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Clinical applications of evoked potentials in neurology: Advances in neurology, Vol. 32
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7(I
Basic text in neurophysiology Basic Neurophysiology
by Beverley Bishop, Medical Examination Publishing Company, 1982. $22.50 (xii + 602 pages) 1SBN 0 87488 600 7 There has, for a long time, been a notable gap in the text-book coverage of the basic sciences; this gap is in the area of neurophysiology. I suspect that the reason for this is that it is notoriously difficult to write a textbook in a field that is expanding frenetically and that is so extensive. The author admits to having spent 20 years teaching neurophysiology to undergraduates and graduates - an admission that is also clearly revealed when one comes to examine the contents of the book in detail. One of the more difficult parts of text-book writing lies in the choice of material, and much of the skill resides in knowing what to
leave out. Beverly Bishop has achieved an admirable degree of success in this process of selection. The book is composed of 21 'units' each dealing with a circumscribed topic and also containing a self-administered catechism upon the material. For example, unit l is entitled 'Ontogeny of the nervous system', and there are 16 pages of informative text, one page of further source-material, and 14 pages of questions and answers. This scheme is followed, with approximately the same proportion of information to testing, throughout the remaining 20 units. It seems an excellent way of stimulating any student to learn a subject, and my only criticism is that the answers to the questions are simply given as a list of the correct numbers in each case. Perhaps a bit of explanation as to why certain answers were correct might not have come amiss.
Blurred image of a moving target Clinical Applications of Evoked P o t e n t i a l s in N e u r o l o g y : A d v a n c e s in N e u r o l o g y , V o l . 3 2
edited by J. Courjon, F. Mauguiere and M. Revol, Raven Press, 1981. $80.24 (xviii + 577pages) ISBN 0 89004 619 0 This book is a recent addition to a list of perhaps a half dozen symposia seeking to define the clinical utility of the evoked potentials. As such, it is noteworthy, deserving of a place in libraries of medical schools, neurologists, encephalographers, and students of human nervous function. As a manual of the techniques, or as a critical exposition of evoked potential approaches, however, it does not consistently give the state of the art nor yield a definitive treatment of the field. Unabashedly empirical in its orientation, the volume covers three major sensory systems (visual, auditory, somatosensory) with 69 short articles emphasizing application of evoked potentials in a broad range of neurological diseases. The attempted breadth of the book is perhaps its greatest shortcoming. By covering so much ground, the book treats few of its many subjects in depth or critically. Many of the articles indulge in weakly supported descriptions of types of evoked potentials expected in different neurological afflictions. Some of the articles do not do justice to either the field or their authors. Such editorial laxity can perhaps be justified on the grounds that the book may provide a truer survey of the uses to which evoked potentials are put than would he
reflected from a reading of the journal literature. If so, one virtue of this book, if such can be called a virtue, is that it contrasts the differences in standards applied to interpreting visual, auditory, and somatosensory evoked potentials. The book is divided into four major sections, each taking approximately a fourth of the 577 pages. The first section deals with visual evoked potentials, starting with an introduction by A. M. Halliday et al. and continuing with several subsections divided in accordance to the optic nerve, chiasmatic and retro-chiasmatic, and general encephalopathic lesions causing changes in visual evoked potentials. The second section is concerned with brainstem auditory evoked potentials, beginning with an introduction by K. H. Chiappa and continuing with discussions of lesions locating in the acoustic nerve, brainstem, cortex, and then with the uses of auditory evoked potentials in neonates, the aged and demented, and neuropsychology. The third section covers somatosensory evoked potentials, with an introduction by Desmedt et al., followed by articles on the effects of central and peripheral lesions and the uses of somatosensory evoked potentials in the studies of pain and in neuropaediatric diseases. The fourth section is devoted to the use of evoked potentials for the diagnosis and evaluation of multiple sclerosis. The articles on visual evoked potentials were disappointing. A broad range of neurological conditions were covered and the introduction clearly pointed out the artifactual effects of visual acuity differ-
The author has previously published what is termed a 'flexible self study systenf in the form of 'Illustrated Lectures m Neurophysiology', and these appear to be videotapes or tape-slide presentations said to be designed as a supplement to this book. I have not had an opportunity to view these, which is unlortunate, since they may go a long way towards making up for the rather poor standard of the illustrations throughout the book. Surely the worst example of an EEG ever published must be the line of squiggles that someone has traced (or more probably copied freehand) on page 402! However, the illustrations, although poor, are simple to understand and from this point of view are in accord with the philosophy underlying the text itself. On the whole, a textbook worth recommending to most undergraduate students. (:, C. J. t,IPPOLD
Department o f Physiology, University (bllege London. Go wer Street, London WCI E 6B 7, U.K.
ences, stimulus parameters, recording techniques, and whether the data were obtained from the left or right eye, males or females, and young or aged people. Yet. the articles that followed compared diverse and poorly documented patient groups, often arbitrarily lmnped together. Questionable practices, such as "grand averages' of evoked potentials for whole groups of patients and use of only peak measurements of latency and amplitude, were relied upon. None of the figures showed no-stimulus controls and only a few displayed repeated averaged evoked potential so that the reader can judge the consistency of the response. The introduction to the auditory evoked potential section by K. H. Chiappa succinctly summarized some eminently reasonable criteria for clinical interpretation of evoked potentials, paraphrased as follows: (1) use of test protocols which demonstrate waveform reproducibility with multiple repeated trials; (2) normal parameters based on results obtained from a large population using standardized stimulation and recording techniques, including a description of bandpass filters; (3) use of definitions of abnormality that exclude at least 98% of normals; (4) special attention paid to recording a clear and consistent early component, as a means of judging the efficacy of stimuli; (5) dependence on intercomponent separation rather than absolute latencies; (6) discussion of localization of conduction defects in light of the uncertainty regarding generator sources. In the main, the articles in the auditory evoked potential section adhered to these recommendations and consequently were among the best and most rigorous in the book. The first three articles of the somatosen-
TINS - February 1983 sory evoked potentials section touched upon some potentially classic work in the field. The first, by J. E. Desmedt and G Cheron, dealt with the evidence validating the use of the onset latency of the N22 component for estimating cortical response latency. The second, by T. Allison et al., compared the short latency somatosensory evoked potentials across species boundaries, ranging from man to rat. The third, by ~. J. Jones and A. M. Halliday, briefly examined the evoked potentials recorded en route and at the cortical level for several categories of diseases. The strength of the approach that they promote stems from the long established database of latency measurements in the clinical neurophysiology of peripheral nerves. These studies set the stage for the remaining articles dealing with specialized techniques for stimulating
71 somatosensory evoked potentials. The impressive numbers of patients listed in the studies of the fourth section indicate clearly the important place that evoked potentials have achieved in the diagnosis and evaluation of multiple sclerosis in neurology today. They also stress the need for more standardized criteria for performing the evoked potential studies and interpreting some of the changes found. Placed at the end of the book, this section is a logical sequel to the preceding articles devoted to the individual testing procedures. In sum, the book is a remarkably ambitious attempt to crystallize the field of clinical evoked potentials at a time when the field is immature and moving rapidly forward, when rigorous standards have yet to be established for most of the techniques
Drug action followed throughout life A g e and the P h a r m a c o l o g y o f Psychoactive Drugs edited by Allen Rasking, Donald S. Robinson and Jerome Levine, Elsevier, 1981. $51.00 (xviii + 212 pages) 1SBN 0 444 00586 2 Psychoactive drugs are extensively employed and the importance of age-related changes in the pharmacokinetics and pharmacodynamics of these substances is widely recognized. In spite of this, there are only isolated publications which provide the practitioner with the necessary information for the optimal use of these drugs in children and in the elderly. Publication of this book fills this gap. By presenting first the relevant basic pharmacodynamic and pharmacokinetic data, the book provides the practitioner with the necessary understanding to guide his clinical decisions, about the use of these drugs, in different developmental stages. At the same time the book also provides the researcher with a comprehensive review, which brings to attention the gaps in existing knowledge. It is a common point of contention that there is an increased responsiveness to psychoactive drugs at both ends of the age spectrum and especially in the aged. Since the ultimate effect of psychoactive drugs depends on the unbound neuronal drug concentration available for interaction with receptor sites, the increased responsiveness in the elderly could be explained by a reduction in the intrinsic free clearance of the drug. This would appear to be the case with at least some anxiolytic benzodiazepines and some neuroleptic butyrophenones.
This effect might be compounded by reduced glomerular filtration in the aged, primarily responsible for the lowered dose requirements of lithium salts in elderly patients. Considering that children and adolescents have a higher renal lithium clearance than their adult counterparts, there is a possibility for relatively higher dose requirements in these age groups. While there seems to be a consistent relationship between the half-life of lithium and age, no consistent relationship between the tricyclic antidepressant nortriptyline and age could be revealed. Entertaining the notion that changes in cerebrovascular permeability might be responsible for the increased sensitivity to drugs, a method of compartmental analysis was developed to study distribution volume of psychotropics. By employing this method it was revealed that cerebrovascular integrity remains intact in the senescent rat. If this finding can be substantiated by further evidence, it would indicate that in man the increase in drug toxicity with aging is not the result of an altered brain concentration of the drug (or its derivatives), but rather of altered receptor sensitivity. There is substantial evidence to believe that the biochemical processes that mediate synaptic neurotransmission are the substrates on which psychotropic drugs exert their effects. Since the relative level of these biochemical processes may deviate significantly in the young and the aged from those occurring in the mature brain, one should expect a differential age-related responsiveness to psychotropics. Agerelated influences on neurotransmitter bal-
described, and when the theoretical bases for interpreting evoked potentials have not been settled. With these limitations in mind, the achievement of the editors is impressive. But the book suffers from an overabundance of articles and would benefit from a harsher editorial policy to winnow out some of the more preliminary studies in favour of longer and more carefully presented work. Without a preface to orient the reader and the morass of three- to four-page articles competing for the reader's attention, the book seemed to lack focus and the inadequacies of individual studies stood out. The book provides a useful but dated reservoir of literature references. WISEYOUNG NYUMC School of Medicine, 550 First Avenue, New York, NY 10016, U.S.A.
ance, include an inverse correlation of hydroxylase-cofactor content in the CSF and age, and an increase in monoamine oxidase activity in the CNS (and also in the periphery) with aging. Since the hydroxylase-cofactor plays an important role in the synthesis of catecholamines (and also of serotonin), and monamine oxidase enzymes are involved in the breakdown of the same biochemical substrates, the age related changes in the concentration of hydroxylase-cofactor and monoamine oxidase activity are in observance with the decrease in monoamine content and aminergic activity with aging. In observance also are the clinical findings that monamine oxidase inhibitor antidepressants are effective and well tolerated in psychogeriatric patients. Considering that monoamine systems contribute to the stimulant action of dexamphetamine, and that interruption of each of the monoamine systems in the neonate leads to increased locomotor activity, the seemingly paradoxical therapeutic effect of methylphenidate in the hyperkinetic syndrome may be explained. In spite of the numerous contributors Age and the Pharmacology o f Pyschoactive Drugs is a well balanced and even book. It is one of those rare books which can be useful for different audiences. It should be recommended for both researchers and practising physicians, using psychoactive drugs in children and in the aged. THOMASA. BAN Professor of Psychiatry, Vanderbilt University, Nashville, Tennessee, U.S.A.
7(I
Basic text in neurophysiology Basic Neurophysiology
by Beverley Bishop, Medical Examination Publishing Company, 1982. $22.50 (xii + 602 pages) 1SBN 0 87488 600 7 There has, for a long time, been a notable gap in the text-book coverage of the basic sciences; this gap is in the area of neurophysiology. I suspect that the reason for this is that it is notoriously difficult to write a textbook in a field that is expanding frenetically and that is so extensive. The author admits to having spent 20 years teaching neurophysiology to undergraduates and graduates - an admission that is also clearly revealed when one comes to examine the contents of the book in detail. One of the more difficult parts of text-book writing lies in the choice of material, and much of the skill resides in knowing what to
leave out. Beverly Bishop has achieved an admirable degree of success in this process of selection. The book is composed of 21 'units' each dealing with a circumscribed topic and also containing a self-administered catechism upon the material. For example, unit l is entitled 'Ontogeny of the nervous system', and there are 16 pages of informative text, one page of further source-material, and 14 pages of questions and answers. This scheme is followed, with approximately the same proportion of information to testing, throughout the remaining 20 units. It seems an excellent way of stimulating any student to learn a subject, and my only criticism is that the answers to the questions are simply given as a list of the correct numbers in each case. Perhaps a bit of explanation as to why certain answers were correct might not have come amiss.
Blurred image of a moving target Clinical Applications of Evoked P o t e n t i a l s in N e u r o l o g y : A d v a n c e s in N e u r o l o g y , V o l . 3 2
edited by J. Courjon, F. Mauguiere and M. Revol, Raven Press, 1981. $80.24 (xviii + 577pages) ISBN 0 89004 619 0 This book is a recent addition to a list of perhaps a half dozen symposia seeking to define the clinical utility of the evoked potentials. As such, it is noteworthy, deserving of a place in libraries of medical schools, neurologists, encephalographers, and students of human nervous function. As a manual of the techniques, or as a critical exposition of evoked potential approaches, however, it does not consistently give the state of the art nor yield a definitive treatment of the field. Unabashedly empirical in its orientation, the volume covers three major sensory systems (visual, auditory, somatosensory) with 69 short articles emphasizing application of evoked potentials in a broad range of neurological diseases. The attempted breadth of the book is perhaps its greatest shortcoming. By covering so much ground, the book treats few of its many subjects in depth or critically. Many of the articles indulge in weakly supported descriptions of types of evoked potentials expected in different neurological afflictions. Some of the articles do not do justice to either the field or their authors. Such editorial laxity can perhaps be justified on the grounds that the book may provide a truer survey of the uses to which evoked potentials are put than would he
reflected from a reading of the journal literature. If so, one virtue of this book, if such can be called a virtue, is that it contrasts the differences in standards applied to interpreting visual, auditory, and somatosensory evoked potentials. The book is divided into four major sections, each taking approximately a fourth of the 577 pages. The first section deals with visual evoked potentials, starting with an introduction by A. M. Halliday et al. and continuing with several subsections divided in accordance to the optic nerve, chiasmatic and retro-chiasmatic, and general encephalopathic lesions causing changes in visual evoked potentials. The second section is concerned with brainstem auditory evoked potentials, beginning with an introduction by K. H. Chiappa and continuing with discussions of lesions locating in the acoustic nerve, brainstem, cortex, and then with the uses of auditory evoked potentials in neonates, the aged and demented, and neuropsychology. The third section covers somatosensory evoked potentials, with an introduction by Desmedt et al., followed by articles on the effects of central and peripheral lesions and the uses of somatosensory evoked potentials in the studies of pain and in neuropaediatric diseases. The fourth section is devoted to the use of evoked potentials for the diagnosis and evaluation of multiple sclerosis. The articles on visual evoked potentials were disappointing. A broad range of neurological conditions were covered and the introduction clearly pointed out the artifactual effects of visual acuity differ-
The author has previously published what is termed a 'flexible self study systenf in the form of 'Illustrated Lectures m Neurophysiology', and these appear to be videotapes or tape-slide presentations said to be designed as a supplement to this book. I have not had an opportunity to view these, which is unlortunate, since they may go a long way towards making up for the rather poor standard of the illustrations throughout the book. Surely the worst example of an EEG ever published must be the line of squiggles that someone has traced (or more probably copied freehand) on page 402! However, the illustrations, although poor, are simple to understand and from this point of view are in accord with the philosophy underlying the text itself. On the whole, a textbook worth recommending to most undergraduate students. (:, C. J. t,IPPOLD
Department o f Physiology, University (bllege London. Go wer Street, London WCI E 6B 7, U.K.
ences, stimulus parameters, recording techniques, and whether the data were obtained from the left or right eye, males or females, and young or aged people. Yet. the articles that followed compared diverse and poorly documented patient groups, often arbitrarily lmnped together. Questionable practices, such as "grand averages' of evoked potentials for whole groups of patients and use of only peak measurements of latency and amplitude, were relied upon. None of the figures showed no-stimulus controls and only a few displayed repeated averaged evoked potential so that the reader can judge the consistency of the response. The introduction to the auditory evoked potential section by K. H. Chiappa succinctly summarized some eminently reasonable criteria for clinical interpretation of evoked potentials, paraphrased as follows: (1) use of test protocols which demonstrate waveform reproducibility with multiple repeated trials; (2) normal parameters based on results obtained from a large population using standardized stimulation and recording techniques, including a description of bandpass filters; (3) use of definitions of abnormality that exclude at least 98% of normals; (4) special attention paid to recording a clear and consistent early component, as a means of judging the efficacy of stimuli; (5) dependence on intercomponent separation rather than absolute latencies; (6) discussion of localization of conduction defects in light of the uncertainty regarding generator sources. In the main, the articles in the auditory evoked potential section adhered to these recommendations and consequently were among the best and most rigorous in the book. The first three articles of the somatosen-
TINS - February 1983 sory evoked potentials section touched upon some potentially classic work in the field. The first, by J. E. Desmedt and G Cheron, dealt with the evidence validating the use of the onset latency of the N22 component for estimating cortical response latency. The second, by T. Allison et al., compared the short latency somatosensory evoked potentials across species boundaries, ranging from man to rat. The third, by ~. J. Jones and A. M. Halliday, briefly examined the evoked potentials recorded en route and at the cortical level for several categories of diseases. The strength of the approach that they promote stems from the long established database of latency measurements in the clinical neurophysiology of peripheral nerves. These studies set the stage for the remaining articles dealing with specialized techniques for stimulating
71 somatosensory evoked potentials. The impressive numbers of patients listed in the studies of the fourth section indicate clearly the important place that evoked potentials have achieved in the diagnosis and evaluation of multiple sclerosis in neurology today. They also stress the need for more standardized criteria for performing the evoked potential studies and interpreting some of the changes found. Placed at the end of the book, this section is a logical sequel to the preceding articles devoted to the individual testing procedures. In sum, the book is a remarkably ambitious attempt to crystallize the field of clinical evoked potentials at a time when the field is immature and moving rapidly forward, when rigorous standards have yet to be established for most of the techniques
Drug action followed throughout life A g e and the P h a r m a c o l o g y o f Psychoactive Drugs edited by Allen Rasking, Donald S. Robinson and Jerome Levine, Elsevier, 1981. $51.00 (xviii + 212 pages) 1SBN 0 444 00586 2 Psychoactive drugs are extensively employed and the importance of age-related changes in the pharmacokinetics and pharmacodynamics of these substances is widely recognized. In spite of this, there are only isolated publications which provide the practitioner with the necessary information for the optimal use of these drugs in children and in the elderly. Publication of this book fills this gap. By presenting first the relevant basic pharmacodynamic and pharmacokinetic data, the book provides the practitioner with the necessary understanding to guide his clinical decisions, about the use of these drugs, in different developmental stages. At the same time the book also provides the researcher with a comprehensive review, which brings to attention the gaps in existing knowledge. It is a common point of contention that there is an increased responsiveness to psychoactive drugs at both ends of the age spectrum and especially in the aged. Since the ultimate effect of psychoactive drugs depends on the unbound neuronal drug concentration available for interaction with receptor sites, the increased responsiveness in the elderly could be explained by a reduction in the intrinsic free clearance of the drug. This would appear to be the case with at least some anxiolytic benzodiazepines and some neuroleptic butyrophenones.
This effect might be compounded by reduced glomerular filtration in the aged, primarily responsible for the lowered dose requirements of lithium salts in elderly patients. Considering that children and adolescents have a higher renal lithium clearance than their adult counterparts, there is a possibility for relatively higher dose requirements in these age groups. While there seems to be a consistent relationship between the half-life of lithium and age, no consistent relationship between the tricyclic antidepressant nortriptyline and age could be revealed. Entertaining the notion that changes in cerebrovascular permeability might be responsible for the increased sensitivity to drugs, a method of compartmental analysis was developed to study distribution volume of psychotropics. By employing this method it was revealed that cerebrovascular integrity remains intact in the senescent rat. If this finding can be substantiated by further evidence, it would indicate that in man the increase in drug toxicity with aging is not the result of an altered brain concentration of the drug (or its derivatives), but rather of altered receptor sensitivity. There is substantial evidence to believe that the biochemical processes that mediate synaptic neurotransmission are the substrates on which psychotropic drugs exert their effects. Since the relative level of these biochemical processes may deviate significantly in the young and the aged from those occurring in the mature brain, one should expect a differential age-related responsiveness to psychotropics. Agerelated influences on neurotransmitter bal-
described, and when the theoretical bases for interpreting evoked potentials have not been settled. With these limitations in mind, the achievement of the editors is impressive. But the book suffers from an overabundance of articles and would benefit from a harsher editorial policy to winnow out some of the more preliminary studies in favour of longer and more carefully presented work. Without a preface to orient the reader and the morass of three- to four-page articles competing for the reader's attention, the book seemed to lack focus and the inadequacies of individual studies stood out. The book provides a useful but dated reservoir of literature references. WISEYOUNG NYUMC School of Medicine, 550 First Avenue, New York, NY 10016, U.S.A.
ance, include an inverse correlation of hydroxylase-cofactor content in the CSF and age, and an increase in monoamine oxidase activity in the CNS (and also in the periphery) with aging. Since the hydroxylase-cofactor plays an important role in the synthesis of catecholamines (and also of serotonin), and monamine oxidase enzymes are involved in the breakdown of the same biochemical substrates, the age related changes in the concentration of hydroxylase-cofactor and monoamine oxidase activity are in observance with the decrease in monoamine content and aminergic activity with aging. In observance also are the clinical findings that monamine oxidase inhibitor antidepressants are effective and well tolerated in psychogeriatric patients. Considering that monoamine systems contribute to the stimulant action of dexamphetamine, and that interruption of each of the monoamine systems in the neonate leads to increased locomotor activity, the seemingly paradoxical therapeutic effect of methylphenidate in the hyperkinetic syndrome may be explained. In spite of the numerous contributors Age and the Pharmacology o f Pyschoactive Drugs is a well balanced and even book. It is one of those rare books which can be useful for different audiences. It should be recommended for both researchers and practising physicians, using psychoactive drugs in children and in the aged. THOMASA. BAN Professor of Psychiatry, Vanderbilt University, Nashville, Tennessee, U.S.A.