A multi-modal neural interface capable of long-term recording and stimulation is essential for advancing brain monitoring and developing targeted therapeutics. Among traditional electrophysiological methods, micro-electrocorticography (μECoG) is appealing for chronic applications because it provides a good compromise between invasiveness and high-resolution neural recording. When combining μECoG with optical technologies, such as calcium imaging and optogenetics, this multi-modal approach enables simultaneous recording of neural activity from individual neurons and the ability to perform cell-specific manipulation. While previous efforts have focused on multi-modal interfaces for small animal models, scaling these technologies to larger primate brains remains challenging. In this paper, we present a multi-modal neural interface, named Smart Dura, a functional version of the commonly used artificial dura with integrated recording and stimulation electrodes for large cortical area coverage of the NHP brain. The Smart Dura is fabricated using a thin-film microfabrication process to monolithically integrate a micron-scale electrode array into a soft, flexible, and transparent substrate with high-density electrodes (up to 256 electrodes) while providing matched mechanical compliance with the native tissue and achieving high optical transparency (exceeding 98%). Our in vivo experiments demonstrate electrophysiological recording capabilities combined with neuromodulation, as well as optical transparency that enables structural and functional imaging. This work paves the way toward a chronic neural interface that can provide large-scale, bidirectional interfacing for multi-modal and closed-loop neuromodulation capabilities to study cortical brain activity in non-human primates, with the potential for translation to humans.

Optogenetics has been a powerful scientific tool for two decades, yet its integration with non-human primate (NHP) electrophysiology has been limited due to several technical challenges. These include a lack of electrode arrays capable of supporting large-scale and long-term optical access, inaccessible viral vector delivery methods for transfection of large regions of cortex, a paucity of hardware designed for large-scale patterned cortical illumination, and limited designs for multi-modal experimentation. To address these gaps, we introduce a highly accessible platform integrating optogenetics and electrophysiology for behavioral and neural modulation with neurophysiological recording in NHPs. We employed this platform in two rhesus macaques and showcased its capability of optogenetically disrupting reaches, while simultaneously monitoring ongoing electrocorticography activity underlying the stimulation-induced behavioral changes. The platform exhibits long-term stability and functionality, thereby facilitating large-scale electrophysiology, optical imaging, and optogenetics over months, which is crucial for translationally relevant multi-modal studies of neurological and neuropsychiatric disorders.

Deciphering neural mechanisms underlying neurostimulation is essential for developing targeted neurorehabilitation strategies, yet understanding the neural perturbations to behavior-related neural activity remains an area of active exploration. This study investigates the use of optogenetic inhibition to perturb motor activity and understand modulations to task-related neural activity in the posterior parietal cortex (PPC) of non-human primates (NHPs). Multiple regions of the PPC near the interparietal sulcus (IPS) were transfected with the inhibitory opsin JAWS. Inhibition was applied during a center-out reaching task, leveraging a large-scale optogenetic interface that allowed for simultaneously monitoring of local field potentials (LFPs) during optical stimulation. Optogenetic inhibition induced significant behavioral effects, including prolonged reach times. Analysis of task-related neural features during the motor planning period revealed significantly increased theta power, theta-gamma phase amplitude coupling (PAC), and trends of increased coherence near the IPS and in the 7a/7b regions of the PPC. Optogenetic inhibition resulted in distinct perturbations to task-related neural activity including increased theta and gamma power, decreased gamma coherence, and diminished theta-gamma PAC in opsin-expressing regions, with minimal effects in opsin-deficient regions. These findings highlight that optogenetic inhibition induces local network decoupling of task-related neural activity. Furthermore, this study demonstrates the potential of this large-scale optogenetic interface to unravel the neural mechanisms underlying neurostimulation and its impact on task-relevant brain dynamics.Clinical Relevance—This work provides insight into how targeted optogenetic inhibition may be used to ameliorate pathological brain activity related to neurological disorders.

This paper describes an in-house method of 3D brain and skull modeling from magnetic resonance imaging (MRI) tailored for nonhuman primate (NHP) neurosurgical planning. This automated, computational software-based technique provides an efficient way of extracting brain and skull features from MRI files as opposed to traditional manual extraction techniques using imaging software. Furthermore, the procedure provides a method for visualizing the brain and craniotomized skull together for intuitive, virtual surgical planning. This generates a drastic reduction in time and resources from those required by past work, which relied on iterative 3D printing. The skull modeling process creates a footprint that is exported into modeling software to design custom-fit cranial chambers and headposts for surgical implantation. Custom-fit surgical implants minimize gaps between the implant and the skull that could introduce complications, including infection or decreased stability. By implementing these pre-surgical steps, surgical and experimental complications are reduced. These techniques can be adapted for other surgical processes, facilitating more efficient and effective experimental planning for researchers and, potentially, neurosurgeons.

Convection-enhanced delivery (CED) is a pressure-based approach of delivering agents, such as viral vectors, throughout large regions of tissue. CED is chiefly characterized by injection volumes and flow rates that far exceed traditional diffusion-based approaches, which improves the feasibility of large-scale, targeted experimental and clinical research such as optogenetics and gene therapy. We present methods for MRI-guidedCEDMRI-guided CED of optogenetic viral vectors in cortical and deep brain structures of nonhuman primates as a case study of CED application in large animal models. We also include a discussion of important experimental materials and parameters, such as cannula designs and infusion flow rates, and a description of bench-side surgical planning approaches for CED.

Chronic interfacing with the brain to record and stimulate neural activity with high spatiotemporal resolution is highly desirable to advance the understanding of neural circuits and design of novel therapeutics. Traditional neural interfaces mainly rely on electrical recording and stimulation, which have inherent limitations such as lack of specificity and a large volume of tissue activation. With the advent of optogenetics, hybrid opto-electrical platforms have emerged as new bidirectional interfaces. In this paper, we introduce our groundwork towards the Smart Dura, a novel device that will ultimately integrate high density recording electrodes and light sources in the form of a chronic implant that can cover large cortical areas in the primate brain (300 mm 2 ) for adaptive recording and stimulation of neural activity in a closed loop. Smart Dura has two main components, the electrical dura for recording and the optical dura for optogenetic stimulation. As the first step to implement this platform, we have implemented the electrical dura as a high density, transparent and flexible $\mu \text{ECoG}$ array, as well as the optical dura, which is a high-density LED array, independently. Both the electrical and optical dura are implemented in flexible polymer substrates that provide mechanical compliance with the brain tissue and can be integrated together in a vertical stack. Here we present the fabrication, bench top characterization and acute in vivo validation of both the electrical and optical dura. This work paves the way towards the ultimate Smart Dura, a functional device that can replace the native dura as a chronic, large-scale bidirectional interface to study cortical brain activity in non-human primates (NHPs), with the potential for translation to humans.

Deciphering the function of neural circuits can help with the understanding of brain function and treating neurological disorders. Progress toward this goal relies on the development of chronically stable neural interfaces capable of recording and modulating neural circuits with high spatial and temporal precision across large areas of the brain. Advanced innovations in designing high-density neural interfaces for small animal models have enabled breakthrough discoveries in neuroscience research. Developing similar neurotechnology for larger animal models such as nonhuman primates (NHPs) is critical to gain significant insights for translation to humans, yet still it remains elusive due to the challenges in design, fabrication, and system-level integration of such devices. This review focuses on implantable surface neural interfaces with electrical and optical functionalities with emphasis on the required technological features to realize scalable multimodal and chronically stable implants to address the unique challenges associated with nonhuman primate studies.

Optogenetics is a powerful neuroscientific tool which allows neurons to be modulated by optical stimulation. Despite widespread optogenetic experimentation in small animal models, optogenetics in non-human primates (NHPs) remains a niche field, particularly at the large scales necessary for multi-regional neural research. We previously published a large-scale, chronic optogenetic cortical interface for NHPs which was successful but came with a number of limitations. In this work, we present an optimized interface which improves upon the stability and scale of our previous interface while using more easily replicable methods to increase our system's availability to the scientific community. Specifically, we (1) demonstrate the long-term (~3 months) optical access to the brain achievable using a commercially-available transparent artificial dura with embedded electrodes, (2) showcase large-scale optogenetic expression achievable with simplified (magnetic resonance-free) surgical techniques, and (3) effectively modulated the expressing areas at large scales (~1 cm2) by light emitting diode (LED) arrays assembled in-house.

Lesioning and neurophysiological studies have facilitated the elucidation of cortical functions and mechanisms of functional recovery following injury. Clinical translation of such studies is contingent on their employment in non-human primates (NHPs), yet tools for monitoring and modulating cortical physiology are incompatible with conventional lesioning techniques. To address these challenges, we developed a toolbox validated in seven macaques. We introduce the photothrombotic method for inducing focal cortical lesions, a quantitative model for designing experiment-specific lesion profiles and optical coherence tomography angiography (OCTA) for large-scale (~5 cm2) monitoring of vascular dynamics. We integrate these tools with our electrocorticographic array for large-scale monitoring of neural dynamics and testing stimulation-based interventions. Advantageously, this versatile toolbox can be incorporated into established chronic cranial windows. By combining optical and electrophysiological techniques in the NHP cortex, we can enhance our understanding of cortical functions, investigate functional recovery mechanisms, integrate physiological and behavioral findings, and develop neurorehabilitative treatments. MOTIVATION The primate neocortex encodes for complex functions and behaviors, the physiologies of which are yet to be fully understood. Such an understanding in both healthy and diseased states can be crucial for the development of effective neurorehabilitative strategies. However, there is a lack of a comprehensive and adaptable set of tools that enables the study of multiple physiological phenomena in healthy and injured brains. Therefore, we developed a toolbox with the capability to induce targeted cortical lesions, monitor dynamics of underlying cortical microvasculature, and record and stimulate neural activity. With this toolbox, we can enhance our understanding of cortical functions, investigate functional recovery mechanisms, test stimulation-based interventions, and integrate physiological and behavioral findings.

Non-human primates (NHPs) are precious resources for cutting-edge neuroscientific research, including large-scale viral vector-based experimentation such as optogenetics. We propose to improve surgical outcomes by enhancing the surgical preparation practices of convection-enhanced delivery (CED), which is an efficient viral vector infusion technique for large brains such as NHPs’. Here, we present both real-time and next-day MRI data of CED in the brains of ten NHPs, and we present a quantitative, inexpensive, and practical bench-side model of the in vivo CED data. Our bench-side model is composed of food coloring infused into a transparent agar phantom, and the spread of infusion is optically monitored over time. Our proposed method approximates CED infusions into the cortex, thalamus, medial temporal lobe, and caudate nucleus of NHPs, confirmed by MRI data acquired with either gadolinium-based or manganese-based contrast agents co-infused with optogenetic viral vectors. These methods and data serve to guide researchers and surgical team members in key surgical preparations for intracranial viral delivery using CED in NHPs, and thus improve expression targeting and efficacy and, as a result, reduce surgical risks.

Objective. Non-human primates (NHPs) are critical for development of translational neural technologies because of their neurological and neuroanatomical similarities to humans. Large-scale neural interfaces in NHPs with multiple modalities for stimulation and data collection poise us to unveil network-scale dynamics of both healthy and unhealthy neural systems. We aim to develop a large-scale multi-modal interface for NHPs for the purpose of studying large-scale neural phenomena including neural disease, damage, and recovery. Approach. We present a multi-modal artificial dura (MMAD) composed of flexible conductive traces printed into transparent medical grade polymer. Our MMAD provides simultaneous neurophysiological recordings and optical access to large areas of the cortex (∼3 cm 2 ) and is designed to mitigate photo-induced electrical artifacts. The MMAD is the centerpiece of the interfaces we have designed to support electrocorticographic recording and stimulation, cortical imaging, and optogenetic experiments, all at the large-scales afforded by the brains of NHPs. We performed electrical and optical experiments bench-side and in vivo with macaques to validate the utility of our MMAD. Main results. Using our MMAD we present large-scale electrocorticography from sensorimotor cortex of three macaques. Furthermore, we validated surface electrical stimulation in one of our animals. Our bench-side testing showed up to 90% reduction of photo-induced artifacts with our MMAD. The transparency of our MMAD was confirmed both via bench-side testing (87% transmittance) and via in vivo imaging of blood flow from the underlying microvasculature using optical coherence tomography angiography. Significance. Our results indicate that our MMAD supports large-scale electrocorticography, large-scale cortical imaging, and, by extension, large-scale optical stimulation. The MMAD prepares the way for both acute and long-term chronic experiments with complimentary data collection and stimulation modalities. When paired with the complex behaviors and cognitive abilities of NHPs, these assets prepare us to study large-scale neural phenomena including neural disease, damage, and recovery.

The primate cortex is a highly complex structure responsible for a variety of sophisticated tasks and behaviors including long-term memory storage, sensation, movement, and vision. However, little is understood with respect to the underlying cortical physiology and dynamics following injury. It is essential that these phenomena are studied in a model which shares a high degree of complexity and evolutionary history with human cortex: the non-human primate (NHP) cortex. Such studies would allow for the development of improved tools and strategies for treating neurological disorders such as stroke. However, current methods of inducing cortical lesions in NHP pre-clinical studies often require surgical skill, produce variable results, and lack controllability of lesion size and location. Methods: To address these challenges for the development of effective therapies, we developed a versatile lesion-based toolbox for studying NHP cortical physiology.First, we demonstrated the photothrombotic technique, wherein intravenous infusion of a photosensitive dye followed by targeted cortical illumination leads to the formation of localized thrombi in the vasculature. With this method, we induced ischemic lesions extending through all layers of sensorimotor cortex in 5 adult macaques. To validate the disruption of blood flow in cortical microvasculature in vivo , we employed optical coherence tomography angiography (OCTA) imaging. Additionally, we implanted a semi-transparent electrocorticography array to record neural activity before, during, and after the induction of lesions. The transparency of the array enabled us to illuminate through the array to induce lesions and acquire OCTA images to register electrodes to ischemic areas in vivo . Thus, we observed the dynamics of the underlying network neural activity as lesions were developing. Histological staining validated neuronal cell death and was used to estimate lesion volumes. Finally, we developed a computational model to predict lesion sizes based on illumination parameters. In combination with behavioral findings, this toolbox can drive the development of future rehabilitative therapies for stroke at clinically relevant time scales in pre-clinical studies.

Stable large-scale optogenetic interfaces for non-human primates (NHPs) have a great potential to answer fundamental questions about brain function and to develop novel therapies for neurological disorders. We have previously reported an interface that enables manipulation and recording from up to 2 cm2 of cortical tissue by combining three technologies: 1- convection enhanced viral delivery to achieve high levels of expression across large cortical areas, 2- semi-transparent micro-electrocorticographic arrays to record from these expressing areas, and 3- artificial dura to protect the brain and provide optical access. Although this interface provided a unique platform to study network activity and brain connectivity, it was based on day-to-day implantation and explantation of the recording array which led to accelerated tissue growth on top of the brain and limited the efficient time window for optical access to only several weeks. We then needed to wait for a month or two to remove the tissue from the surface of the brain and regain optical access. Here, we are optimizing this interface by incorporating the recording array into the artificial dura to reduce the manipulation at the brain surface and increase the efficient optical access window to 3-9 months. We are using a transparent, flexible polymer as an insulator for our recording sites that can be easily molded into the artificial dura. Furthermore, we have optimized our stimulation setup to increase the number of simultaneous light stimulation locations. We believe this optimized interface has a great potential for long-term optogenetic experiments in non-human primates.

In this paper, we outline a method for surgical preparation that allows for the practical planning of a variety of neurosurgeries in NHPs solely using data extracted from magnetic resonance imaging (MRI). This protocol allows for the generation of 3D printed anatomically accurate physical models of the brain and skull, as well as an agarose gel model of the brain modeling some of the mechanical properties of the brain. These models can be extracted from MRI using brain extraction software for the model of the brain, and custom code for the model of the skull. The preparation protocol takes advantage of state-of-the-art 3D printing technology to make interfacing brains, skulls, and molds for gel brain models. The skull and brain models can be used to visualize brain tissue inside the skull with the addition of a craniotomy in the custom code, allowing for better preparation for surgeries directly involving the brain. The applications of these methods are designed for surgeries involved in neurological stimulation and recording as well as injection, but the versatility of the system allows for future expansion of the protocol, extraction techniques, and models to a wider scope of surgeries.

BACKGROUND:Training non-human primates (NHPs) for translational medical experimentation is an essential yet time consuming process. To increase training efficiency, some training systems have been designed for NHPs to use at their home cages. Several autonomous cage-side tablet-based systems have been proposed, but none of these systems allow for remote monitoring and task modification while also being wireless, low-cost, light weight, and portable. NEW METHOD:Here we present ACTS: an Autonomous Cage-side Training System which meets all these criteria. ACTS consists of 1) a touchscreen tablet and a speaker attached to the subject's home cage, 2) an inexpensive reward system made from a slightly modified fish feeder, and 3), a laptop operating the system wirelessly and remotely via a router. RESULTS:We were able to test the system and wirelessly train two macaques in their home cages. Remote access enabled us to control ACTS from up to 90 m, through up to 3 walls, and through a floor of a building. The device is compatible with different reward pellet sizes and could run about two hours with a ∼4 mm pellet size. The animals were able to generalize the task when transferred to a traditional experimental rig. COMPARISON WITH EXISTING METHODS:The low cost and modest skill required to build and implement ACTS lowers the barrier for NHP researchers and caregivers to deploy autonomous, remotely controlled tablet-based cage-side systems. CONCLUSION:ACTS can be used for low-cost, wireless cage-side training of NHPs being prepared for translational medical experimentation.

In non-human primate (NHP) optogenetics, infecting large cortical areas with viral vectors is often a difficult and time-consuming task. Here, we demonstrate the use of magnetic resonance (MR)-guided convection enhanced delivery (CED) of optogenetic viral vectors into primary somatosensory (S1) and motor (M1) cortices of macaques to obtain efficient, widespread cortical expression of light-sensitive ion channels. Adeno-associated viral (AAV) vectors encoding the red-shifted opsin C1V1 fused to yellow fluorescent protein (EYFP) were injected into the cortex of rhesus macaques under MR-guided CED. Three months post-infusion, epifluorescent imaging confirmed large regions of optogenetic expression (>130 mm2) in M1 and S1 in two macaques. Furthermore, we were able to record reliable light-evoked electrophysiology responses from the expressing areas using micro-electrocorticographic arrays. Later histological analysis and immunostaining against the reporter revealed widespread and dense optogenetic expression in M1 and S1 corresponding to the distribution indicated by epifluorescent imaging. This technique enables us to obtain expression across large areas of the cortex within a shorter period of time with minimal damage compared to the traditional techniques and can be an optimal approach for optogenetic viral delivery in large animals such as NHPs. This approach demonstrates great potential for network-level manipulation of neural circuits with cell-type specificity in animal models evolutionarily close to humans.

Blood pressure (BP) is one of the most important monitoring parameters in clinical medicine. For years, the cuff-based sphygmomanometer and the arterial invasive line have been the gold standards for care professionals to assess BP. During the past few decades, the wide spread of the oscillometry-based BP arm or wrist cuffs have made home-based BP assessment more convenient and accessible. However, the discontinuous nature, the inability to interface with mobile applications, the relative inaccuracy with movement, and the need for calibration have rendered those BP oscillometry devices inadequate for next-generation healthcare infrastructure where integration and continuous data acquisition and communication are required. Recently, the indirect approach to obtain BP values has been intensively investigated, where BP is mathematically derived through the “Time Delay” in propagation of pressure waves in the vascular system. This holds promise for the realization of cuffless and continuous BP monitoring systems, for both patients and healthy populations in both inpatient and outpatient settings. This review highlights recent efforts in developing these next-generation blood pressure monitoring devices and compares various mathematical models. The unmet challenges and further developments that are crucial to develop “Time Delay”-based BP devices are also discussed.

Blood pressure (BP) is one of the most important monitoring parameters in clinical medicine. For years, the cuff-based sphygmomanometer and the arterial invasive line have been the gold standards for care professionals to assess BP. During the past few decades, the wide spread of the oscillometry-based BP arm or wrist cuffs have made home-based BP assessment more convenient and accessible. However, the discontinuous nature, the inability to interface with mobile applications, the relative inaccuracy with movement, and the need for calibration have rendered those BP oscillometry devices inadequate for next-generation healthcare infrastructure where integration and continuous data acquisition and communication are required. Recently, the indirect approach to obtain BP values has been intensively investigated, where BP is mathematically derived through the "Time Delay" in propagation of pressure waves in the vascular system. This holds promise for the realization of cuffless and continuous BP monitoring systems, for both patients and healthy populations in both inpatient and outpatient settings. This review highlights recent efforts in developing these next-generation blood pressure monitoring devices and compares various mathematical models. The unmet challenges and further developments that are crucial to develop "Time Delay"-based BP devices are also discussed.