A Wireless System for Monitoring Transcranial Motor Evoked Potentials

Intraoperative neurophysiological monitoring (IONM) is commonly used as an attempt to minimize neurological morbidity from operative manipulations. The goal of IONM is to identify changes in the central and peripheral nervous system function prior to irreversible damage. Intraoperative monitoring also has been effective in localizing anatomical structures, including peripheral nerves and sensorimotor cortex, which helps guide the surgeon during dissection. As part of IONM, transcranial motor evoked potentials (TcMEPs), and somatosensory evoked potentials (SSEPs) are routinely monitored. However, current wired systems are cumbersome as the wires contribute to the crowded conditions in the operating room and in doing so not only it limits the maneuverability of the surgeon and assistants, but also places certain demand in the total anesthesia required during surgery, due to setup preoperative time needed for proper electrode placement, due to the number and length of the wires, and critical identification of the lead wires needed for stimulation and recording. To address these limitations, we have developed a wireless TcMEP IONM system as a first step toward a multimodality IONM system. Bench-top and animal experiments in rodents demonstrated that the wireless method reproduced with high fidelity, and even increased the frequency bandwidth of the TcMEP signals, compared to wired systems. This wireless system will reduce the preoperative time required for IONM setup, add convenience for surgical staff, and reduce wire-related risks for patients during the operation.     

Combined Muscle Motor and Somatosensory Evoked Potentials for Intramedullary Spinal Cord Tumour Surgery

Purpose

To evaluate whether intraoperative neurophysiologic monitoring (IONM) with combined muscle motor evoked potentials (mMEPs) and somatosensory evoked potentials is useful for more aggressive and safe resection in intramedullary spinal cord tumour (IMSCT) surgery.

Materials and Methods

We reviewed data from consecutive patients who underwent surgery for IMSCT between 1998 and April 2012. The patients were divided into two groups based on whether or not IONM was applied. In the monitored group, the procedures were performed under IONM using 75% muscle amplitude decline weaning criteria. The control group was comprised of patients who underwent IMSCT surgery without IONM. The primary outcome was the rate of gross total excision of the tumour on magnetic resonance imaging at one week after surgery. The secondary outcome was the neurologic outcome based on the McCormick Grade scale.

Results

The two groups had similar demographics. The total gross removal tended to increase when intraoperative neurophysiologic monitoring was used, but this tendency did not reach statistical significance (76% versus 58%; univariate analysis, p=0.049; multivariate regression model, p=0.119). The serial McCormick scale score was similar between the two groups (based on repeated measure ANOVA).

Conclusion

Our study evaluated combined IONM of trans-cranial electrical (Tce)-mMEPs and SEPs for IMSCT. During IMSCT surgery, combined Tce-mMEPs and SEPs using 75% muscle amplitude weaning criteria did not result in significant improvement in the rate of gross total excision of the tumour or neurologic outcome.     

Sensory component of cervically evoked motor potentials

The purpose of this paper is to present the hypothesis that cervically elicited motor evoked potentials which have recently gained clinical acceptance for monitoring spinal cord motor function during spine surgery, may be due, in part or in whole, to neural signals travelling through sensory rather than motor tracts. If true, then the interpretation of cervically elicited motor evoked potentials may lead to false conclusions about the status of motor tracts and postoperative motor function.     

Artefact cancellation in motor-sensory evoked potentials: two approaches using adaptive filtration and exponential approximation

Adaptive filtering for artefact cancellation in motor-sensory evoked potentials using signals obtained by subtraction methods (double-stimulus, off-nerve and subthreshold) is proposed. This is advantageous as inherent non-linear distortions can be overcome in an easier way by adaptive filtering. Efficiency is assessed with reference signals synthesised by varying the shape and reducing the amplitude of a ‘pure’ evoked potential in the range from 10% to 50%. The experiments show virtually identical shapes of the ‘pure’ and the filtered signal. The time shift between them is insignificant if a causal filter and small number of Widrow coefficients, e.g. N=8, are used. Further, two-exponential artefact approximation is applied with subsequent direct subtraction from the contaminated signal by a specially designed PC-controlled system for data acquisition and processing. For a fast procedure convergence, one-parametric optimisation of the time-constant τ is used, starting with τ=0.5 ms. The results obtained with artefact-corrupted evoked potentials from several subjects prove the efficiency of the approach. It has the substantial advantage of avoiding the need for reference signals. Both methods have advantages compared with other known software techniques.     

Characterization of an adaptive filter for the analysis of variable latency neuroelectric signals

An adaptive filter system has been developed whereby variable latency neuroelectric signals may be detected and separated from associated noise. The system is based on correlation-averaging techniques which are described in detail. The adaptive property of the system derives from iterative correlation and averaging of the data signals and permits the recognition of signals the specific waveshapes of which are not known in advance. The system consitutes a general pattern recognition device. It has been shown to be applicable to the analysis of evoked potentials of variable latency as well as to the analysis of patterns of EEG activity. Further applications include the analysis of multiple, complex signals such as miniature potentials from single motor units in the spinal cord. The use of an adaptive filter such as this with convergence properties based on broad statistical considerations appears to have greater analytic power than have previous methods.     

The effect of baclofen and diazepam on motor skill acquisition in healthy subjects

Antispastic medication is often used in the clinic together with physiotherapy. However, some of the antispastic drugs, e.g., baclofen and diazepam, may influence the plastic mechanisms that are necessary for motor learning and hence efficient physiotherapy. In the present study, we consequently investigated the influence of baclofen and diazepam on acquisition of a visuomotor skill. The study was designed as a semi-randomized, double-blinded, placebo-controlled, crossover study in 16 healthy human subjects. The motor skill task required the subjects to match a given force trajectory by increasing or decreasing ankle dorsiflexor torque. Subjects trained for a total of 30 min. Transcranial magnetic stimulation of the primary motor cortex leg area was applied to elicit motor evoked potentials in the anterior tibial muscle (TA). Coupling between populations of TA motor units was calculated in the frequency (coherence) domain during isometric dorsiflexion. Subjects receiving placebo showed statistically significant improvement in motor performance (q = 34.1, P = 0.014) accompanied by a statistically significant reduction in intramuscular coherence. Subjects receiving baclofen and diazepam conversely showed no progression in motor performance (P > 0.05), and the training was not accompanied by a decrease in intramuscular coherence. TA motor evoked potentials had significantly lower threshold following the training in the placebo group, whereas this was not the case in the treatment groups. These data indicate that diazepam and baclofen interfere with the acquisition of a motor skill by disrupting some of the neuroplastic changes that are involved in improved motor performance. This suggests that antispastic treatment should be used with caution in subjects receiving concomitant physiotherapy.     

Presynaptic control of group Ia afferents in relation to acquisition of a visuo-motor skill in healthy humans

Sensory information continuously converges on the spinal cord during a variety of motor behaviours. Here, we examined presynaptic control of group Ia afferents in relation to acquisition of a novel motor skill. We tested whether repetition of two motor tasks with different degrees of difficulty, a novel visuo-motor task involving the ankle muscles, and a control task involving simple voluntary ankle movements, would induce changes in the size of the soleus H-reflex. The slope of the H-reflex recruitment curve and the H-max/M-max ratio were depressed after repetition of the visuo-motor skill task and returned to baseline after 10 min. No changes were observed after the control task. To elucidate the mechanisms contributing to the H-reflex depression, we measured the size of the long-latency depression of the soleus H-reflex evoked by peroneal nerve stimulation (D1 inhibition) and the size of the monosynaptic Ia facilitation of the soleus H-reflex evoked by femoral nerve stimulation. The D1 inhibition was increased and the femoral nerve facilitation was decreased following the visuo-motor skill task, suggesting an increase in presynaptic inhibition of Ia afferents. No changes were observed in the disynaptic reciprocal Ia inhibition. Somatosensory evoked potentials (SEPs) evoked by stimulation of the tibial nerve (TN) were also unchanged, suggesting that transmission in ascending pathways was unaltered following the visuo-motor skill task. Together these observations suggest that a selective presynaptic control of Ia afferents contributes to the modulation of sensory inputs during acquisition of a novel visuo-motor skill in healthy humans.     

Changes of motor cortical excitability in human subjects from wakefulness to early stages of sleep: a combined transcranial magnetic stimulation and electroencephalographic study

The effect of sleep on human motor cortical excitability was investigated by evaluating the latency and amplitude of motor evoked potentials in ten subjects using transcranial magnetic stimulation. Motor evoked potentials and electroencephalographic data were recorded simultaneously and analyzed. Recordings were performed before, during and after a sleep period. A significant decrease in motor evoked potentials amplitude and a slight change in motor evoked potentials latency were noted in the recordings during the different sleep stages with a return to baseline values on awakening. A decrease in motor cortical excitability is suggested as explaining the effect of sleep.     

Protection effects of a silver fiber textile against electromagnetic interference in patients with pacemakers

 The use of the wireless cellular phone has increased dramatically, and this use could influence pacemaker function with electromagnetic interference (EMI). A textile lined with silver fiber has been developed for protection against electromagnetic waves. The purpose of this study was to evaluate the EMI protection effects in cardiac pacemaker patients wearing this textile. Participants in this study had pacemakers that were capable of obtaining endocardial electrograms, markers/annotations, and surface electrocardiograms via a programmer. A cellular phone was placed over the pulse generator. The presence of EMI was confirmed when a change in a parameter was observed. When EMI was confirmed, the subject wore a silver fiber shirt (rated at −30 dB), and EMI was evaluated. If the EMI persisted, the subject wore a heavier silver fiber shirt (rated at −50 dB), and again EMI was assessed. The same procedure was performed by using a ham radio device. Thirty-one subjects were tested. There was no EMI observed with the use of a cellular phone. However, interference by a ham device was confirmed in eight subjects (25.8%). Among six subjects, no further interference was observed after the patient wore a −30 dB shirt. For one subject, EMI was eliminated when a −50 dB shirt was used. However, one subject demonstrated persistent EMI when wearing a double layer of −30 dB and −50 dB shirts. Beneficial protection from EMI with the use of clothing lined with silver fiber has been demonstrated in this study. However, electromagnetic waves are diverse in both source and strength. Future studies are needed to confirm the benefits of wearing silver fiber clothing for the reduction of pacemaker–EMI interaction. Received: January 15, 2002 / Accepted: June 18, 2002 Correspondence to:T. Yajima     

Influence of motor unit properties on the size of the simulated evoked surface EMG potential

The purpose of the study was to quantify the influence of selected motor unit properties on the simulated amplitude and area of evoked muscle potentials detected at the skin surface. The study was restricted to a motor unit population simulating a hand muscle whose potentials were recorded on the skin over the muscle. Peak-to-peak amplitude and area of the evoked potential were calculated from the summed motor unit potentials and compared across conditions that simulated variation in different motor unit properties. The simulations involved varying the number of activated motor units, muscle fiber conduction velocities, axonal conduction velocities, neuronal activation times, the shape of the intracellular action potential, and recording configurations commonly used over hand muscles. The results obtained for the default condition simulated in this study indicated that ~7% of the motor unit potentials were responsible for 50% of the size of the evoked potential. Variation in the amplitude and area of the evoked muscle potential was directly related to the number of active motor units only when the stimulus activated motor units randomly, and not when activation was based on a parameter such as motor unit size. Independent adjustments in motor unit properties had variable effects on the size of the evoked muscle potential, including when the stimulus activated only a subpopulation of motor units. These results provide reference information that can be used to assist in the interpretation of experimentally observed changes in the size of evoked muscle potentials.     

用自回归白化滤波器提取脑-机接口信号VEP

利用脑-计算机接口这种新颖的人-机交互模式构建一种脑控拼写装置,其主要问题是实时、准确地从头皮电极记录到的脑电背景信号中提取视觉诱发电位,以决定用户选择按键。由于在一个短时程内可以认为自发脑电是平稳的,利用靶刺激出现前记录到的非靶刺激信号计算自回归模型参数,构造一个白化滤波器,再将实时信号通过白化滤波器滤波,使自发脑电得以白化,然后采用小波分析方法滤除白噪信号。结果表明靶刺激信号更加突出,提高了后续模式分类的正确率。采用模拟自然阅读诱发模式使短时信号的平稳性得到了保障,利用白化滤波器去除自发脑电是可行的。     

Functional Asymmetry of the Frontal Cortex and Lateral Hypothalamus of Cats During an Operant Food-Related Conditioned Reflex

The extent of correlation and the latency of evoked potentials to sound, recorded bilaterally in the frontal cortex and lateral hypothalamus of cats, were studied at different stages of the acquisition of an operant food-related reflex and during sudden transfer to 30% food reinforcement. High correlation coefficients between the evoked responses of the cortex and hypothalamus with left-sided dominance were seen in conditions of high levels of food motivation at the beginning of each experiment and in conditions of the high-probability appearance of the acquired conditioned reflex throughout the rest of the experiment. Comparison of the peak latencies of the early positive (P55-80) components of evoked potentials on the right and left sides showed that shorter latent periods were seen in the cortex on the left side at all behavioral stages, while this occurred (on the left side) in the hypothalamus only when the conditioned reflex was unfixed, while after fixation of the reflex and provision of 30% reinforcement, shorter latent periods were seen on the right side. It is concluded that the high level of left-sided correlation of evoked potentials in the hypothalamus was associated with the motivational and motor components of purposive behavior and was not associated with the emotional tension of the animals provoked by the disruption of the food reinforcement stereotype.     

Contributions of the motor cortex and the cerebellum to a simple learned movement in the monkey

Monkeys were trained to perform isometric plantar flexions of the foot in a simple reaction time situation. In test sessions, the contralateral hindlimb area of the motor cortex was cooled by a cryode placed on the dura until somatosensory evoked potentials disappeared. Movement amplitude decreased to about 70% of initial size; reaction time which was measured on the EMG, and torque signals increased slightly; and the evoked response in the dentate nucleus of the cerebellum remained unchanged. An extensive lesion in the motor cortex by coagulation reduced the movement amplitude to 10% of its preoperational size, but again, did not change reaction time significantly. It is concluded that the motor cortex is not essential for the execution of this overtrained simple movement.     

EEG Correlates of Action Observation in Humans

To investigate electrophysiological correlates of action observation electroencephalogram (EEG) was recorded while participants observed repetitive biological (human) or non-biological movements (at a rate of 2 Hz). Steady-state evoked potentials were analyzed and their neural sources were investigated using low resolution electromagnetic tomography analysis (LORETA). Results revealed significantly higher activation in the primary motor and premotor cortex, supplementary motor area as well as the posterior parietal cortices during observation of biological movements, supporting mirror properties of cortical motor neurons. In addition interregional communication was analyzed. Increased coherence for distributed networks at delta (0.5–4 Hz) and lower alpha (8–10 Hz) frequencies were obtained suggesting integration and functional coupling between the activated cortical regions during human action observation.     

Combined motor imagery and SSVEP based BCI control of a 2 DoF artificial upper limb

A Brain–Computer Interface (BCI) is a device that transforms brain signals, which are intentionally modulated by a user, into control commands. BCIs based on motor imagery (MI) and steady-state visual evoked potentials (SSVEP) can partially restore motor control in spinal cord injured patients. To determine whether these BCIs can be combined for grasp and elbow function control independently, we investigated a control method where the beta rebound after brisk feet MI is used to control the grasp function, and a two-class SSVEP-BCI the elbow function of a 2 degrees-of-freedom artificial upper limb. Subjective preferences for the BCI control were assessed with a questionnaire. The results of the initial evaluation of the system suggests that this is feasible.     

Universal application-specific integrated circuit for bioelectric data acquisition

Use of highly integrated application specific circuits (ASICs) in bioelectric data acquisition systems promise important new insights into the origin of a large variety of health problems by providing light-weight, low-power, low-cost medical measurement devices that allow long-term studies. They also promise significant cost reduction in medical care, as patients in principle become mobile and do not have to be hospitalized for observation. We report on the development and successful implementation of a universal ASIC, designed to meet key characteristics of a broad variety of bioelectric signals in terms of their dynamic range, sampling rate and input referred noise; e.g. electrocardiogram (ECG), electroencephalogram (EEG) and, most constringently, evoked potentials (EPs). Our approach for the first time makes cost-effective use of state-of-the-art microelectronics in medical measurement equipment, thus offering to replace discrete, single application devices used at present.     

Comparison of F-waves of motor unit action potentials activated during voluntary contraction

The system for classifying F-waves was developed to study the properties of F-wave and to compare single motor unit (MU) F-waves with motor unit action potentials (MUAPs) activated during voluntary contraction. The F-waves evoked by submaximal stimulation as well as the EMG signals during voluntary contraction at 6 levels of 10-100% of maximum voluntary contraction (MVC) were measured in the tibialis anterior muscles of 3 healthy volunteers. Nine channel F-wave waveforms in a selected electrode array were classified using a template-matching method. After the detection procedure of MUAPs in voluntary EMG signals, the MUAPs were also classified by the same method. Most of the F-waves (88.4%) were composed of a single MUAP. The numbers of MU classified from single MU F-waves in 3 subjects were 12, 12 and 15, and the numbers of MU classified from the voluntary EMG signals at 6 contraction levels were 20, 27 and 24, respectively. A total of 26 single MU F-waves were identified with the MUs extracted from the data during voluntary contractions. The results suggest that the F-waves are composed of a population of the MUs, which are recruited at a wide range of contraction levels. The classification procedures of F-waves and voluntary EMG signals have made it possible to recognize the same MU in both signals and to analysis the firing thresholds of F-waves.     

Proprioceptive sensory function in Parkinson's disease and Huntington's disease: evidence from proprioception-related EEG potentials

In both Parkinson's disease and Huntington's disease, proprioceptive sensory deficits have been suggested to contribute to the motor manifestations of the disease. Here, proprioceptive sensory function was investigated in Parkinson's disease patients, Huntington's disease patients, and healthy control subjects (each group n=8), using proprioception-related evoked potentials. Proprioception-related potentials were elicited by passive index finger movements and measured with high-density EEG. Conventional median nerve somatosensory evoked potentials (mnSEPs) were recorded in the same session. Analysis included amplitude and latency measures from selected scalp electrodes and dipole source reconstruction. We found a proprioception-related N90 component of normal latency in both Parkinson's disease and Huntington's disease. The source strength of the underlying cortical generator was normal in Parkinson's disease, but marginally reduced in Huntington's disease. Using the source location of the N20–P20 component of the mnSEP as a landmark for postcentral area 3b, the N90 was localized to the precentral motor cortex. At a latency around 170–180 ms proprioception-related potentials were explained by bilateral sensory cortex activation with an altered distribution in Parkinson's disease and a reduction of ipsilateral activation in Huntington's disease. Together, the results show largely normal early proprioception-related potentials, but changes in the cortical processing of kinaesthetic signals at longer latencies in both diseases. Electronic Publication     

A wireless multi-channel neural amplifier for freely moving animals

Conventional neural recording systems restrict behavioral experiments to a flat indoor environment compatible with the cable that tethers the subject to recording instruments. To overcome these constraints, we developed a wireless multi-channel system for recording neural signals from rats. The device takes up to 64 voltage signals from implanted electrodes, samples each at 20 kHz, time-division multiplexes them into one signal and transmits that output by radio frequency to a receiver up to 60 m away. The system introduces <4 μV of electrode-referred noise, comparable to wired recording systems, and outperforms existing rodent telemetry systems in channel count, weight and transmission range. This allows effective recording of brain signals in freely behaving animals. We report measurements of neural population activity taken outdoors and in tunnels. Neural firing in the visual cortex was relatively sparse, correlated even across large distances and was strongly influenced by locomotor activity.     

Modulation of somatosensory evoked responses in the primary somatosensory cortex produced by intracortical microstimulation of the motor cortex in the monkey

Summary Previous studies have shown that the amplitude of somatosensory evoked potentials is diminished prior to, and during, voluntary limb movement. The present study investigated the role of the motor cortex in mediating this movement-related modulation in three chronically prepared, awake monkeys by applying low intensity intracortical microstimulation (ICMS) to different sites within the area 4 representation of the arm. Air puff stimuli were applied to the contralateral arm or adjacent trunk at various delays following the ICMS. Somatosensory evoked potentials were recorded from the primary somatosensory cortex, areas 1 and 3b, with an intracortical microelectrode. The principal finding of this study was that very weak ICMS, itself producing at most a slight, localized, muscle twitch, produced a profound decrease in the magnitude of the short latency component of the somatosensory evoked potentials in the awake money. Higher intensities of ICMS (suprathreshold for eliciting electromyographic (EMG) activity in the target muscle, i.e. that muscle activated by area 4 stimulation) were more likely to decrease the evoked response and produced an even greater decrease. The modulation appeared to be, in part, central in origin since (i) it preceded the onset of EMG activity in 23% of experiments, (ii) direct stimulation of the muscle activated by ICMS, which mimicked the feedback associated with the small ICMS-induced twitch, was often ineffective and (iii) the modulation was observed in the absence of EMG activity. Peripheral feedback, however, may also make a contribution. The results also indicate that the efferent signals from the motor cortex can diminish responses in the somatosensory cortex evoked by cutaneous stimuli, in a manner related to the somatotopic order. The effects are organized so that the modulation is directed towards those neurones serving skin areas overlying, or distal to, the motor output.