Neurometrics

Clinical Applications of Quantitative Electrophysiology

E. Roy John

• Editore: Routledge
• Anno: 2021
• ISBN:
  9781000397833
• Edizione: 1
• Argomento: Psychology
• Categoria: History & Theory in Psychology

Originally published in 1977, this volume attempts to show how the existing state of knowledge and technique in neuroscience can be effectively applied to a variety of practical clinical problems that at the time were dealt with less than adequately. Traditionally, clinical electroencephalography had been one of the major techniques by which our knowledge of neuroscience had been brought to bear upon these problems. The utility of this technique had been sharply limited and constrained by reliance upon qualitative interpretation of electrophysiological observations. In contrast, the approach proposed here is based upon quantitative measurements of salient features extracted from electrophysiological data which reflect various aspects of brain function related to sensory, perceptual and cognitive processes as well as to the structural and functional integrity of different neuroanatomical systems. The Editors call this quantitative approach "neurometrics".

1

Introduction

I.   A Definition of “Neurometrics”

In Volume 1 of this work, we attempted to utilize neuroanatomical, neurochemical, neurophysiological, neuropharmacological, and neuropsychological data from fundamental research in order to construct an integrated functional view of the brain mechanisms which mediate higher processes ranging from arousal and attention to subjective experience and psychopathology. In this volume, we will attempt to show how the existing state of knowledge and technique in neuroscience can be effectively applied to a variety of practical clinical problems that are presently dealt with less than adequately. Traditionally, clinical electroencephalography has been one of the major techniques by which our knowledge of neuroscience has been brought to bear upon these problems. The utility of this technique has been sharply limited and constrained by reliance upon qualitative interpretation of electrophysiological observations. In contrast, the approach which we propose is based upon quantitative measurements of salient features extracted from electrophysiological data which reflect various aspects of brain function related to sensory, perceptual and cognitive processes as well as to the structural and functional integrity of different neuroanatomical systems. We will call this quantitative approach “neurometrics.”¹

Much of our discussion of this new neurometric approach depends upon thorough familiarity with facts, methods and concepts presented in Volume 1. Wherever possible, we have endeavored to refer the reader to the most relevant sections of Volume 1. We have been constrained from presenting overlapping discussions in both volumes by practical reasons and apologize to the reader if it is sometimes necessary to refer to the other volume for complete understanding of the presentation.

¹ We wish to acknowledge our indebtedness to our colleague, Dr. B. Z. Karmel, for independently coining this apt term to describe this approach during one of our many discussions together about our joint studies (see Chapter 8).

II.   Functional Insights Available from Scalp Recordings

A great variety of information about brain functions can be obtained by analyzing the weak electrical activity that can be recorded from the intact human scalp. Not only does this electrical activity contain diagnostically valuable information about neuropathology but it reveals many phenomena related to sensory, perceptual, and cognitive processes that are otherwise extremely difficult to measure in an objective manner. This information is reflected in two major aspects of the electrical activity: (1) the spontaneous fluctuations of voltages generated by the brain comprising the electroencephalogram, or EEG. The physiological origin of the EEG has been described in Chapter 2 of Volume 1; and (2) the evoked fluctuations of voltages occurring after presentation of a sensory stimulus reflect the responses of different brain regions to the afferent input. The physiological origin of evoked potentials (EP) has been discussed in Chapters 3 and 9, and some of the insights provided by EPs have also been presented in Chapters 9 and 10 of Volume 1.

In this Introduction to Volume 2, we will examine a variety of clinical applications of the information derived from these two kinds of electrical activity. It is our intention neither to provide a manual for interpretation of the conventional EEG nor an exhaustive review of the literature on sensory evoked potentials. Such reference works of excellent quality already exist, and will be cited where appropriate. Rather, it is our intention to provide the reader with a general overview of the kinds of information available, how they can be obtained, and the uses to which they are generally put, so that he will more fully comprehend the basis of the quantitative computer methods presented in later chapters, as well as their practical utility.

The clinical utilization of electrophysiological measures has become the almost exclusive prerogative of the neurologist who evaluates the EEG to assess neuropathology. Such clinical practice still depends overwhelmingly on the experience of the skilled electroencephalographer who diagnoses a variety of brain disorders by visual assessment of particular features of the EEG. In the last fifteen years, there has been a great expansion of our knowledge about the electrical activity of the brain, particularly as a result of the development of minicomputers and their application to the precise analysis of electrophysiological processes. Although a vast amount of information has been accumulated during this period, such information has had little impact on clinical practice. Not only has there been a lag in the application of more objective and precise methods of EEG evaluation to such traditional problems as the assessment of neuropathology, but there has been little attempt by psychologists, psychiatrists, pediatricians, and those physicians concerned with visual or auditory function to take advantage of the insights into sensory, perceptual, and cognitive processes which can be obtained by electrophysiological measurements. Such insights can be invaluable in the diagnosis and treatment of certain kinds of patients and are often difficult or impossible to obtain if one relies upon the verbal cooperation of the patient.

All too often, the pediatrician, psychologist, psychiatrist, or other practitioner is forced to draw inferences about subtle nuances of sensory, perceptual, and cognitive function by interpreting the behavior of the patient, the observations of family members or teachers, or the results of psychometric tests that emphasize product rather than process, often rely upon language, and are severely “culture-bound.”

III.   Limitations of Qualitative Analysis of Brain Electrical Activity

There are many reasons to be dissatisfied with this situation. The number of skilled neurologists and encephalographers in every country of the world is grossly inadequate. For example, there are about 3,000 neurologists, including only 250 child neurologists, in the United States, which has a population of about 65 million children aged 15 years and under. Outside major cities, most locales are completely unable to benefit from electroencephalography. Patients presenting symptoms suggesting the presence of neurological diseases are often not submitted to electroencephalographic examination until those symptoms have persisted for some time and have become sufficiently distressing to occasion referral to an electroencephalographer or neurologist located in the nearest major community. The attendant delay may well have adverse consequences for the patient, if not in ultimate prognosis then at least in terms of distress in the intervening period.

Proper evaluation of the EEG takes not only skill but a substantial amount of time; therefore, even in major cities competent EEG examinations are not readily available. Furthermore, because of differences in experience and judgment, not all electroencephalographers evaluate EEGs in the same way. Most serious practitioners of other specialties are forced to depend upon the neurologist for direct assessment of the adequacy of brain function, but the methods of the neurologist are not optimally devised for the objective assessment of subtle nuances of information process in the brain.

IV.   The Neurometric Alternative

With the advent of minicomputers and the development of several new mathematical techniques, it has become possible to obtain rapid, objective, and detailed quantitative analysis of electrophysiological phenomena related to many aspects of brain function. This neurometric methodology promises a number of important advances:

• 1.   Assessment of neuropathology can become much more readily available, and perhaps significantly more sensitive, than has hitherto been the case. Assessment of the amount of damage and prognosis of recovery based upon repeated evaluations after short intervals may be of major utility in decisions about the treatment of patients after strokes or head injury.
• 2.   Development abnormalities reflecting such factors as perinatal trauma, inadequate sensory functions, or the absence of various capacities expected to emerge with maturation can now be recognized early and objectively. Such early identification of brain dysfunction often enables interventions which minimize psychological trauma to both child and parent, and provides valuable bases for guidance of pharmacotherapy, remedial treatment, and rehabilitation;
• 3.   Alterations in brain states caused by centrally active drugs can be described in precise mathematical terms. A quantitative nomenclature for psychoactive drugs can be envisaged, which would provide a measure of the changes in excitability levels and reactivity to stimuli in different brain regions by analysis of the EEG and evoked response changes resulting from medication with such agents. Such a catalog of the magnitude and locale of drug effects might provide a preliminary bioassay method for drug screening by comparison of the profiles of effects of new versus familiar compounds.
• 4.   Changes in brain states related to particular diseases can be quantified. Such assessments may reveal characteristic features of specific disorders, and may permit selection of drugs most appropriate for treatment of the individual patient. Reexamination after initiation of a course of medication might permit adjustment of dosage or indicate the advisability of changing the initial treatment. Such procedures might offer a very useful adjunct to the pharmacotherapy of psychiatric and metabolic disorders. Neurometric assessment may also permit early identification of certain disease processes, permitting more effective intervention. This might be especially useful in detection of brain changes related to cognitive impairment resulting from chronic brain syndrome or senile deterioration.

It can be expected that as practitioners in the diverse fields in which neurometric evaluations would be valuable become cognizant of their availability and potential utility, large service centers will come into existence which will provide the necessary analyses automatically and economically. Computer centers for automatic assessment of brain functions reflected in electrical processes will become an important adjunct to practice in a number of specialties in addition to neurology itself. Recognizing this, plans for such centers are already being elaborated in certain countries, for example, in Sweden (Petersén, 1973). Small general purpose minicomputers and special purpose diagnostic computers already are available which provide the necessary measures in a fashion adequate for routine use. Personnel to operate such centers, to interpret the results of computer assessment of brain function, and to implement treatment based upon such evaluations will be needed. It is our hope that this book will provide an impetus for the training of such neurometricians.

2

Diagnostic Electrophysiology

The purpose of this chapter is to provide an overview of the present status of knowledge about the diagnostic utility of qualitative electrophysiological measures. Later chapters will deal with the techniques of rapid automatic computer implementation of quantitative neurometric indices and results obtained by applying neurometric techniques to a variety of clinical problems.

I. EEG Assessment of Neuropathology

A survey of the value of the EEG in various fields of medicine can be found in Volume 1 of the Handbook of Electroencephalography and Clinical Neurophysiology (Rémond, 1971). It has long been recognized that examination of the patterns of electrical voltages recordable from electrodes affixed to the human scalp by conductive paste or inserted into the scalp as needles can provide a wealth of information about the integrity of the brain generating those voltages. Such examination is based upon the recognition of particular features of waveform and frequency composition characteristic of normal function as well as of particular neurological disorders. The interested reader can find exhaustive reviews of various aspects of the interpretation of the EEG in numerous volumes, for example, Hill and Parr (1963), and atlases of the waveshapes characteristically found in adults (Gibbs & Gibbs, 1964) and in children (Kellaway & Petersén, 1964) are available. Only a general introduction to principles of EEG analysis will be provided here.

A. EEG Recording Methods

1. Electrode Placement

Since the EEG electrode on the scalp is primarily responsive to the electrical activity of the subjacent cortex and its transactions with other brain regions, it is obvious that the information available from an EEG examination will depend substantially upon the loci selected for electrode placement. Many systems for electrode placement have been proposed, each with its own rationale. Some years ago, it was considere...