FIG. 117.
Neither anatomic nor physiologic researches are calculated to demonstrate just what associating fasciculi or what groups of such fasciculi are subservient to any particular co-ordination. Where, for example, the cortical area for vision overlaps that of the centre for forearm and hand, the associating fasciculus underlying the debatable land is subservient to the co-ordinations employed in writing and drawing. In like manner a similar associating bond extending from the centre of auditory word symbols to that of the tongue and lip centres may be considered a chief factor mediating the speech co-ordinations. A child originally has no adequate notion of distance or perspective, but will, in the first week of life, grasp at objects fifty feet away. Its first ideas of space are gathered from its own skin sensations; it learns to distinguish between single impressions when touching foreign bodies, and associated double ones as when it touches a part of its own body. In great part this may even be accomplished by an active infant during the last months of utero-gestation; it has learned thus to separate the conception of its own body from the confused chaos which all impressions originally constitute to the infant; the next lesson is to learn that to reach certain objects it moves a certain distance, while others are immediately in reach. It then discovers, therefore, that the discrimination by the eye is possible, since intervening objects which it has learned to measure by its own body or bodily movements as a gauge permit an approximate judgment of distance, in aid of which comes experiment in the shape of time requirements, since to go so far requires such time, while to go further requires a much greater. The crude ideas of space at this time must involve areas in the cortex devoted to motion and to general sensation situated in the Rolandic region. Those devoted to visual impressions are largely situated in the occipital region, and those devoted to time may be located in the frontal lobes. Further analysis of the more elaborate sense of space possessed by adults, involving the play of equilibrium and the appreciation of movement and direction in foreign objects, shows that cortical areas situated in nearly every part of the hemispheres are subsidiary to it and connected by fibre tracts of different lengths and courses. It is evident, therefore, that the mal-connection of cortical centres is at the root of various tropho-neurotic, nervous, mental, moral and other perversions exhibited in degenerates. Deformity and deficiency of the corpus callosum in some degenerates is but an expression of general defect of associating tracts. Convolutional aberration in others is but an expression of imperfect development of end stations and fibre systems. All mental and moral disturbances are associated with perversions of the functions of the cerebral hemisphere, but the converse, that cerebral hemisphere lesions only are the essential accompaniments of mental symptoms evinced during life, is not true. Lesions of the pons, the crura, and thalami are accompanied by more or less complete obliteration of consciousness, blurring of the perception, confusion in the intellectual sphere, even where the lesion is not of such a character as to disturb the neighbouring ganglia by pressure. Two explanations are possible of this phenomenon. Either the vaso-motor centre for the cortical vessels is under the control of isthmus ganglia partially, and hence isthmus lesions by irritation or destruction of the centre excite or paralyse the vascular tubes of certain cortical districts, or pathologic interruption of the great nerve tracts involves functional disturbance of cortical end stations. The first explanation is applicable in cases where general and widespread disturbance, somnolence, excitement, or depression are found. The latter where the disturbance is partial in character. If all avenues of sensory perception be closed unconsciousness in the way of sleep speedily follows. Interruption of the perception tracts is followed by corresponding phenomena, though less extensive when occurring in the isthmus territory. That an irritative lesion in the line of the centripetal tracts can influence cortical life is shown by thalamus lesions in which hallucinations are sometimes present. Here the cause of the hallucinations is in the lower centre, but the entry of these into the intellectual sphere can take place only in the cortical termination of that tract, since at this point only through the connecting associating tracts can it become a part of the ego.
Meynert traced an enormous division of the crus directly to the frontal lobe and the lenticular nucleus, and showed that this portion through the transverse fibres of the pons was of necessity connected with the cerebellum, and that far other functions are to be located in the cortex than merely muscular innervation, visual and auditory perceptions. The restiform columns derived from spinal fibres enter the cerebellum and terminate chiefly in its hemispheres. The cortex of these hemispheres is connected by radiatory fibres, with the dentated nucleus, which is a recipient of fibres of the auditory nerve. The cortex of the cerebellar hemisphere receives fibres both from the sensorial periphery of the body and the semicircular canals. From this reception area the transverse fibres of the pons originate and enter the crus. It is these which enter the frontal lobe and lenticular nucleus. In no respect does man so much differ from the ape as in the quantitative development of these fasciculi. Their development is intimately associated with the mass of the frontal lobe, and there is every reason for considering them the channel of information of the equilibrium and possibly of the senses of space and time, on which the scope of the mind is so closely dependent. Lesions in these tracts may disturb these sensations, and the entire mental architecture may totter with the withdrawal or weakening of so important pillars. The congenital asymmetry of the peduncular tracts observed in certain cases of mental and moral perversion are not without bearing on the symptoms of those cases. And this explanation would be adjunct to the principle of mal-development of the associating tracts here advanced in explanation of other symptoms of these same states. It is a logical truism that complex cerebral functions have a complex substratum. Nothing could be more unphilosophical, for example, than to speak of “intellectual cells” (Denkzellen) in the cerebral cortex. Simple elements can have but simple functions; complex functions require a union of numerous simpler elements in a complex structural combination.
Such symptoms as epileptic explosions are admittedly connected with no demonstrable anatomical aberration, and yet when epileptic explosions of a certain type are found associated with a cortical lesion they are to be regarded as symptoms of that lesion. Morbid projects, delusions, and moral perversion are simply functional perversions of a properly built cerebral mechanism or the outcome of a visible structural defect. And when the latter is palpably attributable to an error in development and occurs with a certain constancy in similar cases, a fundamental relation must be assumed between the defect and the general tenor of the symptoms.
There is a great difference clinically between the effect of congenital and acquired lesions. When porencephaly (a deformity originally studied by Heschl) dates from infantile or fœtal life, imbecility is always present during life; but where it is developed in the matured brain imbecility does not necessarily result.
Deficiencies in the cerebral vascular system underlie the pathological phenomena on the basis of infantile cerebral paralysis, and allied hereditary and congenital states. The degenerate conditions in the spinal cord are essentially those described by Spitzka as occurring in the brain. Vascular states, either as to irregularities in the number of vessels or in the vessels themselves, underlie, as in the case of the cerebral palsies, hereditary ataxias and other congenital and hereditary spinal cord disorders.[251]