsive neurons. Finally, we added extensions to allow complex stimulation protocols including paired-pulse, spatiotemporal patterned, and closed-loop stimulation.

RESULTS

We demonstrated these novel features using VERTEX's built-in functionalities, with results consistent with other models and experimental work.

COMPARISON WITH EXISTING METHODS

Unlike other tools, our extensions enable both electric field and optogenetic stimulation, provide a range of open- and closed-loop protocols, and offer flexible settings within a large-scale cortical network of neurons with realistic biophysical properties.

CONCLUSIONS

Our extensions provide an all-in-one platform to efficiently and systematically test diverse, targeted, and individualized stimulation patterns.

Small form factor implantable neural probe with efficient flip chip µLED for in vivo optogenetics

Optogenetics is a widely used tool to dissect neural circuits with optical stimulation, but it requires that light is delivered to photosensitive neurons inside the brain. Implantable neural probes with microscale LEDs (µLEDs) are an emerging approach to delivering light to the brain with superior light output control. However, approaches to integrate µLEDs in neural probes depend on complex fabrication processes. Here, we developed an implantable small form factor neural probe that integrates highly efficient commercial flip chip µLEDs using only standard lithography processes in silicon and a custom automated LED mounting approach with custom 3D-printed tools on a pick-and-place machine. The probe has a cross-sectional area under 0.013 mm2 but can output up to 2.5 mW of optical power with an irradiance of 175 mW/mm2. Due to the high plug efficiency of the LED, the neural probe can perform stimulation protocols up to 20 Hz and 80% duty cycles without surpassing estimated hotspot temperature elevations above 1 ºC. The neural probes were validated in vivo, with brain activity in the motor cortex of transgenic mice being reliably modulated by pulsed light emitted from the probe.

Using DeepLabCut-Live to probe state dependent neural circuits of behavior with closed-loop optogenetic stimulation

BACKGROUND

Closed-loop behavior paradigms allow for real-time investigation of state-dependent neural circuits underlying behavior. However, studying context-dependent locomotor perturbations is challenging due to limitations in molecular tools and techniques for real-time manipulation of spinal circuits.

NEW METHOD

We developed a novel closed-loop optogenetic stimulation paradigm that leverages DeepLabCut-Live pose estimation to manipulate primary sensory afferent activity at specific phases of the locomotor cycle in mice. A compact DeepLabCut model was trained to track hindlimb kinematics in real-time and integrated into the Bonsai visual programming framework. This system enabled LED triggered photo-stimulation of sensory neurons expressing channelrhodopsin based on user-defined pose-based criteria, such as stance or swing phase.

RESULTS

Optogenetic activation of nociceptive TRPV1+ sensory neurons during treadmill locomotion reliably evoked paw withdrawal responses. Stimulation during the stance phase generated a brief withdrawal and impacted the duration of the following swing phase. Stimulation during the swing phase increased the height of paw withdrawal during swing and reduced the duration of the following stance phase.

COMPARISON WITH EXISTING METHODS

This method allows for high spatiotemporal precision in manipulating spinal circuits based on locomotor phase. Unlike previous approaches, this closed-loop system accounts for state-dependent nature of sensorimotor responses, enabling controlled, real-time modulation of locomotion.

CONCLUSIONS

Integrating DeepLabCut-Live with optogenetics provides a powerful tool for dissecting the context-dependent role of sensory feedback and spinal interneurons in locomotion. This technique opens new avenues for uncovering the neural substrates of state-dependent behaviors and has broad applicability for studies of real-time closed-loop manipulation based on pose estimation.

Genetics-Based Targeting Strategies for Precise Neuromodulation

Genetics-based neuromodulation schemes are capable of selectively manipulating the activity of defined cell populations with high temporal-spatial resolution, providing unprecedented opportunities for probing cellular biological mechanisms, resolving neuronal projection pathways, mapping neural profiles, and precisely treating neurological and psychiatric disorders. Multimodal implementation schemes, which involve the use of exogenous stimuli such as light, heat, mechanical force, chemicals, electricity, and magnetic stimulation in combination with specific genetically engineered effectors, greatly expand their application space and scenarios. In particular, advanced wireless stimulation schemes have enabled low-invasive targeted neuromodulation through local delivery of navigable micro- and nanosized stimulators. In this review, the fundamental principles and implementation protocols of genetics-based precision neuromodulation are first introduced.The implementation schemes are systematically summarized, including optical, thermal, force, chemical, electrical, and magnetic stimulation, with an emphasis on those wireless and low-invasive strategies. Representative studies are dissected and analyzed for their advantages and disadvantages. Finally, the significance of genetics-based precision neuromodulation is emphasized and the open challenges and future perspectives are concluded.

Optogenetics-Inspired Nanofluidic Artificial Dendrite with Spatiotemporal Integration Functions

Dendrites play an essential role in processing functions by facilitating the integration of spatial and temporal information in biological system. Nanofluidic memristors, which harness ions for signal transmission within electrolyte solutions, closely resemble biological neuronal ion channels and hold the potential for the development of biorealistic neuromorphic devices. Herein, inspired by the optogenetic technique that utilized light to tune the ions dynamic, an optical-controlled nanofluidic artificial dendrite by embedding layered graphene oxide (GO) within a polydimethylsiloxane (PDMS) elastomer is developed. Taking advantage of the confinement effect of ions in the nanochannel, it has demonstrated optically-modulated ionic currents, which can effectively replicate dendritic functions. The mechanism can be attributed to the migration of Na+ ions, driven by the electric potential difference light illumination. The dendritic spatial and temporal multiport integrations are realized, including the dendritic sublinear/superlinear integrations and spike-rate-dependent plasticity (SRDP). Moreover, the hand withdrawal reflex, as a crucial mode of neuroregulation governed by central nerve and brain control signals, is replicated in the nanofluidic dendrite-based neuromorphic system, capable of managing a range of withdrawal states of a mechanical arm. This work offers a new strategy for developing nanofluidic artificial dendrite and paves the way toward developing advanced neuromorphic sensorimotor systems.

Projection-specific and reversible functional blockage in the association cortex of macaque monkeys

The functional manipulation techniques based on optogenetics have been widely and effectively utilized in the rodent brain. However, the applications of these techniques to the macaque cerebral cortex, particularly those to the prefrontal cortex, have been limited due to the extensive size and complex functional organization of each prefrontal area. In this study, we developed projection-specific and reversible functional blockade methods applicable to areas of the macaque prefrontal cortex, based on chemogenetic techniques. In chemogenetics, once a pair of viral vectors has been injected into the regions of projection source and target, the projection-specific functional blockage can be initiated through the oral, intravenous, or intramuscular administration of an appropriate pharmaceutical agent. Two methods were developed using two different effector proteins, an inhibitory DREADD, hM4Di, and tetanus toxin, given the substantial discrepancy in the on-off time course of functional blockade between the two. The Cre-DIO system was combined with hM4Di, and the Tet-On system with tetanus toxin. The effectiveness of these methods was evaluated by developing an electrophysiological assay using photic stimulation and field potential recordings.

Milliseconds photon-to-photon latency projection system for adaptive optogenetics applications

In recent years, dynamic projection mapping, which dynamically and adaptively projects images to suit moving and transforming objects, has attracted much attention. There is another case in which similar projection is necessary for objects under a microscope. Optogenetics can make certain cells photosensitive by genetic modification, and this can be used to input a disturbance to the cells. In particular, when the subject is in motion, the position of the cells to be stimulated changes in accordance with the motion or deformation of the subject, and the projection pattern must be changed dynamically to match this position. This requirement is exactly the same requirement as in dynamic projection mapping . Therefore, in this paper, we propose a projection method for microscopy with milliseconds latency. The proposed method is based on a low-latency digital micromirror device and high-speed vision system to achieve light projection that responds to deformation and movement of the object. The developed prototype system demonstrated a photon-to-photon latency of 6.56 ± 1.76 ms. Furthermore, dynamic projection mapping on a randomly moving target was also successfully demonstrated.

Longitudinal calcium imaging of BNST neurons in mice during optogenetic manipulation of paraventricular thalamus axon terminals

Here, we present a protocol to study neural circuits between the paraventricular thalamus (PVA) and the bed nucleus of the stria terminalis (BNST) in mice by combining calcium imaging with optogenetic stimulation of axon terminals. We describe steps for delivering GCaMP6f and ChrimsonR viruses and implanting the gradient-index (GRIN) lens for use with an Inscopix microscope. We then detail procedures for single-neuron tracking over an extended period through longitudinal recording and data smoothing and processing to enhance analysis.

A toolbox for ablating excitatory and inhibitory synapses

Recombinant optogenetic and chemogenetic proteins are potent tools for manipulating neuronal activity and controlling neural circuit function. However, there are few analogous tools for manipulating the structure of neural circuits. Here, we introduce three rationally designed genetically encoded tools that use E3 ligase-dependent mechanisms to trigger the degradation of synaptic scaffolding proteins, leading to functional ablation of synapses. First, we developed a constitutive excitatory synapse ablator, PFE3, analogous to the inhibitory synapse ablator GFE3. PFE3 targets the RING domain of the E3 ligase Mdm2 and the proteasome-interacting region of Protocadherin 10 to the scaffolding protein PSD-95, leading to efficient ablation of excitatory synapses. In addition, we developed a light-inducible version of GFE3, paGFE3, using a novel photoactivatable complex based on the photocleavable protein PhoCl2c. paGFE3 degrades Gephyrin and ablates inhibitory synapses in response to 400 nm light. Finally, we developed a chemically inducible version of GFE3, chGFE3, which degrades inhibitory synapses when combined with the bio-orthogonal dimerizer HaloTag ligand-trimethoprim. Each tool is specific, reversible, and capable of breaking neural circuits at precise locations.

Evidence for a push-pull interaction between superior colliculi in monocular dynamic vision mode

Visual perception can operate in two distinct vision modes-static and dynamic-that have been associated with different neural activity regimes in the superior colliculus (SC). However, the associated pathway-wide mechanisms remain poorly understood, especially in terms of corticotectal and tectotectal feedback upon encoding the continuity illusion during the dynamic vision mode. Here, we harness functional MRI combined with rat brain lesions to investigate whole-pathway neural interactions in the dynamic vision mode. We find a push-pull mechanism embodying contralateral suppression of SC activity opposing positive ipsilateral neural activation upon monocular visual stimulation. Cortical amplification is confirmed through cortical lesions, while further lesioning the ipsilateral SC leads to a boost in the contralateral SC negative signals, suggesting a tectal origin for the push-pull interaction. These results highlight hitherto unreported frequency-dependent modulations in the tectotectal pathway and further challenge the notion that intertectal connections solely serve as reciprocal inhibitory mechanisms for avoiding visual blur during saccades.

Mapping global brain reconfigurations following local targeted manipulations

Understanding how localized brain interventions influence whole-brain dynamics is essential for deciphering neural function and designing therapeutic strategies. Using longitudinal functional MRI datasets collected from mice, we investigated the effects of focal interventions, such as thalamic lesions and chemogenetic silencing of cortical hubs. We found that these local manipulations disrupted the brain's ability to sustain network-wide activity, leading to global functional connectivity (FC) reconfigurations. Personalized mouse brain simulations based on experimental data revealed that alterations in local excitability modulate firing rates and frequency content across distributed brain regions, driving these FC changes. Notably, the topography of the affected brain regions depended on the intervention site, serving as distinctive signatures of localized perturbations. These findings suggest that focal interventions produce consistent yet region-specific patterns of global FC reorganization, providing an explanation for the seemingly paradoxical observations of hypo- and hyperconnectivity reported in the literature. This framework offers mechanistic insights into the systemic effects of localized neural modulation and holds potential for refining clinical diagnostics in focal brain disorders and advancing personalized neuromodulation strategies.

Optogenetic induction of TDP-43 aggregation impairs neuronal integrity and behavior in Caenorhabditis elegans

BACKGROUND

Cytoplasmic aggregation of TAR DNA binding protein 43 (TDP-43) in neurons is one of the hallmarks of TDP-43 proteinopathy. Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are closely associated with TDP-43 proteinopathy; however, it remains uncertain whether TDP-43 aggregation initiates the pathology or is a consequence of it.

METHODS

To demonstrate the pathology of TDP-43 aggregation, we applied the optoDroplet technique in Caenorhabditis elegans (C. elegans), which allows spatiotemporal modulation of TDP-43 phase separation and assembly.

RESULTS

We demonstrate that optogenetically induced TDP-43 aggregates exhibited insolubility similar to that observed in TDP-43 proteinopathy. These aggregates increased the severity of neurodegeneration, particularly in GABAergic motor neurons, and exacerbated sensorimotor dysfunction in C. elegans.

CONCLUSIONS

We present an optogenetic C. elegans model of TDP-43 proteinopathy that provides insight into the neuropathological mechanisms of TDP-43 aggregates. Our model serves as a promising tool for identifying therapeutic targets for TDP-43 proteinopathy.

Neuromodulation in Small Animal fMRI

The integration of functional magnetic resonance imaging (fMRI) with advanced neuroscience technologies in experimental small animal models offers a unique path to interrogate the causal relationships between regional brain activity and brain-wide network measures-a goal challenging to accomplish in human subjects. This review traces the historical development of the neuromodulation techniques commonly used in rodents, such as electrical deep brain stimulation, optogenetics, and chemogenetics, and focuses on their application with fMRI. We discuss their advantageousness roles in uncovering the signaling architecture within the brain and the methodological considerations necessary when conducting these experiments. By presenting several rodent-based case studies, we aim to demonstrate the potential of the multimodal neuromodulation approach in shedding light on neurovascular coupling, the neural basis of brain network functions, and their connections to behaviors. Key findings highlight the cell-type and circuit-specific modulation of brain-wide activity patterns and their behavioral correlates. We also discuss several future directions and feature the use of mediation and moderation analytical models beyond the intuitive evoked response mapping, to better leverage the rich information available in fMRI data with neuromodulation. Using fMRI alongside neuromodulation techniques provide insights into the mesoscopic (relating to the intermediate scale between single neurons and large-scale brain networks) and macroscopic fMRI measures that correlate with specific neuronal events. This integration bridges the gap between different scales of neuroscience research, facilitating the exploration and testing of novel therapeutic strategies aimed at altering network-mediated behaviors. In conclusion, the combination of fMRI with neuromodulation techniques provides crucial insights into mesoscopic and macroscopic brain dynamics, advancing our understanding of brain function in health and disease. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 1.

Integrating multimodal data to understand cortical circuit architecture and function

In recent years there has been a tremendous growth in new technologies that allow large-scale investigation of different characteristics of the nervous system at an unprecedented level of detail. There is a growing trend to use combinations of these new techniques to determine direct links between different modalities. In this Perspective, we focus on the mouse visual cortex, as this is one of the model systems in which much progress has been made in the integration of multimodal data to advance understanding. We review several approaches that allow integration of data regarding various properties of cortical cell types, connectivity at the level of brain areas, cell types and individual cells, and functional neural activity in vivo. The increasingly crucial contributions of computation and theory in analyzing and systematically modeling data are also highlighted. Together with open sharing of data, tools and models, integrative approaches are essential tools in modern neuroscience for improving our understanding of the brain architecture, mechanisms and function.

Advances in Optogenetics and Thermogenetics for Control of Non-Neuronal Cells and Tissues in Biomedical Research

Optogenetics and chemogenetics are relatively new biomedical technologies that emerged 20 years ago and have been evolving rapidly since then. This has been made possible by the combined use of genetic engineering, optics, and electrophysiology. With the development of optogenetics and thermogenetics, the molecular tools for cellular control are continuously being optimized, studied, and modified, expanding both their applications and their biomedical uses. The most notable changes have occurred in the basic life sciences, especially in neurobiology and the activation of neurons to control behavior. Currently, these methods of activation have gone far beyond neurobiology and are being used in cardiovascular research, for potential cancer therapy, to control metabolism, etc. In this review, we provide brief information on the types of molecular tools for optogenetic and thermogenetic methods─microbial rhodopsins and proteins of the TRP superfamily─and also consider their applications in the field of activation of non-neuronal tissues and mammalian cells. We also consider the potential of these technologies and the prospects for the use of optogenetics and thermogenetics in biomedical research.

Distinct prelimbic cortex neuronal responses to emotional states of others drive emotion recognition in adult mice

The ability to perceive the emotional states of others, termed emotion recognition, allows individuals to adapt their conduct to the social environment. The brain mechanisms underlying this capacity, known to be impaired in individuals with autism spectrum disorder (ASD), remain, however, elusive. Here, we show that adult mice can discern between emotional states of conspecifics. Fiber photometry recordings of calcium signals in the prelimbic (PrL) medial prefrontal cortex revealed inhibition of pyramidal neurons during investigation of emotionally aroused individuals, as opposed to transient excitation toward naive conspecifics. Chronic electrophysiological recordings at the single-cell level indicated social stimulus-specific responses in PrL neurons at the onset and conclusion of social investigation bouts, potentially regulating the initiation and termination of social interactions. Finally, optogenetic augmentation of the differential neuronal response enhanced emotion recognition, while its reduction eliminated such behavior. Thus, differential PrL neuronal response to individuals with distinct emotional states underlies murine emotion recognition.

Analyzing the brain's dynamic response to targeted stimulation using generative modeling

Generative models of brain activity have been instrumental in testing hypothesized mechanisms underlying brain dynamics against experimental datasets. Beyond capturing the key mechanisms underlying spontaneous brain dynamics, these models hold an exciting potential for understanding the mechanisms underlying the dynamics evoked by targeted brain stimulation techniques. This paper delves into this emerging application, using concepts from dynamical systems theory to argue that the stimulus-evoked dynamics in such experiments may be shaped by new types of mechanisms distinct from those that dominate spontaneous dynamics. We review and discuss (a) the targeted experimental techniques across spatial scales that can both perturb the brain to novel states and resolve its relaxation trajectory back to spontaneous dynamics and (b) how we can understand these dynamics in terms of mechanisms using physiological, phenomenological, and data-driven models. A tight integration of targeted stimulation experiments with generative quantitative modeling provides an important opportunity to uncover novel mechanisms of brain dynamics that are difficult to detect in spontaneous settings.

Optogenetics and Its Application in Nervous System Diseases

Optogenetics is an emerging technology that uses the light-responsive effects of photosensitive proteins to regulate the function of specific cells. This technique combines genetics with optics, allowing for the precise inhibition or activation of cell functions through the introduction of photosensitive proteins into target cells and subsequent light stimulation to activate these proteins. In recent years, numerous basic and clinical studies have demonstrated the unique advantages of this approach in the research and treatment of neurological disorders. This review aims to introduce the fundamental principles and techniques of optogenetics, as well as its applications in the research and treatment of neurological diseases.

Heterogeneity of Layer 1 Interneurons in the Mouse Medial Prefrontal Cortex

Cortical Layer 1 (L1) acts as a critical relay for processing long-range inputs. GABAergic inhibitory interneurons (INs) in this layer (Layer 1 interneurons [L1INs]) function as inhibitory gates, regulating these inputs and modulating the activity of deeper cortical layers. However, their characteristics and circuits in the medial prefrontal cortex (mPFC) remain poorly understood. Using biocytin labeling, we identified three distinct morphological types of mPFC L1INs: neurogliaform cells (NGCs), elongated NGCs (eNGCs), and single-bouquet cell-like (SBC-like) cells. Whole-cell recordings revealed distinct firing patterns across these subtypes: NGCs and eNGCs predominantly exhibited late-spiking (LS) patterns, and SBC-like cells displayed a higher prevalence of non-LS (NLS) patterns. We observed both electrical and chemical connections among mPFC L1INs. Optogenetic activation of NDNF+ L1INs demonstrated broad inhibitory effects on deeper layer neurons. The strength of inhibition on pyramidal neurons (PyNs) and INs displayed layer-specific preference. These findings highlight the functional diversity of L1INs in modulating mPFC circuits and suggest their potential role in supporting higher order cognitive functions.

Neuropixels Opto: Combining high-resolution electrophysiology and optogenetics

High-resolution extracellular electrophysiology is the gold standard for recording spikes from distributed neural populations, and is especially powerful when combined with optogenetics for manipulation of specific cell types with high temporal resolution. We integrated these approaches into prototype Neuropixels Opto probes, which combine electronic and photonic circuits. These devices pack 960 electrical recording sites and two sets of 14 light emitters onto a 1 cm shank, allowing spatially addressable optogenetic stimulation with blue and red light. In mouse cortex, Neuropixels Opto probes delivered high-quality recordings together with spatially addressable optogenetics, differentially activating or silencing neurons at distinct cortical depths. In mouse striatum and other deep structures, Neuropixels Opto probes delivered efficient optotagging, facilitating the identification of two cell types in parallel. Neuropixels Opto probes represent an unprecedented tool for recording, identifying, and manipulating neuronal populations.

Optical Precise Ablation of Targeted Individual Neurons In Vivo

Targeted cell ablation is a powerful strategy for investigating the function of individual neurons within neuronal networks. Multiphoton ablation technology by a tightly focused femtosecond laser, with its significant advantages of noninvasiveness, high efficiency, and single-cell resolution, has been widely used in the study of neuroscience. However, the firing activity of the ablated neuron and its impact on the surrounding neurons and entire neuronal ensembles are still unclear. In this study, we describe the depolarization process of targeted neuron ablation by a femtosecond laser based on a standard two-photon microscope in vitro and in vivo. The photoporation damages the cell membrane, depolarizes the membrane potential, and thus disables the neuron's ability to fire action potentials. The dysfunctional neuron after laser ablation affects both the responses of surrounding neighbors and the functions of ensemble neurons in vivo. Although abnormal Ca2+ responses in spatially surrounding neurons are observed, the damage effect is confined to the focal volume. The function of the neuronal ensembles that associate with a specific visual stimulation is not influenced by the ablation of an individual member of the ensemble, indicating the redundancy of the ensemble organization. This study thus provides an insight into the targeted neuron ablation as well as the role of an individual neuron in an ensemble.

Study on Recovery Strategy of Hearing Loss & SGN Regeneration Under Physical Regulation

The World Health Organization (WHO) reports that by 2050, nearly 2.5 billion people are expected to have some degree of hearing loss (HL) and at least 700 million will need hearing rehabilitation. Therefore, there is an urgent need to develop treatment strategies for HL. At present, the main treatment strategies for HL are hearing aids and cochlear implants (CIs), which cannot achieve a radical cure for HL. Relevant studies have shown that the most fundamental treatment strategy for sensorineural hearing loss (SNHL) is to regenerate hair cells and spiral ganglion neurons (SGNs) through stem cells to repair the structure and function of cochlea. In addition, physical stimulation strategies, such as electricity, light, and magnetism have also been used to promote SGN regeneration. This review systematically introduces the classification, principle and latest progress of the existing hearing treatment strategies and summarizes the advantages and disadvantages of each strategy. The research progress of physical regulation mechanism is discussed in detail. Finally, the problems in HL repair strategies are summarized and the future development direction is prospected, which could provide new ideas and technologies for the optimization of hearing treatment strategies and the research of SGN repair and regeneration through physical regulation.

Wireless Devices for Optical Brain Stimulation: A Review of Current Developments for Optogenetic Applications in Freely Moving Mice

Purpose

Optogenetics is an invaluable tool to study brain circuits, but typical systems rely on tethered approaches to deliver light to the brain that hinder natural behavior. With the increasing prevalence of complex behavioral phenotyping in neuroscience experiments, wireless devices for optical stimulation offer great promise to overcome these limitations.

Methods

In this work we critically review recent systems engineering and device design approaches to deliver light to the brain with wireless operation for optogenetic experiments.

Results

We describe strategies used for wireless control and communication, wireless power transfer, and light delivery to the brain with a focus on device integration for in vivo operation in freely behaving mice.

Conclusion

Recent advances in optoelectronic systems, material science, and microtechnology have enabled the design and realization of miniaturized wirelessly-controlled optical stimulators for true untethered experiments in rodent models.

Transparent MXene Microelectrode Arrays for Multimodal Mapping of Neural Dynamics

Transparent microelectrode arrays have proven useful in neural sensing, offering a clear interface for monitoring brain activity without compromising high spatial and temporal resolution. The current landscape of transparent electrode technology faces challenges in developing durable, highly transparent electrodes while maintaining low interface impedance and prioritizing scalable processing and fabrication methods. To address these limitations, we introduce artifact-resistant transparent MXene microelectrode arrays optimized for high spatiotemporal resolution recording of neural activity. With 60% transmittance at 550 nm, these arrays enable simultaneous imaging and electrophysiology for multimodal neural mapping. Electrochemical characterization shows low impedance of 563 ± 99 kΩ at 1 kHz and a charge storage capacity of 58 mC cm⁻² without chemical doping. In vivo experiments in rodent models demonstrate the transparent arrays' functionality and performance. In a rodent model of chemically-induced epileptiform activity, we tracked ictal wavefronts via calcium imaging while simultaneously recording seizure onset. In the rat barrel cortex, we recorded multi-unit activity across cortical depths, showing the feasibility of recording high-frequency electrophysiological activity. The transparency and optical absorption properties of Ti₃C₂Tx MXene microelectrodes enable high-quality recordings and simultaneous light-based stimulation and imaging without contamination from light-induced artifacts.

A toolbox for ablating excitatory and inhibitory synapses

Recombinant optogenetic and chemogenetic proteins are potent tools for manipulating neuronal activity and controlling neural circuit function. However, there are few analogous tools for manipulating the structure of neural circuits. Here, we introduce three rationally designed genetically encoded tools that use E3 ligase-dependent mechanisms to trigger the degradation of synaptic scaffolding proteins, leading to functional ablation of synapses. First, we developed a constitutive excitatory synapse ablator, PFE3, analogous to the inhibitory synapse ablator GFE3. PFE3 targets the RING domain of the E3 ligase Mdm2 and the proteasome-interacting region of Protocadherin 10 to the scaffolding protein PSD-95, leading to efficient ablation of excitatory synapses. In addition, we developed a light-inducible version of GFE3, paGFE3, using a novel photoactivatable complex based on the photocleavable protein PhoCl2c. paGFE3 degrades Gephyrin and ablates inhibitory synapses in response to 400 nm light. Finally, we developed a chemically inducible version of GFE3, chGFE3, which degrades inhibitory synapses when combined with the bio-orthogonal dimerizer HaloTag ligand-trimethoprim. Each tool is specific, reversible, and capable of breaking neural circuits at precise locations.

Widespread innervation of motoneurons by spinal V3 neurons globally amplifies locomotor output in mice

While considerable progress has been made in understanding the neuronal circuits that underlie the patterning of locomotor behaviors, less is known about the circuits that amplify motoneuron output to adjust muscle force. Here, we demonstrate that propriospinal V3 neurons (Sim1+) account for ∼20% of excitatory input to motoneurons across hindlimb muscles. V3 neurons also form extensive connections among themselves and with other excitatory premotor neurons, such as V2a neurons. Optical activation of V3 neurons in a single segment rapidly amplifies locomotor-related motoneuron output at all lumbar segments in in vitro spinal cord and the awake adult mouse. Despite similar innervation from V3 neurons to flexor and extensor motoneuron pools, V3 neurons preferentially activate extensor muscles. Genetically or optogenetically silencing V3 neurons leads to slower and weaker mice with a reduced ability to adjust extensor muscle force. Thus, V3 neurons serve as global command neurons that amplify locomotion intensity.

Abraham Patchornik: The Contemporary Relevance of His Work for Chemistry and Biology

Abraham Patchornik was born in 1926 in Ness Ziona, a town in Palestine founded by his great-grandfather Reuben Lehrer in 1883. He started to study chemistry as an undergraduate at the Hebrew University. However, this was interrupted by the war, and he completed his studies in various locations in West Jerusalem. From 1952 to 1956 Patchornik completed his PhD at the (new) Weizmann Institute of Science with Ephraim Katchalski. After a postdoc at the NIH, he returned to the Weizmann in 1958, when he joined the Department of Biophysics. In 1972-1979, he became chairman of the new Department of Organic Chemistry at the Weizmann, and his own research was geared toward applying creative chemistry to solve biological problems. Patchornik passed away in his hometown of Ness Ziona in 2014. Patchornik was a conceptual leader in peptide and polymer chemistry. Given the importance of selective functional group protection for the construction of oligomeric molecules, he became interested in using "nonstandard", orthogonal chemistry for this purpose, i.e. photosensitive protecting groups (PPGs) in place of thermal reactions. It was R.B. Woodward who suggested this strategy to Patchornik in 1965, while Patchornik was on sabbatical leave at Harvard. However, it was not until Patchornik returned to the Weizmann that this idea of a versatile PPG to enable multistep synthesis was realized. Here, we provide an account of the early photosensitive protecting groups that Patchornik and co-workers developed, and the immense impact they have had on various fields. In particular, we survey the use of PPGs in live cell physiology (i.e., caged compounds), and the development of gene chips via light-directed solid-phase synthesis. Further, we highlight recent work applying new PPGs for "photochemical delivery" of drugs, otherwise termed photopharmacology. Finally, we discuss the relationship between caged compounds and how contemporary neuroscience uses genetically encoded chromophores to control cell function.

Long-range directional growth of neurites induced by magnetic forces

The ability to control the growth and orientation of neurites over long distances has significant implications for regenerative therapies and the development of physiologically relevant brain tissue models. In this study, the forces generated on magnetic nanoparticles internalised within intracellular endosomes are used to direct the orientation of neuronal outgrowth in cell cultures. Following differentiation, neurite orientation was observed after 3 days application of magnetic forces to human neuroblastoma (SH-SY5Y) cells, and after 4 days application to rat cortical primary neurons. The direction of neurite outgrowth was quantified using a 2D Fourier transform analysis, showing agreement with the derived magnetic force vectors. Orientation control was found to be effective over areas >1cm2 using modest forces of ∼10 fN per endosome, apparently limited only by the local confluence of the cells. A bioinformatics analysis of protein expression in cells exposed to magnetic forces revealed changes to cell signaling and metabolic pathways resulting in enhanced carbohydrate metabolism, as well as the perturbation of processes related to cellular organisation and proliferation. Additionally, in cell culture regions where the measured force vectors converged, large (∼100 µm) SH-SY5Y neuroclusters loaded with nanoparticles were found, connected by unusually thick linear neurite fibres. This could suggest a magnetically driven enhancement of neurocluster growth, with the clusters themselves contributing to the local forces that direct outgrowth. Such structures, which have not been previously observed, could provide new insights into the development and possible enhancement of neural circuitry. STATEMENT OF SIGNIFICANCE: A magnetic force approach for directing outgrowth in neuronal cells over macroscopic areas is successfully demonstrated. Cells were incubated with magnetic nanoparticles which were sequestered into intracellular compartments. Permanent magnet arrays created local intracellular magnetic force vectors mediated via the internalized nanoparticles, which were found to precisely guide neurite orientation. Analysis of cellular protein expression suggested the mechanism for directed growth involved specific cell signaling and metabolic pathways. In addition, highly unusual straight and thick neural fibers were observed that connected large 'magnetic' spherical cell clusters. The results reported will advance nanotechnology and cell therapy for neuro-regeneration where magnetic forces could help to reconnect damaged neurons, or even build artificial neuronal architectures.

Opto-CLIP reveals dynamic FMRP regulation of mRNAs upon CA1 neuronal activation

Neuronal diversity and function are intricately linked to the dynamic regulation of RNA metabolism. Electrophysiologic studies of synaptic plasticity, models for learning and memory, are disrupted in Fragile X Syndrome (FXS). FXS is characterized by the loss of FMRP, an RNA-binding protein (RBP) known to suppress translation of specific neuronal RNAs. Synaptic plasticity in CA1 excitatory hippocampal neurons is protein-synthesis dependent, suggesting a role for FMRP in FXS-related synaptic deficits. To explore this model, we developed Opto-CLIP, integrating optogenetics with cell-type specific FMRP-CLIP and RiboTag in CA1 neurons, allowing investigation of activity-induced FMRP regulation. We tracked changes in FMRP binding and ribosome-associated RNA profiles 30 minutes after neuronal activation. Our findings reveal distinct temporal dynamics for FMRP transcript regulation in the cell body versus the synapse. In the cell body, FMRP binding to transcripts encoding nuclear functions is relieved, potentially allowing rapid transcriptional responses to neuronal activation. At the synapse, FMRP binding to transcripts encoding synaptic targets was relatively stable, with variability in translational control across target categories. These results offer fresh insights into the dynamic regulation of RNA by FMRP in response to neuronal activation and provide a foundation for future research into the mechanisms of RBP-mediated synaptic plasticity.

Flexible modeling of large-scale neural network stimulation: electrical and optical extensions to The Virtual Electrode Recording Tool for EXtracellular Potentials (VERTEX)

Background

Computational models that predict effects of neural stimulation can be used as a preliminary tool to inform in-vivo research, reducing the costs, time, and ethical considerations involved. However, current models do not support the diverse neural stimulation techniques used in-vivo, including the expanding selection of electrodes, stimulation modalities, and stimulation paradigms.

New Method

To develop a more comprehensive software, we created several extensions to The Virtual Electrode Recording Tool for EXtracellular Potentials (VERTEX), the MATLAB-based neural stimulation tool from Newcastle University. VERTEX simulates input currents in a large population of multi-compartment neurons within a small cortical slice to model electric field stimulation, while recording local field potentials (LFPs) and spiking activity. Our extensions to its existing electric field stimulation framework include allowing multiple pairs of parametrically defined electrodes and biphasic, bipolar stimulation delivered at programmable delays. To support the growing use of optogenetic approaches for targeted neural stimulation, we introduced a feature that models optogenetic stimulation through an additional VERTEX input function that converts irradiance to currents at optogenetically responsive neurons. Finally, we added extensions to allow complex stimulation protocols including paired-pulse, spatiotemporal patterned, and closed-loop stimulation.

Results

We demonstrated our novel features using VERTEX's built-in functionalities, with results in alignment with other models and experimental work.

Conclusions

Our extensions provide an all in one platform to efficiently and systematically test diverse, targeted, and individualized stimulation patterns.

Multisensory integration of social signals by a pathway from the basal amygdala to the auditory cortex in maternal mice

Social encounters are inherently multisensory events, yet how and where social cues of distinct sensory modalities merge and interact in the brain is poorly understood. When their pups wander away from the nest, mother mice use a combination of vocal and olfactory signals emitted by the pups to locate and retrieve them. Previous work revealed the emergence of multisensory interactions in the auditory cortex (AC) of both dams and virgins who cohabitate with pups ("surrogates"). Here, we identify a neural pathway that relays information about odors to the AC to be integrated with responses to sound. We found that a scattered population of glutamatergic neurons in the basal amygdala (BA) projects to the AC and responds to odors, including the smell of pups. These neurons exhibit increased activity when the female is searching for pups that terminates upon contact. Finally, we show that selective optogenetic activation of BA-AC neurons modulates responses to pup calls, and that this modulation switches from predominantly suppressive to predominantly excitatory after maternal experience. This supports an underappreciated role for the amygdala in directly shaping sensory representations in an experience-dependent manner. We propose that the BA-AC pathway supports integration of olfaction and audition to facilitate maternal care and speculate that it may carry valence information to the AC.

Motion-less depth-selective optogenetic probe using tapered fiber and an electrically tuneable liquid crystal steering element

A miniature electrically tuneable liquid crystal component is used to steer light from -1° to +1° and then to inject into a simple tapered fiber. This allows the generation of various propagation modes, their leakage, and selective illumination of the surrounding medium at different depth levels without using mechanical movements nor deformation. The performance of the device is characterized in a reference fluorescence medium (Rhodamine 6G) as well as in a mouse brain (medullary reticular formation and mesencephalic locomotor regions) during in-vivo experiments as a proof of concept. This device may be further miniaturized to be applied to freely behaving animals for the dynamic selective excitation or inhibition of different brain regions.

Modulation of in vitro Network Activity by Optogenetic Stimulation of Parvalbumin-positive Interneurons During Estrous Cycle

BACKGROUND

Catamenial epilepsy, which is defined as a periodicity of seizure exacerbation occurring during the menstrual cycle, has been reported in up to 70% of epileptic women. These seizures are often non-responsive to medication and our understanding of the relation between menstrual cycle and seizure generation (i.e. ictogenesis) remains limited.

METHODS

Here, we employed the in vitro 4-aminopyridine model of epileptiform synchronization, to analyze the effects induced by optogenetic activation of parvalbumin (PV)-positive interneurons at 8 Hz during estrous and non-estrous phases in female PV-ChR2 mice.

RESULTS

We found that: (i) optogenetic stimulation of PV-positive interneurons induced an initial interictal spike followed by field oscillations occurring more often in estrous (59%) than in non-estrous slices (17%); (ii) these oscillations showed significantly higher power in estrous compared to nonestrous slices (p < 0.001); (iii) significantly higher rates of interictal spikes and ictal discharges were identified in both estrous and non-estrous slices during optogenetic stimulation of PV-positive interneurons compared to periods of no stimulation (p < 0.05); and (iv) ictal events appeared to occur more frequently during optogenetic stimulation in estrous compared to non-estrous slices.

CONCLUSION

Our findings show that optogenetic activation of PV-interneurons leads to more powerful network oscillations and more frequent ictal discharges in estrous than in non-estrous slices. We conclude that during the rodent estrous cycle, PV-interneuron hyperexcitability may play a role in epileptiform synchronization and thus in catamenial seizures.

Recording of Age-Related Changes on Murine and Human Brain Slices

Preparation of brain slices for electrophysiological and imaging experiments has been developed several decades ago, and the method is still widely used due to its simplicity and advantages over other techniques. It can be easily combined with other well established and recently developed methods as immunohistochemistry and morphological analysis or opto- and chemogenetics. Several aspects of this technique are covered by a plethora of excellent and detailed review papers, in which one can gain a deep insight of variations in it. In this chapter, I briefly describe the solutions, equipment, and preparation techniques routinely used in our laboratory. I also aim to present how certain "old school" brain slice lab devices can be made in a cost-efficient way. These devices can be easily adapted for the special needs of the experiments. I also aim to present some differences in the preparatory techniques of acutely isolated human brain tissue.

Photoproximity labeling of endogenous receptors in the live mouse brain in minutes

Understanding how protein-protein interaction networks in the brain give rise to cognitive functions necessitates their characterization in live animals. However, tools available for this purpose require potentially disruptive genetic modifications and lack the temporal resolution necessary to track rapid changes in vivo. Here we leverage affinity-based targeting and photocatalyzed singlet oxygen generation to identify neurotransmitter receptor-proximal proteins in the live mouse brain using only small-molecule reagents and minutes of photoirradiation. Our photooxidation-driven proximity labeling for proteome identification (named PhoxID) method not only recapitulated the known interactomes of three endogenous neurotransmitter receptors (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), inhibitory γ-aminobutyric acid type A receptor and ionotropic glutamate receptor delta-2) but also uncovered age-dependent shifts, identifying NECTIN3 and IGSF3 as developmentally regulated AMPAR-proximal proteins in the cerebellum. Overall, this work establishes a flexible and generalizable platform to study receptor microenvironments in genetically intact specimens with an unprecedented temporal resolution.

Differential roles of medial/lateral entorhinal cortex in spatial/object memory and contribution to hippocampal functional neuronal organization

Episodic memory is subserved by interactions between entorhinal cortex (EC) and hippocampus. Within EC, a functional dissociation has been proposed for medial (MEC) and lateral (LEC) subregions, whereby, MEC processes spatial information while LEC processes information about objects and their location in space. Most of these studies, however, used classical methods which lack both spatial and temporal specificity, thus, the precise role of MEC/LEC in memory could use further clarification. First, we show a possible functional dissociation of MEC/LEC for place/object fear memory, by optogenetic suppression of these areas during memory acquisition. The main output of EC is to the hippocampus. MEC projects mainly towards proximal/superficial CA1 and deep CA3 while LEC towards distal/deep CA1 and superficial CA3. Dentate gyrus (DG), terminations of MEC/LEC are dissociated septotemporally. A functional dissociation has also been proposed for subregions of the hippocampus. Previous studies reported that proximal/distal CA1 process spatial/nonspatial information, respectively. For the second part of the study, we used the immediate-early gene Zif-268 to map neuronal activity in CA1. We first show enhanced Zif-268 expression and cluster-type organization in the proximal CA1 by place exposure and enhanced Zif-268 expression/cluster organization in distal CA1 following object exposure. Second, direct optogenetic stimulation of MEC/LEC, produced a similar enhancement/cluster-type organization in the same areas. Enhanced Zif-268 expression was also observed in CA3 and DG. These results substantiate previous findings and are proof positive that the hippocampus is organized in clusters to encode information generally ascribed to this structure.

Low-NA two-photon lithography patterning of metal/dielectric tapered optical fibers for depth-selective, volumetric optical neural interfaces

Optical neural implants allow neuroscientists to access deep brain regions, enabling to decipher complex patterns of neural activity. In this field, the use of optical fibers is rapidly increasing, and the ability to generate high-quality metal patterns on their non-planar surface would further extend their application. Here, we propose to use alternating metal shielding and dielectric confinement to engineer the mode-division properties of tapered optical fiber neural implants. This is accomplished through an unconventional application of two-photon lithography (TPL), which employs a low-numerical aperture objective to pattern extensive waveguide sections at both low and high curvature radii. The low-NA TPL is used to polymerize a mask of photoresist, while the rest of the taper undergoes wet metal etching. This implies no direct destructive interaction between the laser beam and the metal to be removed, preserving the optical properties of the dielectric waveguide and of the metal coating. The advantages provided by the presented fabrication method, combined with the intrinsic modal properties of the dielectric waveguide, enable the engineering of the light guiding mechanisms, achieving depth-selective light delivery with a high extinction ratio. The device's light emission and collection properties were investigated in quasi-transparent media and highly scattering brain slices, finding that our proposed method facilitates 360° symmetric light collection around the dielectric-confined section with depth resolution. This opens a perspective for the realization of optical neural implants that can interface the implant axis all-around, with low-NA TPL that can also be applied on other types of non-planar surfaces.

Wireless Optogenetic Targeting Nociceptors Helps Host Cells Win the Competitive Colonization in Implant-Associated Infections

The role of nociceptive nerves in modulating immune responses to harmful stimuli via pain or itch induction remains controversial. Compared to conventional surgery, various implant surgeries are more prone to infections even with low bacterial loads. In this study, an optogenetic technique is introduced for selectively activating peripheral nociceptive nerves using a fully implantable, wirelessly rechargeable optogenetic device. By targeting nociceptors in the limbs of awake, freely moving mice, it is found that activation induces anticipatory immunity in the innervated territory and enhances the adhesion of various host cells to the implant surface. This effect mediates acute immune cell-mediated killing of Staphylococcus aureus on implants and enables the host to win "implant surface competition" against Staphylococcus aureus. This finding provides new strategies for preventing and treating implant-associated infections.

Wireless optogenetic stimulation on the prelimbic to the nucleus accumbens core circuit attenuates cocaine-induced behavioral sensitization

Behavioral sensitization is defined as the heightened and persistent behavioral response to repeated drug exposure as a manifestation of drug craving. Psychomotor stimulants such as cocaine can induce strong behavioral sensitization. In this study, we explored the effects of optogenetic stimulation of the prelimbic (PL) to the nucleus accumbnes (NAc) core on the expression of cocaine-induced behavioral sensitization. Using wireless optogenetics, we selectively stimulated the PL-NAc core circuit, and assessed the effects of this treatment on cocaine-induced locomotor activity and accompanying changes in neuronal activation and dendritic spine density. Our findings revealed that optogenetic stimulation of the PL-NAc core circuit effectively suppressed the cocaine-induced locomotor sensitization, accompanied by a reduction in c-Fos expression within the NAc core. Moreover, optogenetic stimulation led to reduction in dendritic spine density, particularly thin and mushroom spine densities, in the NAc core. This study demonstrates that cocaine-induced locomotor sensitization can be regulated by optogenetic stimulation of the PL-NAc core circuit, providing insights into the crucial role of this circuit in psychomotor stimulant addiction.

Hypothalamic deep brain stimulation augments walking after spinal cord injury

A spinal cord injury (SCI) disrupts the neuronal projections from the brain to the region of the spinal cord that produces walking, leading to various degrees of paralysis. Here, we aimed to identify brain regions that steer the recovery of walking after incomplete SCI and that could be targeted to augment this recovery. To uncover these regions, we constructed a space-time brain-wide atlas of transcriptionally active and spinal cord-projecting neurons underlying the recovery of walking after incomplete SCI. Unexpectedly, interrogation of this atlas nominated the lateral hypothalamus (LH). We demonstrate that glutamatergic neurons located in the LH (LHVglut2) contribute to the recovery of walking after incomplete SCI and that augmenting their activity improves walking. We translated this discovery into a deep brain stimulation therapy of the LH (DBSLH) that immediately augmented walking in mice and rats with SCI and durably increased recovery through the reorganization of residual lumbar-terminating projections from brainstem neurons. A pilot clinical study showed that DBSLH immediately improved walking in two participants with incomplete SCI and, in conjunction with rehabilitation, mediated functional recovery that persisted when DBSLH was turned off. There were no serious adverse events related to DBSLH. These results highlight the potential of targeting specific brain regions to maximize the engagement of spinal cord-projecting neurons in the recovery of neurological functions after SCI. Further trials must establish the safety and efficacy profile of DBSLH, including potential changes in body weight, psychological status, hormonal profiles and autonomic functions.

Ultra-fast photoelectron transfer in bimetallic porphyrin optoelectrode for single neuron modulation

Shrinking the size of photoelectrodes into the nanoscale will enable the precise modulation of cellular and subcellular behaviors of a single neuron and neural circuits. However, compared to photovoltaic devices, the reduced size causes the compromised efficiencies. Here, we present a highly efficient nanoelectrode based on bimetallic zinc and gold porphyrin (ZnAuPN). Upon light excitation, we observe ultrafast energy transfer (~66 ps) and charge transfer (~0.5 ps) through the porphyrin ring, enabling 97% efficiency in separating and transferring photoinduced charges to single Au-atom centers. Leveraging these isolated Au atoms as stimulating electrode arrays, we achieve significant photocurrent injection in single neurons, triggering action potential with millisecond light pulses. Notably, Extracranial near-infrared light irradiation of the motor cortex induces neuronal firing and enhances mouse movement. These results show the potential of nanoscale optoelectrodes for high spatiotemporal modulation of neuronal networks without the need for gene transfection in optogenetics.

Large-Scale, High-Density MicroLED Array-Based Optogenetic Device for Neural Stimulation and Recording

Optogenetics has emerged as a pivotal tool in neuroscience, enabling precise control of neural activity through light stimulation. However, the current microLED arrays lack sufficient density and scalability. This study proposes an innovative optogenetic device capable of integrating hundreds of microLEDs and electrocorticography (ECOG) electrodes. Individual or multiple microLEDs in the device can be selectively controlled with a custom controller. The light intensity of microLEDs decreases with increasing brain tissue penetration while maintaining a low temperature rise during pulse stimulations. In addition, interference from microLED pulses on ECOG electrode recordings could be alleviated with local mean subtraction data processing. The optogenetic device enables high-quality neural signal recording and triggers a significant enhancement in neural activity following light stimulation. Integration of microLED arrays and ECOG electrodes in the optogenetic device represents a promising advancement in neuroscientific research, providing improved spatial and temporal recording and control over neural activity.

Overcoming off-target optical stimulation-evoked cortical activity in the mouse brain in vivo

Exogenous opsins allow for in vivo interrogation of brain circuits at unprecedented temporal and spatial precision. Here, we found that optical fiber laser stimulation at wavelengths of 637, 594, or 473 nm within the cortex of mice lacking expression of exogenous opsins resulted in a strong neuronal response in the contralateral visual cortex. Evoked responses were observed even at low laser intensities (fiber tip power 1 mW) and most pronounced at 637 nm. We took advantage of retinal light adaptation by using a dim external light source (20 lux) that abolished the 594 and 473 nm-evoked neuronal responses even at high laser intensities (15 mW). The prevention of 637 nm-evoked responses, however, could only be achieved for stimulation intensities ≤ 2.5 mW. This highlights the need for careful selection of light wavelengths and intensities for optogenetic experiments. Additionally, retinal light adaptation offers an effective solution to minimize unintended activation.

A Prefrontal→Periaqueductal Gray Pathway Differentially Engages Autonomic, Hormonal, and Behavioral Features of the Stress-Coping Response

The activation of autonomic and hypothalamo-pituitary-adrenal (HPA) systems occurs interdependently with behavioral adjustments under varying environmental demands. Nevertheless, laboratory rodent studies examining the neural bases of stress responses have generally attributed increments in these systems to be monolithic, regardless of whether an active or passive coping strategy is employed. Using the shock probe defensive burying test (SPDB) to measure stress-coping features naturalistically in male and female rats, we identify a neural pathway whereby activity changes may promote distinctive response patterns of hemodynamic and HPA indices typifying active and passive coping phenotypes. Optogenetic excitation of the rostral medial prefrontal cortex (mPFC) input to the ventrolateral periaqueductal gray (vlPAG) decreased passive behavior (immobility), attenuated the glucocorticoid hormone response, but did not prevent arterial pressure and heart rate increases associated with rats' active behavioral (defensive burying) engagement during the SPDB. In contrast, inhibition of the same pathway increased behavioral immobility and attenuated hemodynamic output but did not affect glucocorticoid increases. Further analyses confirmed that hemodynamic increments occurred preferentially during active behaviors and decrements during immobility epochs, whereas pathway manipulations, regardless of the directionality of effect, weakened these correlational relationships. Finally, neuroanatomical evidence indicated that the influence of the rostral mPFC→vlPAG pathway on coping response patterns is mediated predominantly through GABAergic neurons within vlPAG. These data highlight the importance of this prefrontal→midbrain connection in organizing stress-coping responses and in coordinating bodily systems with behavioral output for adaptation to aversive experiences.

Revealing single-neuron and network-activity interaction by combining high-density microelectrode array and optogenetics

The synchronous activity of neuronal networks is considered crucial for brain function. However, the interaction between single-neuron activity and network-wide activity remains poorly understood. This study explored this interaction within cultured networks of rat cortical neurons. Employing a combination of high-density microelectrode array recording and optogenetic stimulation, we established an experimental setup enabling simultaneous recording and stimulation at a precise single-neuron level that can be scaled to the level of the whole network. Leveraging our system, we identified a network burst-dependent response change in single neurons, providing a possible mechanism for the network-burst-dependent loss of information within the network and consequent cognitive impairment during epileptic seizures. Additionally, we directly recorded a leader neuron initiating a spontaneous network burst and characterized its firing properties, indicating that the bursting activity of hub neurons in the brain can initiate network-wide activity. Our study offers valuable insights into brain networks characterized by a combination of bottom-up self-organization and top-down regulation.

Direct dorsal root ganglia (DRG) injection in mice for analysis of adeno-associated viral (AAV) gene transfer to peripheral somatosensory neurons

BACKGROUND

Delivering optogenetic genes to the peripheral sensory nervous system provides an efficient approach to study and treat neurological disorders and offers the potential to reintroduce sensory feedback to prostheses users and those who have incurred other neuropathies. Adeno-associated viral (AAV) vectors are a common method of gene delivery due to efficiency of gene transfer and minimal toxicity. AAVs are capable of being designed to target specific tissues, with transduction efficacy determined through the combination of serotype and genetic promoter selection, as well as location of vector administration. The dorsal root ganglia (DRGs) are collections of cell bodies of sensory neurons which project from the periphery to the central nervous system (CNS). The anatomical make-up of DRGs make them an ideal injection location to target the somatosensory neurons in the peripheral nervous system (PNS).

COMPARISON TO EXISTING METHODS

Previous studies have detailed methods of direct DRG injection in rats and dorsal horn injection in mice, however, due to the size and anatomical differences between rats and strains of mice, there is only one other published method for AAV injection into murine DRGs for transduction of peripheral sensory neurons using a different methodology.

NEW METHOD/RESULTS

Here, we detail the necessary materials and methods required to inject AAVs into the L3 and L4 DRGs of mice, as well as how to harvest the sciatic nerve and L3/L4 DRGs for analysis. This methodology results in optogenetic expression in both the L3/L4 DRGs and sciatic nerve and can be adapted to inject any DRG.

Potential and challenges of computing with molecular materials

We are at an inflection point in computing where traditional technologies are incapable of keeping up with the demands of exploding data collection and artificial intelligence. This challenge demands a leap to a new platform as transformative as the digital silicon revolution. Over the past 30 years molecular materials for computing have generated great excitement but continually fallen short of performance and reliability requirements. However, recent reports indicate that those historical limitations may have been resolved. Here we assess the current state of computing with molecular-based materials, especially using transition metal complexes of redox active ligands, in the context of neuromorphic computing. We describe two complementary research paths necessary to determine whether molecular materials can be the basis of a new computing technology: continued exploration of the molecular electronic properties that enable computation and, equally important, the process development for on-chip integration of molecular materials.

Concurrent optogenetic motor mapping of multiple limbs in awake mice reveals cortical organization of coordinated movements

BACKGROUND

Motor mapping allows for determining the macroscopic organization of motor circuits and corresponding motor movement representations on the cortex. Techniques such as intracortical microstimulation (ICMS) are robust, but can be time consuming and invasive, making them non-ideal for cortex-wide mapping or longitudinal studies. In contrast, optogenetic motor mapping offers a rapid and minimally invasive technique, enabling mapping with high spatiotemporal resolution. However, motor mapping has seen limited use in tracking 3-dimensonal, multi-limb movements in awake animals. This gap has left open questions regarding the underlying organizational principles of motor control of coordinated, ethologically-relevant movements involving multiple limbs.

OBJECTIVE

Our first objective was to develop Multi-limb Optogenetic Motor Mapping (MOMM) to concurrently map motor movement representations of multiple limbs with high fidelity in awake mice. Having established MOMM, our next objective was determine whether maps of coordinated and ethologically-relevant motor output were topographically organized on the cortex.

METHODS

We combine optogenetic stimulation with a deep learning driven pose-estimation toolbox, DeepLabCut (DLC), and 3-dimensional triangulation to concurrently map motor movements of multiple limbs in awake mice.

RESULTS

MOMM consistently revealed cortical topographies for all mapped features within and across mice. Many motor maps overlapped and were topographically similar. Several motor movement representations extended beyond cytoarchitecturally defined somatomotor cortex. Finer articulations of the forepaw resided within gross motor movement representations of the forelimb. Moreover, many cortical sites exhibited concurrent limb coactivation when photostimulated, prompting the identification of several cortical regions harboring coordinated and ethologically-relevant movements.

CONCLUSIONS

The cortex appears to be topographically organized by motor programs, which are responsible for coordinated, multi-limbed, and behavior-like movements.