William J. Nowack

Effects of valproate and ethosuximide on thalamocortical excitability.

Sodium valproate and ethosuximide are anticonvulsants employed in the treatment of petit mal epilepsy; both drugs are considered to be thalamically active. Valproate and ethosuximide both decreased the average evoked response following the second of two stimuli delivered to the ventrolateral thalamus at stimulus frequencies in the region of 3 Hz. Ethosuximide, but not valproate, enhanced the average evoked response at high stimulus frequencies an action shared with several convulsant treatments having different modes of action. The clinical effects of valproate and ethosuximide can be related to this differential modulation of thalamocortical excitability.

Development of the Thalamocortical Augmenting Response in the Kitten

Summary: Study of the developing central nervous system can lead to better understanding of the mature central nervous system. The thalamocortical augmenting response is a complex neurophysiological response considered to be related to the occurrence of some forms of epileptic activity. Using a paradigm previously developed in adult cats, we assessed the development of the thalamocortical augmenting response in kittens and found that the relative proportion of thalamocortical activity occurring at high frequencies of thalamic stimulation increased with increasing age. Anticonvulsants effective against petit mal seizures also increase the relative proportion of thalamocortical activity following high frequencies of thalamic stimulation. Developmental changes in the thalamocortical augmenting response can be related to the age‐dependent decreases in the prevalence of petit mal seizures.

Cerebellar Stimulation: Regional Effects on a Thalamocortical System

Summary: Regional effects of electrical stimulation of the cerebellar surface were quantitatively analyzed. Computer controlled stimulus sequences were delivered to ventrolateral thalamus and evoked responses recorded from ip‐silateral sensorimotor cortex in the cat. Threshold and excitability profiles were produced with an on‐line computer, and their modification by cerebellar stimulation was determined. The results of electrical stimulation of the cerebellar surface were: (1) depressed excitability from paramedian lobule and lobulus simplex; (2) uniquely elevated thresholds from paramedian lobule; and (3) a profound and long‐lasting depression of excitability following termination of lobulus simplex stimulation. In comparison with our anticonvulsant drug studies, these data suggest that cerebellar surface stimulation has a far greater capacity to control excitability and threshold responsiveness of thalamocortical systems. Cerebellar electrode placement and temporal pattern of stimulation appear to be important factors in the production of antiepileptic effects.

Neocortical Dynamics and Human EEG Rhythms

by PAUL L. NUNEZ, 730 pp., ill., New York, Oxford University Press, 1995.

Effect of hyperthermia on a thalamocortical system in the kitten and the cat: a preliminary study.

95.00 This book is an extension of Nunezs earlier work and it further develops his theory of the physical-biologic basic science underlying the electromagnetic activity of the brain. It has two stated aims: to facilitate communications among the many disciplines relevant to EEG and to provide a conceptual framework for the data. The chapters in which Nunez participates directly as an author most strongly adhere to these guiding principles to present a coherent and compelling argument, …

Analysis of epileptic activity in a system of interconnected neurons. A biological criticality theory.

Hyperthermia produces many changes in the ongoing electrical activity of the brain. One of the responses which fever can induce is seizure activity. The thalamocortical augmenting response, a complex neurophysiological response, has been related to seizure discharges. The changes in that complex neurophysiological response induced by experimental hyperthermia were assessed in adult cats and in kittens, using analytical methodology first developed in adult cats. The effect of two anticonvulsants (phenytoin and valproate) on those hyperthermia-induced changes in the thalamocortical augmenting response were compared in kittens. The differences between the effects of the two anticonvulsants on the thalamocortical augmenting response can be related to the reported clinical differences between the two anticonvulsants in patients with febrile seizures.

Topographic Brain Mapping of EEG and Evoked Potentials

In this theoretical study of epileptiform activity, the onset of self-sustained activity in a system of interconnected cells is explored using (a) analytical models, and (b) computer simulations. An approximate analytical model demonstrates that the system can be either stable, with self-sustained activity impossible, or potentially unstable, with the possibility of going into self-sustained activity if the firing rate is driven beyond a critical level. The approximations made in this initial model led to substantial discrepancies when the analytical criticality condition was tested against computer simulations in relatively small networks of neurons. Therefore, using a refined analytical model, a numerically more accurate, although computationally cumbersome, criticality condition was derived which agrees well with the simulation results. Two simulation models are used: a deterministic simulation in which the average number of cells firing at each simulation step is calculated and a probabilistic simulation in which the stimulation and firing of each individual neuron is followed. Comparison between the behavior of the probabilistic and deterministic simulations near criticality demonstrates that random fluctuations can force the system toward either self-sustained activity or decay.

Clinical Electroencephalography and Topographic Brajn Mapping: Technology and Practice

This 1990 publication is probably the most authoritative review of the subject currently available. The 13 chapters cover the relevant history, anatomy, physiology, differential diagnosis, medical, and surgical treatments of this condition. Each chapter is excellent, written by a recognized authority, and contains a very large and current bibliography. The historical chapter is fascinating. For the neurologist unacquainted with Rhoton’s beautiful anatomic illustrations, which have been published in journal articles through the years, the chapter on microsurgical anatomy is well worth reviewing. The chapter by Sweet analyzes the literature extensively and reports on a questionnaire that he sent out concerning complications of treatment of trigeminal neuralgia. He concludes with a critique of the commonly held theory that the condition is caused by vascular compression of the root near the pons. These chapters are mentioned here only to indicate the high quality and value of this book. The topic itself is still controversial in that there are many good treatments but each one has a significant failure and complication rate. Thus, there are vigorous proponents of each mode of therapy but no one way to treat the condition. This book attempts to gather together all the pertinent modern material in one location, and the authors have done a very good job.

Fundamentals of EEG Technology (Vol. 2/ Clinical/TI Correlates)

In evaluating a textbook it is necessary to measure what is accomplished versus the needs of the target audience. This text by Duffy, Iyer, and Sunvillo seems to have never made up its mind about the identity of its prospective audience. Chapter 1 is a useful overview of EEG history and technology. Chapters 2 through 9 comprise a rather detailed review of EEG technology that might be most appropriate for EEG fellows and EEG technologists. This material is probably dealt with in too much depth for the advanced medical student/rotator/ beginning neurology resident at whom the remainder of the book seems to be aimed. Chapter 10 is a thoughtful synopsis of the basic neurophysiology pertinent to clinical neurophysiology. Chapters 11 and 12 deal with some basic information useful in the interpretation of EEGs. Chapters 13 through 16 comprise a quick overview of some of the features of classical clinical EEG. Chapters 17 through 20 deal with some of the newer technologies in clinical neurophysiology. Fairly regularly, for further specific information the reader is referred to the literature, but specific citations are scarce or missing, and the reader seeking additional information is left without much of a guide. Finally, there is a chapter which attempts to relate EEG to other neurodiagnostic tests in a variety of conditions. Use of the International Classifications of Seizures and the Epilepsies/Epileptic Syndromes. or mention of why the authors feel those classifications are not appropriate, would be desirable in this chapter. The authors have produced a book which is long on the philosophy of neurophysiological testing but short on facts, other than those regarding technology. Perhaps this can be partially explained by the authors’ stated intent of concentrating upon basic principles rather than upon details. The aspect of this text that is most intriguing to the experienced reader is the inclusion in the list of authors of one of the developers of topographic EEG analysis. The guidelines for topographic EEG studies reflect the crucial role played by the technologist in obtaining such studies. This is obviously a well thought out and common-sense approach which could very well serve as a basis for the development of formal guidelines for this area. The reader, however, would reasonably expect a thorough and in-depth treatment of all aspects oftopographic EEG. In this respect the book is disappointing, providing at best a superficial view of many of the problems associated with topographic EEG interpretations. This book is a workmanlike job. Some areas are covered better than in other texts and others less well. Aside from the inclusion of some brief considerations of up-to-date topics, there unfortunately is little to distinguish this introductory text from other competent texts in EEG and clinical neurop hysiology .

A MODEL OF THALAMOCORTICAL INTERACTIONS AND THEIR ROLE IN THE DEVELOPMENT OF GENERALIZED SEIZURES

This volume is the 2nd in a 2-volume series dealing with the fundamentals of EEG technology by the same authors. Although the authors intended that volumes 1 and 2 should stand independently, the books will often be used together and the frequent references in volume 2 to sections in volume 1 encourage that use. It is possible that the volumes are bound differently to emphasize this independence, but it probably would have been desirable to recognize the inevitable joint use and to bind the 2 volumes in the same way. Readers should be aware that, although classic scalp EEG recording is thoroughly discussed, little or no coverage is devoted to related topics such as evoked potentials, intensive monitoring, intraoperative recordings, and the like, which are often included in books on EEG. I t is clear that such coverage should not reasonably be expected, but a casual reader might nevertheless expect these topics to be dealt with and should be aware, in advance, of the scope of this book. The authors’ clearly expressed opinion that EEG technology has progressed and that now the education of an EEG technologist “. . . requires more than hands-on tutorials concerned with the operations of sophisticated electrical appliances. . .” is most welcome. A broad understanding of the clinical uses of the EEG is essential in the education both of the EEG technologist and of the physician using EEGs. In addition to EEG technologists, these excellent volumes will inevitably be consulted by medical students, rotating housestaff, and beginning neurology residents seeking an introduction to EEG. The degree to which the book meets the needs of this probable additional audience, although not anticipated by the authors, should also be considered. The 1st chapter of this volume consists of an overview of neurophysiology and neuroanatomy. Inevitably, there are some statements in this section which represent the personal opinions of the authors and would therefore be subject to argument by some readers. More indepth discussion of those aspects of neuroanatomy and neurophysiology directly relevant to EEG might be desirable in a text such as this. I t is possible to object to the inclusion of the discussions of areas of less direct relevance. Such discussions are frequently too brief to be recommended without extensive supplementary reading. It would be erroneous to consider this section as more than a brief limited introduction to some of the scientific bases of neurology. There follows a pithy and useful discussion of writing the EEG requisition and documentation on the EEG record. The technologists in my laboratory thought that the suggestions in this chapter were especially useful and to the point. Next comes the high point of this text, the chapter on the role of electroencephalography in seizure disorders. The illustrations of the EEG patterns associated with different seizures are well done, and their presence alone justifies the purchase of this volume. There are frequent helpful hints to the EEG technologist, culled from the extensive experience of the authors, regarding ways to maximize the amount of information obtainable from the EEG tracing. The sage observation that there is no such thing as a “routine EEG examination” and that every EEG recording should be individually modified to best elicit the maximum amount of information helpful to the clinical care of the patient is amply emphasized and illustrated. Several brief chapters follow about EEG in other clinical conditions (eg, cerebrovascular disease, infections, and brain tumors). The notes to the technologist, although less frequent and less voluminous than in the chapter on seizures, are definitely of value. The clinical descriptions of the entities involved are often excessively brief; it is of concern that such brief descriptions might be considered sufficient discussion of the neurologic knowledge that will be expected of the reader. Although this disease-oriented organization seems to meet the goals of the volume less efficiently than a less traditional organization based on type of abnormality, the important information is there. A concluding chapter discusses the use of the EEG in the determination of brain death. Although this section is basically a review of data from other sources, this topic fully warrants the timely repetition and emphasis. It is useful to have the relevant data gathered in one place. I t is virtually required that a reviewer unearth a few arguable points in any book. Those requisite critical quibbles should not be interpreted as detracting significantly from the overall high value of this volume. Without a doubt, the information and points of view in this volume would be of considerable benefit to a neurologist and, more generally, to any physician. Since an EEG technologist might have a different perspective on the value of the volume than a physician, I asked the EEG technologists in my laboratory to review this volume also. They thought that it contained many useful suggestions and much valuable information and that it would be useful both in the education of the new technologist and as a reference for experienced technologists. The emphasis upon what constitutes a good EEG tracing will be of benefit to everyone involved, even peripherally, with EEG. This book, along with its companion volume, should be on the reference shelf of every EEG laboratory. I recommend it highly to EEG technologists, fellows in EEG and advanced neurology residents, and practicing EEGers. General neurologists are encouraged to peruse the volume carefully. More casual readers should use the book but should be aware that supplementary reading is needed.