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 reënforcing 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.