CHAPTER 1
INTRODUCTION
W. P.
A. Prologue
B. Material
C. Brain activity — normal and epileptic
D. The messenger and the interpreter of consciousness
E. The brain and the mind
A. Prologue
The general conclusions embodied in this monograph were presented in the 1956 Vanuxem Lectures. The audience at those lectures was drawn from the various departments of a great university. But most of the listeners had little familiarity with current work on the anatomy and physiology of the human brain. Consequently, the introduction was planned with this in mind. And now, since this book is designed for lay readers interested in speech mechanisms, as well as for the members of the medical profession, the same introduction will be used in this first chapter, with certain subtractions but without change in form.
The principal purpose of our study is to throw new light on the speech mechanisms of the brain — the mechanisms, for example, that enable me to speak to you and enable you to translate my words and understand my meaning. I select the words that are symbols of my thought. You, receiving these symbols, convert them into your own thought. But you hold short sequences of my words within the focus of your attention for a fleeting moment — long enough for conscious consideration — while you add your own interpretation. Then, letting that perception pass, you turn to the next sequence.
It is an astonishingly complex process that any speaker sets in motion. Consideration of it brings us, at once, face to face with the baffling problem of the nature of the physical basis of the mind. Without stopping for definition, let me say simply that I begin with what is called a thought. A succession of nerve impulses then flows out from my brain along the nerves in such a pattern that the appropriate muscles contract, while others relax, and I speak. An idea has found expression in electrical energy, movement, vibrations in the air. The boundary which separates philosophy from neurophysiology and physics has been crossed!
When that sound reaches your ear drums it is converted again into nerve impulses that are conducted along your auditory nerves and into your brain. This stream of nerve impulses results in a secondary mental proposition which resembles, but is far from being identical with, that of the speaker. It is a new perception. Again that strange brain-mind frontier has been crossed — crossed twice by each utterance!
Now, you may well wish to debate with me whether or not there is any boundary between nerve impulse and the mental state of a conscious person. And, furthermore, you might add that a neurophysiologist should confine his attention to neurone mechanisms, since he is only a physiologist after all. And yet in a discussion of speech he can hardly avoid consideration of this problem, and we shall return to it presently. Let me now get back on firmer ground where we can discuss the anatomy and physiology of the human brain briefly and simply.
B. Material
The material for these discussions is drawn from study of the patients in an active neurosurgical practice. During the past ten years my associate and co-author, Dr. Lamar Roberts, and I have been studying problems of speech and of brain dominance — a task to which I had turned somewhat earlier with the help of Dr. Preston Robb (1946). Now Dr. Roberts has collected and reviewed all of the accumulated material.
Many patients came to us seeking a cure for focal cerebral seizures which had been caused by earlier injury, infection, or anoxia of the brain. The few who seemed suitable were selected for operation. The cases used in this sudy are chosen from that group.
Local anaesthesia was used during the operations (osteoplastic craniotomy). This does away with the pain of the procedure and yet leaves the brain normally active after a segment of the skull has been cut and temporarily turned back and the surface of the brain thus exposed. An operation is described in Chapter VII. Since the patients were talking and fully conscious during the procedures, it was possible to discover what parts of the cortex were devoted to the speech function.
We have reviewed 273 such operations upon the dominant hemisphere and an equal number on the opposite side for the purpose of this study, and Dr. Roberts has carried out a special series of speech examinations on seventy-two of the patients. The therapeutic purpose, in each case, was to remove areas of abnormal brain which were responsible for these attacks, without touching parts that were normal or too precious to be forfeited. Periodic follow-up studies show that such operations have stopped the attacks in about fifty per cent of the cases and made the attacks easier to control by medicine in others.
So much for clinical medicine. The problems of epilepsy and the anatomy and physiology of the human brain have been discussed elsewhere and our evidence summarized. But it may serve a useful purpose to say a word here about activity in the normal brain and about the sudden abnormal activity that occurs from time to time in the brain of those who are subject to epileptic seizures.
C. Brain activity — normal and epileptic
The brain (Fig. III-1 on p. 40) is the convoluted organ which fills the great cavity of the skull. It is composed of nerve cells or ganglion cells, each provided with tail-like nerve fibers or expansions. Each living nerve cell is capable of developing energy that is propagated, as an electric current, along its own expansions. The expansions are insulated except at their endings. At the endings there are synapses across which enough energy can be communicated by a chemical process to the body of another nerve cell to fire off energy in it. Thus, further conduction of electric potentials passes through expansions of the second cell, and so by a succession of little activations a stream of impulses passes from one ganglion cell to another and another as determined, no doubt, by complicated facilitations and inhibitions.
It is said that there are ten billion nerve cells (ganglion cells) within the human brain, and each probably has some capacity of generating energy within itself. In addition to these there are even more neuroglial cells which seem to support and nourish and insulate the nerve cells and their branching fibers.
The business of the brain is carried out by the passage of nervous impulses...
