On the Discordant Action of the Double Brain

W. W. Ireland
1891 BMJ (Clinical Research Edition)  
TIlE old metaphysicians felt the difficulty of reconciling the persuasioni of the unity of the mental operations with the evidence that in its relations to the material world the minid was so closely connected witlh a double organ. Even in our owIn day the conjoined functions of the two hemispheres is a question wlhiclh physiologists are shy of examining. The question arises, Do the two sides of the brain perform the same functions? Have we a double set of sensations, perceptions,
more » ... ions, apprehensions, and mnemonic images? and how is the simultaneous action of both sides of the body kept up, and the feeling of uniity of thought, feelings, and actions sustained? It is Inow generally received that the corpus callosum is a real commissure, uniting by its radiating fibres analogous parts of the hemispheres, and uniting heterologous parts of the occipital witlh the frontal lobes through an underband of longitudinal fibres. This view is confirmed by the experiments oni the corpus callosum published by Dr. Mott in the BRITISH AMEDICAL JOURNAL of May 17tlh, 1890. It is, hiowover, surprising that the coinplete absence of this organ has been note(l half a dozen times without entailin-ig any apparent functional deficiency, for examination of the literature shows that wlhere there has been imbecility there hias always been some other grave defect. On the other hand, the cases of Eichler, P'aget, Malinverni, Golly, and the second case of Kaufmann an(l that of Erb show that where the brain is otherwise well developed there may be no disturbance of mobility, co-ordination, general or special sensibility, reflexes, speeclh, or intelligence, whether the defect of the corpus callosum be primary or secondary. This view has leenll also confirined by observations of destruction of the corpus callosum from disease. We know that the limbs of each side perform simultaneous movements under the direction of thIe opposite sides of the brain, and that it is easier for them to perform analogous movements than different ones. Nevertheless,we have the power of simultaneously executing different actions which require distinct mental conceptions for their direction-as, for instance, in piano playing. The power of attenidinig to two or tlhree subjects at once, can le increased by cultivationi. It is no doubt possessed by some men in greater proportion thain by otlhers. Plutarchl says that Julius (Casar during his campaigns would go on, sitting on lhorseback, dictatinig to two secretaries ; and Pliny tells us that CGwsar used to read and write at the same time, or to di(tate anid listeni, or that lhe would keep four clerks employecd at once writing to hiis dietation.2 In the debate on this subject at thwe anniiual meeting at Leeds, I was surprised to hear a distiniguislhed psyclhologist question the statement that a man could attend to two mental operations at once; but at thle very niext meveting my own experienice afforded me a proof of the case ill point. At the request of thle Secretary of tlhe Section I wrote out some remarks wlichl I hlad made, anid at the same time kept on-listeninig to thle debate, whicl could perfectly recall. In genieral, when two mental operations are tlhus transacted at onice, the mind gives its main attention to onIe of them, and the memory ruins along a particular traini of thought, so that the coneomitant ideas are quickly forgotten. Of course, the more powerful the concentration of mind, thie more the mind is occupied with one single pr)ce(ss. The absent-minded man falls inlto onle traini of tlhouglht, and( loses the parallel observations by which 31en(1 uisually keep l u) a knowledge of their situation, the when, where, and llhow of ordinary life. .Most of the senisory fibres from the peripheral orgails cross to the opposite side of the braini, a smaller portion goilng to ' At the Annnial Meeting of the British Medical Association lheld at L.eeds I inti oduced a discussion on "The Discordant Action of the Dual Bra-in in Insanity," in wlhichl some eminent psychologists took part. My address was given orally, not read from a paper, but the following pages Contain the suibstanice, with a few additions from original 1notes and new rP si uy lib vi cap 5, the same side. A larger portion of the nerve fibres from each retina crosses to the opposite optic ganglia, but a smaller portion, representing the temporal side of oine retina and the nasal side of the other does not cross, but passes to the same side of the brain, so that each visual area of the brain receives impression from both eyes. The innervation of the oculomotor muscles is arranged on a corresponding plai.3 Dr. Dupuy reported to the Biological Society of Paris (May 25th, 1889) the case of a young woman who lhad the power of moving lher eyes in differenit directions at the same time. Whlen she did so she saw objects only with one eye, and whein she tried to observe with the otlher at the same time she was seized with giddiness. Dr. Dupuy regarded this as a proof that there were two distinct perceptive centres. He was supported by Brown-S6quard, who took occasion to enforce his view that the two hemispheres are identical in function and can replace each other. In like manner tlle fibres whichl conduct motor impulses from the lhemispheres to the muscles do not all cross over to the opposite side of the body. They may be divided into three sets; those which mainly supply the muscles of the same side as those going to the muscles of the neck and trunk, those which go to both sides in almost equal proportion as to the muscles of the jaw, tllroat, larynx, and diaphragm, and those which mainly cross to supply tlhe other side of the body. Such are those given to the muscles of the arm and leg. In no case does one side of the body derive either its sensory or motor nervous influenices from one side of the brain alone, but from botlh, thouglh in varying proportions. Thlus paralysis of sensation from an injury to one side of the brain is never complete, for each side of the brain always represents a certain though minor amount of sensation from the same side of the body. In like manner loss of motor power may be stated as tlle loss of 95 per cent., or of 50 per ceint., as it affects one or otlher motor cenitre. In the latter case paresis is not apparent, as the muscle being innervated from both sides of the brain, the loss of one half of its innervation is made up by the increased activity of the other side of the brain. On the oth-ier hanid, it appears from close observation that in paralysis of one side of the body there is also a loss of power oIn the opposite side of the body, wlich derives a certain thoughi smaller amount of innervation from tl-he injured side of the brain. Though certain areas of the brain seem to have a closer connection with the inniervation of definite groups of muscles than other portionis of the cortex, it has been found that when these parts have beeni removed or destroyed the museles dependenlt uponi them are for the time thrown out of action. After a longer or shorter interval the paresis disappears, and the lost motor function is reassumed. Such experiments have often been repeated on the brains of animals, and lhave been confirmed by lesions of the cortex observed in manl. One good instance was given by Dr. Byrom Bramwell, in whliceh a tumour occupied the middle of the motor zone oIn one side of tlle brain, as was well displayed by a photograph, without any paralysis having been observed during life. It has beein assumed that in sucll cases it is the analogous portion of the opposite hemisphere which takes up the lost function of the injured side; and this no doubt holds good in some cases. At the same time, while dealing with this question, it would be unfair to pass over the objection of Goltz, wlho removed the motor centres in one side of the brain, and then waited for the animal to recover from the injury to the motor powers and from the loss of sensation. On the theory that this recovery was owing to the correspondinig part of the opposite hemisphere taking up the functions of bothl sides, removal of the motor convolutionis should lhave been followed by paralysis on botlh sides of the body; but the temporary paralysis only affAected tlle muscles of the opposite side. A sinlilar experimeint was performed by Lucianii anid Tamburini. Some pliysiologists lhold that the lost motor fuinction is in tiiine takein up by aniotlher part of the same side of the inijured braini; otlhers that the inniiervationi is supplied by the vicarious actioni of the corpora striata. M. Herzeni, of Lausannie, states that if the sigmoid gyrus be extirpated in a dog, there follows temporary paralysis of the opposite limb; e3 Se thp Able paper on Oculo-motor Centres, by Dr. Spitzka, Journaq q
doi:10.1136/bmj.1.1587.1167 fatcat:ibm3a2s3azegxff742r5jwic6u