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A DSP Architecture for Distortion-Free Evoked Compound Action Potential Recovery in Neural Response Telemetry System
Abstract
Abstract:
This paper presents a digital signal processing (DSP) architecture for real-time and distortion-free recovery of electrically-evoked compound action potentials (ECAPs) from stimulus artifacts and periodic noises in bidirectional neural response telemetry (NRT) system. In this DSP architecture, a low computation-cost bidirectional-filtered coherent averaging (BFCA) method is proposed for programmable linear-phase filtering of ECAPs, which can be easily combined with the alternating-polarity (AP) stimulation method to reject stimulus artifacts overlapped with ECAP responses. Design techniques including the configurable folded infinite-impulse-response (IIR) filter and division-free averaging are also presented for efficient hardware implementation. Implemented in 180-nm CMOS process, the proposed DSP architecture consumes 10.03-mm2 area and 2.35-mW post-layout simulated power. The efficacy of the DSP architecture in recovering ECAPs from recorded neural data contaminated by overlapped stimulus artifacts and periodic noises is validated in in-vivo electrical nerve stimulations. Experiment results show that compared with the previous coherent averaging technique, the proposed DSP architecture improves the signal-to- noise ratio (SNR) of ECAP responses by 11 dB and achieves an 3.1% waveform distortion that is 17.1× lower.
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The electrically evoked compound action potential (eCAP) represents the synchronous firing of a population of electrically stimulated auditory nerve fibers. It can be directly recorded on a surgically exposed nerve trunk in animals or from an intra-cochlear electrode of a cochlear implant. In the past two decades, the eCAP has been widely recorded in both animals and clinical patient populations using different testing paradigms. This paper provides an overview of recording methodologies and response characteristics of the eCAP, as well as its potential applications in research and clinical situations. Relevant studies are reviewed and implications for clinicians are discussed.
Key points:
The brainstem dorsal column nuclei (DCN) process sensory information arising from the body before it reaches the brain and becomes conscious. Despite significant investigations into sensory coding in peripheral nerves and the somatosensory cortex, little is known about how sensory information arising from the periphery is represented in the DCN. Following stimulation of hind-limb nerves, we mapped and characterised the evoked electrical signatures across the DCN surface. We show that evoked responses recorded from the DCN surface are highly reproducible and are unique to nerves carrying specific sensory information.
Abstract:
The brainstem dorsal column nuclei (DCN) play a role in early processing of somatosensory information arising from a variety of functionally distinct peripheral structures, before being transmitted to the cortex via the thalamus. To improve our understanding of how sensory information is represented by the DCN, we characterised and mapped low- (<200 Hz) and high-frequency (550-3300 Hz) components of nerve-evoked DCN surface potentials. DCN surface potentials were evoked by electrical stimulation of the left and right nerves innervating cutaneous structures (sural nerve), or a mix of cutaneous and deep structures (peroneal nerve), in 8-week-old urethane-anaesthetised male Wistar rats. Peroneal nerve-evoked DCN responses demonstrated low-frequency events with significantly longer durations, more high-frequency events and larger magnitudes compared to responses evoked from sural nerve stimulation. Hotspots of low- and high-frequency DCN activity were found ipsilateral to stimulated nerves but were not symmetrically organised. In conclusion, we find that sensory inputs from peripheral nerves evoke unique and characteristic DCN activity patterns that are highly reproducible both within and across animals.
This work presents a bidirectional neural interface circuit that enables simultaneous recording and stimulation with a stimulation artifact cancellation circuit. The system employs a common average referencing (CAR) front-end circuit to suppress cross-channel environmental noise to further facilitate use in clinical environment. This paper also introduces a new range-adapting (RA) SAR ADC to lower the system power consumption. A prototype is fabricated in 0.18 μm CMOS and characterized and tested in vivo in an epileptic rat model. The prototype attenuates stimulation artifacts by up to 42 dB and suppresses cross-channel noise by up to 39.8 dB. The measured power consumption per channel is 330 nW, while the area per channel is 0.17 mm2.
In this paper, a discrete wavelet transform (DWT) based de-noising with its applications into the noise reduction for medical signal preprocessing is introduced. This work focuses on the hardware realization of a real-time wavelet de-noising procedure. The proposed de-noising circuit mainly consists of three modules: a DWT, a thresholding, and an inverse DWT (IDWT) modular circuits. We also proposed a novel adaptive thresholding scheme and incorporated it into our wavelet de-noising procedure. Performance was then evaluated on both the architectural designs of the software and. In addition, the de-noising circuit was also implemented by downloading the Verilog codes to a field programmable gate array (FPGA) based platform so that its ability in noise reduction may be further validated in actual practice. Simulation experiment results produced by applying a set of simulated noise-contaminated electrocardiogram (ECG) signals into the de-noising circuit showed that the circuit could not only desirably meet the requirement of real-time processing, but also achieve satisfactory performance for noise reduction, while the sharp features of the ECG signals can be well preserved. The proposed de-noising circuit was further synthesized using the Synopsys Design Compiler with an Artisan Taiwan Semiconductor Manufacturing Company (TSMC, Hsinchu, Taiwan) 40 nm standard cell library. The integrated circuit (IC) synthesis simulation results showed that the proposed design can achieve a clock frequency of 200 MHz and the power consumption was only 17.4 mW, when operated at 200 MHz.
Electrical vagus nerve stimulation is a treatment alternative for many epileptic and depressed patients whose symptoms are not well managed with pharmaceutical therapy. However, the fixed stimulus, open loop dosing mechanism limits its efficacy and precludes major advances in the quality of therapy. A real-time, responsive form of vagus nerve stimulation is needed to control nerve activation according to therapeutic need. This personalized approach to therapy will improve efficacy and reduce the number and severity of side effects. We present autonomous neural control, a responsive, biofeedbackdriven approach that uses the degree of measured nerve activation to control stimulus delivery. We demonstrate autonomous neural control in rats, showing that it rapidly learns how to most efficiently activate any desired proportion of vagal A, B, and/or C fibers over time. This system will maximize efficacy by minimizing patient response variability and by minimizing therapeutic failures resulting from longitudinal decreases in nerve activation with increasing durations of treatment. The value of autonomous neural control equally applies to other applications of electrical nerve stimulation.
Noise removal of Electrocardiogram has always been a subject of wide research. ECG signals change their statistical properties over time. Wavelet transform is the most powerful tool for analyzing the non-stationary signals. This paper shows that how it is useful in denoising non-stationary signals e.g. The ECG signals. We considered two types of ECG signal, without additional noise and corrupted by powerline interference and we realized the signal's denoising using wavelet filtering. The ECG data is taken from standard MIT-BIH Arrhythmia database, while noise signal is generated and added to the original signal using instructions in MATLAB environment. In this paper, we present Daubechies wavelet analysis method with a decomposition tree of level 5 for analysis of noisy ECG signals. The implementation includes the procedures of signal decomposition and reconstruction with hard and soft thresholding. Furthermore quantitative study of result evaluation has been done based on Signal to Noise Ratio (SNR). The results show that, on contrast with traditional methods wavelet method can achieve optimal denoising of ECG signal.
As the most successful neural prosthesis, cochlear implants have provided partial hearing to more than 120000 persons worldwide; half of which being pediatric users who are able to develop nearly normal language. Biomedical engineers have played a central role in the design, integration and evaluation of the cochlear implant system, but the overall success is a result of collaborative work with physiologists, psychologists, physicians, educators, and entrepreneurs. This review presents broad yet in-depth academic and industrial perspectives on the underlying research and ongoing development of cochlear implants. The introduction accounts for major events and advances in cochlear implants, including dynamic interplays among engineers, scientists, physicians, and policy makers. The review takes a system approach to address critical issues in cochlear implant research and development. First, the cochlear implant system design and specifications are laid out. Second, the design goals, principles, and methods of the subsystem components are identified from the external speech processor and radio frequency transmission link to the internal receiver, stimulator and electrode arrays. Third, system integration and functional evaluation are presented with respect to safety, reliability, and challenges facing the present and future cochlear implant designers and users. Finally, issues beyond cochlear implants are discussed to address treatment options for the entire spectrum of hearing impairment as well as to use the cochlear implant as a model to design and evaluate other similar neural prostheses such as vestibular and retinal implants.
Coherent averaging is used to recover the response to repetitively applied stimuli when that response is embedded in random noise, and when the signal/noise ratio is fractional. In this paper the improvement in s/n ratio due to averaging is calculated; it is also shown that averaging acts as a filter which attenuates periodic interference when it is not time-locked to the stimulus; the characteristics of this filter are derived.
Previous studies have shown that electrical stimulation of the stomach (i.e., gastric pacing) with appropriate parameters is a promising method for treatment of gastroparetic patients. The recording of gastric myoelectric activity (GMA) by serosal electrodes is often used to evaluate the effect of stimulation. However, the major problem with the measurement of GMA during gastric pacing is the stimulus artifacts which are often superimposed on the serosal recording and make analysis difficult. The frequency-domain adaptive filter has been used to reduce the stimulus artifacts but only with limited success. This paper describes a wavelet transform-based method for the reduction of stimulus artifacts in the serosal recordings of GMA. The key of this method lies in the use of the fuzzy set theory to select the stimulus artifact-related modulus maxima in the wavelet domain. Both quantitative and qualitative measures show that significant stimulus artifact cancellation was achieved through a series of computer simulations. Results from both single- and multichannel serosally recorded myoelectric signals during gastric pacing are presented to demonstrate the efficiency of the proposed method for the cancellation of stimulus artifacts.
During the last decade, cochlear implantation has evolved into a well-established treatment of deafness, predominantly because of many improvements in speech processing and the controlled excitation of the auditory nerve. Cochlear implants now also feature telemetry, which is highly useful to monitor the proper functioning of the implanted electronics and electrode contacts. Telemetry can also support the clinical management in young children and difficult cases where neural unresponsiveness is suspected. This article will review recent advances in the telemetry of the electrically evoked compound action potential that have made these measurements simple and routine procedures in most cases. The distribution of the electrical stimulus itself sampled by "electrical field imaging" reveals general patterns of current flow in the normal cochlea and gross abnormalities in individual patients; models have been developed to derive more subtle insights from an individual electrical field imaging. Finally, some thoughts are given to the extended application of telemetry, for example, in monitoring the neural responses or in combination with other treatments of the deaf ear.
In this retinal prosthesis project, a rehabilitative device is
designed to replace the functionality of defective photoreceptors in
patients suffering from retinitis pigmentosa (RP) and age-related
macular degeneration (AMD). The device consists of an extraocular and an
intraocular unit. The implantable component receives power and a data
signal via a telemetric inductive link between the two units. The
extraocular unit includes a video camera and video processing board, a
telemetry protocol encoder chip, and an RF amplifier and primary coil.
The intraocular unit consists of a secondary coil, a rectifier and
regulator, a retinal chip with a telemetry protocol decoder, a stimulus
signal generator, and an electrode array. This paper focuses on the
design, fabrication, and testing of a microchip which serves as the
telemetry protocol decoder and stimulus signal generator. It is
fabricated by MOSIS with 1.2-mm CMOS technology and was demonstrated to
provide the desired biphasic current stimulus pulses for an array of 100
retinal electrodes at video frame rates
Neuromodulation (NM) is the alteration of nervous tissue function through targeted delivery of a stimulus, such as electrical stimulation, into the affected neurological sites in the body. We present a bidirectional NM interface that features 100 mVpp linear input range and ability to sense data concurrent with stimulation (without blanking). The system includes a flexible 8-driver-to-64-contact custom waveform stimulator able to deliver up to 5.1 mA per driver and a 64-contact sensing unit with online blind artifact rejection unit. This artifact rejection unit removes stimulation artifacts from recorded data and allows extraction of neural biomarkers. The NM interface also features an efficient, integrated power management unit that can support various power delivery options. The proposed 64-contact interface satisfies design requirements of human-grade brain implants at unprecedented level of electronic miniaturization compared to state-of-the-art.
Implantable closed-loop neuromodulation devices for use in long-term chronic studies in a lab or clinical trial are expensive to acquire and difficult to modify for specific use cases. This article documents the design and fabrication of a wireless implantable device using only commercially available off-the-shelf (COTS) components. This device, called the Bionode, can record and transmit up to four channels of biopotential data while simultaneously providing biphasic constant-current stimulation. The Bionode is a viable, low-cost, reusable, and easily modifiable research tool with clinical implications that has gained widespread use in various research projects at Purdue University.
The Shewhart and CUSUM control chart techniques have found wide application in the manufacturing industries. However, workpiece quality has also been greatly enhanced by rapid and precise individual item measurements and by improvements in automatic dynamic machine control. One consequence is a growing similarity in the control problems faced by the workpiece quality control engineer and his compatriot in the continuous process industries. The purpose of this paper is to exposit a control chart technique that may be of value to both manufacturing and continuous process quality control engineers: the exponentially weighted moving average (EWMA) control chart. The EWMA has its origins in the early work of econometricians, and although its use in quality control has been recognized, it remains a largely neglected tool. The EWMA chart is easy to plot, easy to interpret, and its control limits are easy to obtain. Further, the EWMA leads naturally to an empirical dynamic control equation.
This brief proposes an efficient very-large-scale integration architecture for folded configurable infinite-impulse response (IIR) filter design, which is used in modern real-time digital signal processing applications such as loudspeaker equalization. The proposed configurable sixth-order IIR filter is designed with three cascaded second-order IIR filters, and the same is used to perform one sixth-order or three second-order or one fourth-order and one second-order IIR filter operations in parallel, where floating-point multiply-accumulate circuit (MAC) is used to design each second-order IIR filter. The proposed sixth-order IIR filter achieves a 58.4% reduction in energy per operation compared with conventional MAC-based architecture using 45-nm technology.
As more is learned about the mechanism of operation of the central nervous system, the characteristic of the mechanism that becomes the most impressive is the exquisite timing of the events. For example, if an impulse of subliminal effectiveness impinges upon a synapse, it leaves a trace which lasts only a few tenths of a millisecond. If within that time another impulse, likewise of subliminal effectiveness, arrives at the same region on the surface of the neuron, the two impulses together will raise excitation to the threshold, and a relayed message will be sent upon its way. Stated in other words, if the two impulses arrive at the synapse at an interval of separation longer than a few tenths of a millisecond, there is no transmission; and the local disturbance that each impulse produces dies out promptly, to leave the junctional area restored to its antecedent state ready for any new impulses that may be coming on. Transmission at any point thus depends upon the arrival of excitation from the various controlling centers in exactly the right time relations. Thereby the flow of impulses is always properly directed toward the end reaction appropriate to the conditioning data picked up by the body receptors. The timing of impulses starts in the beginning of all reactions—in the sensory messages that report changes in the state of the body and in the character of the environment. At least no other interpretation explains as satisfactorily why sensory messages are carried at so wide a range of velocities. For some reason not at all well understood it is necessary for some impulses to shoot out ahead to prepare the central nervous system for other impulses that arrive later. In as simple an event as pricking the skin of the finger with a needle there is first a short burst of impulses carried in fibers conducting at 90 meters or more per second (20). Then there follow impulses at other velocities, many at about twenty meters per second; and finally there is a trail of impulses at about one meter per second. Before any of the last mentioned group arrives at the centers, a complex neurological event has taken place— the withdrawal of the hand; and the sensation of pricking has been appreciated. The sensation aroused by the slow fibers is still, however, that of pain indistinguishable qualitatively from the pain already felt. But in its setting it has a stinging, irritating character. It can be relieved by rubbing the spot, that is, it may be inhibited by sending into the central nervous system a flood of impulses carried in rapidly conducting fibers. It is not my intention in the present paper to follow up this argu-ment, but to let the observations stand as an introductory background to the main theme, which is the basis of the numerous velocities in nerve fibers. Visualization of the wide range of velocities can best be accom-145 146 HERBERT S. GASSER Vol. XLI plished by showing what happens when a sensory nerve is artificially stimulated with an electrical shock of short duration. All the impulses start out together from the locus of the stimulus, but the fast impulses forge ahead. Thus, if a lead be taken at some distance from the point of stimulation, at the beginning of the action potential there are initially recorded the first impulses to arrive; and the other impulses are recorded later, at times inversely proportional to their velocities. As all the velocities are not equally represented among the fibers, the result is an action potential with distinctive elevations. The contour here pre-sented (Pig. 1), taken from the saphenous nerve of the cat, is character-istic of all sensory nerves. It starts with a high elevation contributed by fibers conducting at velocities ranging approximately between 95 and 35 m.p.s. The high elevation is succeeded by a very small one in which velocities between 35 and 22 m.p.s. are represented; and this in turn is followed by a somewhat larger one representing velocities between 22 and 15 m.p.s. In the wake of the latter there are still a few impulses at a velocity slower than 15 m.p.s. Figure 1 (left). Action potential of the saphenous nerve of the cat as recorded after 4 cm. of conduction from the stimulating cathode. The first disturbance in the line marks the moment of stimulation, and the interval between this point and the start of the first high elevation measures the conduction time of the fastest fibers. The potentials contributed by the other fibers follow in succession. Figure 2 (right). Action potential of the saphenous nerve of the rabbit as recorded after 4 cm. of conduction.
This paper presents an infinite impulse response (IIR) temporal filtering technique for real-time stimulus artifact rejection (SAR) based on template subtraction. A system architecture for the IIR SAR algorithm is developed, and the operation of the algorithm with fixed-point computation is analyzed to obtain the number of bits for the internal nodes of the system, considering dynamic range and fraction length requirements for optimum performance. Further, memory initialization with the first recorded stimulus artifact is proposed and shown to significantly decrease the IIR system response time, especially when artifacts are highly reproducible in consecutive stimulation cycles. The proposed system architecture is hardware-implemented on a field-programmable gate array (FPGA) and tested using two sets of prerecorded neural data from a rat and an Aplysia californica (a marine sea slug) obtained from two different laboratories. The measured results from the FPGA verify that the system can indeed remove the stimulus artifacts from the contaminated neural data in real time and recover the neural action potentials that occur on the tail end of the artifact (as close as within 0.5 ms after the artifact spike). The root-mean-square (rms) value of the pre-processed stimulus artifact is reduced on average by a factor of 17 (Aplysia californica) and 5.3 (rat) post-processing.
This paper presents the design of a digital Infinite Impulse Response (IIR) filter for active filtering applications, which are useful for the correction of harmonic currents produced by non linear loads. The designed hardware architecture of the digital IIR filter was coded in VHDL (Very high speed integrated Hardware Description Language) for Field Programmable Gate Array (FPGA) implementation. The obtained computation time of the IIR filter is very low and only equal to 1.62 μs. Numerous simulation results are presented in order to illustrate the efficiency of the designed IIR filter.
If you are working in digital signal processing, control or numerical analysis, you will find this authoritative analysis of quantization noise (roundoff error) invaluable. Do you know where the theory of quantization noise comes from, and under what circumstances it is true? Get answers to these and other important practical questions from expert authors, including the founder of the field and formulator of the theory of quantization noise, Bernard Widrow. The authors describe and analyze uniform quantization, floating-point quantization, and their applications in detail. Key features include: Analysis of floating point round off Dither techniques and implementation issues analyzed Offers heuristic explanations along with rigorous proofs, making it easy to understand 'why' before the mathematical proof is given.
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If you are working in digital signal processing, control or numerical analysis, you will find this authoritative analysis of quantization noise (roundoff error) invaluable. Do you know where the theory of quantization noise comes from, and under what circumstances it is true? Get answers to these and other important practical questions from expert authors, including the founder of the field and formulator of the theory of quantization noise, Bernard Widrow. The authors describe and analyze uniform quantization, floating-point quantization, and their applications in detail. Key features include: Analysis of floating point round off Dither techniques and implementation issues analyzed Offers heuristic explanations along with rigorous proofs, making it easy to understand 'why' before the mathematical proof is given
Bluetooth (over IEEE 802.15.1), ultra-wideband (UWB, over IEEE 802.15.3), ZigBee (over IEEE 802.15.4), and Wi-Fi (over IEEE 802.11) are four protocol standards for short- range wireless communications with low power consumption. From an application point of view, bluetooth is intended for a cordless mouse, keyboard, and hands-free headset, UWB is oriented to high-bandwidth multimedia links, ZigBee is designed for reliable wirelessly networked monitoring and control networks, while Wi-Fi is directed at computer-to-computer connections as an extension or substitution of cabled networks. In this paper, we provide a study of these popular wireless communication standards, evaluating their main features and behaviors in terms of various metrics, including the transmission time, data coding efficiency, complexity, and power consumption. It is believed that the comparison presented in this paper would benefit application engineers in selecting an appropriate protocol.
Medium nerve somatosensory evoked potentials (SSEPs) and intraoperative spinal evoked potentials were analyzed using different analog and zero phase shift digital high pass filter and by power spectrum. Additionally, high pass analog and digital filtering was performed on various sine, triangular and rectangular waves manufactured by a wave form generator. Recordings were also transformed to the 1st and 2nd time derivatives.The great abundance of spectral energy for scalp recorded median nerve SSEPs was below 125 c/sec but lower energy fast frequency components consistently extended to 500 c/sec. Power spectrum of the Erb's point compound nerve action potential revealed a wide band of spectral energy commencing at about 50–100 c/sec, peaking at about 250–270 c/sec and extending to nearly 1000 c/sec. This suggests that synchronous axonal activity generates predominantly faster frequencies above 100 c/sec.High pass analog filter confers phase non-linearity which results in various distortions including latency shift and a morphological change which may be visually similar to the 1st or 2nd time derivatives. High pass zero phase shift digital filter removes selected low frequencies without accompanying phase distortion. This accentuates fast peaks seen at open bandpass as well as transition points between baseline and component ascent or descent. Zero phase shift digital filter may also generate peaks that are not visualized at open pass but which reflect the sum of frequencies which were not removed by filtering. These peaks do not necessarily correspond to discrete singular neuroanatomical structures.Although peaks observed in high pass analog and digital filter appear similar and comparable, their underlying activity may be of different origin. This is because high pass analog filter projects a considerable amount of overlap from earlier onto later waves.For clinical correlation it is important that restricted bandpass analog or digitally filtered recordings be compared with open pass data. Only those peaks visualized in both open and restricted bandpass can be considered authentic. Examples of spinal and scalp SSEPs indicate that selective filtering may, under certain circumstances, distinguish axonal or lemniscal from synaptic generators.RésuméDes potentiels évoqués somatosensoriels (PES) à la stimulation du nerf médian et des potentiels évoqués spinaux en cours d'opération ont été analysés en utilisant divers filtres analogique ou numérique sans déphasage et par le spectre de puissance. De plus, les filtrages passe haut analogique et numérique étaient effectués sur des ondes sinusoïdales, triangulaires ou rectangulaires. Les enregistrements ont également été dérivés.Pour les PES de scalp à la stimulation du nerf médian le maximum de puissance se situait au-desous de 125 c/sec, les composantes de haute fréquence à plus faible puissance s'étendait jusqu'à 500 c/sec. La puissance spectrale du potentiel d'action nerveux composé au point d'Erb a présenté une large bande de puissance commençant vers 100 c/sec, atteignant son maximum vers 250 c/sec et s'étendant jusqu'à près de 1000 c/sec. Ce résultat suggère que l'activité axonale synchrone produit principalement les fréquences les plus hautes, au-dessus de 100 c/sec.Les filtres analogiques passe haut entraînent une non-linéarité de phase, d'où des déformations diverses, telles que variations de latence, modifications de forme trés similaires à la dérivée première par rapport au temps. Les filtres numériques passe haut sans déphasage éliminent certaines basses fréquences déterminées sans pour cela s'accompagner d'une déformation de phase. Ceci amplifie les pics rapides vus avec bandes passantes ouvertes ainsi que les points de transition entre la ligne de base et les composantes ascendantes ou descendantes. Un filtre numérique sans déphasage peut aussi produire des pics qui ne sont pas visibles sans filtrage sélectif mais qui reflètent la sommation de fréquences n'ayant pas été éliminées par le filtrage. Ces pics ne correspondent pas nécessairement à des structures neuroantomiques particulières.Pour effectuer des corrélations cliniques, il est important que des enregistrements filtrés numériquement ou analogiqument avec des bandes passantes restreintes soient comparés avec des données non filtrées. Seuls les pics visible à la fois sans filtrage et avec bande passante restreinte peuvent être considérés comme authentiques. Des exemples de PES de scalp et de PES spinaux indiquent qu'un filtrage sélectif pourraat dans certaines permettre la distinction entre générateurs synaptiques, axonaux ou lemniscaux.
The analysis of stimulus evoked neuromuscular potentials or m-waves is a useful technique for improved feedback control in functional electrical stimulation systems. Usually, however, these signals are contaminated by stimulus artifact. A novel software technique, which uses a two-stage peak detection algorithm, has been developed to remove the unwanted artifact from the recorded signal. The advantage of the technique is that it can be used on all stimulation artifact-contaminated electroneurophysiologic data provided that the artifact and the biopotential are non-overlapping. The technique does not require any estimation of the stimulus artifact shape or duration. With the developed technique, it is not necessary to record a pure artifact signal for template estimation, a process that can increase the complexity of experimentation. The technique also does not require the recording of any external hardware synchronisation pulses. The method avoids the use of analogue or digital filtering techniques, which endeavour to remove certain high frequency components of the artifact signal, but invariably have difficulty, resulting in the removal of frequencies in the same spectrum as the m-wave. With the new technique the signal is sampled at a high frequency to ensure optimum fidelity. Instrumentation saturation effects due to the artifact can be avoided with careful electrode placement. The technique was fully tested with a wide variety of electrical stimulation parameters (frequency and pulse width) applied to the common peroneal nerve to elicit contraction in the tibialis anterior. The program was also developed to allow batch processing of multiple files, using closed loop feedback correction. The two-stage peak detection artifact removal algorithm is demonstrated as an efficient post-processing technique for acquiring artifact free m-waves.
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This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615-627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 micro V have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6-0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74-0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.
Two experimental methods are used and compared for the determination of the frequency spectra of nerve action potentials.
Both methods are shown capable of putting small differences between waveforms into quantitative form, and are applied to the
problem of the comparison of compound nerve action potentials detected at increasing distance between stimulus and detector.
The results show good agreement between experimental results and theoretical predictions based on the dispersion of the compound
nerve action potential. Frequency spectra suggest that the bandwidth of some biological amplifiers are unnecessarily large.
An experimental study of the electrical stimulation of the guinea pig cochlea is made using an electrode on the round window for both stimulation and recording. The neural response is separated from the electrical artifact with a masking procedure combined with a low amplification, "statistical" averaging method [Charlet de Sauvage et al., Hear. Res. 2, 343-346 (1980)]. The high electrical impedance required for recording physiological responses implies the use of a current pulse generator. Monitoring of evoked potentials from the auditory cortex provides evidence that the effects of electrical stimulation (and of masking noise) are of auditory origin. The electrically evoked round window response is of very short latency (less than 0.2 ms). There is a response threshold for both electrical stimulus and masking noise. The response amplitude varies monotonically as a function of masking noise or electrical stimulus intensity. Experiments with high-pass noise masking suggest that the electrical stimulus is mainly acting on basal fibers. The response latency and waveform are independent of electrical stimulus intensity, repetition rate, masker level, or spectrum. Little intersubject variation is noted. Our experiments (reciprocal forward masking by electrical and acoustic stimuli) suggest that a direct, instantaneous electrical stimulation of the fibers occurs. We believe that this response to electrical stimulation represents the mean unit response of the auditory nerve fibers. This approach may be useful in the separate study of cochlear and VIIIth nerve functions and in the analysis (deconvolution) of the acoustically evoked compound AP.
When stimulating muscles, EMG signals recorded in neighboring muscles can be contaminated by stimulus artifacts, and artifact deletion is necessary. We have devised a digital technique for removing stimulus artifacts from rectified EMG recordings in muscles which lie close to a stimulated muscle. This artifact deletion method replaces the rectified EMG during the artifact interval with an estimate of the rectified EMG. Our research requires detection of very small changes in EMG levels. Therefore, the artifact deletion technique described in this paper was designed to leave less than 10 microV of artifact in the rectified EMG post-processing. This technique relies on being able to estimate the artifact duration. Since stimulated muscles have M-waves that can overlap with artifacts, our technique is only appropriate for removing artifacts in muscles which are not being stimulated. Unlike other artifact elimination techniques, our technique does not change the mean value of the rectified EMG, regardless of artifact width. In addition, it provides a more accurate estimate of the rectified EMG during the artifact interval as opposed to sample-and-hold techniques.
This study aimed to compare recordings of the electrically evoked whole nerve action potential (EAP) made using the reverse telemetry system of the Nucleus CI24M device with those recorded from individuals who use the Ineraid cochlear implant system.
Data were collected in a prospective fashion from Nucleus CI24M cochlear implant users and compared with retrospective data collected from patients who use the Ineraid device.
All data were collected at the Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics.
Data are reported from 8 patients who use the Nucleus CI24M cochlear implant and 20 patients who use the Ineraid cochlear implant system.
The interventions described in this study were diagnostic in nature.
EAP growth and refractory recovery data are reported. EAP thresholds recorded from patients who use the Nucleus CI24M device also are compared with behavioral thresholds for the stimulus used to evoke the EAP as well as the stimulation levels needed to program the speech processor.
EAP morphology, growth, and refractory recovery functions recorded using the Nucleus CI24M reverse telemetry system compared favorably with similar measures recorded from Ineraid cochlear implant users.
Reasonable EAP responses can be recorded using the Nucleus CI24M device. More data are needed to determine whether the information about neural responsiveness available with this device will be clinically useful.
The author discusses the accomplishments and challenges in treating sensorineurnal deafness through electrical stimulation.
The main aim of this study was to validate a new technique, neural response telemetry (NRT), for measuring the electrically evoked compound action potential in adult cochlear implant users via their Nucleus C124M implant. Thirty-eight adults were evaluated with a variety of measurement procedures with the NRT software. Electrically evoked compound action potentials were obtained in 31 of the 38 adults (81.6%) and in 132 of the 160 electrodes (82.5%) tested. In addition to validating this technique, we also established a set of default clinical test parameters.
We describe an algorithm for suppression of stimulation artifacts in extracellular micro-electrode array (MEA) recordings. A model of the artifact based on locally fitted cubic polynomials is subtracted from the recording, yielding a flat baseline amenable to spike detection by voltage thresholding. The algorithm, SALPA, reduces the period after stimulation during which action potentials cannot be detected by an order of magnitude, to less than 2 ms. Our implementation is fast enough to process 60-channel data sampled at 25 kHz in real-time on an inexpensive desktop PC. It performs well on a wide range of artifact shapes without re-tuning any parameters, because it accounts for amplifier saturation explicitly and uses a statistic to verify successful artifact suppression immediately after the amplifiers become operational. We demonstrate the algorithm's effectiveness on recordings from dense monolayer cultures of cortical neurons obtained from rat embryos. SALPA opens up a previously inaccessible window for studying transient neural oscillations and precisely timed dynamics in short-latency responses to electric stimulation.
Electrical stimulus artifact corrupting electrophysiological recordings often makes the subsequent analysis of the underlying neural response difficult. This is particularly evident when investigating short-latency neural activity in response to high-rate electrical stimulation. We developed and evaluated an off-line technique for the removal of stimulus artifact from electrophysiological recordings. Pulsatile electrical stimulation was presented at rates of up to 5000 pulses/s during extracellular recordings of guinea pig auditory nerve fibers. Stimulus artifact was removed by replacing the sample points at each stimulus artifact event with values interpolated along a straight line, computed from neighbouring sample points. This technique required only that artifact events be identifiable and that the artifact duration remained less than both the inter-stimulus interval and the time course of the action potential. We have demonstrated that this computationally efficient sample-and-interpolate technique removes the stimulus artifact with minimal distortion of the action potential waveform. We suggest that this technique may have potential applications in a range of electrophysiological recording systems.
The FFT processor is one of the key components in the
implementation of wideband OFDM systems. Architectures with a structured
pipeline have been used to meet the fast, real-time processing demand
and low-power consumption requirement in a mobile environment.
Architectures based on new forms of FFT, the radix-2i
algorithm derived by cascade decomposition, is proposed. By exploiting
the spatial regularity of the new algorithm, the requirement for both
dominant elements in VLSI implementation, the memory size and the number
of complex multipliers, have been minimized. Progressive wordlength
adjustment has been introduced to optimize the total memory size with a
given signal-to-quantization-noise-ratio (SQNR) requirement in
fixed-point processing. A new complex multiplier based on distributed
arithmetic further enhanced the area/power efficiency of the design. A
single-chip processor for 1 K complex point FFT transform is used to
demonstrate the design issues under consideration
This paper presents a general-purpose computer program which is capable of designing a large Class of optimum (in the minimax sense) FIR linear phase digital filters. The program has options for designing such standard filters as low-pass, high-pass, bandpass, and bandstop filters, as well as multipassband-stopband filters, differentiators, and Hilbert transformers. The program can also be used to design filters which approximate arbitrary frequency specifications which are provided by the user. The program is written in Fortran, and is carefully documented both by comments and by detailed flowcharts. The filter design algorithm is shown to be exceedingly efficient, e.g., it is capable of designing a filter with a 100-point impulse response in about 20 s.
A method for designing finite-duration impulse-response (FIR) linear-phase digital filters is presented in which the four possible cases for such filters are treated in a unified approach. It is shown how to reduce each case to the proper form so that the Remez exchange algorithm can be used to compute the best approximation to the desired frequency response. The result is that a very flexible and fast technique is available for FIR linear-phase filter design.
A new modified circuit for implementing high performance IIR
filters based on a pipelined multiply-accumulate (MAC) processor is
proposed. Clever deployment of latches in the circuit allows the results
to be generated once every cycle thereby providing increased performance
with reduced size and power consumption over previously designed
circuits
A novel approach to designing approximately linear phase infinite-impulse-response (IIR) digital filters in the passband region is introduced. The proposed approach yields digital IIR filters whose numerators represent linear phase finite-impulse-response (FIR) filters. As an example, low-pass IIR differentiators are introduced. The range and high-frequency suppression of the proposed low-pass differentiators are comparable to those obtained by higher order FIR low-pass differentiators. In addition, the differentiators exhibit almost linear phases in the passband regions
A real-time IIR filter structure is presented that possesses exact
phase linearity with 10~1000 times fewer general multiplies than
conventional FIR filters of similar performance and better magnitude
characteristics than equiripple or maximally flat group delay IIR
filters. This structure is based on a technique using local time
reversal and single pass sectioned convolution methods to realized a
real-time recursive implementation of the noncausal transfer function
H ( z -1). The time reversed section technique
used to realize exactly linear phase IIR filters is described. The
effects of finite section length on the sectional convolution are
analyzed. A simulation methodology is developed to address the special
requirements of simulating a time reversed section filter. A design
example is presented, with computer simulation to illustrate
performance, in terms of overall magnitude response and phase linearity,
as a function of finite section length. Nine example filter
specifications are used to compare the performance and complexity of the
time reversed section technique to those of a direct FIR implementation
This paper presents a new method for designing digital linear phase, finite impulse response filters with loose frequency response characteristics, but with good time resolution as is required in biological signal conditioning. The design is very simple and has been used with success in the microcomputer implementation of filters for the automated processing of electroencephalographic (EEG) data. Examples and a discussion of possible filter implementations are included. Copyright © 1986 by The Institute of Electrical and Electronics Engineers, Inc.
The electrical stimulus pulse and the surface electrodes commonly used to study compound action potentials of peripheral nerves give rise to an artifact consisting of an initial spike and a longer lasting tail which often interferes with the recorded signal. The artifact has four sources: 1) the voltage gradient between the recording electordes caused by stimulus current flowing through the limb, 2) the common-mode voltage of the limb caused by current escaping through the ground electrode, 3) the capacitive coupling between the stimulating and recording leads, and 4) the high-pass filtering characteristics of the recording amplifier. This paper models these sources and presents several methodological rules for minimizing their effects. Also presented are three computer-based methods for subtracting the residual artifact from contaminated records using estimates of the artifact obtained from: 1) subthreshold stimulation, 2) a second recording site remote from the nerve, or 3) stimulation during the refractory period of the nerve.
Discrete Wavelet Transformations: An Elementary Approach With Applications