Degeneracy: Its Causes, Signs and Results

by Eugene S. Talbot

For the majority of cerebral deformities the causes of the deformity must exist in the germ prior to the appearance of the separate organs of the body. Artificial deformities produce analogous results because they imitate original germ defects either by mechanical removal or by some other interference with a special part of the germ. Early involvement of the germ is shown in the fact that the somatic malformation in degeneracy often involves other parts of the body than the nervous axis: defective development of the uro-genital system, deformities in the face, skull, irregularities of the teeth, misshapen ears and limbs.

Those who seek for the source of the arrested or perverted brain development in the reaction of an abnormally growing and ossifying skull on the skull contents are in error. The premature ossification theory does not hold good even for the microcephali; it is to be doubted if it ever had any justification in view of the often open character of the sutures. Taking the well-studied cases of asymmetry, the variability of a single factor shows that caution is needed in referring cerebral anomalies to any single influence. In Muhr’s case (cited by Spitzka) the atrophic cerebellar hemisphere was on the same side with the atrophic cerebral hemisphere. The internal carotid artery of that side was of lesser calibre and the entire skull half shortened. Here the lagging behind in growth of one half of the skull appears on first sight to explain the retarded development of the corresponding halves of the cerebrum and cerebellum. In view of the atypy of the gyri, however, an atypy not to be explained purely on mechanical grounds, it is more reasonable to believe that the imperfect development of certain vascular channels was either concomitant or secondary to a primitive anomaly of the cerebral hemisphere. The retarded skull growth would have to be looked upon as a tertiary occurrence and the cerebellar defect as a final ensuing result. Ordinarily with defective development of one cerebral hemisphere the cerebellar defect is on the opposite side, herein following the course of the anatomical connections of that development and of the secondary degenerations. The deviation from this rule in Muhr’s case was due to the entering of the abnormal skull-shape, itself secondary to other defects, as an element influencing brain growth at a special period of development. An abnormal shape of the skull, generally associated with a cerebral defect, and hence valuable as a physical sign presumably indicating mental anomalies, may exert an important modifying influence at a late period on the contained brain, but the grosser defects in the cerebral architecture must antedate the period of skull growth and be deeply planted as an original intrinsic fault in the brain blastema itself. The researches of His have shown how important for the definitive shape of the body and its organs are the position of individual cells, the portion of the germ area, the convexity and length of germ curves and the relative rate of growth of different germ areas. And as the experiments of other embryologists have established the possibility of producing monstrosities analogous to cerebral defects by altering the conditions ever so slightly, the general conclusion follows that the fundamental error of development at the foundation of malformations associated with degeneracy is to be located at a very early period of embryonic, or possibly of ovuline life. Certain of these anomalies are due to a disturbance of the balance between the growth of the epiblast and mesoblast derivatives of the brain, others to a disharmony in the development of related associated brain segments; in the severer cases both elements are combined.

It is not difficult to perceive the relation existing between a defective brain weight, paucity of the gyri, deficiency of properly developed cortical cells and such an elementary form of mental aberration as simple imbecility. The subject of the relation between structure and function gains in interest when we leave this domain of simple mental weakness to analyse the relation between structural defects and the positive symptoms of insanity and degeneracy—that is, moral perversion, mental obliquity, delusions, and morbid impulses. Such symptoms are not limited to the higher forms of the degenerate series; they occur, though less constantly and less markedly, in the lower forms.

C. K. Mills,[249] of Philadelphia, on examination of imbecile, paranoiac, and criminal brains, found atypical asymmetry as to gyral and fissure development present. The features of this atypical asymmetry were the existence of a Sylvian fissure shorter on one side than the other, both absolutely and comparatively, and also a more vertical direction of the fissure on one side than on the other, greater exposure of the insula on one side with marked differences in the development of its fissures and gyri, confluence of the central fissure with the Sylvian on one side only, and great tortuosity or bridging of the former fissure in one hemisphere, unusual narrowness, straightness of complication of the precentral or postcentral gyrus on one side; marked difference in the simplicity of complexity of the frontal lobes, great simplicity of the orbital surface on one side, differences in the parietal fissure as to length and interruption, a smaller parietal or marginal or angular gyrus on one side, very great difference in the degrees of confluence and interruption of the fissures in general, exceeding great length vertically of the supertemporal or parallel fissure on one side, unusual differences in the size of the precuneus and cuneus.

A. W. Wilmarth,[250] of Philadelphia, Pa., after a careful study of idiots and imbeciles ranging in intellectual power from the idiot, properly so-called, to the juvenile criminal, paranoiac, and “ne’er-do-well,” finds that the brains of these vary greatly along the line pointed out by Spitzka and Mills. One type of brain in this class of children is very simple in its outward configuration. The convolutions are usually coarse, but little convoluted and comparatively free from secondary folds. The fissures tend to assume a confluent type. Another variety, found chiefly among the lowest grades, might well be termed “atypic.” A brain without a corpus callosum is a marked example. In the frontal lobe of the right hemisphere the first frontal convolution is quite regular. Below this from the centre of the lobe seven fissures passed in different directions, cutting the tube into a number of radiating convolutions, entirely different from its usual appearance. The short fissure of Sylvius (about three inches in length) passed upward, turned sharply, and passed almost directly behind. Two parallel gyri curved around its posterior extremity. The arrangement of the convolutions of the temporal and parietal lobes were so exceedingly irregular and complex that it was impossible to classify them. In the occipital lobe, on the contrary, the gyri were complete in number and of regular arrangements. In the left hemisphere the arrangement of the frontal convolutions was more regular, but the temporal and parietal lobes presented the same complicated area of surface folding, bearing but little resemblance to the normal brain. The tendency of the convolutions to arrange themselves in parallel curves around the posterior extremity of the fissure of Sylvius was well shown in the brain of a boy of exceedingly low intellect. The frontal lobes in this brain are proportionately large; the convolutions straight, especially the third frontal, the fissures shallow. In the left temporal lobe they are nearly obliterated from pressure of fluid in the ventricles. The ascending frontal convolution on each side appears to be wanting. On the left side a large bridging convolution crosses the middle of the fissure of Rolando. Confluence of fissure is a decided feature of idiot brains. Even where confluence is not complete, the tendency of the principal fissure to cut through separating convolutions is very evident. Were the cases where confluence is nearly complete included, the number would be considerably augmented. The fissure of Sylvius passed into the fissure of Rolando in one case on both sides, in another on one side only. In two other cases they were connected by deep secondary fissures. The interparietalis has its origin in the fissure of Sylvius in four cases on both sides, in five cases on one side only. The calcarine fissure passed completely across the gyrus frontitatus on both sides in two cases, on one side in four cases. In one case the first occipital convolution sank nearly beneath the surface, the next occipital gyrus projecting over it, forming a parietal operculum. There also seems to be a strong tendency to form annectant gyri in the upper part of the parieto-occipital fissure. In no less than six hemispheres of 15 brains were these supplementary gyri found more or less complete. In one case on both sides, in five cases on one side, the parieto-occipital fissure cut through the first occipital convolution into the interparietal fissure. A tendency of the transverse occipital fissure to approach the parieto-occipital fissure is very apparent, though in no case do they coincide. The folds of the cerebral cortex, from a lack of the stimulus of healthy growth, sometimes revert to forms resembling those found in other groups of the animal kingdom.

The fundamental factors of thought and action, as Spitzka terms them, are two: perceptions and motor innervation. These are, in other words, the units of thought and action. They can be properly referred to nerve cell groups as their anatomical seat, and, as far as intellect is in question, to the cell group represented in the more or less diffused and dovetailing areas of specialised function in the cortex cerebri (Fig. [116]). But the largest hemisphere known, with the most crowded and most highly developed nerve cells, and the most extensive connections with the periphery, and the most perfect projection of that periphery in its intricately convoluted mass would, functionally speaking, represent nothing but a mass of pigeon-holed impressions stored away without method and without purpose, useless to the organism were it not for those arched fibres uniting the different cortical centres with each other.

FIG. 116.

These fibre constitute by far the greater part of the white centrum oval of the hemisphere. The total transverse section of the crus and the fibre masses from the thalamus and basilar ganglia, does not comprise more than one-third of the entire mass. In the lower animal this relation is different. The projecting fibres, such as those of crus and capsule and the great ganglia, are not as massive as in man, but they are nearly equal to, and in still lower forms exceed, those connecting the gyri with each other. Hence the chief point of contrast noted on examining a transverse frontal section through the cerebral hemisphere of a man and an ape consists in the mass of the centrum ovale of Vieussens. The whole substance in man actually appears hypertrophied when compared with that of lower animals. It is the associating fibres which mainly mediate that complex co-ordination of the separate units of thought and action which constitute the anatomical basis of the highest mental functions (Fig. [117]). The study of the human mind does not resolve itself merely into an analysis of individual faculties such as simple perceptions and motor innervations, but above all requires the establishment of their synthesis into the complex abstractions on which the ego depends.