Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Micro‐needle electrodes of any desired taper and sharpness for insertion into living tissue can be made quickly by electrolytic etching. For stainless steel wire the electrolyte is a mixture of sulfuric and ortho‐phosphoric acids. The wire to be pointed is made the anode of a circuit initially carrying about 0.03 amp. Gross shaping of the needle is done by repeatedly immersing the wire and withdrawing it slowly from the bath. Fine shaping of the point is carried out with reduced current. The electrodes are finished by insulating all but the fine tip with a baking enamel. The process described is adaptable to making a batch of micro‐needles at one time. <s> BIB001 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Abstract An internally or externally paced event results not only in the generation of an event-related potential (ERP) but also in a change in the ongoing EEG/MEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). The ERP on the one side and the ERD/ERS on the other side are different responses of neuronal structures in the brain. While the former is phase-locked, the latter is not phase-locked to the event. The most important difference between both phenomena is that the ERD/ERS is highly frequency band-specific, whereby either the same or different locations on the scalp can display ERD and ERS simultaneously. Quantification of ERD/ERS in time and space is demonstrated on data from a number of movement experiments. <s> BIB002 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> The physical energy that we refer to as a word, whether in isolation or embedded in sentences, takes its meaning from the knowledge stored in our brains through a lifetime of experience. Much empirical evidence indicates that, although this knowledge can be used fairly flexibly, it is functionally organized in ‘semantic memory’ along a number of dimensions, including similarity and association. Here, we review recent findings using an electrophysiological brain component, the N400, that reveal the nature and timing of semantic memory use during language comprehension. These findings show that the organization of semantic memory has an inherent impact on sentence processing. The left hemisphere, in particular, seems to capitalize on the organization of semantic memory to pre-activate the meaning of forthcoming words, even if this strategy fails at times. In addition, these electrophysiological results support a view of memory in which world knowledge is distributed across multiple, plastic-yet-structured, largely modality-specific processing areas, and in which meaning is an emergent, temporally extended process, influenced by experience, context, and the nature of the brain itself. <s> BIB003 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Brain–computer interfaces (BCIs) enable users to control devices with electroencephalographic (EEG) activity from the scalp or with single-neuron activity from within the brain. Both methods have disadvantages: EEG has limited resolution and requires extensive training, while single-neuron recording entails significant clinical risks and has limited stability. We demonstrate here for the first time that electrocorticographic (ECoG) activity recorded from the surface of the brain can enable users to control a one-dimensional computer cursor rapidly and accurately. We first identified ECoG signals that were associated with different types of motor and speech imagery. Over brief training periods of 3–24 min, four patients then used these signals to master closed-loop control and to achieve success rates of 74–100% in a one-dimensional binary task. In additional open-loop experiments, we found that ECoG signals at frequencies up to 180 Hz encoded substantial information about the direction of two-dimensional joystick movements. Our results suggest that an ECoG-based BCI could provide for people with severe motor disabilities a non-muscular communication and control option that is more powerful than EEG-based BCIs and is potentially more stable and less traumatic than BCIs that use electrodes penetrating the brain. M This article features online multimedia enhancements <s> BIB004 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> A quantitative approximation of the cortical surface potential from measured scalp surface potential data is developed. The derivation is based on a local Taylor series expansion (TSE) in the surface normal coordinate. Analytical and numerical results for the four shell spherical head model show that the TSE method improves the spatial deblurring of the surface Laplacian method. The inclusion of the biharmonic term, the extension to other geometries, and the application to electrocorticogram measurements are discussed. <s> BIB005 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Chronically implanted recording electrode arrays linked to prosthetics have the potential to make positive impacts on patients suffering from full or partial paralysis. Such arrays are implanted into the patient's cortical tissue and record extracellular potentials from nearby neurons, allowing the information encoded by the neuronal discharges to control external devices. While such systems perform well during acute recordings, they often fail to function reliably in clinically relevant chronic settings. Available evidence suggests that a major failure mode of electrode arrays is the brain tissue reaction against these implants, making the biocompatibility of implanted electrodes a primary concern in device design. This review presents the biological components and time course of the acute and chronic tissue reaction in brain tissue, analyses the brain tissue response of current electrode systems, and comments on the various material science and bioactive strategies undertaken by electrode designers to enhance electrode performance. <s> BIB006 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> In October 2008, Eberhard Fetz’s group from the University of Washington dem-onstrated that a direct artificial connection from a region of the brain associated with the control of movement to muscles in the limb could restore movement induced by electrical stimulation in monkeys whose arms had been temporarily anesthetized. The report of this progress created tremen-dous public interest as a perceived mile-stone in the development of a seamless neurotechnological solution for restoring function in paralysis. This work relied on the combination of an implanted electrode array in the motor cortex and functional electrical stimulation (FES) to muscles in the paralyzed wrist. Indeed, the combina-tion of FES, a technique that has achieved a track record of clinical utility, with brain–machine interfaces (BMIs) has become the subject of study for several research groups. Based on progress from these groups, we suggest that the technology has reached sufficient maturation that the proof-of-concept clinical demonstration could be accomplished within the next 5 years. In this editorial, we provide a brief overview of the key technologies and several key issues that are being explored, and also discuss the importance of supporting translational neuroprosthetics research and development to achieve this goal.Paralysis resulting from neurological injury or disease places a significant burden on patients, their families and caregivers. Neuroprostheses offer the promise of restoring movement to paralyzed patients by bypassing damaged regions of the ner-vous system, ultimately giving patients the ability to live with greater indepen-dence and improving their quality of life. Indeed, the coordinated stimulation of paralyzed muscles through FES has been shown to be effective and safe for restoring hand grasp <s> BIB007 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Deciphering the neuronal code--the rules by which neuronal circuits store and process information--is a major scientific challenge. Currently, these efforts are impeded by a lack of experimental tools that are sensitive enough to quantify the strength of individual synaptic connections and also scalable enough to simultaneously measure and control a large number of mammalian neurons with single-cell resolution. Here, we report a scalable intracellular electrode platform based on vertical nanowires that allows parallel electrical interfacing to multiple mammalian neurons. Specifically, we show that our vertical nanowire electrode arrays can intracellularly record and stimulate neuronal activity in dissociated cultures of rat cortical neurons and can also be used to map multiple individual synaptic connections. The scalability of this platform, combined with its compatibility with silicon nanofabrication techniques, provides a clear path towards simultaneous, high-fidelity interfacing with hundreds of individual neurons. <s> BIB008 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example. <s> BIB009 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Electrocorticogram (ECoG) recordings, taken from electrodes placed on the surface of the cortex, have been successfully implemented for control of brain machine interfaces (BMIs). Optogenetics, direct optical stimulation of neurons in brain tissue genetically modified to express channelrhodopsin-2 (ChR2), enables targeting of specific types of neurons with sub-millisecond temporal precision. In this work, we developed a BMI device, called an Opto- μECoG array, which combines ECoG recording and optogenetics-based stimulation to enable multichannel, bi-directional interactions with neurons. The Opto- μECoG array comprises two sub-arrays, each containing a 4 × 4 distribution of micro-epidural transparent electrodes (~200 μm diameter) and embedded light-emitting diodes (LEDs) for optical neural stimulation on a 2.5×2.5 mm2 footprint to match the bilateral hemispherical area of the visual cortex in a rat. The transparent electrodes were fabricated with indium tin oxide (ITO). Parylene-C served as the main structural and packaging material for flexibility and biocompatibility. Optical, electrical, and thermal characteristics of the fabricated device were investigated and in vivo experiments were performed to evaluate the efficacy of the device. <s> BIB010 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Successful integration of advanced semiconductor devices with biological systems will accelerate basic scientific discoveries and their translation into clinical technologies. In neuroscience generally, and in optogenetics in particular, the ability to insert light sources, detectors, sensors, and other components into precise locations of the deep brain yields versatile and important capabilities. Here, we introduce an injectable class of cellular-scale optoelectronics that offers such features, with examples of unmatched operational modes in optogenetics, including completely wireless and programmed complex behavioral control over freely moving animals. The ability of these ultrathin, mechanically compliant, biocompatible devices to afford minimally invasive operation in the soft tissues of the mammalian brain foreshadow applications in other organ systems, with potential for broad utility in biomedical science and engineering. <s> BIB011 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Abstract Anticipating sensorimotor events allows adaptive reactions to environment with crucial implications for self-protection and survival. Here we review several studies of our group that aimed to test the hypothesis that the cortical processes preparing the elaboration of sensorimotor interaction is reflected by the reduction of anticipatory electroencephalographic alpha power (about 8–12 Hz; event-related desynchronization, ERD), as an index that regulate task-specific sensorimotor processes, accounted by high-alpha sub-band (10–12 Hz), rather than a general tonic alertness, accounted by low-alpha sub-band (8–10 Hz). In this line, we propose a model for human cortical processes anticipating warned sensorimotor interactions. Overall, we reported a stronger high-alpha ERD before painful than non-painful somatosensory stimuli that is also predictive of the subjective evaluation of pain intensity. Furthermore, we showed that anticipatory high-alpha ERD increased before sensorimotor interactions between non-painful or painful stimuli and motor demands involving opposite hands. In contrast, sensorimotor interactions between painful somatosensory and sensorimotor demands involving the same hand decreased anticipatory high-alpha ERD, due to a sort of sensorimotor “gating” effect. In conclusion, we suggest that anticipatory cortical high-alpha rhythms reflect the central interference and/or integration of ascending (sensory) and descending (motor) signals relative to one or two hands before non-painful and painful sensorimotor interactions. <s> BIB012 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Recent advances in electrodes for noninvasive recording of electroencephalograms expand opportunities collecting such data for diagnosis of neurological disorders and brain–computer interfaces. Existing technologies, however, cannot be used effectively in continuous, uninterrupted modes for more than a few days due to irritation and irreversible degradation in the electrical and mechanical properties of the skin interface. Here we introduce a soft, foldable collection of electrodes in open, fractal mesh geometries that can mount directly and chronically on the complex surface topology of the auricle and the mastoid, to provide high-fidelity and long-term capture of electroencephalograms in ways that avoid any significant thermal, electrical, or mechanical loading of the skin. Experimental and computational studies establish the fundamental aspects of the bending and stretching mechanics that enable this type of intimate integration on the highly irregular and textured surfaces of the auricle. Cell level tests and thermal imaging studies establish the biocompatibility and wearability of such systems, with examples of high-quality measurements over periods of 2 wk with devices that remain mounted throughout daily activities including vigorous exercise, swimming, sleeping, and bathing. Demonstrations include a text speller with a steady-state visually evoked potential-based brain–computer interface and elicitation of an event-related potential (P300 wave). <s> BIB013 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Optogenetics is an exciting new technology that allows targetable fast control and readout of specific neural populations in complex brain circuits. With the rapid development of light-sensitive microbial opsins, substantial gains in understanding the causal relationships between neural activity and behavior in both healthy and diseased brains have been achieved during the last decade. However, the intricate and complex interactions between different neural populations in mammalian brains require novel, implantable, neural interfaces that are capable of manipulating and probing targeted neurons at multiple sites and with high spatiotemporal resolution. Advanced microtechnology has offered the highest potential to meet these demands of optogenetic applications. In this paper, we review a variety of miniaturized optogenetic neural implants developed in recent years, based on different light sources, including lasers, laser diodes, and light-emitting diodes. We then summarize the specifications of these microimplants and their related microfabrication approaches and discuss the major challenges of current techniques and the vision for the future of the field. <s> BIB014 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> We describe recent advances in soft electronic interface technologies for neuroscience research. Here, low modulus materials and/or compliant mechanical structures enable modes of soft, conformal integration and minimally invasive operation that would be difficult or impossible to achieve using conventional approaches. We begin by summarizing progress in electrodes and associated electronics for signal amplification and multiplexed readout. Examples in large-area, surface conformal electrode arrays and flexible, multifunctional depth-penetrating probes illustrate the power of these concepts. A concluding section highlights areas of opportunity in the further development and application of these technologies. <s> BIB015 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Wireless power delivery and telemetry have enabled completely implantable neural devices. Current day implants are controlled, monitored, and powered wirelessly, eliminating the need for batteries and prolonging the lifetime. A brief overview of wireless platforms for such implantable devices is presented in this paper alongside an in-depth discussion of wireless platform for peripheral nerve implants covering design requirements, link design, and safety. Initial acute studies on the performance of the wireless power and data links in rodents are also presented. <s> BIB016 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> In vivo recording of neural action-potential and local-field-potential signals requires the use of high-resolution penetrating probes. Several international initiatives to better understand the brain are driving technology efforts towards maximizing the number of recording sites while minimizing the neural probe dimensions. We designed and fabricated (0.13- $\mu$ m SOI Al CMOS) a 384-channel configurable neural probe for large-scale in vivo recording of neural signals. Up to 966 selectable active electrodes were integrated along an implantable shank (70 $\mu$ m wide, 10 mm long, 20 $\mu$ m thick), achieving a crosstalk of $-\text{64.4}$ dB. The probe base (5 $\times$ 9 mm $^2$ ) implements dual-band recording and a 171.6 Mbps digital interface. Measurement results show a total input-referred noise of 6.4 $\mu$ V $_{\mathrm{rms}}$ and a total power consumption of 49.1 $\mu$ W/channel. <s> BIB017 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Bidirectional interfacing with the nervous system enables neuroscience research, diagnosis, and therapy. This two-way communication allows us to monitor the state of the brain and its composite networks and cells as well as to influence them to treat disease or repair/restore sensory or motor function. To provide the most stable and effective interface, the tools of the trade must bridge the soft, ion-rich, and evolving nature of neural tissue with the largely rigid, static realm of microelectronics and medical instruments that allow for readout, analysis, and/or control. In this Review, we describe how the understanding of neural signaling and material-tissue interactions has fueled the expansion of the available tool set. New probe architectures and materials, nanoparticles, dyes, and designer genetically encoded proteins push the limits of recording and stimulation lifetime, localization, and specificity, blurring the boundary between living tissue and engineered tools. Understanding these approaches, their modality, and the role of cross-disciplinary development will support new neurotherapies and prostheses and provide neuroscientists and neurologists with unprecedented access to the brain. <s> BIB018 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> This review focuses on recent directions stemming from work by the authors and collaborators in the emerging field of neurotechnology. Neurotechnology has the potential to provide a greater understanding of the structure and function of the complex neural circuits in the brain, as well as impacting the field of brain–machine interfaces (BMI). We envision ultralow-power wireless neural interface systems that are life-lasting, fully integrated, and that supports bidirectional data flow with high bandwidth. Moreover, we believe in the importance of building neural interface technology that is truly tetherless, has a very small recording footprint, and little to no mechanical coupling between the sensor and the external world. We believe these developments will impact both neuroscience and neurology, revealing fundamental insight about how the nervous system functions in health and disease. <s> BIB019 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> A successful biomaterial–neural tissue interface should demonstrate biocompatibility, cytocompatibility, the ability to integrate properly within neural tissues, and the prolonged maintenance of desired electrical properties. Neural electrodes implanted in vivo often experience degradation of these properties due to implant micromotion, mechanical mismatch, an extensive foreign-body response, and the formation of glial scar tissue that interfere with signal transmission. However, recent advances in nanotechnology and nanomaterials show great promise to address these problems due to their biologically inspired surface features and enhanced electrical properties. This review will discuss how nanomaterials and nanotechnology are being used to fabricate advanced neural electrodes that demonstrate greater bio-integration properties, enhanced prolonged electrical properties, and an improved signal specificity down to the single molecule range. First, an overview of current biomaterial–neural tissue interface technology is provided, followed by an examination of conventional and newly developed micro- and nano-fabrication methodologies. Nanomaterials that have shown the most promise for neural interfacial applications are then discussed, including carbon nanomaterials, conductive polymers, and hybrid nanomaterials. The purpose of this review is to describe recent advances in nanotechnology for improved biomaterial–neural tissue interfaces, and identify their advantages and disadvantages from a researcher's perspective. <s> BIB020 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Abstract Recently developed classes of ultraminiaturized wireless devices provide powerful capabilities in neuroscience research, as implantable light sources for simulation/inhibition via optogenetics, as integrated microfluidic systems for programmed pharmacological delivery and as multimodal sensors for physiological measurements. These platforms leverage basic advances in biocompatible materials, semiconductor device designs and systems engineering concepts to afford modes of operation that are qualitatively distinct from those of conventional approaches that tether animals to external hardware by means of optical fibers, electrical cables and/or fluidic tubing. Neuroscience studies that exploit the unique features of these technologies enable insights into neural function through targeted stimulation, inhibition and recording, with spatially and genetically precise manipulation of neural circuit activity. Experimental possibilities include studies in naturalistic, three dimensional environments, investigations of pair-wise or group related social interactions and many other scenarios of interest that cannot be addressed using traditional hardware. <s> BIB021 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> The ability to decipher brain functions and understand the neuronal communication networking properties to develop innovative solutions to treat neurodegenerative diseases remains one of the biggest challenges in biomedicine. Since the early days, numerous solutions have been proposed for BMI, largely concentrating on the use of tethered electrodes that are inserted into the brain to either stimulate or suppress neural activities. In recent years, the field of optogenetics has provided a new alternative of utilizing light to stimulate genetically engineered neurons. While the original approach proposed the use of tethered optical cables inserted into the skull to transfer light into the brain for stimulation, numerous advances have been made to incorporate wireless technologies that will allow these devices to be attached to the skull or implanted in the brain. This article presents a review on the current technologies that have been proposed for different wireless optogenetics solutions, ranging from devices that are head mounted to miniature devices that can be embedded deep in the brain. We focus on a comparative analysis of the architecture and structure of the devices, the wireless technology used for signaling to the unit, as well as the energy consumption profile for each of the devices. Finally, the article presents future challenges to further miniaturize wireless optogenetic devices, concentrating specifically on the communication properties. <s> BIB022 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Technologies capable of establishing intimate, long-lived optical/electrical interfaces to neural systems will play critical roles in neuroscience research and in the development of nonpharmacological treatments for neurological disorders. The development of high-density interfaces to 3D populations of neurons across entire tissue systems in living animals, including human subjects, represents a grand challenge for the field, where advanced biocompatible materials and engineered structures for electrodes and light emitters will be essential. This review summarizes recent progress in these directions, with an emphasis on the most promising demonstrated concepts, materials, devices, and systems. The article begins with an overview of electrode materials with enhanced electrical and/or mechanical performance, in forms ranging from planar films, to micro/nanostructured surfaces, to 3D porous frameworks and soft composites. Subsequent sections highlight integration with active materials and components for multiplexed addressing, local amplification, wireless data transmission, and power harvesting, with multimodal operation in soft, shape-conformal systems. These advances establish the foundations for scalable architectures in optical/electrical neural interfaces of the future, where a blurring of the lines between biotic and abiotic systems will catalyze profound progress in neuroscience research and in human health/well-being. <s> BIB023 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Neural interfacing probes are located between the nervous system and the implanted electronic device in order to acquire information on the complex neuronal activity and to reconstruct impaired neural connectivity. Despite remarkable advancement in recent years, conventional neural interfacing is still unable to completely accomplish these goals, especially in long-term brain interfacing. The major limitation arises from physical and mechanical differences between neural interfacing probes and neural tissues that cause local immune responses and production of scar cells near the interface. Therefore, neural interfaces should ideally be extremely soft and have the physical scale of cells to mitigate the boundary between biotic and abiotic systems. Soft materials for neural interfaces have been intensively investigated to improve both interfacing and long-term signal transmission. The design and fabrication of micro and nanoscale devices have drastically decreased the stiffness of probes and enabled single-... <s> BIB024 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> II. NEURAL DEVICE INTERFACES <s> Neural recording electrode technologies have contributed considerably to neuroscience by enabling the extracellular detection of low-frequency local field potential oscillations and high-frequency action potentials of single units. Nevertheless, several long-standing limitations exist, including low multiplexity, deleterious chronic immune responses and long-term recording instability. Driven by initiatives encouraging the generation of novel neurotechnologies and the maturation of technologies to fabricate high-density electronics, novel electrode technologies are emerging. Here, we provide an overview of recently developed neural recording electrode technologies with high spatial integration, long-term stability and multiple functionalities. We describe how these emergent neurotechnologies can approach the ultimate goal of illuminating chronic brain activity with minimal disruption of the neural environment, thereby providing unprecedented opportunities for neuroscience research in the future. <s> BIB025
Implantable neural probe (or electrode/device) defines as the interface between brain-machine interface (BMI) system and neurons-the electroactive cells of the nervous system. Basically, implantable neural devices were evolved as a fundamental neuroscience tool to enhance the understanding of physiological processes  BIB001 BIB007  , and in BMI neural interfaces occupy exceptional ability to substitute for function of the various neurological disorders such as paralysis, epilepsy, other forms of motor dysfunction, or limb loss. The motivation behind developing neural devices is to provide adequate neural stimulation and/or to record the high quality neural signal from a few individual neurons, named action potentials BIB006 . Brain signals may be categorized into EEG BIB002 , electrocorticogram (ECoG) BIB010 , BIB004 , LFPs BIB017 , and action potential BIB008 , based on the location of the recorded signal. A correlation between the position and quality of the acquired signal among different neural technologies is displayed in Fig. 1(a) . EEG (scalp recordings) is the most basic, non-invasive technique to record brain activity, which has found application in the treatment of seizure or epilepsy. EEG also helps to monitor sleep, enables a better understanding of language perception and psychological function of the brain BIB012 BIB003 BIB013  . However, due to several interfering LFPs, EEG is unable to offer nearby data concerning a specific brain region, and suffers from low transfer rates e.g., 5-25 bit/s  , BIB005 . Furthermore, brain tissues are lossy and packed densely, and other brain layers such as skin and cranium function as obstacles that attenuate recorded EEG signal to the surface electrode, thereby limiting the spatiotemporal resolution BIB020 . In contrast, current researches have evaluated the application of invasive BMI such as ECoG (epidural/subdural recordings). As compared to the EEG, ECoG reduces the noise interference and allows to record higher frequency neural signal with higher accuracy. This is due to the fact that the ECoG electrodes are implanted within the cortex, thus accommodating lower tissue interference between the neurons and the electrodes BIB018 . Still, however, ECoG just records neural signals from superficial locales of the brain and unable to collect activity from individual neurons. Gathering signals from individual neurons and accuracy in spatiotemporal resolution over a particular neuron population is fundamental to facilitate a more profound understanding of the human sensory and cognitive system. Consequently, a more invasive method using implantable neural probes collect the LFPs signal from the deep brain region. The recording of LFPs signifies local neural activities which are obtained from specific neuronal densities and comprises action potentials as well as additional membrane potential fluctuations, and provides noteworthy details about the measured brain area BIB024 . Fundamentally, the idea of neural recording relies upon the application that we are focusing on. For an identical activity of the brain, the recorded signal is varied depending on the interfacing technique and recorded signal location. According to Fig. 1(b) , EEG or fMRI help us to examine neural activity from the identical subject for a longer period with a low resolution, whereas an implantable neural probe can achieve neuronal scale resolutions with a short temporal span. From the historical perspective, the field of neural interfaces has shown an upward trend as evidenced in Fig. 1 (c). This study is based on the number of publications (normalized) in the field of neural interfaces since the early 1990s. Among these, the current research trend indicates a significant development towards the implantable neural probe compared to the EEG and ECoG. Ongoing investigations proposed single-neuron activity enables us to guide and better comprehend the wiring of the cerebrum and its connection to discernment, movement, and memory. Nowadays, implantable neural device utilized for confining epileptogenic regions and treating Parkinson's disease. As compared to EEG and ECoG, the implantable neural device is considered to generate the most valuable control signals for neural interfacing BIB018 , BIB024 . These findings crave more breakthroughs in implantable device technologies to have more higher resolution, spatiotemporal span, and multiplexed functionality for neural recordings and stimulations. Recent progress in the field of materials science, stimulation types, system engineering, and mechanical design can facilitate long term in vivo recordings in freely moving animals by using implantable neural probes BIB025 , BIB021 . Some key system parameters for designing implantable neural probes appear in Fig. 2 . In all scenarios, a critical objective is to design a fully implantable, miniaturize, flexible, biointegrated, and wireless platforms BIB022 , [17],  , BIB014 BIB011 BIB019 BIB023 . Use of biocompatible material plays an important role both chemically and mechanically, and prerequisite to permit a durable, least invasive operation of the brain BIB009 . Along with the critical importance of the biocompatibility, mechanical flexibility as well as conformality to the desired tissues forms the foundation of a long-term biointegration BIB015 . Furthermore, wireless power transfer (WPT) to the neural implant ensures tether-free, highly mobile social connections or recordings in naturalistic situations for the tested animals BIB022 , BIB016 ,  . In summary, reducing the size and weight is an inevitable engineering prospect BIB025 .