CONTENTS. Foreword George H. Kraft. Henry L. Lew

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1 EVOKED POTENTIALS Foreword George H. Kraft xi Preface Henry L. Lew xiii Overview of Artifact Reduction and Removal in Evoked Potential and Event-Related Potential Recordings 1 Martin R. Ford, Stephen Sands, and Henry L. Lew Regardless of modality, recording site (spinal and scalp), and clinical population, all evoked potential and event-related potential studies are acquired and measured, and the measurements are only as accurate as the data are relatively free from artifactual influences. There are three approaches to deal with artifact: (1) avoid it, (2) eliminate it, or (3) minimize it. In this overview article, common methods for avoiding, eliminating, and minimizing artifact and more recently developed procedures are reviewed. Fundamental Principles of Somatosensory Evoked Potentials 19 Thoru Yamada, Malcolm Yeh, and Jun Kimura The evoked potential is an electrical activity of the nervous system in response to external sensory stimulation. Studies of somatosensory evoked potentials (SSEP) provide unique opportunities for investigating physioanatomic substrates of sensory pathway and cognitive functions of the sensory system. Progress of clinical investigation and application of SSEP have been stalled in more recent years, although SSEP still remain a useful tool for diagnosis of various neurologic disorders and for the monitoring of spinal cord function during surgery. VOLUME 15 Æ NUMBER 1 Æ FEBRUARY 2004 v

2 Somatosensory Evoked Potentials in Coma Prognosis 43 Lawrence R. Robinson, Paula J. Micklesen Somatosensory evoked potentials increasingly are used for prognosis in comas due to hypoxic-ischemic encephalopathy, traumatic brain injury, and intracranial hemorrhage. This article presents summary data that should allow clinicians caring for coma patients to provide families with a greater degree of certainty regarding outcome than previously has been available. The Use of Evoked Potentials in Intraoperative Neurophysiologic Monitoring 63 Jaime R. López Evoked potential studies have proved useful for diagnostic purposes, and now they are becoming an integral part of assessing intraoperative cerebral ischemia and neural injury. This article reviews the use of somatosensory and brainstem auditory evoked potentials in a variety of neurosurgical and interventional neuroradiologic procedures. Electrophysiologic Intraoperative Monitoring for Spine Procedures 85 Jefferson C. Slimp A primary goal of electrophysiologic intraoperative monitoring is to reduce the risk for neurologic complication. There are specific risks to the spinal cord and nerve roots during surgeries on the spine or spinal cord. The advent of equipment capable of performing somatosensory evoked potentials (SEPs), motor evoked potentials, and electromyography in a multiplexed manner and in a timely fashion brings a new level of monitoring that far exceeds the previous basic monitoring done with SEPs only. Monitoring of the spinal cord with SEPs is an accepted standard of care for cases that place the spinal cord at risk. Likewise, nerve root monitoring with electromyography is a widely practiced form of monitoring and shows great benefit. Motor evoked potentials and reflex monitoring, which address the descending pathways and the interneuronal connections, is efficacious in detecting abnormalities that may be missed by SEPs. The Clinical Use of Dermatomal Somatosensory Evoked Potentials in Lumbosacral Spinal Stenosis 107 Seneca A. Storm, George H. Kraft Dermatomal somatosensory evoked potentials (DSEPs) provide clinicians with a safe, noninvasive technique to determine which patients with anatomic spinal stenosis have the added component of neurogenic compromise. Based on physiologic principles, levelby-level prolongation of DSEP latencies, reduction of amplitude, asymmetry, or a complete absence of response is associated with vi

3 dysfunction in that particular afferent neurologic pathway. Given that lumbosacral spinal stenosis typically develops over time, the degree of abnormality is likely to correspond to the physiologic slowing occurring in the multiple rootlets of the cauda equina. These recordings are not easy to perform and interpret, but when done correctly, they provide the best evidence for the type of neurophysiologic dysfunction in lumbosacral spinal stenosis that responds favorably to surgical decompression. DSEPs might provide a means of neurophysiologically monitoring clinically significant findings in a program of conservative management. Motor Evoked Potentials 117 Young H. Sohn, Mark Hallett Noninvasive electrical stimulation of the human brain first was attempted in the 1950s. In the early 1980s, the first clinical application method of transcranial electrical stimulation was developed. Investigators in the mid-1980s showed that it was possible to stimulate the nerve and the brain using external magnetic stimulation (transcranial magnetic stimulation [TMS]), with little or no pain. TMS now is used commonly in clinical neurology to study central motor conduction time. Depending on the stimulation techniques and parameters, TMS can excite or inhibit brain activity, allowing functional mapping of cortical regions and creation of transient functional lesions. It now is used widely as a research tool to study aspects of human brain physiology, including motor function and the pathophysiology of various brain disorders. Clinical Application of the P300 Event-Related Brain Potential 133 John Polich This article reviews the background and application of the P300 event-related brain potential in clinical situations. The empirical and theoretical background of P300 is discussed with respect to the P3a and P3b subcomponents. Clinical event-related potential applications are described, and methodologic issues are addressed. Practical suggestions are made for future clinical event-related potential applications. Clinical Applications of Event-Related Potentials in Brain Injury 163 Letizia Mazzini Studies have shown event-related potentials (ERPs) to be an objective measure of cortical stimulus processing; ERPs may be useful in studying the effects of brain injury at different stages. This article addresses the potential clinical application of ERPs in the assessment and prognosis of brain injury. The recording of long-latency responses enhances the predictive value in clinical outcome in patients clinically diagnosed as in coma or vegetative state. The use of a complex stimulus or a stimulus that is relevant for the subject, in vii

4 a passive paradigm, improves the accuracy of the test. ERPs also can be used to assess and monitor the integrity of specific brain processes during the performance of cognitive tasks. The experimental data in these patients still are not sufficient to standardize the indications of ERPs for clinical practice. Applications of the P50 Evoked Response to the Evaluation of Cognitive Impairments after Traumatic Brain Injury 177 David B. Arciniegas, Jeannie L. Topkoff This article reviews the applications of the P50 evoked response to paired auditory stimuli (P50 ERP) in the study and evaluation of cognitive impairments after traumatic brain injury (TBI). The cholinergic hypothesis of cognitive impairment after TBI and the relationship of impaired auditory sensory gating to that hypothesis are presented. The neurobiology of impaired sensory gating, the relationship of that neurobiology to the P50 ERP, and the principles of P50 ERP recording are discussed. Studies of the P50 ERP among patients with persistent cognitive complaints after TBI are reviewed. Finally, possible clinical applications and limitations of the P50 ERP in the study, evaluation, and treatment of patients with cognitive impairments after TBI are offered. Clinical Applications of Cognitive Event-Related Potentials in Alzheimer s Disease 205 John M. Olichney, Dieter G. Hillert This article has two main objectives. First, a concise review is presented of the scientific literature on several event-related potential components that have shown sensitivity to Alzheimer s disease. These components include P200, N200, P300, N400, and P600 (or late positive component), each of which taps into different aspects of late sensory or cognitive processing. In general, the long-latency components reflect higher cognitive operations and are not sensitive to the sensory input characteristics, in contrast to the earlier components (ie, in approximately the msec latency range). Second, the still largely untapped potential for the event-related potential technique (eg, novel cognitive paradigms, clinical applications, and advanced brain-mapping techniques) is illustrated to provide a precise biometric characterization of cognitive disorders such as Alzheimer s disease. Principles and Clinical Applications of Auditory Evoked Potentials in the Geriatric Population 235 James Jerger, Henry L. Lew Age-related changes in auditory evoked potentials are complex and complicated by the confounding effects of gender; concomitant high-frequency hearing sensitivity loss; and, in the case of event-related responses, the nature of the task used to elicit the response. viii

5 There is a tendency for amplitude to decline and latency to increase, but these trends are not always clear-cut. There is also a tendency for activation patterns to move forward from parietal to frontal areas as age increases. The dichotic listening tool has revealed age-related changes in interaural and interhemispheric asymmetries. These asymmetries seem to be related to loss in the efficiency of interhemispheric transfer via the corpus callosum. Overview of Dipole Source Localization 251 Manfred Fuchs, Martin R. Ford, Stephen Sands, and Henry L. Lew Truly accurate dipole source localization relies on having (1) reliable, artifact-free evoked potentials and event-related potentials (or magnetoelectroencephalogram) data to start with; (2) landmark and electrode position data obtained with a three-dimensional digitizer; (3) MRI (or CT) data from the same subject (with a means to measure the same landmarks); (4) the capability to apply different dipole and volume conductor models; and (5) the ability to coregister the structural and anatomic data to display the final source solutions. Most important is to have a thorough understanding of the fundamental principles of the localization programs and neurophysiologic processes. Localization programs are simply tools. Used incorrectly, they can yield meaningless results. Used correctly, they can provide a window into neurophysiologic functioning that is not available through any other means. Integrated Technology for Evaluation of Brain Function and Neural Plasticity 263 Paolo M. Rossini, Gloria Dal Forno This article discusses possible mechanisms that underlie central nervous system plasticity during physiologic learning, adaptation to the environment, and neurologic disease. Technologies able to assess brain function and dysfunction and their integrated use are described. Their potential use as powerful means to study new rehabilitation approaches and progress and outcomes of intervention are discussed. Index 307 ix