Degeneracy: Its Causes, Signs and Results

by Eugene S. Talbot

Closely related to the periodical insanities are the epileptic states which play so large a part in many of the phenomena presented by the degenerates. In the epileptic the mental rather than the gross nervous expression merits attention. From what has already been said about epilepsy, it and the periodical insanities are in no small degree the effect of mal-development of the fore brain as compared with the centres of organic life. The great convulsive centre is, according to Spitzka,[262] the reticular grey matter of the brain isthmus, particularly of the pons and medulla. All characteristic features of the full epileptic onset can be produced in animals deprived of the related cerebral cortex. It needs but a slight puncture with a thin needle to produce typical convulsions in the rabbit, and some of the convulsive movements reported by Nothnagel have not only shown the true epileptic character but also that peculiar automatism noted in aberrant attacks. It is in this segment of the nervous system that all the great nerve strands conveying motor impulses, both of a voluntary and automatic and some of a reflex character, are found united in a relatively small area, and just here a relatively slight irritation might produce functional disturbances involving the entire bodily periphery.

The experiments of physiologists have shown that if a sensory irritation of a given spinal nucleus be kept up, after having produced a reflex movement in the same segment, any reaction beyond the plain of that segment is not in the next or succeeding planes but in the medulla oblongata. The motor reaction then manifests itself in laughing, crying, or deglutitory spasms, and, if the irritation be of the severest kind, epileptic or tetanic spasms in addition. Now the occurrence of laughing, crying, or deglutitory spasms could be easily understood if the molecular oscillation induced by the irritation were to travel along the associating tracts from the given spinal segment to the nuclei of the medulla oblongata. For in the medulla are found the nerve nuclei which preside over the facial, laryngeal and pharyngeal muscles. It is not easy at first to understand how tetanus and epilepsy, that is, spasms consisting in movements whose direct projection is not in the medulla oblongata but in the cord, can be produced by irritation of the former.

There are scattered groups of nerve cells in the medulla oblongata which have either no demonstrable connection with the nerve nuclei, or are positively known to be connected with the longitudinal associating strands. These cells hence can safely be regarded as representing a presiding centre over the entire spinal system. No spinal centre exerts any influence even remotely as pronounced as that of the entire cord. This applies to man and other mammals. That the elaboration of the medullary centre was as gradual a process as that of other higher differentiations is illustrated by the case of the frog, whose medulla has acquired the faculty of reproducing general spasms while the spinal cord itself retains this property also; hence here the predominance of the medulla is not so marked as in mammals.

The reticular ganglion of the oblongata is not in the adult a part of the central tubular grey matter, but has, through originally developing from it in the embryo, become ultimately isolated from its mother bed. It constitutes a second ganglionic category, and the association fibres bringing it in functional union with the spinal grey (first category) in lower animals and shown to have assumed the position of projection fibres in the higher, constitute a second projection tract; both together are a second projection system. The scattered grey matter of the medulla has great importance. Anatomically it is (though its cells be scattered diffusely as a rule) a large ganglion with numerous multipolar cells of all sizes, many of them gigantic, sometimes exceeding the so-called motor cells (which they simulate in shape) of the lumbar enlargement in size. Scattered in the “reticular substance” of the medulla from the upper end of the fourth ventricle to the pyramidal decussation, they merit the collective designation of reticular ganglia.

The cells of the reticular formation are known to be connected with the nerve nuclei, on the one hand, and with longitudinal fasciculi, which, since they run into the cord, terminate either in the grey matter or the nerve roots directly, for nerve fibres do not terminate with, as it were, blind ends. Now in the mammalian brain the reticular ganglion lies scattered among fibres which come from the higher centres, and the interpellation might be made whether, after all, the reticular ganglion be not a mere intercalar station for fibres derived from a higher source. Originally the ganglion was an independent station. In reptiles this body of cells is too considerable to account for a termination in them of the few cerebral fibres possessed by these animals. And, on the other hand, the vertical strands are notably increased in their passage through the field of the medulla oblongata.

The medulla oblongata with its reticular ganglion seems to be the great rhythmic centre. In fish the movements of the operculum and mouth, in sharks those of the spiraculum, in perenni-branchiate amphibians the branchial tree, in the infant the suctorial muscles, in all vertebrates the movements of deglutition, of the heart and respiratory muscles, all movements presenting a more or less regular rhythm, are under the control of the medulla oblongata. The early differentiation of this part of the cerebro-spinal axis is related to the manifestations of rhythmic movements in the embryo and their predominant importance in lower animals. The possibility should not be excluded that a rhythmic movement may be spinal, nay even controlled by peripheral ganglia (heart of embryo). A higher development, however, implies the concentration of rhythmic innervations at some point where that anatomical association may be effected which is the expression of the mutual influence these movements exercise among themselves.

Two sets of phenomena must be borne in mind in studying the physiological pathology of the epileptic attack. First, the condition of the epileptic in the interval. Second, the explosion itself. Too much attention is paid to the last, too little attention to the first. The constitutional epileptic is characterised by a general deficiency of tone associated with exaggerated reaction and irritability. Thus the pupils are at once widely dilated and unusually mobile. The muscular system, though generally relaxed, manifests exaggerated reflex excitability. The mental state is characterised at once by great indifference and undue irascibility. In the same way the vascular system is depressed in tone in the interval with rapid marked changes under excitation. The state of the nervous system as a whole Spitzka forcibly compares to that of an elastic band which, being on the stretch continually, is apt to rebound violently when one end is let go. Under normal circumstances the band is less stretched and hence not as liable to fly so far when the check is removed.

An irritation which, in health, produces restlessness of the muscular system, accelerated respiration and pulsation and various mental phenomena within the normal limits, in the epileptic results in more intense phenomena in the same direction. The nervous irritability of the epileptic manifests itself in one direction especially. An important vaso-motor centre for the brain vessels exists, possibly diffused through an area somewhere between the thalamus and subthalamic region above the pyramidal decussation below. The irritability of this centre results in sudden arterial spasm in the carotid distribution (so characteristic a feature of the fit onset); simultaneously with the contraction of the vessel the pupil undergoes an initial contraction, and relaxation instantly results in both cases. The sudden interference with the brain circulation produces unconsciousness, and destroys the checking influence of the higher centres on the reflexes in a manner analogous to any shock affecting the nerve centres. In the meantime, while there has been a sudden deprivation of arterial blood and a sinking of intracranial pressure so far as the great cerebral masses are concerned, there has been as sudden an influx of blood to the unaffected district of the vertebral arteries whose irrigation territory is now the seat of an arterial hyperæmia. The result of this is that the great convulsion centre, the medulla, being over-nourished, functional excess, that is, convulsion, occurs unchecked by the cerebral hemispheres, which are disabled by their nutritive shock. The unconsciousness and coma of epilepsy more resemble shock than they do cerebral anæmia or syncope. The impeded return circulation of venous blood now comes into play. The contraction of the neck muscles explains this obstruction and especially the accumulation of venous blood in the cerebral capillaries of the medulla.

True epilepsy presents an enormous number of sub-groups, exhibiting every variety of deviation from the ideal convulsive form, and the existence of these forms tends to demonstrate the views just expressed. In ordinary petit mal the initial arterial spasm has but to be confined to the surface of the hemispheres, leaving the thalamus ganglia undisturbed, and it can readily be understood how the momentary unconsciousness or abolition of cortical function can occur without the patient falling, his automatic ganglia still carrying on their functions. At the same time with the lesser spasm there would be a less extensive sinking of intracranial pressure with less consecutive collateral hyperæmia of the lower centres and therefore no convulsion.

In certain cases the arterial spasm fails to affect the entire cortical surface simultaneously; some one trunk may be more pervious, and as afflux of blood may occur in its special field where certain impressions and motor innervations are stored, the result will then be that the function of the relatively well-nourished territory will be exalted. If it be a visual perception territory, sights, colours or luminous spectra will be seen; if it be an olfactory territory, odours will be smelt; if a tactile centre, crawling, tingling and cold sensation are felt; if a speech centre, cries, phrases, and songs may be observed. This explains the manifold epileptic aura, which is simply an isolated, exaggerated, and limited cortical function. The recurrence of the aura is readily explicable on the ground of the well-known physiological law that any nervous process, morbid or normal, having run through certain paths, those paths will be the paths of least resistance for that process to follow in the future.