Localization Of Function In The Nervous System

DIVISION OF LABOR.--Division of labor is the law in the organic world as

in the industrial. Animals of the lowest type, such as the amoeba, do

not have separate organs for respiration, digestion, assimilation,

elimination, etc., the one tissue performing all of these functions. But

in the higher forms each organ not only has its own specific work, but

even within the same organ each part has its own particular function

assigned. Thus we have seen that the two parts of the neurone probably

perform different functions, the cells generating energy and the fibers

transmitting it.



It will not seem strange, then, that there is also a division of labor

in the cellular matter itself in the nervous system. For example, the

little masses of ganglia which are distributed at intervals along the

nerves are probably for the purpose of reenforcing the nerve current,

much as the battery cells in the local telegraph office reenforce the

current from the central office. The cellular matter in the spinal cord

and lower parts of the brain has a very important work to perform in

receiving messages from the senses and responding to them in directing

the simpler reflex acts and movements which we learn to execute without

our consciousness being called upon, thus leaving the mind free from

these petty things to busy itself in higher ways. The cellular matter of

the cortex performs the highest functions of all, for through its

activity we have consciousness.



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

person 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.

It is through the activity of this thin covering of cellular matter of

the cerebrum, the cortex, that our minds operate; here are received

stimuli from the different senses, and here sensations are experienced.

Here all our movements which are consciously directed have their origin.

And here all our thinking, feeling, and willing are done.



DIVISION OF LABOR IN THE CORTEX.--Nor does the division of labor in the

nervous system end with this assignment of work. The cortex itself

probably works essentially as a unit, yet it is through a shifting of

tensions from one area to another that it acts, now giving us a

sensation, now directing a movement, and now thinking a thought or

feeling an emotion. Localization of function is the rule here also.

Certain areas of the cortex are devoted chiefly to sensations, others to

motor impulses, and others to higher thought activities, yet in such a

way that all work together in perfect harmony, each reenforcing the

other and making its work significant. Thus the front portion of the

cortex seems to be devoted to the higher thought activities; the region

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 made to work together 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 example, in the motor region one

small area seems connected with movements of the head, one with the arm,

one with the leg, 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 must

bear in mind, however, that these regions 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 of monkeys

has been successful in mapping out motor areas so accurately that such

small centers as those connected with the bending 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 harmonizing our thoughts, emotions, and acts.