becomes a deaf mute. The processes that go on while the child is learning to speak are constantly accompanied by association processes with memory pictures in other centers, especially visual and tactile images. The greater the number of images stored up in the cortex, and the more effective the associations between them, the greater will be the intellectual capacity of the brain in question. The speech centers, like those which preside over reading and writing and which will be discussed below, are found only in one hemisphere-in the left hemisphere in right-handed people, usually in the right hemisphere in left-handed people. The motor speech center is probably identical with the centers of the facial, hypoglossus, etc. The speech tract (see p. 47) connects these centers in the left hemi

sphere with the nuclei of the seventh, twelfth, and other nerves on both sides of the brain.

When the child learns to read, the graphic memory pictures are deposited in the visual center in the occipital lobe (the interpretation of written speech is lodged principally in the angular gyrus). They reach the consciousness, however, only by association with the auditory center and with the motor speech center, because, in learning to read, the graphic image is always converted into an auditory image and into a motor speech image (reading aloud). In later life many people are more and more able to dispense with these association processes.

In learning to read, the graphic images are deposited as innervation feelings of the movements concerned in writ

SPEECH, WRITING, ETC.

71

ing in the center for the right arm, and in the adjoining posterior third of the middle frontal convolution. They become intimately associated with visual and auditory images on that side of the brain; therefore, the motor graphic images of the letters are produced before the visual images.

In some individuals the visual graphic associations are more prominent, while in others the kinesthetic associations are better developed. Hence the cortical areas in which these processes are enacted are the central convolutions, the superior temporal convolution, and the convolutions of the parietal and occipital lobe. The frontal lobe

oculus 3

linqua 2 k

auris

brachium

Fig. 22.

is regarded as the anatomic basis of the higher intellectual functions. But it is to be remembered that the complicated processes by which we are enabled to think necessitate very complex associations, the sum of which can not possibly be confined to the activity of a single lobe.

It is seen by Figure 21 that the left hemisphere is the more important as regards the distribution of the centers. The "latent" cortical areas are white. The dotted areas correspond with the psychosensory and psychomotor areas,

1 Some authorities place the writing center in the inferior parietal lobule.

projection tracts and association tracts, while the other convolutions of the cortex (white) are said to contain exclusively association fibers. (For the details see Plate 21.) Figure 22 is intended to illustrate the processes concerned in the acts of speech, writing, etc. The connections effected in speaking, writing, and reading are seen in the following scheme:

1. Sensory speech tract 2. Motor speech tract

3. Optic tract

4. Kinesthetic tract for movements

I center.

II center.

III center.

required in speaking and writing IV center.

5. Motor tract for writing

V center (center for the arm).

By a we will designate the ideation, which is not regarded as bound to a particular center, but rather as the effect of the entire associative activity. A part of the more important associations is added (as a).

Writing from dictation : 1—I (a III) — V (a IV) — 5.

To avoid repetition, any further important particulars in regard to the physiology of other portions of the brain will be referred to under the head of General Symptomatology, Part IV, 3, Topical Diagnosis.

A word in regard to the coordination of motor acts. Even the slightest motor act necessitates the cooperation

1 If mechanical, without concept associations (x).

of several muscle groups. The regulation of the proper working of the various muscles concerned in any simple or complicated act is called coordination.

Even a very simple muscular act requires the coordination of antagonistic muscles; how much more then the complex motor processes made up of a succession of different single acts, such as walking, speaking, etc., where not only each individual motor act, but also the proper chronologic succession, requires careful regulation.

Cooperating muscle groups derive their peripheral and probably also their central neurons, or at least a part of them, from cells that are intimately connected with each other (coordination centers and coordination tracts of the brain and spinal cord). Thus the nuclei of the ocular muscles and the nuclei of the hypoglossus are very intimately connected. Even a single cell may send out through the collaterals motor impulses to various muscles, and thereby assist in the coordination of the muscular act.

The sensory impressions, especially impressions of muscular sense, play an important part in coordination, and it still remains to speak of this controlling influence and of the influence of the cerebellum on static coordination.

There is no doubt that the cerebellum exercises an influence on the static coordination and equilibrium of the body in the erect position and while walking. For this purpose it receives, through centripetal nerve tracts, the impressions of muscular sense, and optic, tactile, and other impressions from the periphery of the body. That portion of the posterior column which does not join the fillet makes its way from the nuclei in the posterior cord through the restiform bodies to the cerebellum. We further know that the cerebellum receives fibers through the cerebellar lateral tract (function unknown), from the vestibular nerve (semicircular canals-organ of equilibrium?), and from the trigeminus (direct sensory cerebellar tract). In the interpretation of the cerebellar influence on coordination, however, we are still in the speculative stage.

As the cerebellum possesses various connections with the cerebrum, it is quite conceivable that it may exert some controlling influence on the motor centers in the cortex, and, therefore, indirectly on muscular activity. But, unfortunately, it does not appear to be directly connected with these centers.

The fibers of the pons connect the cerebellum with the ganglia in the opposite side of the pons, where, as we have seen, both the frontal and the temporo-occipital pontal tract terminate. It appears, therefore, that each hemisphere of the cerebellum is in direct communication with the frontal, temporal, and occipital lobes of the opposite cerebral hemisphere.

In addition, there is a communication by means of the brachium between the red nucleus of the tegmentum (which in turn is connected with the optic thalamus, etc.) and the opposite hemisphere of the cerebellum. Although these connections between the cerebellum and cerebrum are well known, their functions are not understood, but it may be said that they appear to be in some way associated with coordination.

There is some anatomic basis for the theory that the muscles are directly influenced by the cerebellum. The cerebellum is connected, by means of the olivary fibers in the restiform body, with the olive of the opposite side, and from this point the central tegmental tract (mesial fillet) is continued upward, while the "olivary tracts" descend in the lateral column to cells in the anterior horn (?). When all is said, however, we must admit that we have no definite knowledge on this point.

It remains to be mentioned, in regard to the cerebellum, that it does not contain any separate centers like those in the cerebrum. Any one part of the cerebellum can be supplied by another. In general it may be said that it is credited with a static, tonic, and sthenic influence on muscular activity.