Low-invasive neural recording in mouse models with diabetes via an ultrasmall needle-electrode

Diabetes is known to cause a variety of complications, having a high correlation with Alzheimer's disease. Electrophysiological recording using a microscale needle electrode is a promising technology for the study, however, diabetic brain tissue is more difficult to record neuronal activities than normal tissue due to these complications including the development of cerebrovascular disease. Here we show an electrophysiological methodology for diabetic db/db mice (+Leprdb/+Leprdb) using a 4-μm-tip diameter needle-electrode device. The needle electrode minimized the tissue injury when compared to a typical larger metal electrode, as confirmed by bleeding during penetration. The proposed electrode device showed both acute and chronic in vivo recording capabilities for diabetic mice while reducing the glial cells' responses. Because of these device characteristics, the 4-μm-tip diameter needle-electrode will allow electrophysiological studies on diabetes models of not only mice, as proven in this study, but also other animals.

An AC-Coupled 1st-order Δ-ΔΣ Readout IC for Area-Efficient Neural Signal Acquisition

The current demand for high-channel-count neural-recording interfaces calls for more area- and power-efficient readout architectures that do not compromise other electrical performances. In this paper, we present a miniature 128-channel neural recording integrated circuit (NRIC) for the simultaneous acquisition of local field potentials (LFPs) and action potentials (APs), which can achieve a very good compromise between area, power, noise, input range and electrode DC offset cancellation. An AC-coupled 1st-order digitally-intensive Δ - Δ Σ architecture is proposed to achieve this compromise and to leverage the advantages of a highly-scaled technology node. A prototype NRIC, including 128 channels, a newly-proposed area-efficient bulk-regulated voltage reference, biasing circuits and a digital control, has been fabricated in 22-nm FDSOI CMOS and fully characterized. Our proposed architecture achieves a total area per channel of 0.005 mm2, a total power per channel of 12.57 μ W , and an input-referred noise of 7.7 ± 0.4 μ V rms in the AP band and 11.9 ± 1.1 μ V rms in the LFP band. A very good channel-to-channel uniformity is demonstrated by our measurements. The chip has been validated in vivo, demonstrating its capability to successfully record full-band neural signals.

An Implantable Neuromorphic Sensing System Featuring Near-sensor Computation and Send-on-Delta Transmission for Wireless Neural Sensing of Peripheral Nerves

This paper presents a bio-inspired event-driven neuromorphic sensing system (NSS) capable of performing on-chip feature extraction and "send-on-delta" pulse-based transmission, targeting peripheral-nerve neural recording applications. The proposed NSS employs event-based sampling which, by leveraging the sparse nature of electroneurogram (ENG) signals, achieves a data compression ratio of >125×, while maintaining a low normalized RMS error of 4% after reconstruction. The proposed NSS consists of three sub-circuits. A clockless level-crossing (LC) ADC with background offset calibration has been employed to reduce the data rate, while maintaining a high signal to quantization noise ratio. A fully synthesized spiking neural network (SNN) extracts temporal features of compound action potential signals consumes only 13 μW. An event-driven pulse-based body channel communication (Pulse-BCC) with serialized address-event representation encoding (AER) schemes minimizes transmission energy and form factor. The prototype is fabricated in 40-nm CMOS occupying a 0.32-mm² active area and consumes in total 28.2 μW and 50 μW power in feature extraction and full diagnosis mode, respectively. The presented NSS also extracts temporal features of compound action potential signals with 10-μs precision.

Light-induced uncertainty and information limits of optical neural recording

Cutting-edge methods of laser microscopy combined with fluorescent protein engineering and spectral analysis provide a unique resource for high-resolution neuroimaging, enabling a high-fidelity, high-contrast detection of fine structural details of neural cells and intracellular compartments. In addition to their extraordinary imaging abilities in real space, such methods can help resolve the neural states in a multidimensional space of neural responses whereby individual neurons and neural populations encode information on external stimuli. This study shows, however, that laser-induced biochemical processes in neural cells can give rise to an uncertainty of neural states, setting an upper bound on the information that optical measurements can provide on neural states, neural encodings, and neural dynamics. Comparison of absorbed laser power with the native biochemical energy budget of neuronal firing suggests that each readout photon in optical recording comes at a cost of precision of neural encoding and a loss of information encoded by the neural response. A quantitative measure for such a measurement-induced neural uncertainty can be defined, as this study shows, in terms of the Fisher information, relating the lower bound of this uncertainty to the loss of the Shannon information capacity of neural states.

Soft, Wireless and subdermally implantable recording and neuromodulation tools

Progress in understanding neuronal interaction and circuit behavior of the central and peripheral nervous system strongly relies on the advancement of tools that record and stimulate with high fidelity and specificity. Currently, devices used in exploratory research predominantly utilize cables or tethers to provide pathways for power supply, data communication, stimulus delivery and recording, which constrains the scope and use of such devices. In particular, the tethered connection, mechanical mismatch to surrounding soft tissues and bones frustrate the interface leading to irritation and limitation of motion of the subject, which in the case of fundamental and preclinical studies, impacts naturalistic behaviors of animals and precludes the use in experiments involving social interaction and ethologically relevant three-dimensional environments, limiting the use of current tools to mostly rodents and exclude species such as birds and fish. This review explores the current state-of-the-art in wireless, subdermally implantable tools that quantitively expand capabilities in analysis and perturbation of the central and peripheral nervous system by removing tethers and externalized features of implantable neuromodulation and recording tools. Specifically, the review explores power harvesting strategies, wireless communication schemes, and soft materials and mechanics that enable the creation of such devices and discuss their capabilities in the context of freely-behaving subjects. Highlights of this class of devices includes wireless battery-free and fully implantable operation with capabilities in cell specific recording, multimodal neural stimulation and electrical, optogenetic and pharmacological neuromodulation capabilities. We conclude with discussion on translation of such technologies which promises routes towards broad dissemination.

pMAT: An open-source software suite for the analysis of fiber photometry data

The combined development of new technologies for neuronal recordings and the development of novel sensors for recording both cellular activity and neurotransmitter binding has ushered in a new era for the field of neuroscience. Among these new technologies is fiber photometry, a technique wherein an implanted fiber optic is used to record signals from genetically encoded fluorescent sensors in bulk tissue. Fiber photometry has been widely adapted due to its cost-effectiveness, ability to examine the activity of neurons with specific anatomical or genetic identities, and the ability to use these highly modular systems to record from one or more sensors or brain sites in both superficial and deep-brain structures. Despite these many benefits, one major hurdle for laboratories adopting this technique is the steep learning curve associated with the analysis of fiber photometry data. This has been further complicated by a lack of standardization in analysis pipelines. In the present communication, we present pMAT, a 'photometry modular analysis tool' that allows users to accomplish common analysis routines through the use of a graphical user interface. This tool can be deployed in MATLAB and edited by more advanced users, but is also available as an independently deployable, open-source application.

Headpost Surgery for in vivo Electrophysiological Recording in the Mouse Inferior Colliculus during Locomotion

The inferior colliculus (IC) is a critical midbrain integration center for auditory and non-auditory information. Although much is known about the response properties of the IC neurons to auditory stimuli, how the IC neural circuits function during movement such as locomotion remains poorly understood. Mice offer a valuable model in this respect, but previous studies of the mouse IC were performed in anesthetized or restrained preparations, making it difficult to study the IC function during behavior. Here we describe a neural recording protocol for the mouse IC in which mice are head-fixed, but can run on a passive treadmill. Mice first receive a headpost surgery, and become habituated to head-fixing while being on a treadmill. Following a few days of habituation, neural recordings of the IC neuron activity are performed. The neural activity can be compared across different behavioral conditions, such as standing still versus running on a treadmill. We describe how to overcome the challenges of headpost surgery for awake IC recording, presented by the location and overlying bones. This protocol allows investigations of the IC function in behaving mice, while allowing precise stimulus control and the use of recording methods similar to those for anesthetized preparations.

Probe-antenna and multifunctional switch for biomedical neural implants

A probe-antenna and a multifunctional single-pole-four-throw switch are proposed for biomedical neural implants. The multifunctional switch is fabricated in TSMC 90-nm CMOS process and occupies the core area of 297 × 248 μm². Operating in transmitter/receiver mode, the switch achieves the insertion loss of 4.5/4.8 dB, return loss of 16.7/15.4 dB, isolation of 19.2/20.3 dB and P1dB of 4/5 dBm at 60 GHz. Based on the dipole antenna, the antenna with probe function is designed and fabricated on the Roger 4003C two-layer printed circuit board. This probe-antenna achieves the input matching over 59.35-65 GHz. According to the simulation, it achieves the radiation efficiency of 69.8/34.4% and gain of 3.88/5.47 dBi without/with a drop of deionized water on the feed. The probe/electrode function is verified by performing impedance measurement on the deionized water, phosphate buffered saline (PBS) solution, and solution with conductivity of 1413 μS/cm.

Array processing of neural signals recorded from the peripheral nervous system for the classification of action potentials

BACKGROUND

Recording from the peripheral nervous system is key in the development of implantable neural interfaces. Despite a long history of using implantable electrodes for neuro-stimulation, it is difficult to make recordings from the nerves as signal amplitudes are often too small to be detected. Methods exist that are suitable for recording evoked potentials, but these require artificial stimulation of the nerve and thus have limited use in implanted neural interfaces.

NEW METHOD

In order to address these issues new methods are developed to analyse spontaneously occurring action potentials by extending an approach called velocity selective recording, which uses longitudinally spaced electrodes to record action potentials as they propagate. The new methods using image processing techniques to automatically identify and classify action potentials without any prior knowledge of their morphology.

RESULTS

Simulations are developed to test the methods, and a detailed experimental validation is performed using in-vivo recordings from the L5 dorsal rootlet of rat. Results show that this new approach can discriminate action potentials from both simulated and real recordings and the experimental validation demonstrates an ability to detect dermal stimulation by changes in the firing patterns of different axons.

COMPARISON TO EXISTING METHODS

This framework, unlike existing methods, is intrinsically suitable for recordings of spontaneous neural activity. Further it improves upon both the computational complexity and the overall performance of existing methods.

CONCLUSION

It is possible to perform on-line discrimination and identification of action potentials without any prior knowledge of their morphology using new image processing inspired methods.

Technological advancements and opportunities in Neuromarketing: a systematic review

Neuromarketing has become an academic and commercial area of interest, as the advancements in neural recording techniques and interpreting algorithms have made it an effective tool for recognizing the unspoken response of consumers to the marketing stimuli. This article presents the very first systematic review of the technological advancements in Neuromarketing field over the last 5 years. For this purpose, authors have selected and reviewed a total of 57 relevant literatures from valid databases which directly contribute to the Neuromarketing field with basic or empirical research findings. This review finds consumer goods as the prevalent marketing stimuli used in both product and promotion forms in these selected literatures. A trend of analyzing frontal and prefrontal alpha band signals is observed among the consumer emotion recognition-based experiments, which corresponds to frontal alpha asymmetry theory. The use of electroencephalogram (EEG) is found favorable by many researchers over functional magnetic resonance imaging (fMRI) in video advertisement-based Neuromarketing experiments, apparently due to its low cost and high time resolution advantages. Physiological response measuring techniques such as eye tracking, skin conductance recording, heart rate monitoring, and facial mapping have also been found in these empirical studies exclusively or in parallel with brain recordings. Alongside traditional filtering methods, independent component analysis (ICA) was found most commonly in artifact removal from neural signal. In consumer response prediction and classification, Artificial Neural Network (ANN), Support Vector Machine (SVM) and Linear Discriminant Analysis (LDA) have performed with the highest average accuracy among other machine learning algorithms used in these literatures. The authors hope, this review will assist the future researchers with vital information in the field of Neuromarketing for making novel contributions.

Low power switched-resistor band-pass filter for neural recording channels in 130nm CMOS

In this work, we present a low-power 2^nd order band-pass filter for neural recording applications. The central frequency of the passband is set to 375Hz and the quality factor to 5 to properly process the neural signals related to the onset of epileptic seizure, and to strongly attenuate all the out of band biological signals and electrical disturbances. The biquad filter is based on a fully differential Tow Thomas architecture in which high-valued resistors are implemented through switched high-resistivity polysilicon resistors. A supply voltage as low as 0.8V and MOS transistors operating in the sub-threshold region are exploited to achieve a power consumption as low as 170nW, when driving a 1pF load capacitance. The filter exhibits a tuning range of the resonance frequency from 200Hz to 400Hz, and an area footprint of only 0.021 mm². Very low power consumption and area occupation are key specifications for integrated, multiple-sensors, neural recording systems.

Long-term labeling of microelectrode tracks with fluorescent latex microspheres

BACKGROUND

After physiological recordings are performed in behaving animals, it is valuable to identify microelectrode tracks in histological sections so that neuronal responses can be correlated with brain anatomy. However, no good method currently exists for long-term labeling, so that microelectrode tracks can be recovered months or even years after recording sessions.

NEW METHOD

Penetrations were made into the brains of mice with microelectrodes coated with fluorescent dyes packaged into 0.2 μm polystyrene microspheres, followed by survival periods of 3 days, 2, 4, or 6 months. Sections were examined by fluorescence microscopy before and after cytochrome oxidase histochemistry to identify microelectrode tracks.

RESULTS

After all 4 survival periods, 0.2 μm fluorescent microspheres clearly marked the tracks of microelectrode penetrations.

COMPARISON WITH EXISTING METHODS

Fluorescent microspheres label microelectrode penetrations for longer than do fluorescent lipophilic dyes, such as FM 1-43FX. The label appears punctate, and resistant to degradation, because it is protected by the barrier of the polystyrene micro-container.

CONCLUSIONS

Coating of microelectrodes with fluorescent microspheres allows one to identify the penetration track in histological sections half a year later. This technique may be useful when electrophysiological recording sessions are being carried out in behaving animals, with plans to identify electrode tracks in histological sections many months later.

Fully implantable neural recording and stimulation interfaces: Peripheral nerve interface applications

BACKGROUND

Peripheral nerve interfacing has many applications ranging from investigation of neural signals to therapeutic intervention for varied diseases. This need has driven technological advancements in the field of electrode arrays and wireless systems for in-vivo electrophysiological experiments. Hence we present our fully implantable, programmable miniaturized wireless stimulation and recording devices.

NEW METHOD

The method consists of technological advancements enabling implantable wireless recording up to 128 channels with a sampling rate of 50Khz and stimulation up to ±4 mA from 15 independent channels. The novelty of the technique consists of induction charging cages which enables freely moving small animals to undergo continuous electrophysiological and behavioral studies without any impediments. The biocompatible hermetic packaging technology for implantable capsules ensures stability for long-term chronic studies.

RESULTS

Electromyographs wirelessly recorded from leg muscles of a macaque and a rat using implantable technology are presented during different behavioral task studies. The device's simultaneous stimulation and recording capabilities are reported when interfaced with the vagus and pelvic nerves.

COMPARISON WITH EXISTING METHOD(S)

The wireless interfacing technology has a large number of recording and stimulating channels without compromising on the signal quality due to sampling rates or stimulating current output capabilities. The induction charging technology along with transceiver and software interface allows experiments on multiple animals to be carried out simultaneously.

CONCLUSIONS

This customizable technology using wireless power transmission, reduced battery size, and miniaturized electronics has paved way for a robust, fully implantable, hermetic neural interface system enabling the study of bioelectronic medical therapies.

Three-dimensional drivable optrode array for high-resolution neural stimulations and recordings in multiple brain regions

The brain-computer interface (BCI) devices are of prime important for study of nervous system as well as diagnosis and treatment of neurological disorders. To meet the needs of the BCI devices in high-density integration and multi-functionalization, 3-dimensional (3D) drivable optrode array with laser diodes (LDs) coupled waveguides was developed. The unique device realizes the 3D integration of the optrodes and avoids fiber tangle and tissue heating by adopting LD coupled waveguide structure. Besides, the postoperative position adjustment of the optrode array was achieved by integrating with a 3D printed micro-drive. Most importantly, high-resolution neural stimulations and recordings were achieved for study of working memory related neural circuits in four brain regions of mice including prelimbic cortex (PrL), mediodorsal thalamic nucleus (MD), dorsal medial caudate nucleus (dmCP) and posterior motor cortex 2 (pM2). The results indicate that this novel device is promising for the research of complex neural networks.

Electrodeposited platinum-iridium coating improves in vivo recording performance of chronically implanted microelectrode arrays

Reliable single unit neuron recordings from chronically implanted microelectrode arrays (MEAs) are essential tools in the field of neural engineering. However, following implantation, MEAs undergo a foreign body response that functionally isolates them from the brain and reduces the useful longevity of the array. We tested a novel electrodeposited platinum-iridium coating (EPIC) on penetrating recording MEAs to determine if it improved recording performance. We chronically implanted the arrays in rats and used electrophysiological and histological measurements to compare quantitatively the single unit recording performance of coated vs. uncoated electrodes over a 12-week period. The coated electrodes had substantially lower impedance at 1 kHz and reduced noise, increased signal-to-noise ratio, and increased number of discernible units per electrode as compared to uncoated electrodes. Post-mortem immunohistochemistry showed no significant differences in the immune response between coated and uncoated electrodes. Overall, the EPIC arrays provided superior recording performance than uncoated arrays, likely due to lower electrode impedance and reduced noise.

SiNAPS: An implantable active pixel sensor CMOS-probe for simultaneous large-scale neural recordings

Large-scale neural recordings with high spatial and temporal accuracy are instrumental to understand how the brain works. To this end, it is of key importance to develop probes that can be conveniently scaled up to a high number of recording channels. Despite recent achievements in complementary metal-oxide semiconductor (CMOS) multi-electrode arrays probes, in current circuit architectures an increase in the number of simultaneously recording channels would significantly increase the total chip area. A promising approach for overcoming this scaling issue consists in the use of the modular Active Pixel Sensor (APS) concept, in which a small front-end circuit is located beneath each electrode. However, this approach imposes challenging constraints on the area of the in-pixel circuit, power consumption and noise. Here, we present an APS CMOS-probe technology for Simultaneous Neural recording that successfully addresses all these issues for whole-array read-outs at 25 kHz/channel from up to 1024 electrode-pixels. To assess the circuit performances, we realized in a 0.18 μm CMOS technology an implantable single-shaft probe with a regular array of 512 electrode-pixels with a pitch of 28 μm. Extensive bench tests showed an in-pixel gain of 45.4 ± 0.4 dB (low pass, F_-3 dB = 4 kHz), an input referred noise of 7.5 ± 0.67 μV_RMS (300 Hz to 7.5 kHz) and a power consumption <6 μW/pixel. In vivo acute recordings demonstrate that our SiNAPS CMOS-probe can sample full-band bioelectrical signals from each electrode, with the ability to resolve and discriminate activity from several packed neurons both at the spatial and temporal scale. These results pave the way to new generations of compact and scalable active single/multi-shaft brain recording systems.

Recovery of early neural spikes from stimulation electrodes using a DC-coupled low gain high resolution data acquisition system

BACKGROUND

Neural responses to electrical stimulation provide valuable information to probe and study the network function. Especially, recording neural responses from the stimulated site provides improved neural interfacing method. However, it is difficult to measure short-delayed responses at the stimulated electrode due to the saturation of the amplifier after stimulation which is called "stimulus artifact". Despite the advances in handling stimulation artifacts, it is still very challenging to deal with the artifacts if one tries to stimulate and record from the same electrode.

NEW METHOD

In this paper, we developed a system consisting of 24 bit ADC and low gain DC-amplifier which allows us to record the entire responses including saturation-free stimulus artifact and neural responses with excellent resolution.

RESULTS

Our approach showed saturation-free recording after stimulation, which makes it possible to recover neural spike as early as in 2 ms at the stimulating electrode with digital elimination methods.

COMPARISON WITH EXISTING METHODS

With our system we could record neural signals after stimulation that was difficult with high gain and high pass filtered recording system due to amplifier saturation.

CONCLUSIONS

Our new system can enhance interface performance with its higher robustness and with simple system configuration.

Frequency-dependent, transient effects of subthalamic nucleus deep brain stimulation on methamphetamine-induced circling and neuronal activity in the hemiparkinsonian rat

Methamphetamine-induced circling is used to quantify the behavioral effects of subthalamic nucleus (STN) deep brain stimulation (DBS) in hemiparkinsonian rats. We observed a frequency-dependent transient effect of DBS on circling, and quantified this effect to determine its neuronal basis. High frequency STN DBS (75-260Hz) resulted in transient circling contralateral to the lesion at the onset of stimulation, which was not sustained after the first several seconds of stimulation. Following the transient behavioral change, DBS resulted in a frequency-dependent steady-state reduction in pathological ipsilateral circling, but no change in overall movement. Recordings from single neurons in globus pallidus externa (GPe) and substantia nigra pars reticulata (SNr) revealed that high frequency, but not low frequency, STN DBS elicited transient changes in both firing rate and neuronal oscillatory power at the stimulation frequency in a subpopulation of GPe and SNr neurons. These transient changes were not sustained, and most neurons exhibited a different response during the steady-state phase of DBS. During the steady-state, DBS produced elevated neuronal oscillatory power at the stimulus frequency in a majority of GPe and SNr neurons, and the increase was more pronounced during high frequency DBS than during low frequency DBS. Changes in oscillatory power during both transient and steady-state DBS were highly correlated with changes in firing rates. These results suggest that distinct neural mechanisms were responsible for transient and sustained behavioral responses to STN DBS. The transient contralateral turning behavior following the onset of high frequency DBS was paralleled by transient changes in firing rate and oscillatory power in the GPe and SNr, while steady-state suppression of ipsilateral turning was paralleled by sustained increased synchronization of basal ganglia neurons to the stimulus pulses. Our analysis of distinct frequency-dependent transient and steady-state responses to DBS lays the foundation for future mechanistic studies of the immediate and persistent effects of DBS.

Chronic intracortical neural recordings using microelectrode arrays coated with PEDOT-TFB

Microelectrode arrays have been extensively utilized to record extracellular neuronal activity for brain-machine interface applications. Modifying the microelectrodes with conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) has been reported to be advantageous because it increases the effective surface area of the microelectrodes, thereby decreasing impedance and enhancing charge transfer capacity. However, the long term stability and integrity of such coatings for chronic recordings remains unclear. Previously, our group has demonstrated that use of the smaller counter ion tetrafluoroborate (TFB) during electrodeposition increased the stability of the PEDOT coatings in vitro compared to the commonly used counter ion poly(styrenesulfonate) (PSS). In the current work, we examined the long-term in vivo performance of PEDOT-TFB coated microelectrodes. To do so, we selectively modified half of the microelectrodes on NeuroNexus single shank probes with PEDOT-TFB while the other half of the microelectrodes were modified with gold as a control. The modified probes were then implanted into the primary motor cortex of rats. Single unit recordings were observed on both PEDOT-TFB and gold control microelectrodes for more than 12 weeks. Compared to the gold-coated microelectrodes, the PEDOT-TFB coated microelectrodes exhibited an overall significantly lower impedance and higher number of units per microelectrode specifically for the first four weeks. The majority of PEDOT-TFB microelectrodes with activity had an impedance magnitude lower than 400 kΩ at 1 kHz. Our equivalent circuit modeling of the impedance data suggests stability in the polymer-related parameters for the duration of the study. In addition, when comparing PEDOT-TFB microelectrodes with and without long-term activity, we observed a distinction in certain circuit parameters for these microelectrodes derived from equivalent circuit modeling prior to implantation. This observation may prove useful in qualifying PEDOT-TFB microelectrodes with a greater likelihood of registering long-term activity. Overall, our findings confirm that PEDOT-TFB is a chronically stable coating for microelectrodes to enable neural recording.

STATEMENT OF SIGNIFICANCE

Microelectrode arrays have been extensively utilized to record extracellular neuronal activity for brain-machine interface applications. Poly(3,4-ethylenedioxythiophene) (PEDOT) has gained interest because of its unique electrochemical characteristics and its excellent intrinsic electrical conductivity. However, the long-term stability of the PEDOT film, especially for chronic neural applications, is unclear. In this manuscript, we report for the first time the use of highly stable PEDOT doped with tetrafluoroborate (TFB) for long-term neural recordings. We show that PEDOT-TFB coated microelectrodes on average register more units compared to control gold microelectrodes for at least first four weeks post implantation. We collected the in vivo impedance data over a wide frequency spectrum and developed an equivalent circuit model which helped us determine certain parameters to distinguish between PEDOT-TFB microelectrodes with and without long-term activity. Our findings suggest that PEDOT-TFB is a chronically stable coating for neural recording microelectrodes. As such, PEDOT-TFB could facilitate chronic recordings with ultra-small and high-density neural arrays.

The need for and the challenges of measuring renal sympathetic nerve activity

Renal denervation (RDN) was primarily developed to treat hypertension and is potentially a new method for treating arrhythmias. Because of the lack of a standardized protocol to measure renal sympathetic nerve activity, RDN is administered in a blind manner. This inability to assess efficacy at the time of treatment delivery may be a large contributor to the ambiguity of RDN outcomes reported in the hypertension literature. The advancement of RDN as a treatment of hypertension or arrhythmias will be hampered by the lack of delivery assessment, a deficiency that the cardiovascular electrophysiology community, with its expertise in recording and mapping, may have a role in addressing and overcoming. The development of endovascular recording of renal nerve action potentials may provide a useful accessory tool for RDN. Innovation in this area will be crucial as we as a community reconsider the therapeutic value of RDN.

Implantable neurotechnologies: a review of micro- and nanoelectrodes for neural recording

Electrodes serve as the first critical interface to the biological organ system. In neuroprosthetic applications, for example, electrodes interface to the tissue for either signal recording or tissue stimulation. In this review, we consider electrodes for recording neural activity. Recording electrodes serve as wiretaps into the neural tissues, providing readouts of electrical activity. These signals give us valuable insights into the organization and functioning of the nervous system. The recording interfaces have also shown promise in aiding treatment of motor and sensory disabilities caused by neurological disorders. Recent advances in fabrication technology have generated wide interest in creating tiny, high-density electrode interfaces for neural tissues. An ideal electrode should be small enough and be able to achieve reliable and conformal integration with the structures of the nervous system. As a result, the existing electrode designs are being shrunk and packed to form small form factor interfaces to tissue. Here, an overview of the historic and state-of-the-art electrode technologies for recording neural activity is presented first with a focus on their development road map. The fact that the dimensions of recording electrode sites are being scaled down from micron to submicron scale to enable dense interfaces is appreciated. The current trends in recording electrode technologies are then reviewed. Current and future considerations in electrode design, including the use of inorganic nanostructures and biologically inspired or biocomapatible materials are discussed, along with an overview of the applications of flexible materials and transistor transduction schemes. Finally, we detail the major technical challenges facing chronic use of reliable recording electrode technology.

Measurement of evoked potentials during thalamic deep brain stimulation

BACKGROUND

Deep brain stimulation (DBS) treats the symptoms of several movement disorders, but optimal selection of stimulation parameters remains a challenge. The evoked compound action potential (ECAP) reflects synchronized neural activation near the DBS lead, and may be useful for feedback control and automatic adjustment of stimulation parameters in closed-loop DBS systems.

OBJECTIVES

Determine the feasibility of recording ECAPs in the clinical setting, understand the neural origin of the ECAP and sources of any stimulus artifact, and correlate ECAP characteristics with motor symptoms.

METHODS

The ECAP and tremor response were measured simultaneously during intraoperative studies of thalamic DBS, conducted in patients who were either undergoing surgery for initial lead implantation or replacement of their internal pulse generator.

RESULTS

There was large subject-to-subject variation in stimulus artifact amplitude, which model-based analysis suggested may have been caused by glial encapsulation of the lead, resulting in imbalances in the tissue impedance between the contacts. ECAP recordings obtained from both acute and chronically implanted electrodes revealed that specific phase characteristics of the signal varied systematically with stimulation parameters. Further, a trend was observed in some patients between the energy of the initial negative and positive ECAP phases, as well as secondary phases, and changes in tremor from baseline. A computational model of thalamic DBS indicated that direct cerebellothalamic fiber activation dominated the clinically measured ECAP, suggesting that excitation of these fibers is critical in DBS therapy.

CONCLUSIONS

This work demonstrated that ECAPs can be recorded in the clinical setting and may provide a surrogate feedback control signal for automatic adjustment of stimulation parameters to reduce tremor amplitude.