Showing papers in "Journal of Clinical Neurophysiology in 2002"
TL;DR: Examples of real EEG segments, containing epileptic seizure activity or interictal spikes contaminated by artifacts, show that spatial filtering by preselection can be a useful tool during EEG review.
Abstract: Review and analysis of continuous EEG recordings may be impeded by physiological artifacts such as blinks, eye movements, or cardiac activity. Spatial filters based on artifact and brain signal topographies can remove artifacts completely without distortion of relevant brain activity. The authors describe the basic principle of artifact correction by spatial filtering and they review different approaches to estimate artifact and brain signal topographies. The main focus is on the preselection approach, which is fast enough to be applied while paging through the segments of a digital EEG recording. Examples of real EEG segments, containing epileptic seizure activity or interictal spikes contaminated by artifacts, show that spatial filtering by preselection can be a useful tool during EEG review. Advantages and disadvantages of the different spatial filter approaches are discussed.
789 citations
TL;DR: Transcranial magnetic stimulation is now established as an important noninvasive measure for neurophysiologic investigation of the central and peripheral nervous systems in humans and these techniques will open up new possibilities for investigating the physiologic function of the brain.
Abstract: Transcranial magnetic stimulation (TMS) is now established as an important noninvasive measure for neurophysiologic investigation of the central and peripheral nervous systems in humans. Magnetic stimulation can be used for stimulating peripheral nerves with a similar mechanism of activation as for electrical stimulation. When TMS is applied to the cerebral cortex, however, some features emerge that distinguish it from transcranial electrical stimulation. One of the most important features is designated the D and I wave hypothesis, which is now widely accepted as a mechanism of TMS of the motor cortex. Transcranial electrical stimulation excites the pyramidal tract axons directly, either at the initial segment of the neuron or at proximal internodes in the subcortical white matter, giving rise to D (direct) waves, whereas TMS excites the pyramidal neurons transsynaptically, giving rise to I (indirect) waves. There are still other phenomena with mechanisms that remain to be elucidated. First, not only excitatory effects but also inhibitory effects can be elicited by TMS of the cerebral cortex (e.g., the silent period and intracortical inhibition). The inhibitory effect may also be used to investigate cerebral functions other than the motor cortex, such as the visual, sensory cortices, and the frontal eye field, from which no overt response like the motor evoked potential can be elicited. Second, there is an abundance of intraregional functional connectivities among different cortical areas that can also be revealed by TMS, or TMS in combination with neuroimaging techniques. Last, repetitive transcranial stimulation exerts a lasting effect on brain function even after the stimulation has ceased. With further investigation of the neural mechanisms of TMS, these techniques will open up new possibilities for investigating the physiologic function of the brain as well as opportunities for clinical application.
376 citations
TL;DR: The suggested coil is likely to have the ability of deep brain stimulation without the need to increase the intensity to levels that stimulate cortical regions to a much higher extent and possibly cause undesirable side effects.
Abstract: Noninvasive magnetic stimulation of the human central nervous system has been used in research and the clinic for several years. However, the coils used previously stimulated mainly the cortical brain regions but could not stimulate deeper brain regions directly. The purpose of the current study was to develop a coil to stimulate deep brain regions. Stimulation of the nucleus accumbens and the nerve fibers connecting the prefrontal cortex with the nucleus accumbens was one major target of the authors' coil design. Numeric simulations of the electrical field induced by several types of coils were performed and accordingly an optimized coil for deep brain stimulation was designed. The electrical field induced by the new coil design was measured in a phantom brain and compared with the double-cone coil. The numeric simulations show that the electrical fields induced by various types of coils are always greater in cortical regions (closer to the coil placement); however, the decrease in electrical field within the brain (as a function of the distance from the coil) is markedly slower for the new coil design. The phantom brain measurements basically confirmed the numeric simulations. The suggested coil is likely to have the ability of deep brain stimulation without the need to increase the intensity to levels that stimulate cortical regions to a much higher extent and possibly cause undesirable side effects.
360 citations
TL;DR: The well-established benefits of TES MEP monitoring decidedly outweigh the associated risks, and otherwise unexplained intraoperative seizures and possibly arrhythmias are indications to abort TES.
Abstract: This article reviews intraoperative transcranial electrical stimulation (TES) motor evoked potential (MEP) monitoring safety based on comparison with other clinical and experimental brain stimulation methods and clinical experience in more than 15000 cases. Comparative analysis indicates that brain damage and kindling are highly unlikely. There have been remarkably few adverse events. Pulse train TES-induced or coincidental seizures (n = 5) are rare, probably because of very brief (<0.03 second) stimuli, anesthesia, and the general absence of predisposing cerebral conditions. Soft bite blocks may prevent tongue or lip laceration (n = 29) or mandibular fracture (n = 1). Rare cardiac arrhythmia (n = 5) and intraoperative awareness (n = 1) may be coincidental. Minor scalp burns (n = 2) are rare. Although possible, no spinal epidural recording electrode complications or injuries resulting from TES-induced movement were found. There have been no recognized adverse neuropsychological effects, headaches, or endocrine disturbances. Comprehensive relative contraindications include epilepsy, cortical lesions, convexity skull defects, raised intracranial pressure, cardiac disease, proconvulsant medications or anesthetics, intracranial electrodes, vascular clips or shunts, and cardiac pacemakers or other implanted biomedical devices. Otherwise unexplained intraoperative seizures and possibly arrhythmias are indications to abort TES. With appropriate precautions in expert hands, the well-established benefits of TES MEP monitoring decidedly outweigh the associated risks.
332 citations
TL;DR: A widespread loss of functional interactions in the &agr; and &bgr; bands is confirmed, and the first evidence for loss of &ggr; band synchronization in Alzheimer’s disease is provided.
Abstract: The purpose of this study was to investigate interdependencies in whole-head magnetoencephalography (MEG) of Alzheimer patients and healthy control subjects. Magnetoencephalograms were recorded in 20 Alzheimer patients (11 men; mean age, 69.0 years [standard deviation, 8.2 years]); Mini-Mental State Examination score, 21.3 points; range, 15 to 27 points) and 20 healthy control subjects (9 men; mean age, 66.4 years [standard deviation, 9.0 years]) during a no-task eyes-closed condition with a 151 channel whole-head MEG system. Synchronization likelihood (a new measure for linear as well as nonlinear interdependencies between signals) and coherence were computed for each channel in different frequency bands (2 to 6, 6 to 10, 10 to 14, 14 to 18, 18 to 22, 22 to 40 Hz). Synchronization was lower in Alzheimer patients in the upper alpha band (10 to 14 Hz), the upper beta band (18 to 22 Hz), and the gamma band (22 to 40 Hz). In contrast, coherence did not show significant group differences at the p<0.05 level. The synchronization likelihood showed a spatial pattern (high synchronization central, parietal and right frontal; low synchronization, occipital and temporal). This study confirms a widespread loss of functional interactions in the alpha and beta bands, and provides the first evidence for loss of gamma band synchronization in Alzheimer's disease. Synchronization likelihood may be more sensitive to detect such changes than the commonly used coherence analysis.
318 citations
TL;DR: Digital EEG allows one to combine recorded EEG channels into new montages without the need to record new data, and properties of spatial filters are introduced, and it is shown how they can be used to develop source montages with signals that estimate the activity in specific brain regions.
Abstract: Digital EEG allows one to combine recorded EEG channels into new montages without the need to record new data Using spherical splines, voltages can be estimated at any point on the head This allows one to generate various montages with the recorded or virtual electrodes at standardized locations, to interpolate bad electrodes, and to generate topographic maps over the whole head Simulations of EEG activity originating in various brain regions are used to illustrate the effects of known generators on various montages and on whole-head maps Some properties of spatial filters are introduced, and it is shown how they can be used to develop source montages with signals that estimate the activity in specific brain regions The usefulness and validity of a source montage designed to focus on temporal lobe activity is illustrated with simulations and examples of temporal lobe spikes and seizures Additional tools such as cross-correlation among channels, fast Fourier transform, and phase maps are described These tools are useful in estimating time lags between source channels and in interpreting propagating spike and seizure activity In combination, these tools help to analyze and to enhance activities that may be hard to detect from the background scalp EEG in traditional montages
238 citations
TL;DR: The role of sleep and sleep deprivation in the EEG evaluation of epilepsy is discussed and seizures appear to have a very close relationship with sleep in certain epilepsy syndromes.
Abstract: There is an extremely intimate relationship between sleep and epilepsy. In this manuscript I will review the influence that sleep has on epilepsy. Sleep is a potent activator of interictal epileptiform discharges. Sharp waves are infrequent during wakefulness in benign focal epilepsy of childhood, but may occur in runs of several discharges per page in sleep. The interictal discharges become almost continuous in non-REM sleep in the syndrome of encephalopathy with electrical status epilepticus during slow wave sleep. In some patients with West syndrome a hypsarrhythmia pattern may only appear in sleep whereas in others there may be an increase in discharges in a semiperiodic fashion resulting in a burst-suppression like pattern. Seizures appear to have a very close relationship with sleep in certain epilepsy syndromes. In benign focal epilepsy of childhood the seizures occur almost exclusively in sleep, while supplementary sensorimototor area seizures tend to occur in clusters during sleep. Juvenile myoclonic epilepsy has a close relationship with the sleep-wake cycle with seizures tending to occur predominantly on awakening. I also discuss the role of sleep and sleep deprivation in the EEG evaluation of epilepsy.
164 citations
TL;DR: In Fabry patients, small fiber dysfunction is more prominent than large fiber dysfunction, confirming previous findings of sural nerve biopsies and suggesting a higher vulnerability of small-diameter nerve fibers than of the thickly myelinated fibers.
Abstract: Fabry disease is an X-linked recessive disease with a reduction of lysosomal alpha galactosidase A and consecutive storage of glycolipids e.g., in the brain, kidney, skin, and nerve fibers. Cardinal neurologic findings are hypohidrosis, painful episodes, and peripheral neuropathy. So far, the neurophysiological findings regarding the extent of large and small fiber dysfunction are contradictory. This study evaluated large and small nerve fiber function in a homogeneous group of Fabry patients. In 24 of 30 Fabry patients with creatinine below 194.7 mmol/L the authors assessed median, ulnar, and peroneal motor conduction velocity (MCV) and median, ulnar, and sural sensory conduction velocity (SCV) nerve conduction to study the function of thickly myelinated nerve fibers. In addition, the authors studied sympathetic skin responses (SSR) at both hands and feet in 24 patients. To evaluate A beta nerve fiber function, the authors determined vibratory detection thresholds (VDT) at the first toe in 30 patients. Function of A delta and C fibers was assessed by quantitative sensory testing of cold detection threshold (CDT) and heat-pain detection thresholds (HPDT). Nerve conduction studies showed significantly decreased amplitudes of MCVs and SCVs in Fabry patients as compared to controls. However, individual results of MCV and SCV studies were only mildly impaired. SSRs were present in all tested patients but SSR amplitudes were significantly decreased in Fabry patients in comparison to controls. VDT, CDT, and HPDT were significantly elevated in Fabry patients as compared to controls. However, only six patients had pathologic VDT, 19 had increased CDT, and 25 had elevated HPDT at a high level of stimulation. In Fabry patients, small fiber dysfunction is more prominent than large fiber dysfunction, confirming previous findings of sural nerve biopsies. The results suggest a higher vulnerability of small-diameter nerve fibers than of the thickly myelinated fibers.
156 citations
TL;DR: Brainstem auditory evoked potential (BAEP) changes during intraoperative monitoring may reflect damage to or potentially reversible dysfunction of the ear, the eighth nerve, or the brainstem auditory pathways up to the level of the mesencephalon.
Abstract: Brainstem auditory evoked potential (BAEP) changes during intraoperative monitoring may reflect damage to or potentially reversible dysfunction of the ear, the eighth nerve, or the brainstem auditory pathways up to the level of the mesencephalon. They may also be caused by other physiologic mechanisms such as anesthesia, hypothermia, and acoustic masking from drilling noise, or they may result from technical factors that prevent proper stimulus delivery or recording of an evoked potential that is actually present. Cochlear ischemia or infarction resulting from compromise of the internal auditory artery and inner ear damage during temporal bone drilling will affect all BAEP components, including wave I. Direct mechanical or thermal trauma to the eighth nerve will delay, attenuate, and possibly eliminate waves III and V, but wave I, which is generated at the cochlear end of the eighth nerve, may be preserved. During scraping of tumor off the eighth nerve, force applied in an ear-toward-brainstem direction can avulse the fragile fibers of the distal eighth nerve at the area cribrosa. Prolonging the I-to-III interpeak interval during retraction of the cerebellum and brainstem reflects stretching of the eighth nerve, and is often reversible. Vasospasm within the eighth nerve can cause similar, potentially reversible BAEP changes. Damage to the brainstem auditory pathways at or below the level of the mesencephalon will delay and attenuate or eliminate wave V. Wave III is affected similarly if the damage is at or caudal to the region of the superior olivary complex. These BAEP changes may reflect direct mechanical or thermal damage to the brainstem, brainstem compression, or ischemia or infarction resulting from vascular compromise. During BAEP monitoring, examination of the pattern of BAEP changes, analysis of their correlation with surgical maneuvers, and investigation for possible contributory technical factors can help to determine the cause of the BAEP changes and provide the appropriate information to the rest of the surgical team.
147 citations
TL;DR: In conclusion, bilateral arm and leg muscle MEPs with median and tibial peripheral nerve and cortical SSEPs provide sufficiently rapid detection and differentiation of cord ischemia from confounding factors.
Abstract: Thoracoabdominal aneurysm surgery carries an approximate 10% risk of intraoperative paraplegia. Abrupt cord ischemia and the confounding effects of systemic alterations and limb or cerebral ischemia challenges neurophysiologic spinal cord monitoring. This investigation sought a rapid differential monitoring approach to predict or help prevent paraplegia. Thirty-one patients were monitored with motor evoked potentials (MEPs) and median and tibial somatosensory evoked potentials (SSEPs). MEPs involved single-pulse transcranial electrical stimulation with D wave recording (n = 16), arm and leg muscle MEPs following multiple-pulse transcranial electrical stimulation (n = 12), or both (n = 3). D wave recordings required averaging, invasive epidural electrode insertion, and produced both false positives and false negatives. Muscle MEPs were instantaneous and reliably sensitive and specific for cord ischemia. Cortical and peripheral nerve SSEPs provided rapid detection of systemic alterations and cerebral or limb ischemia. Cord and subcortical SSEPs required excessive averaging time. In conclusion, bilateral arm and leg muscle MEPs with median and tibial peripheral nerve and cortical SSEPs provide sufficiently rapid detection and differentiation of cord ischemia from confounding factors. There were two predicted intraoperative spinal cord infarctions (6.5%) and nine circumstantial examples of possible contributions to deficit prevention.
93 citations
TL;DR: This paper reviews the present knowledge about the cellular origins of vigilance states (wakefulness and slow-wave sleep) from the perspective of their involvement in the triggering of epileptic seizures and shows that sleep is dominated by a cortically generated slow (<1 Hz) oscillation resulting from the complex interplay within networks of neurons and glia.
Abstract: This paper reviews the present knowledge about the cellular origins of vigilance states (wakefulness and slow-wave sleep) from the perspective of their involvement in the triggering of epileptic seizures. The data stem from intracellular recordings (most of them dual impalements of pairs of neurons and glia), extracellular ionic concentrations (mainly K and Ca ) and simultaneous intracortical field potentials from the cortex of cats. These data were corroborated with recordings from naturally sleeping animals and humans. It is shown that sleep is dominated by a cortically generated slow (<1 Hz) oscillation resulting from the complex interplay within networks of neurons and glia, which are modulated by the more diffuse action of extracellular currents of ions. Wakefulness is produced through the activation of brainstem and basal forebrain structures, which disrupt sleep oscillations and elicit a global change of the extraneuronal milieu, with profound modifications of glial and cerebral blood flow parameters. Paroxysmal events arising during quiet sleep evolve within the cortex from normal slow sleep oscillations. The synchronization of large cortical and eventually subcortical territories relies on the propagation of increased currents of K through the glial syncytium, which compensate for the reduced synaptic efficacy due to the depletion of extracellular Ca.
TL;DR: In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits and the use of SSEP monitoring in improving postoperative outcome is less well established.
Abstract: In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits. Many factors affect the amplitude and latency of SSEP waveforms during surgery. Somatosensory evoked potential amplitude decreases with ischemia and anoxia because of temporal dispersion of the afferent volley and conduction block in damaged axons. In conjunction with surgical manipulations, minor drops in blood pressure may result in substantial SSEP changes that reverse when perfusion pressure is increased. Irreversible anoxic injury to central nervous system white matter with loss of SSEP waveforms is dependent on calcium influx into the intracellular space. Somatosensory evoked potential monitoring may be less sensitive for detecting acute insults in the presence of preexisting white matter lesions. Increased extracellular potassium from acute baro-trauma can block axonal conduction transiently even when there is no axonal disruption. Marked temperature-related drops in SSEP amplitude may occur after exposure of the spine but before instrumentation and deformity correction. Hypothermia may increase false-negative outcomes. Short-interval double-pulse stimulation may improve the sensitivity of the SSEP in detecting early ischemic changes. For neurosurgical procedures on the spinal cord the use of SSEP monitoring in improving postoperative outcome is less well established.
TL;DR: TCES with recording of muscle responses was the preferred MEP monitoring technique at the plurality of the centers, and SEPs and MEPs should be used together to optimally monitor the spinal cord.
Abstract: Centers responding to a survey of MEP monitoring practices predominantly used transcranial electrical brain stimulation (TCES) with brief pulse trains and/or spinal cord stimulation (SCS) to elicit MEPs; transcranial magnetic stimulation and single-pulse TCES were not techniques of choice. Most centers using TCES had patient exclusion criteria (e.g., cochlear implants, cardiac pacemakers, prior craniotomy or skull fracture, history of seizures). Adverse effects included rare tongue injuries or seizures from TCES, and minor bleeding from needle electrodes in muscle. Spinal cord, peripheral nerve, and muscle recording sites were all employed. TCES with recording of muscle responses was the preferred MEP monitoring technique at the plurality of the centers. MEPs suitable for monitoring were obtained in about 91.6% of patients overall. Most of the failures were attributed to technical factors; preexisting neurologic dysfunction precluded MEP monitoring in approximately 1.7% of patients. Almost all centers monitored SEPs concurrently with MEPs. Overall, both measures remained stable during about 90.2% of cases. Adverse MEP changes occurred in about 8.3%; a little over half of these were accompanied by SEP changes. Adverse SEP changes without MEP changes occurred in about 1.5% of cases. SEPs and MEPs should be used together to optimally monitor the spinal cord.
TL;DR: The findings in 10 severely affected RSD patients who progressed to multifocal or generalized tonic dystonia are in accordance with an impairment of inhibitory interneuronal circuits at the level of the brainstem or spinal cord.
Abstract: Reflex sympathetic dystrophy (RSD) is a syndrome dominated by sensory, autonomic, and motor features of the extremities. In this study, 10 severely affected RSD patients who progressed to multifocal or generalized tonic dystonia underwent H-reflex evaluation, needle electromyography (EMG), polysomnography, somatosensory evoked potentials, and transcranial magnetic stimulation. H-reflex evaluation revealed an impaired vibratory inhibition of the H-reflex and a higher facilitation peak in the recovery curve between 200 to 350 msec. Needle EMG revealed an impaired reciprocal inhibition, and many patients were unable to alter the amount of muscle activity voluntarily. Evaluations of the stretch reflex showed a markedly decreased threshold and abnormal responses to tonic and phasic changes. Polysomnography performed in five patients revealed no abnormal EMG activity during nonrapid eye movement and rapid eye movement sleep, but EEG arousal phenomena provoked abnormally high and brief bursts of surface EMG activity in all registered muscle groups. Somatosensory evoked potentials and transcranial magnetic stimulation were normal. Taken together, the findings in these patients with tonic dystonia of RSD are in accordance with an impairment of inhibitory interneuronal circuits at the level of the brainstem or spinal cord.
TL;DR: This paper briefly reviews some automatic methods that have been previously developed for identifying sleep related events and discusses the leg movement event, respiratory event, sleep spindle and rapid-eye-movement detection methods.
Abstract: Recent advances in the computing power and storage devices have made computer-based recording of polysomnograms (PSGs) very attractive. Digital PSGs offer the possibility of automating many tedious and time-consuming tasks of identifying sleep related events. Automation not only alleviates these laborious tasks, but also introduces a measure of objectivity in the scoring of various discrete events. In this paper we briefly review some automatic methods that have been previously developed by the authors. Automatic sleep staging methods is emphasized with some illustrative results on inter-scorer variations. We also discuss the leg movement event, respiratory event, sleep spindle and rapid-eye-movement detection methods.
TL;DR: Results indicate that topographic parameters of cognitive response control present with superior long-term reliability and that they may be applied as electrophysiologic trait markers of response control mechanisms in the human brain.
Abstract: The execution (Go) and the inhibition (NoGo) of a motor response are basic cognitive processes that can be assessed by means of a simple neuropsychological Go-NoGo task: the Continuous Performance Test (CPT). Simultaneous electrophysiologic investigations revealed that the NoGo condition of the CPT is associated with a clearly more anterior brain electrical activity compared with the Go condition. Recently, it has been shown that this NoGo anteriorization effect during a response control paradigm can be measured quantitatively with the electrophysiologic centroid method. The objective of the current study, therefore, was to determine the long-term reliability of the topographic measures of cognitive response control (i.e., location of the Go and the NoGo centroid and the NoGo anteriorization). For this purpose, a 21-channel EEG was recorded twice from 13 healthy volunteers during their execution of a cued CPT (O-X version). The time interval between test and retest was 2.74 years (range, 2.41 to 2.97 years). Statistical analysis of the event-related Go and NoGo potentials revealed an excellent test-retest reliability, as expressed by Pearson's product moment correlation coefficients of more than 0.85 (P < or = 0.0005) and intraclass correlation coefficients of more than 0.90 (P
TL;DR: There is a subset of patients for whom solely outpatient presurgical EEG monitoring can be used to help plan successful temporal lobectomy, and this subset is limited to patients with refractory temporal lobe epilepsy, the authors conclude.
Abstract: Most epilepsy centers obtain ictal EEG recordings to localize the epileptogenic zone during presurgical evaluations. Inpatient monitoring is standard practice but is expensive and can be inconvenient. The authors sought to determine whether outpatient monitoring can be safe and effective as the sole method of recording seizures in the presurgical evaluation of patients with refractory temporal lobe epilepsy. They reviewed the data of seven temporal lobectomy patients whose presurgical monitoring was performed entirely outside the hospital. Mean baseline seizure frequency was at least 9.1 seizures per week. An average of 7.4 seizures was recorded over 9.4 days of monitoring. Only one patient had any antiepileptic drug taper; none suffered any complications. After temporal lobectomy on the side of demonstrated ictal onset, postoperative follow-up averaged 5.5 years. At the most recent follow-up, all patients were either seizure free or had only rare disabling or nocturnal seizures (four patients had outcomes in Engel's class I and three patients in Engel's class II). A comparison group who underwent standard inpatient monitoring was similar in average seizure frequency, monitoring duration, number of seizures recorded, and postoperative outcome, although all but one had antiepileptic drugs tapered during monitoring. The authors conclude that there is a subset of patients for whom solely outpatient presurgical EEG monitoring can be used to help plan successful temporal lobectomy.
TL;DR: Transcranial magnetic stimulation findings differ depending on the epilepsy syndrome, lending support to the concept that there are distinct pathophysiologies underlying each condition.
Abstract: Transcranial magnetic stimulation has been used to study generalized and focal epilepsies for more than a decade. The technique appears safe and has yielded important information about the mechanisms underlying epilepsy. Transcranial magnetic stimulation findings differ depending on the epilepsy syndrome, lending support to the concept that there are distinct pathophysiologies underlying each condition. In most studies of generalized epilepsies, transcranial magnetic stimulation has indicated a state of relative hyperexcitability of excitatory cortical interneurons and possibly inhibitory interneurons as well, which can be reversed through the actions of anticonvulsant medications. Transcranial magnetic stimulation studies in patients with a seizure focus in the motor cortex indicate increased cortical excitability and reduced inhibition, but in patients with seizure foci located elsewhere the findings are similar to those in generalized epilepsies. Transcranial magnetic stimulation has also been used to study the mode of action of anticonvulsants and may prove to be a useful means of testing the potential for new drugs to act as anticonvulsants. Repetitive transcranial magnetic stimulation may prove to have a therapeutic role by producing long-lasting cortical inhibition after a train of impulses.
TL;DR: This review describes the wide spectrum of episodic phenomena that can occur during sleep, which include arousal disorders of nonrapid eye movement (NREM) sleep, rapid eye movement(s) sleep behavior disorder, movement disorders, psychiatric disorders, and epileptic seizures.
Abstract: This review describes the wide spectrum of episodic phenomena that can occur during sleep. These phenomena include arousal disorders of nonrapid eye movement (NREM) sleep, rapid eye movement (REM) sleep behavior disorder, movement disorders, psychiatric disorders, and epileptic seizures. Each of these entities is discussed in detail, focusing on their clinical manifestations, diagnosis, and treatment. Essential historic elements that distinguish these events and the role of video-EEG-polysomnography in their differential diagnosis are emphasized.
TL;DR: A method based on residual error analysis to improve the lesion conductivity estimate is proposed, which can identify lesion tissue conductivity with only a few percent error and guarantees source localization errors less than 5 mm.
Abstract: EEG-based source localization techniques use scalp-potential data to estimate the location of underlying neural activity. EEG source location reconstruction requires the assumption of a source model and the assumption of a conductive head model. Brain lesions can present conductivity values that are dramatically different from those of surrounding normal tissues and have to be included in head models for accurate neural source reconstruction. It is therefore necessary to analyze subjects' anatomic images (using MRI or computed tomography) to identify lesion type and to assign the appropriate conductivity value. Source localization accuracy may be influenced by uncertainties in tissue conductivity assignment during head model construction. The authors present a sensitivity study quantifying the effect of uncertainty in brain lesion conductivity assignment on EEG dipole source localization. They adopted an eccentric-spheres head model in which an eccentric bubble approximated the effects of actual brain lesions. After simulating EEG signal measurement in 64 different pathologic situations, an inverse dipole fitting procedure was carried out, assuming an incorrect lesion conductivity assignment ranging from a half to twice the real value. Incorrect lesion conductivity assignment led to markedly wrong source reconstruction for highly conductive lesions like liquid-filled ones (localization errors as much as 1.7 cm). Conversely, low sensitivity to uncertainties in conductivity assignment was found for lesions with low conductivity like calcified tumors. The authors propose a method based on residual error analysis to improve the lesion conductivity estimate. This procedure can identify lesion tissue conductivity with only a few percent error and guarantees source localization errors less than 5 mm.
TL;DR: The results of the current study suggest that sensorimotor integration is impaired in cervical dystonia, probably by an altered control of proprioceptive (vibratory) input.
Abstract: The authors studied the effects of sensorimotor integration (corticocortical inhibition and facilitation during muscle vibration [MV]) in dystonic patients. Eleven patients with cervical dystonia and 11 age-matched healthy control subjects were enrolled in the study. They were examined using transcranial magnetic stimulation (TMS) and tonic proprioceptive input (MV). Paired-pulse transcranial magnetic stimulation was done at interstimulus intervals of 3 msec (intracortical inhibition) and 13 msec, the intensity of the conditioning stimulus was 70% of the motor threshold, and the test stimulus was 120%. Motor evoked potentials were recorded from the vibrated extensor carpi radialis muscle and its antagonist, the flexor carpi radialis. Duration of MV trains (80 Hz; amplitude, 0.5 mm) was 4 seconds. The authors found differences between patients and healthy control subjects during MV only. Intracortical inhibition was pronounced significantly only in control subjects, whereas intracortical facilitation was significant in patients only (P < 0.05). Furthermore, the significant reduction of motor evoked potentials at 13-msec interstimulus intervals, which can be found in healthy subjects frequently, was observed in one dystonia patient only. The results of the current study suggest that sensorimotor integration is impaired in cervical dystonia, probably by an altered control of proprioceptive (vibratory) input.
TL;DR: This study presents an empirically tested model with procedures and criteria for attaining improved reliability in transient EEG arousal assessments in infants using the modified Atlas Task Force standards.
Abstract: Infant arousal scoring based on the Atlas Task Force definition of transient EEG arousal was evaluated to determine (1). whether transient arousals can be identified and assessed reliably in infants and (2). whether arousal and no-arousal epochs scored previously by trained raters can be validated reliably by independent sleep experts. Phase I for inter- and intrarater reliability scoring was based on two datasets of sleep epochs selected randomly from nocturnal polysomnograms of healthy full-term, preterm, idiopathic apparent life-threatening event cases, and siblings of Sudden Infant Death Syndrome infants of 35 to 64 weeks postconceptional age. After training, test set 1 reliability was assessed and discrepancies identified. After retraining, test set 2 was scored by the same raters to determine interrater reliability. Later, three raters from the trained group rescored test set 2 to assess inter- and intrarater reliabilities. Interrater and intrarater reliability kappa's, with 95% confidence intervals, ranged from substantial to almost perfect levels of agreement. Interrater reliabilities for spontaneous arousals were initially moderate and then substantial. During the validation phase, 315 previously scored epochs were presented to four sleep experts to rate as containing arousal or no-arousal events. Interrater expert agreements were diverse and considered as noninterpretable. Concordance in sleep experts' agreements, based on identification of the previously sampled arousal and no-arousal epochs, was used as a secondary evaluative technique. Results showed agreement by two or more experts on 86% of the Collaborative Home Infant Monitoring Evaluation Study arousal scored events. Conversely, only 1% of the Collaborative Home Infant Monitoring Evaluation Study-scored no-arousal epochs were rated as an arousal. In summary, this study presents an empirically tested model with procedures and criteria for attaining improved reliability in transient EEG arousal assessments in infants using the modified Atlas Task Force standards. With training based on specific criteria, substantial inter- and intrarater agreement in identifying infant arousals was demonstrated. Corroborative validation results were too disparate for meaningful interpretation. Alternate evaluation based on concordance agreements supports reliance on infant EEG criteria for assessment. Results mandate additional confirmatory validation studies with specific training on infant EEG arousal assessment criteria.
TL;DR: The effects of skull holes were less prominent for deep dipoles than for superficial dipoles and Skull discontinuities can be major determinants for the distribution of extracranial EEG signals.
Abstract: The purpose of this study was to quantify the distortion of electrical fields by skull foramina using an in vitro model. Extracranial voltage generated by current dipoles located inside a human calva immersed in saline were measured when a 4-mm hole was open and when it was blocked with paraffin wax. Dipoles were located either along the internal surface of the bone (superficial dipoles) or at increasing distances from the bone (deep dipoles). With the hole open, extracranial signals had a substantially greater amplitude than with the hole blocked. The locations of the largest voltage values recorded outside the skull depended on the distance of the recording electrode from the hole rather than on the location of the internal dipole. For superficial dipoles, voltage values with the hole open were as much as 116 times greater than when the hole was blocked. Furthermore, when the hole was open, the largest extracranial signals were seen at the hole even when the dipole was 5 to 6 cm away from the hole. The effects of skull holes were less prominent for deep dipoles than for superficial dipoles. Skull discontinuities can be major determinants for the distribution of extracranial EEG signals. These results have implications for EEG interpretation and for source localization.
TL;DR: A close interaction between proprioceptive input and PT generation is suggested, with Parkinsonian resting tremor increased significantly in the directly stimulated opponens pollicis muscle and the parkinsonian postural tremor accelerated significantly during ipsilateral median nerve stimulation.
Abstract: Previous studies have shown a modification of parkinsonian tremor (PT) by proprioceptive input induced by passive joint movements. The authors investigated the impact of electrically evoked proprioceptive input on PT. In eight patients with PT they recorded surface EMG from the opponens pollicis muscle, and forearm extensors and flexors. Rhythmic electrical stimulation was applied to the ipsilateral median nerve at the wrist using a submaximal stimulus intensity and stimulus frequencies between two stimuli per second and five stimuli per second. The tremor frequency did not adapt to the stimulus frequency. Tremor frequency of parkinsonian resting tremor increased significantly in the directly stimulated opponens pollicis muscle (mean +/- standard deviation, 4.35 +/- 0.64 Hz without stimulation versus 4.53 +/- 0.68 Hz with stimulation; P < 0.05, paired t-test), the not directly stimulated forearm muscles (4.90 +/- 0.72 Hz versus 5.18 +/- 0.73 Hz, P < 0.001), and the upper arm muscles (5.13 +/- 0.61 Hz versus 5.36 +/- 0.68 Hz, P < 0.01). Furthermore, the parkinsonian postural tremor accelerated significantly during ipsilateral median nerve stimulation (5.31 +/- 0.99 Hz versus 5.44 +/- 1.03 Hz, P < 0.05). Parkinsonian resting tremor in the forearm muscles also accelerated significantly during ipsilateral ulnar nerve stimulation (4.85 +/- 0.57 Hz versus 5.05 +/- 0.65 Hz, P < 0.05). Contralateral median nerve stimulation had no significant effect. These results suggest a close interaction between proprioceptive input and PT generation.
TL;DR: The objective of this study was to define the distribution of epileptiform discharges in patients with HS and HS associated with microscopic dysplasia, and to examine their relationship with hippocampal atrophy and cell loss.
Abstract: The EEG characteristics of isolated hippocampal sclerosis (HS) and HS associated with other types of temporal lobe pathology are not well defined. The pathologic substrate may be an important variable in determining seizure-free outcome. The objective of this study was to define the distribution of epileptiform discharges in patients with HS and HS associated with microscopic dysplasia, and to examine their relationship with hippocampal atrophy and cell loss. Thirty-four patients (15 women and 19 men; mean age, 30.6 +/- 11.2 years), all with good outcomes after temporal lobectomy (Engel classes I and II), were included. The characteristics studied were frequency and distribution of spikes, MRI-based hippocampal volume ratios, and quantitative hippocampal cell density in various subregions. The isolated HS group showed a trend to a higher percentage of epileptiform discharges maximal at the anterior temporal electrodes (89.87 +/- 17.0%; 79.5 +/- 28.2% in the dual-pathology group). The isolated HS group had, on average, significantly more cell loss (P < 0.001). There was a significant negative correlation between the amount of cell loss in the CA1 area and both anterior temporal spikes and hippocampal ratios (P < 0.05). Isolated HS and dual pathology show minimal differences in interictal spike distribution and frequency. More widespread spike distributions in severe isolated HS compared with patients with less cell loss is probably the result of less organized limbic circuitry.
TL;DR: MEP monitoring focuses on evaluating the descending motor pathways in unanesthetized subjects because it reliably elicits MEPs in awake subjects and does not cause undue discomfort, and magnetic transcranial stimulation is not at this time a suitable technique for intraoperative MEP monitoring.
Abstract: Somatosensory evoked potential (SEP) monitoring during scoliosis surgery has been shown to reduce postoperative neurologic deficits (Nuwer et al., 1995), and is recognized as a safe and effective technique for intraoperative monitoring of the integrity of the spinal cord (American Academy of Neurology, 1990). However, since scalp-recorded SEPs are mediated principally by the dorsal column pathways within the spinal cord (Emerson, 1988), they may fail to detect damage to the descending motor pathways. Fortunately this is rare; situations that compromise the anterior spinal cord usually compromise the posterior spinal cord as well. This undoubtedly explains why SEP monitoring improves postoperative motor outcomes. However, there are welldocumented (though fortunately rare) cases in which intraoperative SEPs have failed to detect motor tract damage (e.g., Ben-David et al., 1987a; Zornow et al., 1990 ). This has led to the development of motor evoked potential (MEP) monitoring. Many different MEP monitoring techniques have been tried. The common features are stimulation of the nervous system rostral to, and recording of electrical responses caudal to, the spinal cord region at risk. Stimulation techniques employed have included transcranial electrical stimulation (TCES) of cerebral cortex, transcranial magnetic stimulation (TCMS) of cerebral cortex, and electrical stimulation of the spinal cord. Recording sites have included spinal cord caudal to the region at risk, peripheral nerves, and muscles. Each of these techniques has its own advantages and disadvantages, and some have been largely abandoned as the field has evolved. Cortical stimulation can produce ‘D‘ (‘direct‘) waves, reflecting direct depolarization of the axon hillocks of the neurons that give rise to the pyramidal tracts, as well as ‘I‘ (‘indirect‘) waves, which reflect activation of cortical interneurons with subsequent trans-synaptic activation the cortical outflow neurons (Patton and Amassian, 1954; 1960). D-waves and I-waves can be recorded directly as they travel along the spinal cord. However, temporal summation of multiple EPSPs at the spinal cord alpha motor neuron is required to produce responses in peripheral nerve and muscle. Responses to single cortical stimuli can be difficult to record in the anesthetized state, in part because I-waves are suppressed by surgical anesthesia (Hicks et al., 1992; Woodforth et al., 1999). However, stimulators that deliver stimulus trains can produce trains of D-waves that are sufficient to fire the alpha motor neurons, facilitating intraoperative monitoring of peripheral nerve or EMG responses to cortical stimulation. Magnetic transcranial stimulation is the technique of choice for evaluating the descending motor pathways in unanesthetized subjects because it reliably elicits MEPs in awake subjects and does not cause undue discomfort. However, TCMS does not produce stable, robust MEPs in anesthetized patients. The D-waves to TCMS tend to be smaller than those to TCES and, depending on the stimulating coil configuration and orientation, TCMS may elicit primarily I-waves (Burke and Hicks, 1998), which are suppressed by anesthesia. Because of this, magnetic transcranial stimulation is not at this time a suitable technique for intraoperative MEP monitoring. Indeed, none of the centers responding to a recent survey of MEP monitoring techniques reported that they were are currently using TCMS-MEP as a standard monitoring technique (Legatt, 2002). Transcranial electrical stimulation may be accomplished in two ways. One entails the use of speciallydesigned high-intensity stimulators. While these devices Journal of Clinical Neurophysiology 19(5):383–386, Lippincott Williams & Wilkins, Inc., Philadelphia © 2002 American Clinical Neurophysiology Society
TL;DR: A close temporal and prognostic relationship between electrical and behavioral recovery after hypoxic-ischemic brain injury is demonstrated and patterns of EEG restitution during the first 4 hours predict later behavioral recovery.
Abstract: SummaryPrevious studies have shown that parameters of EEG restitution reflect the severity of global hypoxic-ischemic brain injury. Here, the hypothesis is tested that patterns of EEG restitution during the first 4 hours predict later behavioral recovery. Time course and correlations between behavio
TL;DR: Although comparisons of simple H-reflexes and H- Reflexes during vibration did not differentiate the patients in the early stages of Parkinson’s disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.
Abstract: Differentiating the early stages of Parkinson's disease from the normal consequences of aging or from other common neurologic conditions can be diagnostically problematic. The purpose of this study was to compare methodologies for measuring motor neuron excitability of Parkinson's disease patients with a control group. H-reflexes were monitored in 16 patients diagnosed in the early stages of Parkinson's disease (Hoehn & Yahr stages I and II) compared with 30 subjects who were disease free. Methods of measurement included H-reflex latencies, the relative values of maximum H-reflexes to maximum direct motor responses (H-to-M ratio), the relative values of H-reflex amplitudes during vibration compared with control H-reflex amplitudes (Hv-to-Hc ratio), and double-stimulation H-reflex recovery curves using different interstimulus interval parameters. No significant differences were observed for the H-to-M or Hv-to-Hc ratios, or for the H-reflex latencies. The H-reflex recovery curves for the patients with Parkinson's disease demonstrated significantly greater ratio amplitudes than the control group during the double-stimulus responses between the 150-msec and 700-msec interstimulus intervals. Although comparisons of simple H-reflexes and H-reflexes during vibration did not differentiate the patients in the early stages of Parkinson's disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.
TL;DR: Public policy issues for intraoperative monitoring include billing, coding, reimbursement, staffing, device approval, and liability, along with a discussion of the respective roles of physicians and non-physicians in monitoring.
Abstract: Public policies are in place for health care to insure high quality, organized delivery of care to patients. Public policy issues for intraoperative monitoring include billing, coding, reimbursement, staffing, device approval, and liability. Staffing issues include privileging, credentialing, certifying, training, and professionalism. Those staffing processes provide ways that the profession passes judgment on individual's skills, knowledge, abilities, and training relevant to monitoring. These issues are reviewed here, along with a discussion of the respective roles of physicians and non-physicians in monitoring. Various billing codes for intraoperative monitoring are reviewed along with the circumstances in which they are to be used. Policy on the use of non-approved devices is also presented.
TL;DR: Examination of H-reflex parameters among the pathophysiologic conditions of essential tremor (ET), Parkinson’s disease (PD), combinedessential tremor with Parkinson's disease (ETPD), and a control group found no statistically or clinically significant differences.
Abstract: The purpose of this study was to examine H-reflex parameters among the pathophysiologic conditions of essential tremor (ET), Parkinson's disease (PD), combined essential tremor with Parkinson's disease (ETPD), and a control group. H-reflex latencies, amplitude of maximum H-reflex to maximum M-response ratio (H:M), vibration H-reflex to control H-reflex (Hv:Hc), and H-reflex recovery curves (HRRCs) were recorded and compared between a control group and patient groups with ET, early-stage PD, and with ETPD. No statistically or clinically significant differences were found between the patient groups and the control group for latency, H:M ratio, or Hv:Hc ratio. Significantly greater ratio values were observed for the PD group over the other groups for the HRRC tests at each interstimulus interval between 200 and 300 msec (p < 0.05), but values were not different between PD and ETPD patients for intervals between 350 and 1,000 msec. Patients with ET, PD, and ETPD apparently have different underlying pathologies. HRRC tests do not distinguish ET patients from normal, but differentiates specifically between PD and ETPD, and normal individuals. HRRC testing may be a useful method for evaluating pathologies between ET, PD, and ETPD patients.