Stimulus artefact in somatosensory evoked potential measurement

When an electrical stimulus is used to evoke action potentials in peripheral nerves or the spinal cord, the stimulus causes an artefact which may interfere with measurement of the evoked potentials. This artefact, unlike all other sources of noise in the measurement, cannot be reduced by ensemble averaging. Confusion about the origin and transmission of stimulus artefact has led to considerable frustration in spinal somatosensory evoked potential (SSEP) measurements. The three mechanisms by which stimulus artefact is coupled into the measuring system are identified, and means for their reduction are discussed.     

An evoked potential study of spinal pathways projecting to the cerebral somatosensory areas in the dog

Summary Evoked potentials from stimulation of the hindlimbs were recorded in the cerebral somatosensory areas of dogs using Nembutal anaesthesia. Various transections of the low thoracic spinal cord were made in order to determine the pathways projecting to these areas. The shortest latency cortical activation was obtained via two pathways: the dorsal column pathway and the spinocervical tract which is located in the dorsomedial part of the lateral funiculus (DLF). Cortical activation after longer latency was obtained via ventral pathways in both the contralateral and ipsilateral spinal halves. The cortical potentials elicited by adequate (hair) stimuli depended mainly on transmission via the dorsal column and DLF pathways.     

兔脑缺血的视觉和听觉诱发电位的变化

阻断兔双侧椎动脉（ＢＶＡ）和左颈总动脉（ＬＣＣＡ）后，夹闭右颈总动脉（ＲＣＣＡ）３、５、７ｍｉｎ，松开ＲＣＣＡ再灌流，记录听觉脑干诱发电位（ＢＡＥＰｓ）、中潜伏期听觉诱发电位（ＭＡＥＰｓ）以及视觉诱发电位（ＶＥＰｓ）。发现不全阻断脑血流后２．５ｍｉｎ，ＭＡＥＰｓ Ｎ０消失；４．５ｍｉｎ，ＶＥＰｓ Ｎ１和Ｐ２消失，ＢＡＦＰ３ Ⅰ～Ⅴ波峰值潜伏期延长，而振幅无明显变化。完全阻断脑血流１．５ｍｉｎ，ＶＥ     

Application of adaptive filtering to steady-state evoked response

A new method to detect steady-state evoked potentials (EPs) is presented. The technique is based on a two-weight recursive least squares (RLS) adaptive filter and the T _circ ² statistic. Simulations with known sinusoids buried in Gaussian noise and in EEG noise indicate that the adaptive filter can detect signals at 3 or 4 times lower signal-to-noise ratios that the discrete Fourier transform (DFT). Qualitatively similar results were obtained with human visual evoked potential recordings.     

椎－基底动脉供血不足患者脑干听觉诱发电位的观察

检查５８例椎－基底动脉供血不足患者脑干听觉诱发电位（ｂｒａｉｎｓｔｅｍａｕｄｉｔｏｒｙｅｖｏｋｅｄｐｏｔｅｎｔｉａｌＢＡＥＰ），异常率为６３．８％。ＢＡＥＰ异常可反映内耳前庭缺血、中枢缺血或两者皆有。ＢＡＥＰ检测对脑干缺血性疾病的诊断有一定的价值。     

提升小波在诱发电位提取中的应用研究

目的诱发电位信号的少次甚至单次提取一直是信号处理领域关注的热点问题之一,探讨如何利用提升小波有效提取诱发电位信号。方法首先基于仿真脑电数据,比较提升小波方法与多孔算法的去噪效果,选出具有最优小波基和分解层数的提升小波方法,再应用提升小波方法提取实际诱发电位信号。结果提升小波方法提取诱发电位信号波形特征明显,提高了信噪比,且其运算量只有传统方法的一半左右。结论提升小波的方法在诱发电位的应用中效果明显,有应用前景。     

A tracing evoked potential estimator

The paper presents an adaptive Gaussian radial basis function neural network (RBFNN) for rapid estimation of evoked potential (EP). Usually, a recorded EP is severely contaminated by background ongoing activities of the brain. Many approaches have been reported to enhance the signal-to-noise ratio (SNR) of the recorded signal. However, non-linear methods are seldom explored due to their complexity and the fact that the non-linear characteristics of the signal are generally hard to determine. An RBFNN possesses built-in non-linear activation functions that enable the neural network to learn any function mapping. An RBFNN was carefully designed to model the EP signal. It has the advantage of being linear-in-parameter, thus a conventional adaptive method can efficiently estimate its parameters. The proposed algorithm is simple so that its convergence behaviour and performance in signal-to-noise ratio (SNR) improvement can be mathematically derived. A series of experiments carried out on simulated and human test responses confirmed the superior performance of the method. In a simulation experiment, an RBFNN having 15 hidden nodes was trained to approximate human visual EP (VEP). For detecting gene rate=0.005) speeded up the estimation remarkably by using only 80 ensembles to achieve a result comparable to that obtained by averaging 1000 ensembles.     

三碘甲状腺原氨酸对大鼠体感诱发电位的影响

连续腹腔注射三碘甲状腺原氨酸(T_3)过程中,观察成年雄鼠(Sprague-Dawley)体感诱发电位(SEPs)的变化,以探讨T_3对大鼠本体感觉传导功能活动的影响。实验结果显示,在正常大鼠颅顶(C_3)可记录到N_1,P_1,N_2及P_2成份,注射T_3后大鼠SEPs的P_1,N_2和P_2成份的峰值潜伏期随着给药时间的延长而缩短,而N_1成份的峰值潜伏期无变化。由此町见,T_3对大鼠本体感觉传导成份具有选择性和特异性影响。     

利用小波分析技术提取诱发电位的方法研究

本文利用小波分析技术对诱发电位的提取进行了探讨，选用基于三次Ｂ样条的正交小波构造共轭滤波器函数，将诱发信号分解在不同的惊讶上，将特定尺度上的信号按时变加权原则叠架后获取诱发信号。计算机仿真和人体实验表明该方法在减少刺激次数，提高信噪比方面有着明显的效果。     

A tracing evoked potential estimator

The paper presents an adaptive Gaussian radial basis function neural network (RBFNN) for rapid estimation of evoked potential (EP). Usually, a recorded EP is severely contaminated by background ongoing activities of the brain. Many approaches have been reported to enhance the signal-to-noise ratio (SNR) of the recorded signal. However, non-linear methods are seldom explored due to their complexity and the fact that the non-linear characteristics of the signal are generally hard to determine. An RBFNN possesses built-in non-linear activation functions that enable the neural network to learn any function mapping. An RBFNN was carefully designed to model the EP signal. It has the advantage of being linear-in-parameter, thus a conventional adaptive method can efficiently estimate its parameters. The proposed algorithm is simple so that its convergence behaviour and performance in signal-to-noise ratio (SNR) improvement can be mathematically derived. A series of experiments carried out on simulated and human test responses confirmed the superior performance of the method. In a simulation experiment, an RBFNN having 15 hidden nodes was trained to approximate human visual EP (VEP). For detecting human brain stem auditory EP (BAEP), the approach (40 hidden nodes and convergence rate = 0.005) speeded up the estimation remarkably by using only 80 ensembles to achieve a result comparable to that obtained by averaging 1000 ensembles.     

Free radicals and brain damage due to transient middle cerebral artery occlusion: the effect of dimethylthiourea

The objective of this study was to assess whether dimethylthiourea (DMTU), an established free radical scavenger, ameliorates ischaemic damage due to 2–3 h of transient middle cerebral artery (MCA) occlusion, induced by an intraluminal filament. A major point adressed was whether DMTU given before MCA occlusion only delayed the maturation of the damage, or if it had a lasting effect on infarct size. The end point was morphological, and either encompassed triphenyltetrazolium chloride (TTC) staining of tissue slices after 24 h or 48 h of recovery, or histopathological assessment of infarct size after 7 days of recovery. In a preliminary series of experiments, rats were subjected to 3 h of MCA occlusion, and infarct volume was assessed by TTC staining after 24 h of recovery. DMTU in a dose of 750 mg/kg reduced infarct volume by more than 50%. However, due to a high mortality rate, that protocol was not subsequently pursued. When the ischaemia duration was reduced to 2 h and the DMTU dose to 400 mg/kg, a similar amelioration of the tissue damage was observed. However, since DMTU reduced a spontaneous rise in body temperature to 39.0–39.5°C, DMTU-treated animals in the main series of experiments with 24 and 48 h of recovery were treated so that they had the same temperature rise as the saline controls. Under such constant temperature conditions, the effect of DMTU at 24 h of recovery was borderline (P= 0.052) and at 48 h it was nil. The lack of a lasting effect of DMTU was supported by the findings on evaluation of infarct area after 7 days of recovery. The results raise the important question whether DMTU, and perhaps other free radical scavengers, delay rather than ameliorate the ischaemic lesion developing after transient MCA occlusion.     

Two-dimensional spectral processing of sequential evoked potentials

The processing of sequential evoked potentials (EPs) is investigated using two-dimensional processing techniques. Two-dimensional EP arrays or images are formed by stacking sequential recordings. Processing is accomplished in the frequency domain by 2-D low-pass filtering using Gaussian filters. Auditory brainstem responses (ABRs), which are the early auditory EPs, are used to investigate the effects of the 2-D filtering on real data. Gaussian filtering improves signal-to-noise ratios by reducing high frequency noise effectively in both intra-EP and inter-EP dimensions. Applications to intra-operative monitoring are simulated with real ABR data.     

Stationarity of the somatosensory evoked potential

The validity of the somatosensory evoked potential for serial neurological evaluation requires an understanding of normal variations in the responses Studies were conducted in 15 normal adult volunteers during two nights of sleep and in five normal adult volunteers during waking hours. The response amplitudes and latencies obtained during the day were demonstrated to be stationary by use of the runs or sign test Similarly, the earliest portions of the scalp recorded evoked potential were stationary during sleep Later portions of the responses had significantly lower amplitudes and demonstrated increased latency during deep sleep. The stability of the early portions of the SSEP suggest that it is a reliable tool for serial neurological evaluation. In private practice     

The effects of TRH analogues on cerebral ischaemia produced by middle cerebral artery occlusion in the rat

Summary This study examined the effects of two stabilised analogues of TRH, RX 77368 and CG 3509, in a rat cerebral ischaemia model produced by unilateral occlusion of the middle cerebral artery. The analogues were given intraventricularly after artery occlusion. The extent of the cortical ischaemia was evaluated after 10 days by somatosensory evoked potential (SEP) recording, followed by tetrazolium staining of brain slices for NADH-diaphorase activity. RX 77368 (2×10 g; 15 min, 24 h) significantly improved the survival rate, protected the SEP and reduced the area of infarct. In contrast, neither a smaller dose of RX 77368 (2×3 g) nor a 4 h delay in the treatment had any significant beneficial effects. Although CG 3509 (2×10 g) resulted in an apparent improvement in survival, its overall effects were not statistically significant. The findings indicate that stabilised TRH analogues may have beneficial effects when given to animals with focal cerebral ischaemia.     

Identification of noise sources in surface recording of spinal somatosensory evoked potentials

The poor signal-to-noise ratio associated with the acquision of evoked potentials is a well established fact. The problem is compounded if non-invasive techniques, using surface electrodes, are employed. The paper identifies several sources of noise associated with the acquisition of spinal somatosensory evoked potentials using surface electrodes. In addition, the relative contribution of these sources is determined experimentally for six spinal levels ranging from lower lumbar to upper thoracic. These data will prove useful in the design of digital signal processing schemes such as adaptive noise cancellation, where levels of uncorrelated noise severely limit system performance.     

Topographic mapping of somatosensory evoked potentials helps identify motor cortex more quickly in the operating room

Summary Median nerve somatosensory evoked potentials were recorded from exposed cerebral cortex during craniotomies. This technique is valuable when knowledge of the motor cortex location can influence surgical decisions about resection limits or biopsy sites. Two different recording techniques were compared: strips of electrodes and arrays of electrodes. The arrays recorded electrical potentials suitable for topographic mapping. We found that motor cortex could be identified more quickly when using the topographic mapping of SEPs from arrays. We conclude that topographic mapping of SEP from sensorimotor regions during craniotomies works well in general and can be done more quickly than the traditional electrode strip technique.     

Detection and multichannel SVD-based filtering of trigeminal somatosensory evoked potentials

Very weak and noisy trigeminal somatosensory evoked potentials (TSEPs) are considered, which are successfully evoked by electrical stimulation of the trigeminal nerve of 15 patients with endosseous oral implants. As TSEP analysis provides an objective means of assessing neuronal function, it is considered to be a promising tool for investigating tactile sensation through anchoring implants in bone. For this purpose, a study of TSEP signals acquired from patients with endosseous oral implants has been carried out. Since TSEPs are severely contaminated by background ongoing electrical activities of the brain, a methodology is developed for statistically detecting the transient signal (TSEP) in the biological noise (EEG). For nine out of 15 patients, transient signals are detected in the background EEG activity. The TSEPs of these nine patients are subjected to further analysis. A multichannel singular value decomposition (SVD)-based filtering method is applied which successfully separates out the most energetic TSEPs from the background EEG, thereby increasing significantly the SNR of the recorded signals and improving extraction of the characteristic components of the TSEPs. It is shown that the most prominent feature of the TSEP signals for patients with endosseous oral implants is a wave with peak latency between 9 and 15 ms, generally followed by a wave between 25 and 28 ms or 34 and 38 ms for the specific cortical response areas.     

体温过低对大鼠脑干听觉诱发电位和中潜伏期反应的影响

目的：探讨体温过低对大鼠脑干听觉诱发电位（BAEP）和中潜伏期反应（MLR）的影响。方法：计算机平均叠加技术颅表记录大鼠BAEP和MLR，体表物理降温法逐步降低大鼠体温，传感探头式数字体温计监测大鼠直肠温度，体温每降低1 ℃测试1次BAEP和MLR，观察波峰潜伏期（PL）和波幅的变化及各波消失的临界体温。结果：随体温逐渐降低（36 ℃-22 ℃），BAEP和MLR各波PL逐步延长；BAEP Ⅰ、Ⅱ、Ⅳ 3主波和MLR N1、P3 2主波的波幅在体温过低至26 ℃以下时方先后出现显著降低；BAEP和MLR各波在体温19 ℃-21 ℃全部消失，且两者同步消失。结论：体温过低对大鼠BAEP和MLR均有显著影响。