The Integrative Action of the Nervous System

The shaded regions, marked " EYES," indicate in the frontal and occipital regions respectively the portions of cortex which, under faradization, yield conjugate movements of the eyeballs. But it is questionable whether these reactions sufficiently resemble those of the "motor" area to be included with them. They are therefore marked in vertical shading instead of stippling, as is the "motor" area. S. F. = superior frontal sulcus. S. Pr. = superior precentral sulcus. I. Pr. = inferior precentral sulcus.

tional centres. A practical outcome of this is that it is essential for accurately detailed localization, when the opening through the skull is of moderate size, not to trust to the anatomical details of Figure y^ (from Griinbaum and Sherrington). —Brain of a chimpanzee {Troglodytes niger). Left hemisphere; mesial surface. The extent of the "motor" area on the free surface of the hemisphere is indicated by the black stippling. On the stippled area, " LEG " indicates that movements of the lower limb are directly represented in all the regions of the " motor " area visible from this aspect. Such mutual overlapping of the minuter sub-divisions exists in this area that the diagram does not attempt to exhibit them. The pointing line from " Anus, etc.," indicates broadly the position of the area whence perineal movements are primarily elicitable.

Sulc. central. = central fissure. Sulc. calcarin. = calcarine fissure. Su/c. /arieto occip. — parieto-occipital fissure. Sulc. calloso marg. = calloso-marginal fissure. Sulc. precentr. marg. = pre-central fissure. The single italic letters mark spots whence, occasionally and irregularly, movements of the foot and leg (//), of the shoulder and chest (j), and of the thumb and fingers (A) have been evoked by strong faradization. Similarly the shaded area marked " EYES " indicates a field of free surface of cortex which under faradization yields conjugate move- ments of the eyeballs. The conditions of obtaimnent of these reactions separates them from those characterizing the "motor" area.

the exposed cerebral surface, but to obtain orientation in the topo- graphy by application of the electrodes and observation of the movement, if any, which is excited. In our early experiments we thought to obtain much help by having at hand a brain of the same species already experimented upon and thought to save time in recording the results of the fresh experiment upon chart outlines prepared from the specimen already worked upon. But the variation of the convolutions from individual |

to individual has been too great to allow of these expedients. | As an exception to the above general rule two landmarks of \ relative constancy are the genua of the sulcus centralis, the \ are two (Fig. 72) ; the upper, opposite the junction between i leg area and arm area, may be termed the cruro-brachial ; the : brachio-facial. In the orang there is in addition a third genu, ■ which from its relation to the functional topography may be \ called the labio-linguaL In the orang the facial area of the ?

cortex is considerably longer from above down than in the i chimpanzee or gorilla. It is a general belief that for excitation of the cortex in man \ there is needed an intensity of faradism much greater than that \ sufficing for the cortex of the monkey. Actually comparing the ' excitability of the cortex of the anthropoid with that of the bonnet monkey by employing exactly the same current in each '■ case, we found the excitability as measured by the least intensity \

of current required to evoke motor reaction practically the ' cortex of the anthropoid, though undoubtedly far more complex ~\ in many ways than that of the lower ape, remains as readily ; amenable to electric stimulation. Cushing of Baltimore and \ brain, and that it is not necessary to employ strong faradization. \ In the majority of the anthropoids upon which we have experi- \ mented cortical epilepsy has been quite easily provoked, just as ^ In the precentral gyrus, the sequence of representation of 1

the musculature starting from below upward follows broadly \ that known for the lower apes. The sequence runs — tongue, 1 jaw, mouth, nose, ear, eyelids, neck, hand, wrist, elbow, shoulder, \ chest, abdomen, hip, knee, ankle, toes, and perineal muscles. ; It is noticeable that movements of the eyeballs do not occur \ in this list As did Beevor and Horsley in their orang,^^? so j we in the chimpanzee, gorilla, and orang find a frontal area \ extending into the middle and inferior frontal convolutions excitation of which gives conjugate deviation of the eyeballs to the opposite side. We find this area separated from the area yielding the other movements by an intervening space. We find this intervening space broken, however, by small areas whence movements of the eyeballs can be elicited, partially bridging between it and the upper facial region on the precentral convolution.

The sequence of representation of movement which we note follows a plan more in accordance with the order of the spinal series of segments than that hitherto obtained. Between the place of representation of shoulder and that of hip is an area which, next to the shoulder, yields unilateral movement of the chest muscles, and, next to the hip, yields unilateral movement of the abdominal muscles, and furthest upward lies a focus for perineal muscles.

In our experience, in accord with the original observations by Hitzig^ on the lower apes, the electrodes when placed upon the surface of the post-central convolution fail to evoke any obvious effect, though when placed with an even weaker current upon the precentral they evoke the regular reaction. In our experience, though small lesions in the precentral convolution caused marked paralyses and descending spinal degenerations, similar and larger lesions in the post-central did not produce even temporary paralysis nor any unequivocal degeneration.

With regard to the degenerations, it is noteworthy that from a hand-area lesion the spinal pyramidal degeneration shows in some chimpanzees a ventral direct pyramidal tract of size not obviously inferior to that of a man. But this ventral direct tract does not appear to be present in all individual chim- panzees,— a fact agreeing with Flechsig's^^ discovery of its variability in man. The hand-area lesion gives a heavy degen- eration of the homolateral pyramidal tract in the lateral column on the same side as the cerebral lesion.

As regards symptoms resulting from the cortical lesions, extirpation of a great part if not of the whole of the hand area from the right hemisphere caused an immediate severe crossed brachioplegia without the slightest sign of paresis in either face or leg. The paresis affected the fingers most ; these were kept helplessly semi-extended, the wrist being dropped. The elbow seemed little if at all affected, but the shoulder seemed dis- tinctly paretic, there being difficulty in raising or abducting the upper arm. The paresis diminished quite rapidly, and in six weeks' time the animal had in large measure recovered the usefulness of the limb.

A lesion in the leg-area similarly caused temporary paresis of the opposite leg, especially in the toes and at the ankle-joint. The lesion was smaller and the recovery more rapid than with the arm-area lesion. The knee-jerk, which showed no alteration under the arm-area lesion, here showed exaltation immediately, that is, a quarter of an hour after the leg-area lesion. Weeks later, when the paresis to inspection had passed off, the knee- jerk still exhibited greater briskness on the crossed side.

We have seen often confirmed what our predecessors '^^'^ with the orang have well pointed out, namely, the greater integration of localized representation of movements in the anthropoid as compared with the lower ape. There is not one of the fingers that we have not seen move separately and alone under excita- tion of certain points of the cortex ; again, isolated movement of the pinna of the ear, of the tip of the tongue, rare in the lower monkeys, are easily obtainable in the anthropoid.

As to the extent of the so-called motor area, from our obser- vations we think it probable that in the anthropoid brain as much of that area lies hidden from the surface in the sulci as is actually exposed on the free surface on the convolutions. Nevertheless we indorse the opinion expressed by Beevor and Horsley that the so-called motor area in the anthropoid brain forms a smaller fraction of the total surface than it does in the lower types of monkey. If it has grown in extent — as undoubt- edly it seems to have done — other regions belonging to those so-called "silent" fields whence electric stimulation excites no obvious response have increased still more. It is especially with the exploration of that great inexcitable field that research has to deal. The discoveries of Flechsig, v. Monakow, Dejerine,

Mott, Campbell, the Vogts, and others yearly advance further in the problem. The results on the gorilla ^25 confirm those we have obtained on the chimpanzee, though in the gorilla and orang in my experience eyeball movements have been elicited from a larger field of the frontal cortex than in the chimpanzee, an upper area yielding eye movement on a level with the hand area being more readily discoverable. That the free surface of the post-central convolution belongs to the motor cortex we have not found. Brodman^^* and Campbell ^"^* have since called attention to marked structural differences between the cortex respectively behind and in front of the central sulcus. The arrangement of the fibres and the character of the cells is different. Ramon-y-Cajal,^^* using the Golgi method, and Flechsig^^ia following the myelinization, had also previously drawn distinction between the structure of the two convolutions divided by this great fissure ; and observations by Mott, A. Tschermak, and others had indicated an especially close connection of the post-central gyrus with ascending pre- sumably afferent paths. Evidence of this last by excitation methods is of course difficult to obtain, but nothing in our experiments is contrary to it, and some occasional results that have come before me in experimenting by excitation lend them- selves to such an explanation. To enter upon these here would lead too far from our main interest now.

It is natural to inquire whether reciprocal innervation is exemplified by reactions from the cortex. That inhibition of muscular contraction is obtainable by artificial excitation of the cortex was early noted by Bubnoff and Heidenhain ^ in the dog and by Exner ^^ in the rabbit. I have myself worked chiefly with the monkey .^^^' ^^* In that animal the ocular axes are par- allel, and the setting of the eyeball in the orbit is such that the tensions of its connections, apart from unequal activity of its extrinsic muscles, are in equilibrium when the globes are approximately parallel. That is their primary position. This can be shown in various ways. Thus, if the III, IV, and VI nerves are all severed the eyeballs assume this primary position.

If one eyeball be then rotated by the finger or fixation forceps to right or left or up and down a considerable resistance is felt, and on letting it go the globus springs back at once to the primary position. So also in chloroformization. In the early stage of chloroformization the eyes enter various positions of squint — in the monkey a very usual position is bilateral diver- gence upward and outward. When the narcosis has become profound, the eyes revert to approximate paralleHsm in the primary position. On being then displaced by the finger they at once swing into the primary median position again. So also immediately after death, before rigor mortis has set in.

If III and IV cranial nerves of one side, e, g. left, have been severed, so that rectus externus remains the only unparalyzed ocular muscle, appropriate excitation of the cortex cerebri pro- duces conjugate movement of both eyes towards the opposite side, /. e. from left toward right, the left eye travelling however only so far as the median line. Inhibition of the tonus and of the active contraction of rectus externus can thus be elicited from the cortex. The reaction is obtainable from all that por- tion of the cortex which on excitation gives conjugate lateral deviation of the eyes, i. e, from the area discovered by Ferrier '^ in the frontal region, and from that discovered by Schafer ^^"* in the occipital region.

This inhibition is obtainable from the frontal area after com- plete removal of the occipital lobe. It is conversely obtainable from the occipital area after complete removal of the frontal area. After a deep frontal section across the hemisphere and into the lateral ventricle (partly entering the internal capsule) so as to sever occipital from frontal cortex in the manner practised by Munk and Obregia,^28 ^he reaction is obtainable undiminished from both the frontal and from the occipital areas separately.

The cortex is not essential to the reaction. It is obtain- able from the corona radiata underlying the frontal cortex after complete ablation of the frontal cortex itself It is obtainable from the corona radiata running downwards and forwards from the occipital cortex after free removal of the latter. It is obtain- able by direct excitation of the internal capsule itself From the internal capsule it is elicitable at two distinct places, one in front of the other behind the genu of the capsule. It is obtain- able by excitation of the cross-section of corpus callosunt about 3-5 millimeters behind the genu; also from corpus callosunt at the splenium. The section was laid bare as in Mott and Schafer's ^2^* second method. The reaction as obtained from corpus callosunt has in my hands proved comparatively irregu- lar. It is evident that the action of arrest may take place, in centres which are subcortical.

E. H. Hering and myself^'^ made observations on limb movements elicited from the cortex and found evidence of a similar co-ordination in regard to them. As in the experi- ments of Bubnoff and Heidenhain,*''^ the degree of narcotiza- tion formed an important condition for the observations. The narcosis must not be too profound. It is best, starting with the animal in a condition of deep etherization, to allow that condition gradually to diminish. As this is done it almost constantly happens that at a certain stage of anaesthesia the limbs, instead of hanging slack and flaccid, assume and maintain a position of flexion at certain joints, notably at elbow and hip. This condition of tonic contraction having been assumed, the narcosis is as far as possible kept at that particular grade of intensity. The area of cortex cerebri previously ascertained to produce under faradization extension of the elbow-joint or hip-joint is then excited.

For clearness of description let us suppose the left hemi- sphere excited, and the limb affected the right. The result of excitation of the appropriate focus in the cortex, e. g, that presiding over extension of the elbow, is an immediate relaxation of the biceps with active contraction of the tri- ceps. As regards the condition of the biceps, the relaxa- tion is usually so striking that merely to place the finger on it is enough to convince the observer that the muscle relaxes. The following is however a good mode of studying the phe- nomenon: in a monkey with strongly developed musculature the fore arm, maintained by the above-mentioned steady tonic flexion at an angle with the upper arm of somewhat less than

90° is lightly supported by the one hand of the observer, while with the finger and thumb of the other the belly of the contracted biceps is felt through the skin. On exciting the cortex the contracted mass becomes suddenly soft, melting under the observer's touch. At the same time the observer's hand supporting the animal's fore arm tends to be pushed down with a force unmistakably greater than that which the mere weight of the limb would exert. If the triceps itself be felt at this time, it is easy to perceive that it enters contraction, becom- ing increasingly hard and tense, even when its points of attach- ment are allowed to approximate, and the passive tensile strain in it should lessen. If the limb be left unsupported the movement is one of simple extension at the elbow-joint. On discontinuing the excitation of the cortex the fore arm usually immediately, or almost immediately, returns to its previous posture of flexion, which is again as before steadily maintained. Conversely, when, as not unfrequently occurs in conditions of narcosis resembling that above referred to, the arm has assumed a posture of extension and this is tonic and maintained, the opportunity may be taken to excite the appropriate focus in the cortex for flexion of fore arm or upper arm. Triceps is then found to relax, and biceps at the same time to enter into active contraction. If the biceps be hindered from actually moving the arm, the prominence at the back of the upper arm due to the contracted triceps is seen simply to sink down and become flattened. When examined by palpation the muscle is felt to become more or less suddenly soft, and the biceps at the same time to become more tense than before. The move- ment of the limb, when allowed to proceed unhindered, is flexion with some supination.

It is noteworthy that in this experiment not every part of the large triceps mass becomes relaxed ; a part of the muscle which extends from the humerus to the scapula does not in this experiment relax with the rest of the muscle. This part, if the scapula be fixed, acts as a retractor of the upper arm, and is not necessarily an antag- onist of the flexors of the elbow. This part of the triceps we observed sometimes enter active contraction at the same time

as the flexors of the elbow. Under use of currents of moderate intensity we found that not from one and the same spot in the cortex can relaxation and contraction of a given muscle be evoked at different times, but that the two effects are provocable at different, sometimes widely separate, points of the cortex, and are there found regularly. We obtained analogous results in the muscles acting at the hip-joint In the narcotized animal the hip-joint is being main- tained in flexion, the thighs being drawn up on the trunk, excitation of the region of the cortex previously ascertained, when the limbs hang slack, to evoke extension of the hip, pro- duces relaxation of the flexors of the hip and at the same time active contraction of the extensors of the thigh. We examined particularly the psoas-iliacuSy and the tensor fascice femorisy also the short and long adductor muscles. Each of these was found to relax under appropriate cortical excitation. If the knee were held by the observer it was found at the time of relaxation of the flexors of the hip to be forced downward by active extension of the hip.

Similarly with other groups of antagonistic muscles, both those of the small apical joints of the limb, e. g» flexors and extensors of, the digits, and those of the large proximal joints, e.g. adductors and abductors of the shoulder. At these also instances of reciprocal innervation were obtained. By antagonis- tic muscles I mean only what are termed true antagonistics ; I do not include the cases where one muscle fixes a joint enabling another muscle to thus act better on another joint — H. E. Her- ing's pseudoantagonists.^^^ Hering has carefully analyzed ^^^ the co-ordination of such pseudoantagonists in the action of clenching the fist. He has shown that when that movement is evoked in the monkey by excitation of the cortex cerebri the ex- tensors of the wrist are thrown into action simultaneously with the long flexor of the fingers. But there was no evidence that the true antagonists were ever thrown into simultaneous activity.

That a part of the triceps brachii (that retracting the upper arm) should actively contract exactly when another part (that ex- tending the elbow) becomes relaxed is exactly comparable with 1 a phenomenon which can be noted in the limb under spinal re- ■ flexes, both in triceps itself and in quadriceps femoris. Beevor and j others have shown that different parts of what in gross anatomy \ is denominated one single muscle are used separately in various i

movements. And Hering and I similarly saw in the quadriceps 1 femoris, on exciting the cortical region yielding extension of the j hip, a relaxation of a part of the quadriceps (a part which flexes j the hip) with contraction of another part (which extends the 1 knee). I have also noted that in the monkey by stimulating i the appropriate cortical area for flexion of the knee the knee- jerk is temporarily depressed or suppressed completely. The results obtained from the internal capsule were as strik- i

ing as those obtained from the cortex itself. From separate points | of the cross-section of the capsula, relaxation of various muscles i was evoked. Among the muscles whose inhibition was directly i observed were supitiator longus and biceps brachii, the triceps, the j deltoid^ the extensor cruris^ the hamstring group, the flexor \ muscles of the ankle-joint, and the sternomastoid. The spots in the cross-section of the capsula which yielded j the inhibitions were constant, that is, the position of each when I observed remained constant throughout the experiment. The \ area of the capsular cross-section at which the inhibition of the i activity of, e, g. the triceps, muscle can be evoked is separate I from (that is to say not the same as) that area whence excitation j evokes contraction of the triceps (or of that part of the triceps ! inhibition of which is now referred to). On the other hand, the i area of the section of the internal capsule, whence inhibition of 1 the muscle is elicited, corresponds with the area whence con- traction of its antagonistic muscles can be evoked. Yet synchro- \ nous contraction of such pairs of muscles as gastrocnemius and i peroneus longus is obtainable from the cortex. The observa- \ tions make it clear that " reciprocal imiervation " in antagonistic ! muscles is obtainable by excitation of the fibres of the internal \ capsule. Topolanski ^^^ observed them on exciting the corpora \ quadrigemina (rabbit). It is probable therefore that the in- ] hibition elicitable from the cortex cerebri is not in these cases j