Sensory Paths Research Articles

Collateral afferent excitation of reticular formation of brain stem.

The demonstrable capacity of afferent stimulation to arouse a sleeping subject, and the obvious benefits of reducing sensory inflow in predisposing to sleep, are in seeming disharmony with recently discovered influences for wakefulness exerted by the central reticular core of the brain stem. Direct stimulation of this part of the neuraxis reproduces the electrical pattern of wakefulness in the cerebral cortex (14) while at the same time it facilitates lower motor activity (16), and so arouses the nervous system generally (9). The ascending course of this reticular activating system is distinct from that of afferent pathways in the brain stem (19) and selective destruction of its cephalic portion is followed by the EEG synchrony and behavioral somnolence, hitherto attributed to deafferentation of the cerebrum (7, 8). Such consequences do not follow selective interruption of ascending somatic and auditory paths in the midbrain and after this latter injury both somatic and auditory stimuli are still capable of awakening the sleeping animal and activating its EEG (7, 8). It seemed likely that the apparent conflict might be resolved if evidence were forthcoming that collaterals from afferent paths turned into the reticular activating system in the brain stem and exerted their admittedly important arousing and awakening influences, indirectly, by modifying its activity. The present study has explored this possibility by probing the brain stem for alterations in electrical activity evoked by somatic and auditory stimuli. The findings establish the existence of collaterals from these sensory systems to the brain stem reticular formation, the rich wealth of which has never previously been suspected, though indications for it have been afforded by earlier anatomical investigation (2, 11, 13) and by study of the atypical route of conduction of the ‘secondary response’ to sciatic stimulation (5). Though the results are presented here only with reference to the problem under discussion, it is felt that implications of these findings may be broad indeed, for they appear to enlarge outlooks in afferent conduction far beyond those which have been envisioned within the circumscribed limits imposed by classical sensory paths.

Behavioral and EEG changes following chronic brain stem lesions in the cat

The effect upon behavior and the EEG of chronic lesions in the rostral brain stem has been studied in a series of cats. Of lesions in sensory paths, in the periaqueductal grey, or in the midbrain tegmentum and basal diencephalon, only the latter, in a position to interrupt the ascending reticular activating system, were followed by chronic somnolence and EEG synchrony. Activation of the synchronized EEG by somatic and auditory stimulation was still possible either after the reticular activating system or after long sensory paths had been interrupted immediately behind the thalamus. Collateral sensory excitation of the reticular activating system in the lower brain stem, and the direct arrival of afferent impulses at some site above the midbrain, thus serve equally well to induce EEG arousal, but only in the former instance does prolonged wakefulness follow. Poverty of behavior after lesions of the reticular activating system suggests that its influences may be directed both cephalically to activate the EEG and caudally to facilitate motor activity, in maintaining the waking state.

The sensory paths in the spinal cord and brain stem of man. First report: Studies on the long ascending paths of the spinal cord, the secondary trigeminal paths and on their correspondence. Short note on the central gustatory path of man

The sensory paths in the spinal cord and brain stem of man. First report: Studies on the long ascending paths of the spinal cord, the secondary trigeminal paths and on their correspondence. Short note on the central gustatory path of man

The sensory paths in the spinal cord and brain stem of man, Second report: On the traetus sacrc-bnlbares. Contributions to the study of the central pathways of the visceral sense of the pelvic cavity, inclusive of the genital-sense

The sensory paths in the spinal cord and brain stem of man, Second report: On the traetus sacrc-bnlbares. Contributions to the study of the central pathways of the visceral sense of the pelvic cavity, inclusive of the genital-sense

Chronic Mercury Poisoning

The most prominent symptoms of chronic mercury poisoning are erethism, tremor and stomatitis. The psychic disturbance known as erethism is the first of the symptoms to develop; it is a peculiar form of timidity most evident in the presence of strangers. The name is derived from the Greek word ' red ' and is attributed to the blushing embarrassment of the sufferer. John Pearson of London (1758-1826) first gave the symptom complex the name erethism (Almkvist, 1929). The man affected is easily upset and embarrassed, loses all joy in life and lives in constant fear of being dismissed from his job. He has a sense of timidity and may lose self control before visitors. Thus, if one stops to watch such a man in a factory, he will sometimes throw down his tools and turn in anger on the intruder, saying he cannot work if watched. Occasionally a man is obliged to give up work because he can no longer take orders without losing his temper or, if he is a foreman, because he has no patience with men under him. Drowsiness, depression, loss of memory and insomnia may occur, but hallucinations, delusions and mania are rare. The most characteristic symptom, though it is seldom the first to appear, is mercurial tremor. It is neither as fine nor as regular as that of hyper thyroidism. It may be interrupted every few minutes by coarse jerky movements. It usually begins in the fingers, but the eyelids, lips and tongue are affected early. As it progresses it passes to the arms and legs, so that it becomes very difficult for a man to walk about the workshop, and he may have to be guided to his bench. At this stage the con dition is so obvious that it is known to the layman as ' hatter's shakes.' The tremor often passes away if the patient gives up his work before it has reached a serious stage; if this is delayed the tremor may persist for 15 or 20 years. Alcoholism favours its development, and it is claimed that no total abstainer has ever suffered from tremor in severe form. Stomatitis manifests itself by salivation and tenderness of the gums. The gums are swollen and bleed readily and, rarely, a mercurial line is seen on the gums; it usually resembles the blue line of lead poisoning, though sometimes it is dark brown. Neal and his colleagues (1941) report that dermo graphia, excessive perspiration, pallor and an abnormal readiness to blush are manifestations of chronic mercurialism, while Adler (1891), Jacobsohn (1920) and Tylecote (1912) have reported increased deep tendon reflexes as part of the clinical picture. These symptoms of chronic mercury poisoning must be clearly differentiated from those of acute mercurial poisoning, which rarely arises in industry and usually results from the use of drugs such as ercury bichloride, taken in excess, either by ccident or with suicidal intent. Diarrhoea is usually the first symptom: the stools, faeculent at first, soon become watery, profuse and blood stain d. They often contain pieces of mucous membrane and have a disagreeable odour. Marked tene mus and severe pain in the lower abdomen are usually present. In some cases vomiting occurs even when the poison has not been taken by mouth. Renal symptoms are also common; there is a mark d reduction in the output of urine, which may lead to complete anuria. The urine contains red and white blood cells as well as albumin and epithelial and granular casts. Headache and somnolence follow and death from uraemia usually occurs within several days. As to poisoning by organic mercury compounds, Evans and Perry (1943) reported immediate death following the intravenous administration of mer curial diuretics in six patients, and many more cases have been reported in the United States. Hunter, Bomford and Russell (1940) drew attention to the extremely different nature of poisoning with methyl mercury compounds. Salivation, stomatitis and erethism were absent, and the nervous system alone is i volved. The symptoms were severe generalized ataxia, dysarthria, and gross constriction of the visual fields, while memory and intelligence w re unaffected. There was an intense and wide spread degeneration of certain sensory paths of the nervous system, the peripheral nerves and posterior spinal roots being affected first; the posterior columns and the granular layer of the middle lobe of the cerebellum later. Mercury fulminate is handled in explosives fac tories where detonators and percussion caps are made. The substance readily gives rise to derma titis. Generally the uncovered parts of the body are attacked by an erythema, accompanied by intense F 55

OBSERVATIONS ON SUBCORTICAL SOMATIC SENSORY MECHANISMS OF CATS UNDER NEMBUTAL ANESTHESIA

OBSERVATIONS ON SUBCORTICAL SOMATIC SENSORY MECHANISMS OF CATS UNDER NEMBUTAL ANESTHESIA

Morphogenesis of the brain

AbstractThe fundamental structure of the brain stem is uniform throughout the vertebrate series, not essentially because it expresses an architypical pattern, but because of the constancy of peripheral connections and their internal relationships, both of which are parts of an apparatus of adjustment to environment which is common to vertebrates. Other parts of the brain are more variable because, with complication of the behavior pattern in higher forms, more elaborate and diversified mechanisms of correlation and integration are requisite.The brain stem between the olfactory bulb and other primary sensory centers is plastic tissue not dominated by any single sensory‐motor system; it is the meeting place of descending and ascending sensory paths. Here the chief apparatus of correlation and integration is elaborated. From it emerge the complex thalamic and cortical adjustors. The pallium is not a primary constituent of the vertebrate brain. The pallial type of organization gradually emerged from the more ancient subpallial type and comes to mature expression in the cerebral cortex. Several instructive stages in the progressive differentiation of cortical structure and connections are seen in the amphibian forebrain, but the process is not consummated. Amphibia have no cerebral cortex, though cortical primordia are evident here and in various fishes. Static concepts of architypes and the dialectic of ‘form‐analytic’ argumentation are replaced by a more dynamic treatment of morphogenesis.

XXI.—The Independence of Peripheral Sensory Neurons in view of the Results of Experimental Section of the Optic Nerve in the Rabbit

The problem of the amount of independence possessed by the units which go to make up the nervous system is one which has long occupied the attention of neuro-pathologists, and is still far from solved. That degenerative changes, as the result of peripheral injury, may extend across several intermediate neurons is indicated by the work of many investigators, notably v. Monakow, Campbell, Bolton, etc. Thus after enucleation of the eyeball changes have been met with in the visual cortex, showing that degeneration has travelled over the neurons situated at the basal ganglia of the cerebrum to the neurons in the visual cortex itself. Interruption of the sensory conduction path affects the integrity of themore centrally placed neurons. The question of the stability of the peripheral neurons under similar conditions has not received attention. Birch-Hirschfeld in 1900 published the results of a large series of experiments upon the retina, including a few cases of the effects of experimental section of the optic nerve.

ON THE RELATION OF THE OPTIC THALAMUS TO RESPIRATION, CIRCULATION, TEMPERATURE, AND THE SPLEEN

From what has already been said, it is apparent that changes in respiration and blood pressure may be produced by stimulation of a very large portion of the optic thalamus; that no one region controls these phenomena; that the spleen shows variations in volume only when marked blood pressure changes occur, and that such a change has been observed on stimulation of many places in the thalamus. Furthermore, the regions in the thalamus from which such effects are obtained are those in which the large afferent paths end; namely, the fillet and superior cerebellar peduncle, and a region directly connected with the vagus nucleus. The portions of the thalamus which proved inert to stimulation were those which in our previous investigation also were inactive; namely, the median nucleus, and the upper anterior end of the lateral-the region through which the fibers of the median nucleus pass. These phenomena are similar in every respect to those observed when an afferent nerve is stimulated. In what has gone before, it has been shown that the respiratory and circulatory changes occurred when one of the sensory paths, or a path running directly to the medullary nuclei governing these functions was stimulated. In explaining these phenomena, therefore, there is no necessity for invoking the existence of special centers.

FATIGUE STUDIED IN REACTION TIME EXPERIMENTS

The delay in response towards the close of reaction time experiments is evidently due to fatigue affecting some higher central process which is concerned in the maintenance of a close linkage between the central terminations of the sensory tracts and the so‐called voluntary motor centres. This is judged to be the case for the following reasons :—1. An intermittent and prolonged series of auditory stimuli towards which attention does not require to be sharply directed has no distinct fatiguing effect on succeeding reaction time responses for hearing. Hence, one concludes that the delay in response, which occurs after a prolonged series of reaction times (hearing), is not due to a fatigue of the auditory path.2. If, in a series of reaction time experiments, the sensory tracts be changed, as in passing from reaction time (sight) to reaction time (hearing) and then back again to sight, one finds that fatigue is apparently more marked at the close than if the stimulated sensory tracts remained the same throughout. At least, there is no sign of recuperation.As in this case the motor channel remains the same while the higher central one only varies to the extent of being directed towards a different “sensory centre,” the sensory path alone being changed, the fatigue effects must be due to alterations in the higher central links or in the motor path.They are evidently not due to alterations in the last‐mentioned path, as there are no signs of fatigue when this motor path is kept in slight activity of the same type as that existing in reaction time experiments. That is to say, the mere voluntary tapping of the Morse key at the rate of 10 per minute produces no appreciable fatigue.3. The effects of unexpected stimuli are more easily explained on the supposition that the time interval in reaction time is most largely dependent upon the close central linkage.4. The effect of disposition upon the duration of reaction time is most readily understood when one recognises the importance of the central linkage.5. The feelings of fatigue, such as sleepiness, difficulty in keeping the attention fixed, etc., which a person suffers from at the close of a long series, point to a central disturbance affecting the connecting links between sensory and motor channels.

Flechsig on the Localisation of Mental Processes in the Brain

Two Treatises∗ recently published contain the views of Professor Flechsig, of Leipzig, upon the present state of our knowledge of brain function. The first is in the form of an oration delivered in 1894 in the University Church of Leipzig, of which a new edition appeared last year. The second is a shorter pamphlet, which contains an account of the most recent researches in the structure of the brain. In the oration the notes occupy three times the space of the text; in the other treatise the notes are not so long. In both these notes are important, and form in some passages the most interesting part of the work. He holds that the time has now come when the old introspective psychology must turn for guidance to anatomy and physiology. It is only within the last few years that such claims could be entertained. The localisation of mental operations in the brain was made by Hippocrates from observations of the loss of function caused by diseases or wounds of the head. Polybos, the son-in-law of the great Greek physician, held that the brain was the centre of the nerves and the central organ of the thinking soul; and Erasistratos, of Alexandria, first taught that the superior intelligence of man depended upon the greater size of the human brain, and the more complicated structure of the convolutions. A new era began with the experiments of Fritsch and Hitzig in our own day. Since then experimental physiology and clinical observations, going hand in hand together, have led to the accumulation of a large fund of knowledge about the several functions of the nervous centres. Another path of discovery was opened by Golgi through his new method of differentiating the finer structure of the grey masses of the brain by his silver colourings; and also by Kölliker, who, working with low powers, was able to demonstrate the course of the motor and sensory nerve paths and of the association system in the brain.