SYSTEM.] PHYSIOLOGY 41 of value in cerebral physiology but have been successfully applied to the diagnosis of various diseases of the nervous system. The motor areas as determined by Ferrier in the monkey are shown in tig. 30. Dr Ferrier has also indicated the corresponding motor areas in man by carefully comparing the convolutions with those of the monkey. 1 An inspection of the figures shows that the areas which, when stimu lated, give rise to definite movements are distributed only over a part of the cortex. As stimulation gives rise to no movements over other regions of the brain, these have been assumed to be connected with psychi cal states, such as sensation, volition, &c. Much controversy has arisen as to the real FIG. 30. A. Li ft hemisphere of monkey. B. Upper surface of hemisphere of monkey. The numbers in A and B correspond. 1, advance of opposite leg as in walking ; 2, complex movements of thigh, leg, and foot, with adapted movements of trunk; 3, movements of tail; 4, retraction and adduction of opposite fore-limb ; 5, extension forward of opposite arm and hand, as if to reach or touch something in front ; a, Z>, c, d, individual and combined move ments of lingers and wrists, ending in clenching of fist ; (5, supination and flexion of forearm, by which the hand is raised towards the mouth ; 7, action of zygomatics, by which the angle of the mouth is retracted and elevated ; 8, elevation of ala of nose and upper lip, with depression of lower lip, so as to expose the canine teeth on the opposite side ; 9, opening of mouth with protrusion of tongue ; 10, opening of mouth with retraction of tongue ; 11, retraction of angle of mouth ; 12, eyes opening widely, pupils dilating, head and eyes turning towards opposite side ; 13, 13 , eyeballs moving to opposite side, pupils generally contracting ; 14, sudden retraction of opposite ear ; 15, subiculum cornu ammonis,- torsion of lip and nostril on same side. (Ferrier.) nature of these so-called " motor areas." It has been clearly ascer tained that the effects are not due to diffusion of the electric currents influencing other parts of the brain. That there is to some extent such diffusion between the electrodes there can be no doubt, but the exact correspondence between the area stimulated and the movements produced, and the fact that shifting the electrodes a very short distance to one side or another is followed by different results, show that the effect is somehow owing to changes excited by the electric current in that particular area of grey matter. Hitzig, Ferrier, and others have also found that removal of the layer of grey matter of a "motor centre" is followed by enfeeble- ment of the movements assigned to the area, but in the course of a few days the paralytic symptoms disappear. The latter effect cannot be due to the corresponding centre on the opposite side taking up the work as subsequent destruction of the latter pro duced the usual paralysis on the side opposite to the lesion, but did not cause a repetition of the paralysis on the side opposed to the first lesion" (Carville and Duret). It would appear, therefore, that after destruction of a centre on one side some other part of the same hemisphere may take up the functions of the destroyed part. Goltz of Strasburg has removed large portions of the grey cortex (even to the extent of almost the whole of one hemisphere) by a jet of water so as to avoid haemorrhage, and still recovery of motor power took place after a time, although there remained "clumsiness in the execution of certain movements." His opinion is that the paralytic phenomena are caused by the injury exciting an inhibitory action on lower centres. This view, substantially that advocated for many years by Brown-Sequard does not explain why it is that gentle irritation of the centre by a weak Faradaic current calls forth movements of a definite character. The evidence, therefore, is strongly in favour of the view that there are definite motor areas of grey matter on the cortex, that is, in ordinary circumstances these areas are intimately related to specific muscles or groups of muscles. It is quite possible, however, that each group of muscles does not depend on one area alone, but on several, whilst it is more intimately related to one than to the others. This would account also for the fact that movements of a group of muscles may be excited by stimulation of other areas than those mapped out by Ferrier and Hitzig. Recently areas associated with definite move ments of the thorax, abdomen, and pelvis have been discovered by Horsley and Schafer, and thus almost all the muscular mechanisms have been connected with some of the cerebral convolutions. 1 For figures of human brain showing motor areas, see Foster s Physiology, 4th ed., figs. 86 and 87, pp. 627, 628. Ferrier has also attempted to differentiate sensory centres. On Sensory stimulating the angular gyrus he obtained movements of the eye centres. and associated movements of the head, and he regarded the pheno mena as being " merely reflex movements on the excitation of sub jective visual sensation." He then found that, "when the angular gyrus of the left hemisphere was destroyed, the animal was blind on the right eye soon after the operation, but recovered sight com pletely on the following day." On destroying the angular gyri of both hemispheres, an animal became permanently blind in both eyes. In neither case was there motor paralysis. By similar processes of thought and experiment he placed the auditory centre- in the superior temporo-sphenoidal convolution, the centres of taste and smell at the extremity of the temporo-sphenoidal lobe, and that of touch in the gyrus uncinatus and hippocampus major. On the other hand, Goltz asserts that even after removal of a con siderable part of the cortex the animal is not actually blind, but suffers from an imperfection of sight; and he states that he "can no more obtain distinct evidence of localization in reference to vision or other sensations than in reference to movements." Ferrier s view is supported by the observations of Muuk, who finds that destruction of a considerable portion of the occipital lobes causes blindness. Munk has put forth the important distinction that there may be blindness in the sense of total deprivation of vision, and " psychical blindness," or the "inability to form an intelligent comprehension of the visual impressions received " ; and he supposes that the grey matter of the cortex over the occipital lobes has to do with the elaboration of simple visual impressions into perceptions. In like manner he concludes that other parts of the cortex may have to do with the elaboration of tactile, olfactory, gustatory, and auditory sensations. This is a likely hypothesis, and not very dissimilar to what has been held for many years, the only novelty being that there is localization in these actions. At present the question cannot be regarded as settled ; but it may be stated generally that the posterior portion of the brain has to do chiefly with the reception of sensory impressions, and the middle and lateral regions with the transmission outwards of motor impulses. But there still remains the anterior portion. Electrical irritation of the pra?-frontal region of the cortex in the monkey causes no -motor reaction. Complete destruction causes no paralysis of motion and no sensory disturbance. Dr Ferrier states : "Removal or destruction by the cautery of the antero-frontal lobes is not followed by any definite physiological results. The animals retain their appetites and instincts, and are capable of exhibiting emotional feeling. The sensory faculties sight, hearing, touch, taste, and smell remain unimpaired. The powers of voluntary motion are retained in their integrity, and there is little to indicate the presence of such an extensive lesion or a removal of so large a part of the brain. And yet, notwithstanding this apparent absence of physiological symptoms, I could perceive a very decided alteration in the animal s character and behaviour, though it is difficult to state in precise terms the nature of the change. The animals operated on were selected on account of their intelligent character. After the operation, though they might seem to one who had not compared their present with the past fairly up to the average of monkey intelligence, they had undergone a considerable psychological altera tion. Instead of, as before, being actively interested in their surroundings, and curiously prying into all that came within the field of their observation, they remained apathetic or dull, or dozed off to sleep, responding only to sensations or impressions of the moment, or varying their listlessness with restless and purposeless wanderings to and fro. While not actually deprived of intelli gence, they had lost to all appearance the faculty of attentive and intelligent observation " (Functions of the Brain, 1st ed., p. 231). Thus the frontal lobes appear to have to do with cognition and intellectual action. If so, the grey matter on the surface of the brain may be mapped put into three great areas an area concerned in cognitions and volitions in front, a motor or ideo-motor area in the middle, and a sensory area behind. These distinctions are no doubt arbitrary to a considerable extent ; but, if they are retained as the expressions of a working hypothesis, they are of service. Long ago, and prior to the researches above alluded to, Dr Hughlings Jackson pointed out that disease of certain areas of grey matter on the cortex of the hemispheres may occasion epileptiform convulsions, localized to particular groups of muscles. The theory of the localization of motor functions has been of great service in the diagnosis and prognosis of such diseases. As to the localization of the faculty of language in the third left frontal convolution, founded on pathological evidence, see APHASIA, vol. ii. p. 171. The functions of the nervous system have now been described ; but they are so complicated and so closely related to each other as to make it no easy matter to form a conception of the system working as a whole. The progress of discovery naturally tends to differentiation, and probably to attach too much importance to one organ as compared with the others, so that we are in danger of losing sight of the solidarity of the whole nervous system. Probably every nervous action, however minute and evanescent, affects more or less the entire system, and thus there may be an under-current of nervous action streaming into and out of the nerve-centres, along with a perpetual series of interactions in the centres them selves, contributing to and accounting for the apparent continuity of conscious experience. Certain relations of one nerve-centre to the others are indicated in fig. 31. No one now doubts that con- Con sciousness has an anatomical substratum, but the great problem scious- of the relation between the two is as far from solution as in the ness.
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