Cerebration

“ Carpenter's theory, which, as yet, we are unable to make our way over, under, or through; and, at present, our conclusion is, that unconscious cerebration is an hypothesis all in the air, and unsupported by any foundation of physiological fact.
Whether the activities of the cerebral convolutions are unattended with consciousness until they have been reflected upon the sensorium, is a question which perhaps physiological experiment, or even more likely pathological research, will answer before long. ”

“ They reminded him of the fireflies of the green hells he had been in during the war.
"You are now skirting the convolutions of the cerebellum," his guardian angel told him. "They are electronic tubes which receive sensory impressions and translate them into impulses for cerebration. Here in the cerebellum the bulk of the associations is being evoked; these are then distributed throughout the hemispheres of the cortex or higher brain. Oh I do wish you wouldn't get seasick, Dr. Lee; some of our visitors do, you know; it's those wavy, wavy movements." ”

“ The seat of the nerves that direct automatic motion is not in the brain, but appears to be in the body, near the spine. When it is not injured, what used to be called unconscious cerebration may continue for several seconds after death. ”

“ Hence the data thus far accumulated in evidence of the actual structure, size, and weight, of the human brain fall far short of what is requisite for a solution of many questions in reference to the relations between cerebration and mental activity. From time to time men of science have sought by example, as well as by precept, to lessen such impediments to scientific research. ”

“ Other changes of a more complex character are also unattended with conscious phenomena. Unconscious cerebration occurs in which very complicated acts, including those, perhaps, of ideation, are perfectly performed. ”

“ But the power to alter, postpone, or entirely inhibit, nervous movements is but a part of the general work ascribed to the cerebrum as the organ of the mind. Numerous experiments performed upon the lower animals, together with observations on man, show the cerebrum to be the seat of the mental activities, and to make possible, in some way, the processes of consciousness, memory, volition, imagination, emotion, thought, and sensation. ”

“ To act, they must receive an impulse either from without or within. Exterior excitement we can produce artificially, by acting on the peripheral nerves; interior excitation is produced by the cerebrum, and we may say that, from the point of view of physiology, the cerebrum has no other function than to put in action the different motor centres. It is a simple excitant, with this important difference—that external impressions can determine only a certain number of movements, while the brain provokes an immense variety. ”

“ Intellect, Emotion, and Volition. Physiologists assign to the cerebrum its functions, and neurological, as well as phrenological writers, have located them as represented in Fig. 68. True, there is no structural division between the parts of the cerebrum to indicate this diversity of function, nor is there any perceptible limit between the sensory and motor filaments of the game nerve. As no one has any reason for denying that separate portions of the brain may manifest distinct functions of the mind, we shall assume it as a conceded proposition. ”

“ The cerebellum has its unconscious action in the processes of respiration and in the involuntary movements which are made in response to the senses, as in winking, starting back at a sound, etc. The cerebrum acts automatically in oases familiar to all. A large part of our mental activity consists of this unconscious brain work. There are many cases in which the mind has obviously reasoned more clearly and more successfully in this automatic condition, when left entirely to itself, than when we have been cudgeling our brains, so to speak, to get the solution. ”

“ With disease or willful destruction of the cerebral tissue the personal initiative is affected-- the animal becomes more distinctly a mechanism; the cerebellum is probably concerned in the coordination of muscular movements; and the medulla is a centre for the higher and more complicated respiratory reflexes, yawning, coughing, and so on. The great majority of reflex actions centre, however, in the spinal cord, and do not affect the brain. ”

“ The cerebellum may be regarded as the physiological and the cerebrum as the psychic brain, for the cerebellum is void of intelligence and volition, but has important influences on the body. It may be considered, like the spinal cord, an intermediate structure between the controlling and conscious brain and the corporeal organs. ”

“ From it in turn come a great many connecting nerve cells whose axons pass along the spinal cord and form nerve junctions with the motor nerve cells; and so nervous disturbances coming from the cerebellum can arouse the muscles to activity. We all know that walking or any other locomotor act, after it has once been learned, is carried on successfully without our performing any intellectual work in connection with it. What we do have to do is to start the act, and this is done through a discharge from the cerebrum ”

“ Cerebral Control over Lower Nervous Centres.—There accrues to the brain, especially to the fore-brain of higher Vertebrates, another function besides that of grafting psychical qualities upon the reactions of the nervous system. This function is exhibited as power to control in greater or less measure the pure reflexes enacted by the system. These pure reflexes have the character of fatality, in the sense that, given a particular stimulus, a particular reaction unvaryingly follows; the same group of muscles or the same gland is invariably thrown into action in the same way. ”

“ For there is no reason to regard the cerebrum as an exception to the general principle that, while each part of the organism tends to form itself in accordance with the mode in which it is habitually exercised, this tendency will be especially strong in the nervous apparatus, in virtue of that incessant regeneration which is the very condition of its functional activity. It scarcely, indeed, admits of doubt that every state of ideational consciousness which is either very strong or is habitually repeated leaves an organic impression on the cerebrum ”

“ The cerebellum thus appears to be the great brain center whence are issued the commands and directions which guide the muscular actions and movements of our lives. Contrariwise, the true functions of the cerebellum are proved by experiments in which this part of the brain has been left intact while the cerebrum or true brain has been removed—an operation absolutely painless, as will presently be more particularly mentioned. A bird or higher animal in such a case will lose all power of volition; it will be deprived of sight, hearing, and other senses; it will die of hunger unless fed ”

“ That the nervous tissue of the cerebrum should be thus the instrument of the mind need not surprise us when we think how the muscles and joints of the tumbler, the vocal organs of the singer, the finger-ends of the watchmaker; the palate of the tea-taster, grow to the uses they are steadily put to; and, much more, both in the case of the brain and all other organs, grow to the uses they are earliest put to. ”

“ In coming to a conclusion respecting the function of this organ, we find that it can not be directly connected with sensation or volition. The sensations appear pronounced and the movements vigorous after destruction of the cerebellum. The marked feature in all deep cerebellar disorders is the maladjustment of muscular actions to the preservation of equilibrium and to harmonious movements. The consciousness of a normal relation between the person and the external world seems overthrown, the violent activities which ensue being plainly attempts to restore this lost feeling. ”

“ The gray matter of the cerebellum, the medulla, and the cord may receive impressions from the senses and respond to them with movements, but their response is in all cases wholly automatic and unconscious. A person45 whose hemispheres had been injured in such a way as to interfere with the activity of the cortex might still continue to perform most if not all of the habitual movements of his life, but they would be mechanical and not intelligent. He would lack all higher consciousness. ”

“ The cerebellum is the auditory brain, and from it the acoustic nerves take their rise. For, since the ear is the sense of the whole motor system, and consequently of half the animal, it inevitably follows, that an appropriate or special nervous mass must be developed for it, just as the myelon or spinal chord has been for the trunk. An organ, which is so constantly active, must necessarily have a large nervous mass. The cerebellum is consequently not a brain in the general sense, but one which is wholly individualized. ”

“ Some maintain that consciousness is not manifested apart from the action of the cerebrum, that all nerve-activities below this organ are reflex, their only distinctions being in the matter of complexity. Others are equally positive that consciousness accompanies all nerve-actions, while still others assert that certain organs below the cerebrum—viz., the pons Varolii, cerebellum, optic lobes—form a sensorium commune where consciousness in some form appears. ”

“ The nerves are large in proportion to the substance of the brain, and the brain proper is narrow in front and hollowed out beneath, where it rests on the orbits. But these proofs of a low kind of intelligence and of great muscular power are accompanied by structures which mimic or sketch out those of the human brain in an extraordinary manner. The cerebellum, or little brain, is large, as it is the organ which has much to do with regulating and co-ordinating the movements of the muscles, but it is quite covered by the back part, or posterior lobes, of the brain. ”

“ But above all those is the cerebrum, or brain-proper, consisting of two large lobes of nervous substance, which in man are so large that, when viewed vertically, they cover and conceal the cerebellum. To this organ is specially assigned emotion, volition, and ratiocination. It is the assumed seat of the mind; and, in a truer sense than the skull—
The dome of thought, the palace of the soul ”

“ The cerebellum, or lesser brain, lies in the back of the cranium, and is covered over in man by the posterior lobe of the cerebrum. It is, at it were, astride of the back of the cerebro-spinal axis, and consists of two hemispheres joined by a central mass. On its under surface is a depression which receives the medulla oblongata. The cerebellum is separated from the cerebrum by a horizontal partition of membrane, a portion of the dura mater. In some animals, as in the cat, this partition is partly bone. ”

“ This general law of development is modified by differences in the cerebral texture. Men possessing comparatively small brains may have a vast range of thought and acute reasoning powers. Anatomists have found these peculiarities to depend upon the quantity of gray matter which enters into the composition of the brain.
In the cerebro-spinal system there are three different kinds of reflex actions. (1.) Those of the spinal cord and medulla oblongata are performed without any consciousness or sensation on the part of the subject. ”

“ Here, also, the complex actions involved in walking are controlled and regulated by lower centres situated in the cerebellum. In like manner a person will unconsciously close the eyelid under the stimulus of strong light. Here the impression caused by the light stimulus, upon reaching the medulla along an afferent nerve, is deflected to a motor nerve and, without any conscious control of the movements, the muscles of the eyelid receive the necessary impulse to close. Actions which are thus directed from a lower centre without conscious control, are usually spoken of as reflex acts. ”

“ With a passing mention of the cerebellum, the three-lobed organ shown in Diagram 61, and seen again in a more advanced stage in Diagram 63, we may dismiss the two hinder divisions of the brain.
The cerebellum lies on the upward path of fibres from the cord to the higher centres in the fore-brain. It is a somewhat complicated organ, and its functions are not yet fully known. The older physiologists took a very extreme view of its importance, assigning to it, among other romantic duties, that of providing a habitation for the soul. ”

“ The lower centers are directly connected by nerves with the sense organs, glands and muscles, while the higher centers have direct connections with the lower and only through them with the sense organs, glands and muscles. In other words, the sensory nerves run into the cord or brain stem, and the motor nerves run out of these same, while interconnecting nerve strands extend between the lower centers in the cord and brain stem and the higher centers in the cerebrum and cerebellum. ”

“ Fig. 254. Longitudinal section through the brain of Scyllium canicula at an advanced stage of development.
cer. cerebral hemisphere; pn. pineal gland; op. th. optic thalamus, connected with its fellow by a commissure (the middle commissure) . In front of it is seen a fold of the roof of the fore-brain, which is the choroid plexus of the third ventricle; op. optic chiasma; pt. pituitary body; in. infundibulum; cb. cerebellum; au.v. passage leading from the auditory vesicle to the exterior; mel. medulla oblongata; c.in. internal carotid artery. ”

“ Hence the organs of consciousness and control, being organs of adaptation and readjustment of reaction, will be more pronounced the farther the animal scale is followed upward to its crowning species, man. The cerebrum and especially the cerebral cortex may be regarded as the highest expression of the nervous organ of individual adaptation of reactions. Its high development in man makes him the most successful animal on earth’s surface at the present epoch. ”