BODY AND MIND. In seeking to'deal with the perennial problem of "Body and Mind" our first task is to state in general terms how activities of the body are related to activities of the mind, accepting the distinction between body and mind at its face value—as it is understood in general speech. A body is something that can move in space and can be seen and touched, whereas the mind is revealed in consciousness, which is direct experience of mental activity and, as such, incapable of further definition. It is a matter of observed fact that mind or mental activity does occur in relation to bodily activity. We do not meet with minds independently of bodily organisms—at any rate, not in normal circumstances—and whereas at the time of Aristotle it was thought that the chief seat of the mind was the heart, it is now recognized by everyone that the brain—the most complex and dominant part of the nervous system—is that part of the body which is in immediate relationship to the mind, or to mental activity.
Two general questions arise. One is as to the various parts of the brain with which different kinds of mental activity are di rectly correlated. This is the question of cerebral localization. The other question is as to the exact nature of the relationship be tween mental activity and whatever kind of brain activity is correlated with it.
as first worked out by Fritz, Hitzig, Munk, Ferrier, etc., and developed in modern times by Sherrington, Head and others, is a theory of the localiza tion, not of different kinds of mental activity, but of different kinds of physiological activity correlated therewith. The part of the brain chiefly concerned is the cerebral cortex, which is a layer of "grey" matter, one-eighth to one-twelfth of an inch in thick ness, covering the two cerebral hemispheres. This cerebral cortex is a great "projection area," which acts as the ultimate receiving station for sensory impulses, and the primary transmitting station for motor impulses of a volitional, or at least of a conscious, type. Its extent is greatly increased by the "convolutions" into which it is thrown. The nerve fibres running from the cerebral cortex to the lower parts of the nervous system are mainly motor in nature, and carry impulses which pass through sub-cortical "centres" and eventually reach the various muscles on the opposite side of the body. The fibres that run into the cerebral cortex are mainly sensory in nature, and come eventually from the optic thalamus and other sub-cortical "centres" which receive impulses from the various sense organs—eye, ear, skin, etc.—likewise on the oppo site side of the body. Within the cortex itself there run short "tangential" fibres which link up one part of the cortex with closely neighbouring parts. These are special association fibres which probably have to do with "immediate memory"—the memory for recent events. They are found to be degenerated in the brains of patients dying of chronic alcoholism, where an out standing symptom is loss of memory for recent events.
Besides these tangential fibres, there are longer association fibres running from any one part of the cortex to more distant parts, including a mass of fibres, known as the "corpus callosum," linking the two cerebral hemispheres together.
By means of these association fibres and projection fibres, which link up cortical centres with one another, and, through sub-cortical centres, with the sense-organs and muscles of the body, an elaborate and complex system of "integrative action" (Sherrington) is possible, whereby the organism is enabled to react as a unity to its environment, and to obtain a unitary ex perience of that environment.
It has been discovered by physiological research that voluntary movement, or at least consciously-initiated movement, occurs in relation to physical change in a very special and restricted part of the cerebral cortex, viz., in the precentral convolution, the con volution in front of the fissure of Rolando. The localization is very precise, in that centres for movement of different muscles of the body are spatially distinct from one another. The muscles of the lower limb are represented in the upper part of the precentral convolution. The muscles of the trunk are represented in the middle part, and the muscles of the shoulder, upper arm, lower arm and hand are represented lower down. Lower down still the muscles of the face, tongue, lips and larynx are represented, so that the lowest part of the precentral convolution is concerned with the movement of the muscles of speech. In the post central convolution, just behind the fissure of Rolando, there is localization of brain change correlated with cutaneous sensibility. The cutaneous sensations arise from the skin covering the sets of muscles represented by the corresponding areas in the precentral convolution. Other forms of sensory experience are correlated with change in other parts of the cerebral cortex. Visual sensation is related to change in the occipital lobe—at the back of the brain. Auditory sensation is related to change in the first and second convolutions of the temporal lobe—the lobe at the side of the cerebral hemisphere below the fissure of Silvius. Sensations of taste and smell are probably related to change in the cerebral cortex covering the mesial surface of the hemisphere.
These motor and sensory areas are not to be regarded as having clear-cut boundaries, or as adjoining one another like a mosaic pattern. There is probably depth-localization in the cerebral cortex in addition to correlation according to relationship of sur face extent. Many details of the localization theory are still in dispute, especially as regards the more complex problems, such as that of aphasia (Henry Head). Moreover, some forms of affective experience, such as pleasure, pain, and emotional con sciousness, are probably directly correlated with brain-change in the optic thalamus and other sub-cortical centres. What is not in dispute is that the different kinds of sensory experience are in direct relation to change in locally distinct parts of the cerebral cortex, and that consciously initiated motor experience is in very detailed relation to other areas of the cerebral cortex. Not only is there localization of brain changes concerned with sensory and motor consciousness, there is also a certain degree of localization of brain changes concerned with higher forms of mental activity. But such localization is not so precise, and its exact nature is still in dispute. In the view of Henry Head there is no exact "point to-point" correspondence between brain change and mental process.
The further, and more ulti mate question now arises : What exactly is the relationship be tween any particular form of mental activity and its corresponding physiological correlate, or brain-event? Let us take as a definite example the visual perception of a patch of red colour. The physiological correlate of this experience is some kind of pro toplasmic change in a definite part of the occipital cortex—a change ultimately describable in terms of molecular, atomic and intra-atomic movements or vibrations. Obviously, the two sides in this relation are entirely different from one another.
Of the various possible ways in which they may be conceived to be related, one is that the physical change in the occipital cortex produces the mental experience—the per ception of red ; and that there is a causal relationship between the two occurrences, a temporal sequence, in which the brain-event comes first and the mind-event comes second. Or again, let us take the experience of voluntarily moving the arm. Correspond ing to that a physical change occurs in a definite part of the precentral convolution. Here, too, according to the same theory, the brain-event comes first. The change in the precentral con volution occurs because of antecedent change elsewhere in the brain. It produces both the experience of voluntary movement of the arm and also motor impulses which pass down the pyra midal tract to reach the muscles of the arm, causing their con traction. The theory thus illustrated is the theory of Materialism in its crude form. According to this theory there is always a sequence between brain change and consciousness, whether motor or sensory. The brain change always comes first and is the cause of the conscious change. Consciousness is always an effect, never a cause. Like the melody that floats from the harp-string or the shadow that accompanies the pedestrian's footsteps, it remains ineffective.
A second general theory of the psycho-physical relation is that mind and brain are two distinct substances or entities in causal interaction with one another. The mind is rela tively passive in sensory perception and relatively active in the conscious initiation of muscular movement. One powerful argu ment against both these theories is that based upon the nature of the causal relation. In cases where a causal sequence is ad mitted and is regarded as intelligible, there is generally some thread of identity which can be postulated as running through the sequence, such that cause and effect can be conceived as earlier and later stages of a continuous process. But brain change is one thing, mental process is another ; and so great is the dis parity between them that it is impossible for the mind to pass smoothly and continuously, in thought, from the one to the other. For the theory of materialism there is also the difficulty that the form of causation assumed is a one-sided one, viz., one passing from the physical to the mental but not vice-versa, and there fore unique in the annals of scientific theory. A further difficulty with materialism is that it makes matter the only real agent, re garding the mind as passive on every occasion. In this it is con trary to direct experience, and leads to absurd results. Indeed, we can draw up an argument according to which it refutes itself. Thus if the brain is the only real agent and the mind is always re sult and never cause, i.e., is always essentially passive, then mental activity is illusory. If mental activity is illusory, then in tellectual activity is illusory. If intellectual activity is illusory, the products of intellectual activity are illusory. Now one such product is this theory of materialism, therefore this theory is illusory. No doubt, this "refutation" is too short and easy a way with materialism, but it does emphasize a serious difficulty in the theory.
We now come to the theory of Parallelism, which represents an attempt to evade the aforementioned diffi culties of materialism and interaction, especially that arising from the impossibility of conceiving any causal relation between realities so disparate in nature as the physical and the mental. According to the parallelist hypothesis, there is a point-to-point correspondence between mental processes and certain physical processes (their "physical correlates") in the organism, but with out interaction. There is no temporal sequence between brain event and mind-event, and no causal relation. The theory is a direct descendant of Spinoza's monistic doctrine that thought and extension are two distinct but corresponding aspects or "at tributes" of one universal substance—God or Nature. Brain change is one manifestation of reality, and the consciousness cor responding to that brain change is another manifestation of the same reality. This theory may take different forms. The mental process and the corresponding physical process may be regarded as two aspects of something that is different from either, some thing that is "in itself" neither merely mental nor merely physi cal ; or the physical process may be regarded as the more real of the two, manifesting consciousness as an additional characteristic, when of a certain degree of complexity ; or, thirdly, the psychical process may be regarded as the true and ultimate reality, of which the physical process is the "appearance," or the aspect under which this reality appears to another "centre of consciousness" or subject of experience.
Two fundamental criticisms have been brought against the par allelist hypothesis. In the first place, it is argued that, whereas physical processes are multiple, mental processes show a unity. There is a unity of mind to which nothing on the physical side corresponds. Secondly, it is contended that whereas the mind is essentially teleological or purposive in nature, the body is me chanical in both structure and function, and there can be no parallelism between a teleological series and a mechanical series. But neither argument can hold its ground. On the one side, the mind is not a complete unity, and on the other, the brain shows a certain degree of unity in its working, in accordance with the integrative action of the nervous system. Again, there may be as much teleology or purposiveness in brain activity as there is in mental activity. "Mere mechanism" is a myth, handed down from i8th-century physics. In its place we should put an "or ganic" theory of the physical universe, such as that sketched out by A. N. Whitehead. In an organism or totality, the whole is greater than the sum of its parts. The entire system is likewise greater than the sum of its subsidiary totalities. There is at least a possibility that the whole physical universe is an organism. A more serious difficulty in Parallelism is that it definitely rules out the possibility of individual survival of bodily death. At death the brain disintegrates. If the mind is the reality of the brain, then the individual mind, the personality, must disappear at death. There are two objections to the acceptance of such a position. One is that it might in time be overturned by the discovery of definite facts, such as are claimed by spiritualists and others to be already in existence, viz., evidence of personal survival. The other is that it seems to run counter to our deepest convictions, and to be in conflict with the results of arguments based on the nature of our value-experiences.
Further arguments against parallelism, of a more materialistic trend, are to be found in the recent work of Henry Head on aphasia and of Pavlov on conditioned reflexes. Among alternative theories of the psycho-physical relation, space permits merely the mention of William James's "transmission theory," and Bergson's view that the brain is solely a motor organ and that "pure" memory (as distinct from rote memory or habit) has no cerebral correlate. Despite the number and variety of the theories brought forward to explain the relation of body and mind, they all remain highly disputable. This probably means that the human mind has not yet succeeded in fashioning con cepts adequate for use in so stupendous a task.
A. Strong, Why the Mind has a Body (19o3) ; Bibliography.-C. A. Strong, Why the Mind has a Body (19o3) ; C. S. Sherrington, The Integrative Action of the Nervous System (1906) ; W. McDougall, Body and Mind (i9n) ; H. Bergson, Matter and Memory (Eng. trans., 1911) ; A. N. Whitehead, Science and the Modern World (1925) ; H. Head, Aphasia and Kindred Disorders of Speech (1926) ; W. Brown, Mind and Personality, (1926) ; H. Driesch, Mind and Body (Eng. trans., 1927) ; I. Pavlov, Conditioned Reflexes, (Eng. trans., 1927) ; W. M. Marston, Materialism, Vitalism and Psy chology (1928), and Emotions of Normal People (1928). (W. BR.)
