Single unit recording capabilities of a 100 microelectrode array

We have developed a three-dimensional silicon electrode array which provides 100 separate channels for neural recording in cortex. The device is manufactured using silicon micromachining techniques, and we have conducted acute recording experiments in cat striate cortex to evaluate the recording capabilities of the array. In a series of five acute experiments, 58.6% of the electrodes in the array were found to be capable of recording visually evoked responses. In the most recent acute study, the average signal-to-noise ratio for recordings obtained from 56 of the electrodes in the array was calculated to be 5.5:1. Using standard window discrimination techniques, an average of 3.4 separable spikes were identified for each of these electrodes. In order to compare the two-dimensional mapping capabilities of the array with those derived from other technologies, orientation preference and ocular dominance maps were generated for each of the evoked responses. Histological evaluation of the implant site indicates some localized tissue insult, but this is likely due to the perfusion procedure since high signal-to-noise ratio neural responses were recorded. The recording capabilities of the Utah Intracortical Electrode Array in combination with the large number of electrodes available for recording make the array a tool well suited for investigations into the parallel processing mechanisms in cortex.     

The Utah intracortical Electrode Array: a recording structure for potential brain-computer interfaces

We investigated the potential of the Utah Intracortical Electrode Array (UIEA) to provide signals for a brain-computer interface (BCI). The UIEA records from small populations of neurons which have an average signal-to-noise ratio (SNR) of 6:1. We provide specific examples that show the activities of these populations of neurons contain sufficient information to perform control tasks. Results from a simple stimulus detection task using these signals as inputs confirm that the number of neurons present in a recording is significant in determining task performance. Increasing the number of units in a recording decreases the sensitivity of the response to the stimulus; decreasing the number of units in the recording, however, increases the variability of the response to the stimulus. We conclude that recordings from small populations of neurons, not single units, provide a reliable source of sufficiently stimulus selective signals which should be suitable for a BCI. In addition, the potential for simultaneous and proportional control of a large number of external devices may be realized through the ability of an array of microelectrodes such as the UIEA to record both spatial and temporal patterns of neuronal activation.     

Noninvasive electrodes for electrocochleography in the chinchilla

This study compares noninvasive vs invasive electrodes for electrocochleography in chinchillas. Summating potential (SP) amplitude, action potential (AP) amplitude, and AP threshold, recorded with five types of noninvasive electrodes, were compared with simultaneous bulla recordings. Noninvasive electrodes included a needle electrode over the bulla, gold Tiptrode (Etymotic Research, Elk Grove Village, Ill), Enhancer I (Nicolet Instrument Corp, Madison, Wis), Coats (Lifetech Inc, Austin, Tex) electrode, and a locally constructed tympanic membrane (TM) electrode. Stimuli included 100-microsecond clicks and 6000-Hz tone bursts (with a 1 millisecond rise/fall time and a 5 millisecond plateau). Stimuli were initially presented at 110 dB peak equivalent sound pressure level for the clicks and 100 dB peak equivalent sound pressure level for the tone bursts. Intensity was then decreased in 10-dB decrements until no replicable AP activity was observed. The TM damping for the TM electrode was measured with 0.5, 1, 2, 4, and 6 kHz and click stimuli. The AP was clear and replicable for all electrodes used in the study, although the amplitude was substantially less for the noninvasive electrodes as opposed to the invasive electrode. The invasive electrode provided the largest amplitude SP recording, but SP could generally be clearly recorded with the needle electrode, Enhancer I, and the Coats electrode. The TM electrode and gold Tiptrode provided SP recordings less consistently. The AP threshold could be recorded with all the electrodes in the study and was generally within 10 dB of threshold recorded invasively. Electrode variables, including ease of electrode placement and potential injury, were examined. The Tiptrode and Enhancer I electrodes posed relatively few problems during placement.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrode pitting in resistance spot welding of aluminum alloy 5182

Electrode pitting was investigated in resistance spot welding of 1.5-mm-thick sheet aluminum alloy 5182 using a medium-frequency direct-current welder and electrodes with a tip face curvature radius of 50 mm and tip face diameter of 10 mm. Detailed investigation of the metallurgical interactions between the copper electrode and aluminum alloy sheet was carried out using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results indicated that electrode degradation, which eventually leads to weld failure, proceeded in four basic steps: aluminum pickup, electrode alloying with aluminum, electrode tip face pitting, and cavitation. Since pitting and cavitation result from Al pickup and alloying, periodic electrode cleaning could extend electrode tip life by limiting the buildup of Al on the tip face. This work is part of the effort to improve electrode tip life in resistance spot welding of aluminum alloys for automotive applications.     

Protocol for microneurography with concentric needle electrodes

In 1968, the method of human percutaneous microneurography with solid tungsten electrodes was introduced. Since then many investigators used this technique to study peripheral mechanisms in the somatosensory, motor and autonomic systems of conscious humans. Although some modifications of the method were described, the basic construction of the recording electrode has remained the same over the years. In the present protocol we describe in detail the procedures of microneurography using a thin diameter concentric needle electrode. There are some advantages with the concentric electrodes in comparison with the tungsten needles: (1) the electrical and mechanical properties of the electrode are stable which allows repeated use, (2) its restricted and one-dimensionally directed recording area provides the possibility to study topographical aspects within even a part of a peripheral nerve fascicle, and (3) multi-channel recordings can be achieved by adding more recording surfaces to the electrode. Based on recent investigations evaluating the recording properties of concentric electrodes we propose a novel procedure for signal analysis where template matching is incorporated. The analyses described in this protocol might also be applicable for extracellular recordings from muscle or elsewhere within the nervous system.     

Effects of TiC composite coating on electrode degradation in microresistance welding of nickel-plated steel

Electrode degradation has been studied during series-mode microresistance welding of thin-sheet nickel-plated steel to nickel. The main focus of the study was the effects of a TiC metal matrix composite coating. The results indicated that electrode degradation was caused predominantly by material loss due to pitting (as a result of the fracturing of local bonds between the electrode tip and sheet) and also by microscopic extrusion or plastic deformation (as a result of the softening of electrode tip regions). The composite coating improved tip life by about 70 pct, mainly because the TiC particles contained in the coating discouraged local bonding between the electrodes and sheets, and probably also improved the resistance to surface extrusion. It was also found that the use of an oxide-dispersion-strengthened copper alloy (Cu-Al₂O₃) improved tip life by only about 15 pct compared to the conventional precipitation-strengthened Cu-Cr-Zr electrode alloy.     

The impact of critical incidents in paediatric hospitals: a review

Recent data have implicated the size of surface electrodes as an important factor affecting peripheral nerve excitation. Therefore, we studied the effects of electrode size on the basic excitatory responses and on stimulus characteristics. Four different sizes of self-adhesive surface electrodes were applied over the medial and lateral gastrocnemius muscle of 20 healthy subjects. The excitatory levels were sensory threshold, motor threshold, pain threshold, and maximally tolerated painful stimulation. Stimulus parameters included a symmetric biphasic waveform, 200 microseconds phase duration, and a pulse repetition rate of 50 pps. Amplitude was increased until the appropriate excitatory response was achieved. At this amplitude level, the computerized recording system collected data of stimulus peak current, peak voltage, and phase charge as well as isometric plantar flexion force. Repeated measure analysis of variance and Newman-Keuls post hoc tests revealed that increasing electrode size significantly decreased voltage but increased current and phase charge magnitudes. With increasing electrode area, the ratios of voltage/current decreased nonlinearly, while the ratios of charge/voltage increased nonlinearly. The comfort of stimulation for the same amount of plantar flexion force improved significantly as electrode size became larger. We concluded that electrode size affects the stimulus parameters, comfort, and force generation associated with electrically induced excitatory responses. Electrode size should be considered an integral part of the attempt to improve subject response to transcutaneous electrical stimulation.     

Simultaneous multisite recordings and stimulation of single isolated leech neurons using planar extracellular electrode arrays

Planar extracellular electrode arrays provide a non-toxic, non-invasive method of making long-term, multisite recordings with moderately high spatial frequency (recording sites per unit area). This paper reports advances in the use of this approach to record from and stimulate single identified leech neurons in vitro. A modified enzyme treatment allowed identified neurons to be extracted with very long processes. Multisite extracellular recordings from the processes of such isolated neurons revealed both the velocity and direction of action potential propagation. Propagation in two cell types examined was from the broken stump towards the cell body (antidromic). This was true for spontaneous action potentials, action potentials produced by injecting current into the cell body and extracellular stimulation of the extracted process via a planar extracellular electrode. These results extend previous findings which have shown that the tip of the broken stump of extracted neurons has a high density of voltage-activated sodium channels. Moreover they demonstrate the applicability of extracellular electrode arrays for recording the electrical excitability of single cells.     

Evaluation of direct bladder stimulation with stainless steel woven eye electrodes

Encouraged by recent clinical reports of micturition induced in patients by direct bladder stimulation, we conducted a study of optimum methods of direct bladder stimulation. During surgery six male cats received eight large surface-area woven eye electrodes sutured to the bladder wall serosa, four on the bladder dome and four adjacent to the trigone area. Two additional small surface-area single knot electrodes were sutured in the trigone area. Suprapubic and intraperitoneal tubes were placed for pressure recording and bladder filling. Leg and pelvic floor EMG electrodes were also used for tethered recordings. One to eight weeks after surgery, optimum stimulation methods were evaluated as the animal freely moved about a urodynamic recording cage. Electrodes in the trigone region were more effective than electrodes on the dome and induced bladder contractions and voiding similar to spontaneously induced voiding with bladder filing. Large surface area, woven eye electrodes, composed of multistranded 316LVM stainless steel wire, were more effective than smaller surface area single knot electrodes. High stimulating frequencies (40 Hz) were better than lower frequencies (10 to 20 Hz), and a 1 millisecond pulse duration was optimal. Pulsing with stimulating currents from 10 to 25 mA induced effective bladder contractions with voiding when applied for 3 seconds. However, lower currents using longer stimulation periods were also effective. Bipolar electrodes with both electrodes on the bladder wall were superior to monopolar arrangements with the positive ground electrode along the animal's back. We concluded that in the able-bodied cat model, bladder contractile activity for micturition can be induced with direct bladder stimulation and with little discomfort. An effective stimulation protocol consists of capacitor-coupled monophasic pulses with large surface area bipolar electrodes in the trigone region. Stimulating parameters of 40 Hz, 1 msec., 10 to 25 mA applied for 3 seconds were optimal. In addition, based on corrosion resistance observations, the electrodes are quite suitable for long-term studies.     

Ambulatory monitoring of A/EEG in the preoperative assessment of partial epilepsy

INTRODUCTION: Electroencephalography, together with new neuroimaging techniques is still the main diagnostic tool for pre-operative assessment of epilepsy. The electrical episodes, both ictal and intercritical, are random paroxystic phenomena with regard to presentation, so the conventional EEG is sometimes of limited value. Therefore, in recent years, long duration EEG monitoring techniques have been favoured, with or without simultaneous recording of clinical behaviour, permitting recording for an indefinite period. Amongst these techniques, monitoring using cassette recording (A/EEG) if of specific interest since it permits the study of outpatients. OBJECTIVE: The main aim of surgical treatment of epilepsy is to abolish or reduce the number of crises. Therefore it is essential to localize the epileptogenic area as precisely as possible. The A/EEG has made a major contribution to the procedure of pre-operative assessment because of the considerable information it gives regarding the recording and character of the crises. MATERIAL AND METHODS: During the past three years, preoperative assessment has been carried out in our hospital on 44 patients with drug-resistant partial epilepsy. A total of 103 long duration cassette recordings (A/EEG) were done. Of these, 58 were done with surface electrodes and individualized set-up depending on the EEG findings, 8 with semi-invasive (sphenoid) electrodes, and 37 recordings used implanted sub-dural electrode strips. RESULTS: Combined study of the results obtained with these techniques permitted localization of the lesive-epileptogenic complex in 42 of these patients. We present the results obtained and conclude that A/EEG monitoring is useful in the pre-operative assessment of epilepsy.     

Monopolar needle electrode spatial recording characteristics

The recording characteristics of the monopolar needle in three dimensions have not been well established. A simple spherical recording territory is commonly assumed with the very tip proposed to have a greater spatial recording sensitivity by some authors. We demonstrate by enlarged physical modeling in a homogeneous volume conductor that the recorded amplitude diminishes more gradually radially away from the conical surface than distally past the tip or proximal to the insulation edge. The sensitivity over the exposed metallic surface is found to be uniformly proportional to the area, which results in relatively less sensitivity at the tip than the middle and proximal portions of the conical recording surface. The overall spatial amplitude recording characteristics can be better described by an apple shape than a sphere, centered at the midportion of the exposed conical surface. A better appreciation of the actual spatial recording characteristics of the monopolar needle electrode can result in more accurate physiologic interpretations of quantitative motor unit analysis.     

Motor evoked potentials: appropriate positioning of recording electrodes for diagnosis of spinal disorders

The interpretation of normal and pathological findings of motor evoked potential obtained by the use of transcranial magnetic stimulation depends on adequate examination technique, including the appropriate positioning of the recording electrodes over the muscle. On the basis of knowing the location of the motor end plate zones in muscles, magnetic stimulation of the motor cortex of 30 healthy adults was performed in order to explore the influence of the position of the surface recording electrodes on potential parameters and to establish the standard location of the recording electrodes over the biceps brachii, medial vastus, anterior tibial and abductor hallucis muscles for diagnostic use in spine disorders. The cortical latencies and peak-to-peak amplitudes of the evoked potentials were analysed by varying the location of the recording electrodes and the stimulus intensities. The latencies were significantly shorter when the different electrode lay more proximally over the muscle belly. Reproducible potentials with sharp negative onset and maximum amplitude were recorded with a separation of 5-7.5 cm between the different electrode, located over the motor end plate area, and the different electrode, located over the distal myotendinous junction. This implies that the parameters of evoked potentials depend on the position and separation distance of the recording electrodes over the muscles and that it is possible to record the potentials using a lower stimulus intensity and, above all, on relaxed muscles, which may prove to be applicable for intraoperative monitoring of the spinal cord using magnetic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morbidity of chronic recording with intracranial depth electrodes in 170 patients

A consecutive series of 170 patients who have been submitted to intracranial depth electrode recordings is reviewed to assess the overall morbidity of the technique. Most patients had bitemporal and frontal electrodes inserted and were monitored for an average period of 18 days. A surgically amenable focus was found in 85% of the cases. There were 4 cases of infection including 2 cerebral abscesses which required surgical evacuation. One patient with frontal lobe atrophy developed an acute subdural hematoma after electrode implantation. There was no death or neurological deficit in the entire series. Morbidity was encountered mainly in the neuropsychological sphere, several patients having developed transient postictal psychosis after repetitive seizures. Our recording technique has been associated with low surgical morbidity. Patients undergoing depth electrode recordings should be closely monitored to minimize the occurrence of psychotic episodes associated with drug withdrawal and increased seizure frequency.     

Integration of excitatory postsynaptic potentials in dendrites of motoneurons of rat spinal cord slice cultures

We examined the attenuation and integration of spontaneous excitatory postsynaptic potentials (sEPSPs) in the dendrites of presumed motoneurons (MNs) of organotypic rat spinal cord cultures. Simultaneous whole cell recordings in current-clamp mode were made from either the soma and a dendrite or from two dendrites. Direct comparison of the two voltage recordings revealed that the membrane potentials at the two recording sites followed each other very closely except for the fast-rising phases of the EPSPs. The dendritic recording represented a low-pass filtered version of the somatic recording and vice versa. A computer-assisted method was developed to fit the sEPSPs with a generalized alpha-function for measuring their amplitudes and rise times (10-90%). The mean EPSP peak attenuation between the two recording electrodes was determined by a maximum likelihood analysis that extracted populations of similar amplitude ratios from the fitted events at each electrode. For each pair of recordings, the amplitude attenuation ratio for EPSP traveling from dendrite to soma was larger than that traveling from soma to dendrite. The linear relation between mean ln attenuation and distance between recording electrodes was used to map 1/e attenuations into units of distance (micron). For EPSPs with typical time course traveling from the somatic to the dendritic recording electrode, the mean 1/e attenuation corresponded to 714 micron for EPSPs traveling in the opposite direction, the mean 1/e attenuation corresponded to 263 micron. As predicted from cable analysis, fast EPSPs attenuated more in both the somatofugal and somatopetal direction than did slow EPSPs. For EPSPs with rise times shorter than approximately 2.0 ms, the attenuation factor increased steeply. Compartmental computer modeling of the experiments with biocytin-filled and reconstructed MNs that used passive membrane properties revealed amplitude attenuation ratios of the EPSP traveling in both the somatofugal and somatopetal direction that were comparable to those observed in real experiments. The modeling of a barrage of sEPSPs further confirmed that the somato-dendritic compartments of a MN are virtually isopotential except for the fast-rising phase of EPSPs. Large, transient differences in membrane potential are locally confined to the site of EPSP generation. Comparing the modeling results with the experiments suggests that the observed attenuation ratios are adequately explained by passive membrane properties alone.     

Improved nerve cuff electrode recordings with subthreshold anodic currents

A method has been developed for improving the signal amplitudes of the recordings obtained with nerve cuff electrodes. The amplitude of the electroneurogram (ENG) has been shown to increase with increasing distance between the contacts when cuff electrodes are used to record peripheral nerve activity [9]. The effect is directly related to the propagation speed of the action potentials. Computer simulations have shown that the propagation velocity of action potentials in a length of a nerve axon can be decreased by subthreshold extracellular anodic currents. Slowing the action potentials is analogous to increasing the cuff length in that both result in longer intercontact delays, thus, larger signal outputs. This phenomenon is used to increase the amplitudes of whole nerve recordings obtained with a short cuff electrode. Computer simulations predicting the slowing effect of anodic currents as well as the experimental verification of this effect are presented. The increase in the amplitude of compound action potentials (CAP's) is demonstrated experimentally in an in vitro preparation. This method can be used to improve the signal-to-noise ratios when recording from short nerve segments where the cuff length is limited.     

Tri-axial recording of event-related potentials during passive cognitive tasks in patients with Alzheimer''s disease

A novel dynamic mathematical microelectrode model (a model of solvent and solute kinetics in electrolyte-filled microelectrodes) was deduced from experimental observations made on standard (single-barrelled, 3.0 M KCl-filled, approximately 10 M[ohm]) electrodes using (a) electrodiffusion, electro-osmosis, and continuity equations that were placed into the constraints of electrode geometry, and (b) handbook/textbook parameter values, only. The model proved to be able to faithfully reproduce all observed electrochemical and electrical electrode properties, i.e. even those that constituted no part of the model's experimental basis. In theoretical tests, the model shows, for the standard electrode that (a) inside the electrode, any profiles in electrical potential and electrolyte concentration are occurring at the most distal part (approximately 50 microm) of the tip region, (b) asymmetrical shifts in electrolyte concentration just inside the electrode tip opening are the true cause of the electrode's current rectification, and (c) strong transelectrode currents are producing water flows across the electrode orifice that may affect the volume of smaller and medium-sized cells. In further tests, the model shows, among other things, for non-standard electrodes that (a) decreasing the electrode electrolyte concentration will give rise to marked decreases in electrolyte leakage from the electrode, but only very minor changes in tip potential, and (b) increasing the surface charge of the electrode glass (increases in zeta potential) and/or decreasing the electrode electrolyte concentration will produce increases in electro-osmotic water transport, which may be desirable for the intracellular injection of water-soluble (electro-neutral) substances.     

基于电热场耦合条件下稀土电解槽电极结构优化模拟

以3kA钕电解槽为研究模型,考虑到电热场在电解过程中的相互影响,运用COMSOL有限元模拟软件建立了的电热耦合模型,并对不同配比的电极插入深度、极间距进行仿真模拟。结果表明,在一定槽电压下,电极插入深度与极间距之间存在配比关系,配比关系影响电流和温度分布。电热场耦合后,在4.2V槽电压下,电极插入深度为220 mm、极间距75 mm时的电流效率较高,电解过程更加稳定。     

Novel popout with nonsense strings: effects of predictability of string length and spatial location

The implanted system was composed of four silver ball electrodes placed in the burr hole of the skull, a reference placed subcutaneously near the nose, two electrodes for EMG, and a ground. The dural attachment was 0.1 mm in diameter. A cassette connector was placed on the back. Implanted cables between the cassette connector and all electrodes consist of twisted fine wires placed in a silicone tube 0.5 mm in diameter. The implanted electrode system weighed 0.8 g. The outlet cables were of the same materials used for implanted cables and placed in a silicone tube 1.5 mm in diameter. The impedance matching between these cables was successful and assured the minimum contamination of artifacts in the EEG recording of freely moving mice. Long-term (4-5 weeks) recording, thus, became possible without damage to the implanted materials. Monopolar recordings demonstrated the localized paroxysmal discharges during general tonic clonic convulsion in El mice. Several artifacts are presented.     

Factors responsible for computed electrogastrographic parameters in humans

OBJECTIVES: Clinical knowledge about myoelectrical frequency is well known, but the factors responsible for recorded myoelectrical amplitude remain less clear. METHODS: We assembled an electrogastrographic system that could automatically compute the dominant myoelectrical frequency and power and power ratio. We enrolled 50 healthy volunteers (25 men and 25 women) to study their myoelectrical characteristics. Three surface electrodes were placed in the fundic, stomach body, and antral positions for two 30-min recordings in the fasting and postprandial states. RESULTS: The three different electrodes recorded similar dominant frequencies of about 3 cpm before and after a meal. The fasting dominant powers from these electrodes were 52.9 +/- 14.7, 44.6 +/- 11.5, and 50.1 +/- 15.1 dB, respectively (p < 0.01), whereas the postprandial dominant powers were 61.6 +/- 28.8, 54.3 +/- 26.6, and 61.9 +/- 27.8 dB, respectively (p < 0.01). Meal ingestion did increase the power (p < 0.05). Women had a lower dominant power than men (p < 0.001). Moreover, the dominant powers of each electrode were significantly correlated with body mass index (r = 0.3-0.36, p < 0.05) regardless of meal ingestion. The postprandial power ratio was not influenced by electrode position, gender, or body mass index. CONCLUSIONS: Myoelectrical dominant frequencies and power ratios are similar throughout the whole stomach area, whereas a lower power area exists on the stomach body. Gender-related variation in dominant power seems to be an effect of body size. The power ratio is the only reliable parameter for expressing myoelectrical amplitude.     

Light scattering changes follow evoked potentials from hippocampal Schaeffer collateral stimulation

We assessed relationships of evoked electrical and light scattering changes from cat dorsal hippocampus following Schaeffer collateral stimulation. Under anesthesia, eight stimulating electrodes were placed in the left hippocampal CA field and an optic probe, coupled to a photodiode or a charge-coupled device camera to detect scattered light changes, was lowered to the contralateral dorsal hippocampal surface. Light at 660 +/- 10 (SE) nm illuminated the tissue through optic fibers surrounding the optic probe. An attached bipolar electrode recorded evoked right hippocampal commissural potentials. Electrode recordings and photodiode output were simultaneously acquired at 2.4 kHz during single biphasic pulse stimuli 0.5 ms in duration with 0.1-Hz intervals. Camera images were digitized at 100 Hz. An average of 150 responses was calculated for each of six stimulating current levels. Stimuli elicited a complex population synaptic potential that lasted 100-200 ms depending on stimulus intensity and electrode position. Light scattering changes peaked 20 ms after stimuli and occurred simultaneously with population spikes. A long-lasting light scattering component peaked 100-500 ms after the stimulus, concurrently with larger population postsynaptic potentials. Optical signals occurred over a time course similar to that for electrical signals and increased with larger stimulation amplitude to a maximum, then decreased with further increases in stimulation current. Camera images revealed a topographic response pattern that paralleled the photodiode measurements and depended on stimulation electrode position. Light scattering changes accompanied fast electrical responses, occurred too rapidly for perfusion, and showed a stimulus intensity relationship not consistent with glial changes.