Noise and selectivity of velocity-selective multi-electrode nerve cuffs

Using a multi-electrode nerve-signal recording cuff and a method of signal processing described previously, activity in axons with different propagation velocities can be distinguished, and the relative amplitude of the small-fibre signals increased. This paper is, largely, an analysis of the selectivity and noise of this system though impedance measurements from an actual cuff are included. The signal processor includes narrow band-pass filters. It is shown that the selectivity and noise both increase with the centre frequencies of these filters. A convenient approach is to make the filter frequencies inversely related to the artificial time delays so that the filter ‘Q’s are approximately constant and the noise densities are equal for all velocity filters. Numerical calculations, using formulae for this system and for the conventional tripole, based on a fixed cuff size and tissue resistivity, find the number of action potentials per second that must pass through the cuff so that the signal power equals the noise power. For slow fibres (20 m/s), the rate is 14 times lower for the multi-electrode cuff than the tripole, a significant advantage for recording from these fibres.     

Measurement of the performance of nerve cuff electrodes for recording

New designs of cuff electrodes for the recording of signals from peripheral nerves are typically tested in acute animal experiments before long-term evaluation takes place. A reproducible, cost-effective and fast method is presented for evaluating cuff electrodes with respect to signal amplitude, noise rejection, and, in some cases, selectivity, as an alternative to acute in vivo experiments. Comparisons with a computer model and with signals obtained from rabbit tibial nerve give good agreement with the new method. It is shown that an imperfect closure of the cuff around the nerve can easily lead to more than 50% loss of the signal amplitude. Noise from sources external to the cuff is not significantly affected by the closing mechanism, but is strongly reduced by a tripolar cuff configuration as compared with a monopolar one (reduction factor 2.8 to 58, mean=6.5, n=6). In dual-channel cuffs, cross-talk is below 1.2% indicating a very high selectivity.     

A method for simultaneously recording neural activity and rotation in the rat

An apparatus is described which allows the simultaneous recording of neural activity and rotational behaviour in the rat. Rotational behaviour is measured, coded and stored on magnetic tape along with neural activity from chronically implanted electrodes, allowing off-line computer analysis.     

Transverse tripolar stimulation of peripheral nerve: a modelling study of spatial selectivity

Various anode-cathode configurations in a nerve cuff are modelled to predict their spatial selectivity characteristics for functional nerve stimulation. A 3D volume conductor model of a monofascicular nerve is used for the computation of stimulation-induced field potentials, whereas a cable model of myelinated nerve fibre is used for the calculation of the excitation thresholds of fibres. As well as the usual configurations (monopole, bipole, longitudinal tripole, ‘steering’ anode), a transverse tripolar configuration (central cathode) is examined. It is found that the transverse tripole is the only configuration giving convex recruitment contours and therefore maximises activation selectivity for a small (cylindrical) bundle of fibres in the periphery of a monofascicular nerve trunk. As the electrode configuration is changed to achieve greater selectivity, the threshold current increases. Therefore threshold currents for fibre excitation with a transverse tripole are relatively high. Inverse recruitment is less extreme than for the other configurations. The influences of several geometrical parameters and model conductivities of the transverse tripole on selectivity and threshold current are analysed. In chronic implantation, when electrodes are encapsulated by a layer of fibrous tissue, threshold currents are low, whereas the shape of the recruitment contours in transverse tripolar stimulation does not change.     

A method for recording unit neural activity in unanaesthetized sheep and goats

A chronic preparation has been made in horned sheep and goats for recording unit activity in unanaesthetized animals. The micro-electrode manipulator is supported by means of a metal bar permanently attached to the animal's horns. A perforated lucite block, implanted into the roof of the cranium, rendered a large part of the brain accessible for recording. A brief outline is given of the advantages of sheep and goats for experimental work on brain function and behavior.     

Analysis and microelectronic design of tubular electrode arrays intended for chronic,multiple singleunit recording from captured nerve fibres

The paper discusses proposals for recording multiple single-unit potentials from nerve fibres that become captured in an array of tube electrodes. Capturing may be through regeneration of cut fibres or by placement of dissected filaments into grooves which are then covered. The factors contributing to signal-to-noise ratios obtainable with this type of electrode are discussed. The design, construction and bench-test results are given for an electrode array in which thin-film microelectronic techniques are used to build a densely packed, flexible, 3-dimensional electrode array consisting of a bundle of plastic tubes with flat metal contacts at midtube.     

Noise characteristic design of CMOS source follower and voltage amplifier for active semiconductor microelectrodes for neural signal recording

A noise performance design method for the pre-amplifiers of an active neural probe is given. The on-chip circuitry of the active neural probe consists of CMOS devices that show high-/ low-frequency noise, so that the device noise can become dominant. Analysis of the signal-to-device-noise ratio (SDNR) for the CMOS source follower buffer and two-stage differential voltage amplifier is given. Closed-form expressions for the output noise power are derived and exploited to tailor the parameters that are controllable during circuit design. The output SDNR is calculated considering the real extracellular action potentials, the electrode-electrolyte interface and the noise spectrum of CMOS devices from typical foundries. It is shown that the output device noise power can be much higher than the output signal power if the devices at the input stage of the pre-amplifier are made as small as given fabrication technology permits. Quantitative information of the circuit parameters to achieve an SDNR higher than 5 for neural spikes with 60μV amplitude are provided for both preamplifier types.     

A model of myelinated nerve fibres for electrical prosthesis design

Starting with the spatially extended non-linear node model (Reilly et al., 1985), which incorporates Frankenhaeuser-Huxley non-linearities at each of several nodes in a row, a model is developed to describe many aspects of the behaviour of mammalian nerve fibres in a quantitative way. By taking into account the effects of temperature and by introducing a realistic nerve morphology, a good fit is obtained between the shape, duration and conduction velocity of simulated and in vivo action potentials in mammals. The resulting model correctly predicts the influence of physiological variations of body temperature on various aspects of nerve behaviour. It is shown that the absolute refractory period predicted by the model is within physiological ranges. Both in vivo and in the model, the spike amplitude and the spike conduction velocity are reduced in the relative refractory period. It is concluded that single-node models (although widely used) cannot replace this multiple nonlinear node model, as the stimulus repetition rates that can be followed by the simulated nerve fibre are limited by impulse conduction properties, rather than by the frequency following behaviour of a single node.     

Microdrive and method for single unit recording in the active rat

A technique for recording single unit activity in the active rat with microelectrodes is described. The microdrive used is small and light enough to be carried in a well that is chronically implanted on the head of the rat. The device permits standard microelectrodes to be lowered without rotation, a feature which reduces chance of damage to the fine tips and to the brain tissue. The microdrive itself may be rotated in the well and several penetrations in a single preparation are possible. The electrodes used are capable of recording unit activity of high amplitude and stability. Units may be held for minutes or hours depending on the intensity of the rat's behavior.     

Modelling motor cortex stimulation for chronic pain control: Electrical potential field, activating functions and responses of simple nerve fibre models

This computer modelling study on motor cortex stimulation (MCS) introduced a motor cortex model, developed to calculate the imposed electrical potential field characteristics and the initial response of simple fibre models to stimulation of the precentral gyrus by an epidural electrode, as applied in the treatment of chronic, intractable pain. The model consisted of two parts: a three-dimensional volume conductor based on tissue conductivities and human anatomical data, in which the stimulationinnduced potential field was computed, and myelinated nerve fibre models allowing the calculation of their response to this field. A simple afferent fibre branch and three simple efferent fibres leaving the cortex at different positions in the precentral gyrus were implemented. It was shown that the thickness of the cerebrospinal fluid (CSF) layer between the dura mater and the cortex below the stimulating electrode substantially affected the distribution of the electrical potential field in the precentral gyrus and thus the threshold stimulus for motor responses and the therapeutic stimulation amplitude. When the CSF thickness was increased from 0 to 2.5 mm, the load impedance decreased by 28%, and the stimulation amplitude increased by 6.6 V for each millimetre of CSF. Owing to the large anode-cathode distance (10 mm centre-to-centre) in MCS, the cathodal fields in mono- and bipolar stimulation were almost identical. Calculation of activating functions and fibre responses showed that only nerve fibres with a directional component parallel to the electrode surface were excitable by a cathode, whereas fibres perpendicular to the electrode surface were excitable under an anode.     

Audio-visual recording of patient-GP consultations for research purposes: a literature review on recruiting rates and strategies

Objective

To identify ethical processes and recruitment strategies, participation rates of studies using audio or video recording of primary health care consultations for research purposes, and the effect of recording on the behaviour, attitudes and feelings of participants.

Methods

A structured literature review using Medline, Embase, Cochrane Library, and Psychinfo. This was followed by extensive hand search.

Results

Recording consultations were regarded as ethically acceptable with some additional safeguards recommended. A range of sampling and recruitment strategies were identified although specific detail was often lacking. Non-participation rates in audio-recording studies ranged from 3 to 83% for patients and 7 to 84% for GPs; in video-recording studies they ranged from 0 to 83% for patients and 0 to 93% for GPs. There was little evidence to suggest that recording significantly affects patient or practitioner behaviour.

Conclusions

Research involving audio or video recording of consultations is both feasible and acceptable. More detailed reporting of the methodical characteristics of recruitment in the published literature is needed.

Practice implications

Researchers should consider the impact of diverse sampling and recruitment strategies on participation levels. Participants should be informed that there is little evidence that recording consultations negatively affects their content or the decisions made. Researchers should increase reporting of ethical and recruitment processes in order to facilitate future reviews and meta-analyses.     

Development and evaluation of silk fibroin-based nerve grafts used for peripheral nerve regeneration

Silk fibroin (SF), derived from natural silk long used as a textile material, has recently become an important biomaterial for tissue engineering applications. We have previously reported on good in vitro biocompatibility of SF fibers with peripheral nerve tissues and cells. In the present study, we developed a novel biomimetic design of the SF-based nerve graft (SF graft) which was composed of a SF-nerve guidance conduit (NGC) inserted with oriented SF filaments. The SF-NGC prepared via well-established procedures exhibits an eggshell-like microstructure that is responsible for its superior mechanical and permeable properties beneficial to nerve regeneration. The SF graft was used for bridge implantation across a 10-mm long sciatic nerve defect in rats, and the outcome of peripheral nerve repair at 6 months post-implantation was evaluated by a combination of electrophysiological assessment, FluoroGold retrograde tracing and histological investigation. The examined functional and morphological parameters show that SF grafts could promote peripheral nerve regeneration with effects approaching those elicited by nerve autografts which are generally considered as the gold standard for treating large peripheral nerve defects, thus raising a potential possibility of using these newly developed nerve grafts as a promising alternative to nerve autografts.     

Magnetic and electrical stimulation of undulating nerve fibres: a simulation study

Mathematical models of myelinated nerve fibres are highly stylized abstractions of real nerve fibres. For example, nerve fibres are usually assumed to be perfectly straight. Such idealizations can cause discrepancies between theoretical predictions and experimental results. One well-known discrepancy is that the currently used models predict (contradictory to experimental findings) that an activation of nerve fibres is not possible with a pure transverse electric field. This situation occurs when a magnetic coil is placed symmetrically above a straight nerve fibre for magnetic nerve stimulation, or when an anode and a cathode are placed equidistantly on a line perpendicular to the fibre in the case of electrical stimulation. It is shown that this discrepancy does not occur if the physiological undulation of peripheral nerve fibres is included in the models. Even for small undulation amplitudes (e.g. 0.02 mm), it is possible to activate the fibre in these positions. For physiological undulations, as found in the literature, and favourable (off-centre) positions, the typical reduction of the thresholds is in a range between one and five, compared with perfectly straight fibres.     

Magnetic and electrical stimulation of undulating nerve fibres: a simulation study

Mathematical models of myelinated nerve fibres are highly stylised abstractions of real nerve fibres. For example, nerve fibres are usually assumed to be perfectly straight. Such idealisations can cause discrepancies between theoretical predictions and experimental results. One well-known discrepancy is that the currently used models predict (contradictory to experimental findings) that an activation of nerve fibres is not possible with a pure transverse electric field. This situation occurs when a magnetic coil is placed symmetrically above a straight nerve fibre for magnetic nerve stimulation, or when an anode and a cathode are placed equidistantly on a line perpendicular to the fibre in the case of electrical stimulation. It is shown that this discrepancy does not occur if the physiological undulation of peripheral nerve fibres is included in the models. Even for small undulation amplitudes (e.g. 0.02 mm), it is possible to activate the fibre in these positions. For physiological undulations, as found in the literature, and favourable (off-centre) positions, the typical reduction of the thresholds is in a range between one and five, compared with perfectly straight fibres.     

载NGF海藻酸凝胶-聚乳酸复合导管修复兔面神经缺损实验研究

目的    观察载神经生长因子（nerve growth factors, NGF）海藻酸凝胶-聚乳酸复合导管修复面神经缺损的作用。  方法    建立白兔面神经缺损模型,将面神经断端植入制备好的载NGF海藻酸凝胶-聚乳酸复合导管内2 mm,使面神经两断端之间距离为10 mm,将导管两端与神经固定缝合皮肤。再随机将12只大白兔分为术后4、8、12周组。实验结束后切开大白兔面神经吻合部位,选取神经导管近、中和远端组织进行HE染色,观察神经生长及导管降解情况。  结果    实验白兔手术伤口Ⅰ期愈合,无局部坏死、移植物排出及全身不良反应。术后4周导管壁有巨噬细胞浸润,导管近端雪旺细胞、成纤维细胞增生,新生小血管丰富;8周可见导管壁变薄,有成纤维细胞附着,巨噬细胞浸润,导管内有神经束样结构,束间纤维分隔,外层纤维包膜增厚,新生小血管减少;12周可见神经导管壁进一步分解,胶原纤维增生,导管内神经纤维结构接近正常,轴突样结构增粗,外层纤维包膜变薄。  结论    载NGF海藻酸凝胶-聚乳酸复合导管能较好的引导面神经再生,具有良好的组织相容性。     

神经信号检测和功能激励微电极

多学科交叉研究神经功能重建已经成为神经科学和微电子学的一个新的研究热点,主要介绍神经功能重建系统的重要部件——神经微电极。阐述神经电极与神经细胞的耦合原理,从不同角度介绍神经微电极的分类和发展并描述了其具体的微机电工艺实例,对神经微电极的生物相容性也做了介绍。     

Source analysis of median nerve and finger stimulated somatosensory evoked potentials: Multichannel simultaneous recording of electric and magnetic fields combined with 3d-MR tomography

Summary At the current state of technology, multichannel simultaneous recording of combined electric potentials and magnetic fields should constitute the most powerful tool for separation and localization of focal brain activity. We performed an explorative study of multichannel simultaneous electric SEPs and magnetically recorded SEFs. MEG only sees tangentially oriented sources, while EEG signals include the entire activity of the brain. These characteristics were found to be very useful in separating multiple sources with overlap of activity in time. The electrically recorded SEPs were adequately modelled by three equivalent dipoles located: (1) in the region of the brainstem, modelling the P14 peak at the scalp, (2) a tangentially oriented dipole, modelling the N20-P20 and N30-P30 peaks, and part of the P45, and (3) a radially oriented dipole, modelling the P22 peak and part of the P45, both located in the region of the somatosensory cortex. Magnetically recorded SEFs were adequately modelled by a single equivalent dipole, modelling the N20-P20 and N30-P30 peaks, located close to the posterior bank of the central sulcus, in area 3b (mean deviation: 3 mm). The tangential sources in the electrical data were located 6 mm on average from the area 3b. MEG and EEG was able to locate the sources of finger stimulated SEFs in accordance with the somatotopic arrangement along the central fissure. A combined analysis demonstrated that MEG can provide constraints to the orientation and location of sources and helps to stabilize the inverse solution in a multiple-source model of the EEG.     

股神经和闭孔神经肌支转位的解剖学测量和神经纤维定量

目的　探索股神经肌支转位修复闭孔神经损伤与闭孔神经肌支修复股神经损伤的应用解剖。 方法　游标卡尺测量20具成人尸体股神经和闭孔神经肌支的长度;6具死亡3~10 h内尸体,其股神经和闭孔神经的肌支经Karnovsky-Roots法染色后,图像分析仪测量它们的横切面积和神经纤维数量。 结果　股神经肌支中股内侧肌长支最长,近端横断面积最大;闭孔神经肌支中股薄肌支最长,大收肌支近端横切面积最大。每条肌支内均以躯体运动纤维含量最高,股神经肌支中股内侧肌长支躯体运动纤维数量最多,而闭孔神经肌支中大收肌支最多,其次是股薄肌支。各肌支中γ-薄髓神经纤维的含量,股神经的肌支中以股内侧肌短支和股直肌支较高;而闭孔神经肌支中短收肌支含量最高。 结论　基于各肌支长度、近端横断面积和神经纤维数量的综合考虑,股神经和闭孔神经损伤修复中,股内侧肌长支和股薄肌支宜为供体神经;股内侧肌短支和股直肌支以及大收肌支宜为受体神经。     

Microcomputer-based system for 24-hour recording of oesophageal motility and pH profile with automated analysis

A system developed for long-term simultaneous recording of eosophageal motility and pH in the ambulant patient is described. The system consists of a microprocessor based data-acquisition and preprocessing device, a personal computer for postprocessing, report generation and data storage, a miniature two-sensor pressure catheter and a pH electrode. Identification and classification of oesophageal contractions are performed in separate steps, using online preprocessing software for identification and offline postprocessing software for categorisation, classification and report generation. Contractions are categorised as peristaltic, simultaneous or nontransmitted and classified according to their amplitude, duration and propagation velocity. The method described reduces the amount of data from 870 kbyte to approximately 40kbyte per 24 hours in a multiparameter recording device, and offers the opportunity for offline postprocessing with different sets of criteria. The system has been found to be accurate and reliable in 24-hour studies in both healthy volunteers and patients with non-cardiac chest pain.