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