What is known as the brain of man is really a trinity of three brains, known respectively as (1) the medulla oblongata, (2) the cerebellum, and (3) the cerebrum. If one wishes to limit the mental activity to conscious intellectual effort, then and then only is he correct in considering the cerebrum or large brain as "the brain."
The Medulla Oblongata.– The medulla oblongata is an enlargement of the spinal cord at the base of the brain. Its office is that of controlling the involuntary activities of the body, such as respiration, circulation, assimilation, etc. In a broad sense, its activities may be said to be of the nature of highly developed and complex reflex activities. It manifests chiefly through the sympathetic nervous system which controls the vital functions. It does not need to call on the large brain in these matters, ordinarily, and is able to perform its tasks without the plane of ordinary consciousness.
The Cerebellum.– The cerebellum, also known as "the little brain," lies just above the medulla oblongata, and just below the rear portion of the cerebrum or great brain. It combines the nature of a purely reflex center on the one hand, with that of "habit mind" on the other. In short, it fills a place between the activities of the cerebrum and the medulla oblongata, having some of the characteristics of each. It is the organ of a number of important acquired reflexes, such as walking, and many other familiar muscular movements, which have first been consciously acquired and then become habitual. The skilled skater, bicyclist, typist, or machinist depends upon the cerebellum for the ease and certainty with which he performs his movements "without thinking of them." One may be said never to have thoroughly acquired a set of muscular movements such as we have mentioned, until the cerebellum has taken over the task and relieved the cerebrum of the conscious effort. One's technique is never perfected until the cerebellum assumes control and direction of the necessary movements and the impulses are sent forth from below the plane of ordinary consciousness.
The Cerebrum.– The cerebrum, or "great brain" (which is regarded as "the brain" by the average person), is situated in the upper portion of the skull, and occupies by far the larger portion of the cavity of the skull. It is divided into two great divisions or hemispheres. The best of the modern authorities are agreed that the cerebrum has zones or areas of specialized functioning, some of which receive the sensory reports of the nerves and organs of sense, while others send forth the motor impulses which result in voluntary physical action. Many of these areas or zones have been located by science, while others remain as yet unlocated. The probability is that in time science will succeed in correctly locating the area or zone of each and every class of sensation and motor impulse.
The area of thought, memory, and imagination has not been clearly located, except that these mental states are believed to have their seat in the cortex or outer thin rind of gray brain matter which envelopes and covers the mass of brain substance. It is, moreover, considered probable that the higher processes of reasoning are performed in or by the cortex of the frontal lobes. The cortex of a person of average intelligence, if spread out on a flat surface, measures about four square feet. The higher the degree of intelligence possessed by a lower animal or human being, as a rule, the deeper and more numerous are the folds or convolutions of the cortex, and the finer its structure. It may be stated as a general rule, with but very few exceptions, that the higher the degree of intelligence in a lower animal or human being, the greater is the area of its cortex in proportion to the size of the brain. The cortex, it must be remembered, is folded into deep furrows or convolutions, the brain in shape, divisions, and convolutions resembling the inner portion of an English walnut. The interior of the two hemispheres of the cerebrum is composed largely of connective nerves which doubtless serve to produce and maintain the unity of function of the mental processes.
While physiological psychology has performed great work in discovering brain-centers and explaining much of the mechanism of mental processes, it has but touched the most elementary and simple of the mental processes. The higher processes have so far defied analysis or explanation in the terms of physiology.
CHAPTER IV
Consciousness
THE fact of consciousness is the great mystery of psychology. It is difficult even to define the term, although every person of average intelligence understands what is sought to be conveyed by it. Webster defines it as "knowledge of one's own existence, sensations, mental operations, etc.; immediate knowledge or perception of any object, state, or sensation; being aware; being sensible of." Another authority defines the term as "the state of being aware of one's sensations; the power, faculty, or mental state of being aware of one's own existence, condition at the moment, thoughts, feelings, and actions." Halleck's definition is: "That indefinable characteristic of mental states which causes us to be aware of them."
It will be seen that the idea of "awareness" is the essence of the idea of consciousness. But, at the last, we are compelled to acknowledge that it is impossible to closely define consciousness, for it is something so entirely unique and different from anything else that we have no other terms at all synonymous to it. We can define it only in its own terms, as will be seen by reference to the definitions above given. And it is equally impossible to clearly account for its appearance and being. Huxley has well said: "How it is that anything so remarkable as a state of consciousness comes about by the result of irritating nervous tissue, is just as unaccountable as the appearance of the jinnee when Aladdin rubbed his lamp." All that we can ever know regarding the nature of consciousness must be learned from turning the consciousness in ourselves back upon itself – by focusing consciousness upon its own mental operations by means of introspection. By turning inward the conscious gaze we may perceive the flow of the stream of thought from its rise from the subconscious regions of the mind to its final disappearance in the same region.
It is a common error to suppose that we are directly conscious of objects outside of ourselves. This is impossible, for there is no direct knowledge of such outside objects. We are conscious merely of our sensations of, or mental images of, the outside objects. All that it is possible for us to be directly conscious of are our own mental experiences or states. We cannot be directly conscious of anything outside of our own minds. We are not directly conscious of the tree which we see; we are directly conscious merely of the sensation of the nerves arising from the impact of the light waves carrying the image of the tree. We are not directly conscious of the tree when we touch it and perceive its character in that way; we are directly conscious merely of the sensation reported by the nerves in the finger tips which have come in contact with the tree. We are directly conscious even of our own bodies only in the same way. It is necessary for the mind to experience that of which it may become conscious. We are conscious only of (1) that which our mind is experiencing at this moment, or (2) that which it has experienced in the past, and which is being re-experienced this moment by the process of the memory, or which is being re-combined or re-arranged this moment by the imagination.
But it must not be thought that every mental state or mental fact is in the field of consciousness. This error has been exploded for many years. The fact is now recognized that the field of consciousness is a very narrow and limited one, and that the great field of mental activity lies outside of its narrow limits. Beyond and outside of the narrow field of consciousness lies the great subconscious storehouse of memory in which are stored the experiences of the past, to be drawn again into the field of consciousness by an effort of the will in the act of recollection, or by association in ordinary remembrance. In that great region, also, the mind manifests many of its activities and performs much of its work. In that great region are evolved the emotions and feelings which play such an important part in our lives, and which often manifest a vague disturbing unrest long before they rise to the plane of consciousness. In that great region are produced the ideas, feelings, and conceptions which arise to the plane of consciousness and manifest that which men call "genius."
On the subconscious plane the imagination does much of its work, and startles its owner by presenting him with the accomplished result in the field of consciousness. In the subconscious field is performed that peculiar process of mental mastication, digestion, and assimilation with which all brain workers are familiar, and which absorbs the raw mental material given it, separates, digests, and assimilates it, and re-presents it to the conscious faculties sometime