Part 3 (2/2)
Certain areas of the cortex are devoted chiefly to sensations, others to ht activities, yet in such a way that all work together in perfect harnificant Thus the front portion of the cortex seeion on both sides of the fissure of Rolando, to motor activities; and the rear and lower parts to sensory activities; and all are bound together and ether by the association fibers of the brain
In the case of the higher thought activities, it is not probable that one section of the frontal lobes of the cortex is set apart for thinking, one for feeling, and one for willing, etc, but rather that the whole frontal part of the cortex is concerned in each In the motor and sensory areas, however, the case is different; for here a still further division of labor occurs For exaion one small area seems connected with , one with the face, and another with the organs of speech; likewise in the sensory region, one area is devoted to vision, one to hearing, one to taste and smell, and one to touch, etc We ions are not mapped out as accurately as are the boundaries of our states--that no part of the brain is restricted wholly to either sensory or motor nerves, and that no part works by itself independently of the rest of the brain We name a tract from the predominance of nerves which end there, or from the chief functions which the area performs The motor localization seems to be the most perfect Indeed, experimentation on the brains ofout motor areas so accurately that such s of one particular leg or the flexing of a thumb have been located Yet each area of the cortex is so connected with every other area by the millions of association fibers that the whole brain is capable of working together as a unit, thus unifying and harhts, emotions, and acts
6 FORMS OF SENSORY STIMULI
Let us next inquire how this mechanisive us sensations In order to understand this, we must first know that all forms of matter are composed ofthis motion to the air or the ether which surrounds they in the forhout space These waves, or radiations, are incredibly rapid in so out its energy in the for its part to perans of the sensory nerves must meet this advance half-way, and be so constructed as to be affected by the different for upon them
[Illustration: FIG 14--The prisht are shown the relation of vibration rates to teht and to cheiven in billions per second--After WITMER]
THE END-ORGANS AND THEIR RESPONSE TO STIMULI--Thus the radiations of ether froht, are so rapid that billions of them enter the eye in a second of time, and the retina is of such a nature that its nerve cells are thrown into activity by these waves; the impulse is carried over the optic nerve to the occipital lobe of the cortex, and the sensation of sight is the result The different colors also, from the red of the spectrum to the violet, are the result of different vibration rates in the waves of ether which strike the retina; and in order to perceive color, the retina must be able to respond to the particular vibration rate which represents each color
Likewise in the sense of touch the end-organs are fitted to respond to very rapid vibrations, and it is possible that the different qualities of touch are produced by different vibration rates in the ato When we reach the ear, we have the organ which responds to the lowest vibration rate of all, for we can detect a soundfrohest vibration rate which will affect the ear is some forty thousand per second
Thus it is seen that there are great gaps in the different rates to which our senses are fitted to respond--a sudden drop from billions in the case of the eye toThis s in nature which man has never discovered si him to become conscious of their existence
There are undoubtedly ”s in heaven and earth than are dreamt of in our philosophy”
DEPENDENCE OF THE MIND ON THE SENSES--Only as the senses bring in thehich to build Thus have the senses to act as reat outside world and the brain; to be the servants who shall stand at the doorways of the body--the eyes, the ears, the finger tips--each ready to receive its particular kind of iht path to the part of the cortex where it belongs, so that the ht,” ”A sound,” or ”A touch” Thus does the et the in Thus and only thus does the mind secure the crude material from which the finished superstructure is finally built
CHAPTER IV
MENTAL DEVELOPMENT AND MOTOR TRAINING
Education was long looked upon as affecting the lected Later science has shown, however, that the mind cannot be trained _except as the nervous system is trained and developed_ For not sensation and the si and every other act of the mind are dependent on the nervous systeets its first mental experiences in connection with certain anized nervous system Froether that they cannot be separated The mind and the brain are so vitally related that it is i a like office for the other; and it is likewise i the other to suffer in its development
1 FACTORS DETERMINING THE EFFICIENCY OF THE NERVOUS SYSTEM
DEVELOPMENT AND NUTRITION--Ignoring the native differences in nervous systeh the influence of heredity, the efficiency of a nervous systeely dependent on two factors: (1) The development of the cells and fibers of which it is coor The actual number of cells in the nervous system increases but little if at all after birth Indeed, it is doubtful whether Edison's brain and nervous systereater number of cells in it than yours or enius and that of an ordinary man is not in the _number_ of cells which it contains, but rather in the development of the cells and fibers which are present, potentially, at least, in every nervous systeist tells us that in the nervous system of every child there are tens of thousands of cells which are so immature and undeveloped that they are useless; indeed, this is the case to soree in every adult person's nervous system as well Thus each individual has inherent in his nervous systee, the utilizing of whichof which will certainly leave him on the plane of mediocrity The first problem in education, then, is to take the unripe and inefficient nervous syste mind that the possibilities which nature has stored in it shall become actualities
UNDEVELOPED CELLS--Professor Donaldson tells us on this point that: ”At birth, and for a long time after, many [nervous] systems contain cell ele a functional part of the tissue, and yet under some conditions capable of further develop in the developing cortex no other source is known than the nuclei or granules found there in its earliest stages These elements are metamorphosed neuroblasts--that is, elementary cells out of which the nervous matter is developed--which have shrunken to a volume less than that which they had at first, and which reement necessary for their full development, they expand into well-ranules and the fully developed cells are always found, even in mature brains, and therefore it is inferred that the latter are derived from the former
The appearances there also lead to the conclusion that iven case are far beyond the number that actually does so The possible number of cells latent and functional in the central systely represented by the granules as well as by the cells which have already undergone further developrowth the proportion of developed cells increases, and sonize potential nerve cells in the granules, the impression is carried away that this increase implies the formation of new elements
As has been shown, such is not the case”[1]
DEVELOPMENT OF NERVE FIBERS--The nerve _fibers_, no less than the cells, h a process of development It has already been shown that the fibers are the result of a branching of cells At birth many of the cells have not yet thrown out branches, and hence the fibers are lacking; while rown out are not sufficiently developed to transmit impulses accurately Thus it has been found that ht of the body for several seconds by clasping the fingers around a small rod, but it takes about a year for the child to become able to stand It is evident that it requiresto a rod than to stand; hence the conclusion is that the difference is in the earlier develop than of those concerned in standing Likewise the child's first attempts to feed his about which he is so aard, are partial failures not so much because he has not had practice as because his nervous machinery connected with those movements is not yet developed sufficiently to enable hi calls ”unripe” How, then, shall the undeveloped cells and systerow to full maturity and efficiency?
2 DEVELOPMENT OF NERVOUS SYSTEM THROUGH USE
IMPORTANCE OF STIMULUS AND RESPONSE--Like all other tissues of the body, the nerve cells and fibers are developed by judicious use The sensory and association centers require the constant stians, and the motor centers require the constant sti from them out to the muscles In other words, the conditions upon which both motor and sensory develophts and sounds and tastes and s else which serves as proper stians, and to every form of intellectual and social interest; and (2) no less important, an opportunity for the freest and most complete forms of response and motor activity
[Illustration: FIG 15--Sche the projection of the hborhood of the medulla, and their termination in the different areas of localized function in the cortex S, fissure of Sylvius; M, the medulla; VII, the roots of the facial nerves]
An illustration of the effects of the lack of sensory stiman, whose brain was studied by Professor Donaldson after her death Laura Bridgman was born a nore of nearly three years At this ti coht eye was so badly affected that she could see but little; and it, too, becaht She lived in this condition until she was sixty years old, when she died Professor Donaldson submitted the cortex of her brain to aareas on the two hemispheres with each other He found that as a whole the cortex was thinner than in the case of normal individuals He found also that the cortical area connected with the left eye--naion--was ht eye, which had retained its sight longer than the other He says: ”It is interesting to notice that those parts of the cortex which, according to the current vieere associated with the defective sense organs were also particularly thin The cause of this thinness was found to be due, at least in part, to the small size of the nerve cells there present Not only were the large and medium-sized cells smaller, but the impression made on the observer was that they were also less numerous than in the normal cortex”
EFFECT OF SENSORY STIMULI--No doubt if we could exarown up in an environment rich in stimuli to the eye, where nature, earth, and sky have presented a changing panorama of color and form to attract the eye; where all the sounds of nature, from the chirp of the insect to the roar of the waves and the murmur of the breeze, and frohtiest sweep of the great orchestra, have challenged the ear; where many and varied odors and perfue of tastes have tempted the palate; where many varieties of touch and temperature sensations have been experienced--no doubt if we could examine such a brain we should find the sensory areas of the cortex excelling in thickness because its cells ell developed and full sized fro into them from the outside world On the other hand, if we could examine a cortex which had lacked any one of these stimuli, we should find some area in it undeveloped because of this deficiency Its owner therefore possesses but the fraction of a brain, and would in a corresponding degree find his mind incomplete