Z. Neurol. 201, 297--309 (1972) © by Springer-Verlag 1972

The Electrode, the Brain and the Mind* WILDER P~.NFIELD Honorary Consultant, Montreal Neurological Institute, Montreal, Canada

Key words: Brain - - Mind - - Electrode - - Neurophysiology - - Neurology, History - - History of Neurology - - Medizingeschichte. Fritsch u. Hitzig haben mit ihrer VerSffentlichung ,,~ber die elektrisehe Erreg. barkeit des GroBhirns" einen neuen Anfang zum Verst&ndnis der Gehirnfunktionen gefunden1. Sic entdeekten fiir die neurologischen Forseher eine neue experimentelle Methode und zeigten zugleich, da6 das Gehirn nicht als Ganzes funktioniert, sondern mittels vielf~ltiger intracerebraler Mechanismen, die durch elektrische StrSme aktiviert werden. Ich spreche im Namen aller Neurologen der ganzen akademischen Welt, wenn ich diese deutsehen Neurologen wiirdige. Ich persSnlich empfinde tiefe Dankharkeit fiir die deutsche Neurologie. Im Jahre 1928 habe ich 6 Monate lang in Breslau mit dem hervorragenden Neurelogen, Forscher und Neurochirurgen Otfried Foerster gearbeitet. Er war mir ein Lehrer, Freund und guter Gef~hrte. I1 convient tout ~ fair que les neurelogues frangais se joignent ici, ~ Munich, leurs coll~gues allemands ~ l'occasion de ce centenaire. De 1800 h 1870, Paris fur le centre mondial de ]a neurologie et les travaux de pionnier de Flourens et des eliniciens frangais attir~rent les savants du monde entier. Ils attir~rent aussi les phr~nologistes de tous les coins de rEuropo et de l'Am~rique, et Paris ne reeompensa que trop g~n~reusement ces pseudoscientists. En effet, grace ~ ]curs soci~t6s secretes, ils purent mettre sur pied leur monumentale com~die des bosses du crane, fumisterie maintenant d'int~r~t purement historique. Quant ~ moi, en rant qu'ancien ~tudiant am6ricain k Paris et maintenant citoyen du Canada et de Montreal, une des plus grandes villes frangaises du monde, je sais ¢oute l'importance des brillantes legons que nous ont donn~es les neurologues de langue frangaise d'Europe aussi hien que du Canada frangais, et je tiens ~ reudre hommage k eeux qui perp~tuent encore ces illustres traditions. H~las! Vous vous serez sans doute apergus que je n'ai ni la bosse du Frangais ni celle de l'Allemand, mais je veux me joindre ~ vous de tout eceur pour l'avancement de notre cause commune, la Neurologie. " H o w is the m i n d a t t a c h e d to t h e b o d y ?" I~ was Aristotle, i n the F o u r t h C e n t u r y B.C., who asked this q u e s t i o n s. Hippocrates gave a * The Fri~sch and Hitzig Centennial Lecture, Deutsche Gesellschaft fiir Neurologic and La Soci~t6 Neurologique de France, Miinchen, October 8, 1970. 1 Arch. Anat. Physiol. wiss. Med. 87, 800--332 (1870). 2 Laslett, P. (Ed.): The Physical Basis of the Mind. Oxford: Blackwell 1950. Quoted by C. S. Sherrington in the Introduction. 20 z. Neurol., Bd. 201

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partial answer. He had addressed himself to the problem a few years earlier. He had been discussing epilepsy, t h a t ancient explosive disturbance of the brain, when he spoke to his students as follows: "Men ought to know t h a t . . . through [the brain] in particular, we think, see, hear and distinguish the ugly from the good . . . To consciousness," he continued, "the brain is messenger." Epilepsy was ready, even then, to teach the physician who could observe with an open mind. Five centuries after Hippocrates, another Greek physician, Galen, voiced the common opinion t h a t spirits within the body conveyed messages out to arms and legs to make them carry out the decisions of the will. This served the average man as an adequate explanation through the middle ages until, at last, the experimental method was introduced into science. Then - - it was in 1792 - - the Professor of Anatomy at Bologna, Luigi Galvani, first, and the Professor of Physics at Pavia, Allessandro Volta, second, discovered a strange new form of energy. They recognized it in the muscle and the attached nerve of the leg of a frog. This new form of energy which caused the muscle to contract came, in time, to be called electricity. I t had now become evident t h a t electric currents moved along the spinal cord and nerves out to the muscles. Galen's theory of the spiritmessengers was suddenly out of date. Physiologists wondered about the function of the brain. They had no obvious method of approach. Hughlings Jackson was not yet born and Hippoerates's conclusions, drawn from study of epileptics, had been forgotten. They used strong electric currents to stimulate nerves and spinal cord, and they produced convulsions b y applying such currents to the brain. But the thoughtful use of the experimental method waited from 1792 until 1870 for Fritsch and Hitzig to apply it to the brain. I n their paper, they summarize existing opinion in regard to brain function. Curiously enough, they do not refer to the paper of a French surgeon, Paul Broca, published 9 years earlier, a paper t h a t seems to us so important in retrospect a. But Fritseh and Hitzig refer, instead, to the 1825 publication of Bouillaud, stating t h a t it is well known t h a t the s y m p t o m complex now called "aphasie" can be produced b y a lesion in an excentric portion of the brain. They state, also, t h a t paralysis of arm or leg has been described b y numerous authors and they quote Gabriel Andral who had written, in 1834, t h a t there must be, somewhere in the brain, a distinct localization (si~ge distinct) for movements of the upper and lower extremity. They speak further of the existence of two pathways through brain-stem and spinal cord - - one from without inward, which they describe as "The 3 Broca, P.: Sur la si~ge de la facult~ du langage articul~. Bull. Soc. Anat. (Paris), 2 S~rie, 6, 355 (1861).

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P a t h of the Reflexes ;" the other was from the centrum outward, "The P a t h of the Will." (Die Bahn des Willens, der seelischen Impulse.) The technique used in their own experiments went somewhat as follows: T h e y connected two wires to a source of electrical energy and inserted the free end of each wire into a cork, bringing it through until the terminal poles were 2 to 3 m m apart. Then, tal~ing the cork in his hand, the operator touched the terminals of this bipolar electrode to his own wet tongue. Finding t h a t the current was gentle enough to cause no more t h a n a tingling there, he was ready to apply the terminals to the cerebral cortex of a laboratory animal. How astonished they m u s t have been when the sleeping dog moved one paw on the opposite side of the body as though he were making a voluntary movement! 50 years later, when I was a student in the laboratory of Sir Charles Sherrington at Oxford, we used t h a t same technique - - electric circuit, perforated cork, wet tongue and all! I remember well the burning tingle on m y tongue. I n this commemorative lecture, I propose to ask, and shall a t t e m p t to answer, two questions: _First; W h a t did Fritseh and Hitzig believe they had proven ~. Second." W h a t reasonable conclusions can I present to you at the close of a century during which the method of cortical stimulation has been employed b y physiologists throughout the academic world ? W h a t Fritsch and Hitzig concluded was quite " c o n t r a r y , " they said, "to the thinking" of the great Flourens, and of most of those t h a t followed him and who believed the soul to be a sort of general function of the total action of the brain. The opinion of Fritseh and Hitzig was t h a t brain function was discharged b y "isolated mechanical means" rather t h a n total action. I t is " m u c h more certain, " t h e y said, " t h a t the single spiritfunctions (seelische _Funl~tionen) make entrance into the material structure or arise out of the same in circumscribed centres of the cerebral cortex." (,,Zu ihrem Eintritt in die Materie oder zur Entstehung aus der-

selben au] circumscr@te Zentra der Groflhirnrinde angewiesen sind.") Their basic conclusion about "isolated mechanical means" was correct. F r o m 1870 onward, men searched more and more for brain mechanisms and spoke less often of "total action." Thus, the way was prepared for the work of the physiologists, Leopold Goltz, Sir Charles Sherrington and I v a n Pavlov, as well as the neurologists in London and Paris, led b y Hughlings Jackson and Jean-Martin Charcot. And there were m a n y other explorers, of course, who were swept across the new frontier to search for gold in the unknown land of brain research. During the "Gold R u s h " in America's Wild West, not all who "struck it rich" could spend their gold to good advantage. Nor have all who made discoveries in neurology known how to interpret their findings. Here is the challenge t h a t the lucky ones must face. 20*

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We must approach the brain of man as Sherrington approached the nervous system of other mammals. We must identify individual reflex mechanisms wherever possible and yet strive to understand how these mechanisms are integrated into a functional whole. This is the underlying problem of neurophysiology. I n 1928, when I came to Breslau, Otfried Foerster was removing brainscars for epilepsy. Victor Horsley and others had made brain removals, attempting to cure this condition, before him. But Foerster was a neurologist. He had an enquiring mind and a driving interest in neuro-anatomy. He operated under local anaesthesia and he had reached the important conclusion that gentle electrical stimulation might have the same effect on the cerebral cortex as the irritation of a local epfleptogenic lesion. He was a lone worker. His written records were meagre. He depended largely on his memory which, one must admit, was unusually accurate. He was not a pathologist and he had no one to do pathology for him at the Wenzelhancke Krankenhaus. The excised material from all his cases was waiting, still in formalin. Here was m y opportunity. While practising neurosurgery in New York, I had worked for 6 years on experimental brain-wounds, hoping to throw light on the cause of epilepsy. Now I could do the same for the scarred brain of human epileptics. I examined Foerster's specimens, 12 in all, and we published a study of traumatic epilepsy in two papers, one in German and the other in English 4. I t was clear that here there was a new use for the electrode. I t could be employed during operations under local anaesthesia on cooperative, conscious patients for two practical purposes: 1. To discover the epileptogenie focus and 2. to map out the anatomy of the brain, thus making surgical removal safer and more effective. We believed there was a great future for this method of radical treatment of epilepsy. Thus Foerster had shown the way to a further field in neurosurgery. For me, he had raised the curtain on a new stage. I saw that I could enter the field of neurophysiology after all, through neurosurgery. This was what I had hoped to do when I turned away from m y graduate studies of mammalian neurophysiology in Oxford to become a neurosurgeon. But I saw, too, that no individual could do the job alone and do it well enough. W h a t was needed was a team of experts, working in harmony and 4 Foerster, 0., Penileld, W.: Der Narbenzug am und im Gehirn bei traumatischer Epilepsie in seiner Bedeutung fiir das Zustandekommen tier Anf/~lle und ffir die therapeutische Bek~mpfung derselben. Z. ges. Neurol. Psyehiat. 12~, 475---572 (1930). Foerster, 0., Peniiold, W. : The structural basis of traumatic epilepsy and results of radical operation. Brain 63, 99--119 (1930).

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using special equipment. There m u s t be close proximity of patient to laboratory. I n other words, what was needed was a clinical institute. F r o m Breslau I went to Montreal and b y good fortune 6 years later (September 1934 to be exact) the Montreal Neurological Institute opened its doors. Most important of all, an endowment for its scientific work had been added b y the Rockefeller Foundation of New York. There was another neurological institute t h a t opened its doors in 1934. I t was built for Professor Foerster in Breslau. TMs, too, received assistanee from the Rockefeller Foundation. But, as Foerster's biographer, Klaus Zfileh,remarked s,the Breslau institute cametoo late inFoerster'slife. But there were other reasons too why tMs institute did not serve the intended purpose. My wife and I returned to Breslau in 1937. The clouds of war were gathering fast over Germany. I revisited the Wenzelhaneke K r a n k e n h a u s and saw the new research institute standing at a little distance. I t s doors were strangely locked. Within, there was a feeling of fear. Work went on, but something was missing. I suppose it is always true t h a t creative acMevement in scientific work is stifled when the atmosphere of freedom and trust is lost and when authority comes from an external source. Foerster did not complain. B u t he seemed a very old m a n at 64. He was stooped and the circulation in his legs had almost stopped. Like H a r v e y Cushing, he had been overtaken b y the neurosurgeon's enemy, the peripheral arteriosclerosis t h a t develops in the lower extremities during long hours of operating. When we took our leave from Otfried Foerster and Ms charming wife, he said, " D o n ' t make the mistake t h a t I have made. We need more rest and holidays t h a n other men." Then he pointed to the m a n y volumes of t h a t magnificent Bumke-Foerster Handbuch on the shelf. " T h a t almost killed me," he said, " a n d it was out of date as soon as it was finished." The Foerster Neurological Institute was destroyed, alas, during the war while the m a n and his wife died together, far away. Let the work of his hands be his memorial. And let us, in the words of the Psalmist, " n u m b e r our days, t h a t we m a y apply our hearts unto wisdom." I t was the method of Fritsch and Hitzig, followed b y Foerster's new approach to the t r e a t m e n t of focal epilepsy, t h a t made it possible for us in the Montreal Neurological Institute to study the a n a t o m y and the physiology of the brain of conscious m a n at operation. With a group of colleagues, each of whom has made his own contribution, I was able to organize a system of accurate observation and recording. Thus, we could m a p out the motor areas, the sensory areas and the speech areas and certain areas in which there were psychical responses of another type. 5 Ziilch, K. J.: Otfried Foerster - - Physician and Naturalist. November 9, 1 8 7 3 - June 15, 1941. Berlin-Heidelberg-New York: Springer 1969.

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These have been described in previous publications, many of them with m y associates, and I shall not repeat those descriptions here s. Professor Rasmussen, who was one of m y companions in this work and who, I am proud to say, became Director after me, is discussing the parameters of sensory and motor stimulation in this Centennial Jubilee. For m y par~, I shall talk of the physiological principles that underly the use of stimulation, and what it teaches us about brain function. Beyond that, in the few minutes that remain, I shall approach the ultimate riddle - the mind of man and the mind's corresponding mechanism. No honest scientist can claim that either dualism or monism has been proven. He can only wait hopefully until he understands what the mind is. Sherrington expressed the matter this way, when writing a Foreword for The Integrative Action o] the Nervous System: "That our being," he said, "should consist of two fundamental elements offers, I suppose, no greater inherent improbability than that it should rest on one only." This is the scientist's attitude. Fritseh and Hitzig spoke of a "eentrum" through which the mind "entered the material structure and where it emerged from the same." Let me express such thinking in another way. There must be a special mechanism in the brain whose action corresponds with the activity of the mind. During deep sleep, there is no evidence of mind although life continues and certain reflexes are active, such as those of posture and respiration. A specific mechanism within the brain must have been switched off when he dropped asleep. One can only say that the mind is gone. When the mechanism switches on again, the man is said to waken and the mind is present. I t is "attached", as Aristotle expressed it. Clinical experience has shown us that no interference with the cerebral cortex, whether due to surgery, injury or disease, can quite banish the mind, but interference with the function of the higher brain-stem does banish it (Fig. 1). The coma that is produced is often like deep sleep. 6 Penfield,W. : The cerebral cortex of man. (With T. Rasmussen). New York: Macmillan 1950. Epilepsy and the functional anatomy of the human brain. {With H. Jasper). Boston: Little, Brown and Co. 1954. - - Speech and brain-mechanisms. {With L. Roberts). Princeton: Princeton University Press 1959. The brain's record of auditory and visual experience. A final summary. (With P. Perot). Brain 86, 595---696 {1963). Engrams in the human brain. Proe. roy. Soc. Med. 61, 831--840 {1968). Consciousness, memory and man's conditioned reflexes. In: On the Biology of Learning, ed. Karl H. Pribram. New York-Chicago-San Francisco-Atlanta: Harcourt, Brace & World 1969. Epilepsy, neurophysiology, and some brain mechanisms related to consciousness. In: Basic Mechanisms of the Epilepsies, ed. H. Jasper, A. A. Ward, and A. Pope. Boston: Little, Brown and Co. 1969. -

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Fig. 1. The darkly shaded brain-stem and cerebellum and the spinal cord are shown as they would appear if the hemispheres were removed. The "higher brain stem" may be understood to include the diencephalon, mesencephalon (midbrain) and probably upper portion of metencephalon (pons). The thalamus on each side and the ventrally placed hypothalamus are included in the diencephalon. (Penfield, W., Roberts, L., 1959)

Allow me to explain, very briefly, how an electrical stimulus operates - - whether it is applied b y the experimenter's electrode or when it is derived from a local epileptic irritation in gray matter. Gentle electrical stimulation of the cerebral cortex has two results: a) interference and b) activation. a) Interference with local ganglionic function is inevitably produced in the neighbourhood of the electrode. b) Active responses are produced only b y stimulation of those areas from which neuronal conduction can produce activation of a distant ganglionic station. Take the positive motor responses, for example. The areas where they can be produced are summarized b y a m a p in Fig. 2. If, for example, when the electrode is placed on the precentral convolution in the area Fritsch and Hitzig discovered, it produces m o v e m e n t of a m a n ' s right hand (or a dog's paw,) one must not j u m p to the conclusion that, normally, this is where the stream of nerve impulses begins during complicated voluntary use of the hand. I n m y Sherrington lecture, I analyzed our experience with electrical Stimulation of the h u m a n cortex% The final conclusion was t h a t positive responses to stimulation, when they appear at all, are "due to dromic 7

Penfield, W . :

Press 1958.

The excitable cortex of conscious man. Liverpool: University

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Fig. 2. Primary transmitting areas (sensory, stippled; motor, lined) and some secondary sensory and motor areas in the cortex of the left hemisphere as outlined by electrical stimulation. Parts of the mesial surfaces are shown. The temporal lobe is cut and turned down to expose its superior surface. Note the primary auditory sensation area on the transverse gyrus of Heschl. Stimulation of the normally buried insular cortex produces sensory and motor responses in the alimentary system, mouth to rectum. (Penfield, W., Roberts, L., 1959)

cortico-fugal c o n d u c t i o n " along axones. This is shown d i a g r a m a t i c a l l y in t h e b o x a t t h e far left in Fig. 3. T h e o t h e r boxes i n d i c a t e t h a t , from m o t o r areas, s t i m u l a t i o n gives rise to d r o m i c c o n d u c t i o n from t h e cortex outw a r d b u t , f r o m t h e o t h e r areas, t h e s t r e a m of a c t i v a t i n g impulses flows from t h e c o r t e x i n w a r d . Thus, s t i m u l a t i o n of a n y sensory a r e a o f c o r t e x p r o d u c e s a c t i v e responses in r e l a t e d nuclei o f diencephalic g r a y m a t t e r . A n d finally, s t i m u l a t i o n of t h e i n t e r p r e t i v e c o r t e x o f t h e t e m p o r a l lobes p r o d u c e s one of t w o t y p e s o f response b y a c t i v a t i n g one o f two s e c o n d a r y ganglionic s t a t i o n s a t a d i s t a n c e from t h e i n t e r p r e t i v e cortex. T h e r e are, then, t w o a d d i t i o n a l s e c o n d a r y s t a t i o n s whose l o c a t i o n is still to be identified. I will r e t u r n to this p r o b l e m in a m o m e n t . I f F r i t s c h a n d H i t z i g were here w i t h us t o d a y , t h e y w o u l d h a v e questions to ask. W e would show t h e m t h e m a p in Fig. 2 t h a t outlines t h e a r e a s o f c o r t e x t h a t give positive m o t o r or sensory response to cortical

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Fig. 3. Positive Responses: Stimulation (or epileptogenic discharge) interferes with the normal use of gray matter near the electrode. It produces active response only when the electrode is applied to one of those areas of cerebral cortex from which axonal conduction along a functional tract can activate some distant ganglionic station. This is suggested in the box at the far left. Positive cortical responses may be placed in three main groups: 1. Muscular movement; 2. sensation; 3. psychical responses. Psychical responses are of two chief types: a) Interpretive (illusion of perception) or b) experiential (play-back of the stream of consciousness). The mechanism of interpretation (perception) and the mechanism of recall of conscious experience have yet to be clearly localized

stimulation when the patient is fully conscious. We would explain t h a t when convolutions in front of the m o t o r gyrus or behind it are removed, stimulations of t h a t g y m s still produce m o v e m e n t s and the patient can still c a r r y t h e m out himself if he wishes. I n doing so, he can direct the m o v e m e n t s in accordance with the sensory information he is receiving t h r o u g h the visual, the a u d i t o r y and the somatic-sensory convolutions, provided these convolutions have n o t themselves been removed. This proves t h a t the sensory a n d the m o t o r convolutions are, in fact, interm e d i a r y stations, not end stations nor places of origin. T h e n we would show t h e m the drawing of a frontal transection of the h u m a n brain as illustrated in Fig. 4. I t is evident t h a t the p a t t e r n of impulses required for conscious discriminating use of the hand, in accordance with the sensory information available, m u s t be established after selective integration has taken place within and t h r o u g h the higher brain stem. A n d the message m u s t move out to the m o t o r cortex as indicated b y the broken lines. F u r t h e r support of this is f o u n d in the following simple observation t h a t H e r b e r t Jasper and I reported as a p a r t of the tribute to H a n s Berger, the founder of eleetroencephalography in 1949 s. 8 Jasper, H., Penfield, W.: Electrocortigograms in man. Arch. Psychiai. Nervenkr. 183, 163--174 (1949).

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Fig. 4. Bilateral motor-control system. The angulated frontal transection passes through the human brain as shown in the inset. Motor areas of cortex from leg to mouth are shown in the precentral gyrus. The ganglionic area in which epileptogenic discharge produces (grand rnal) generalized convulsion is suggested by the dotted zone. This, it may be concluded, is the general area from which, in normal circumstances, the patterned impulses come that produce voluntary motor activity

D u r i n g a r o u t i n e operation, m u l t i p l e recording electrodes were p l a c e d on t h e m o t o r g y r u s a n d elsewhere on t h e exposed cerebral c o r t e x of a p a t i e n t . H e was a s k e d to clench t h e o p p o s i t e fist w h e n he should h e a r a signal a n d to r e l a x i t w h e n he h e a r d a second signal. Thus, v o l u n t a r y n e u r o n a l impulses w o u l d replace t h e s t i m u l a t o r of F r i t s c h a n d H i t z i g a n d be recorded, we hoped, in J a s p e r ' s eleetrocorticograph. This p r o v e d to be t h e case. A t t h e t i m e when t h e m a n clenched his fist, a n d a g a i n w h e n he r e l a x e d his fist, t h e g r a p h showed t h e a r r i v a l o f electrieal p o t e n t i a l s a t t h e electrode resting on t h e h a n d a r e a of t h e m o t o r g y r u s a n d o n l y in t h a t electrode. N o change was r e c o r d e d elsewhere on t h a t g y r u s nor elsewhere o v e r t h e surface of t h e e x p o s e d cortex. This w o u l d prove t h e a r r i v a l o f a n electrical message f r o m deep w i t h i n t h e brain, i f a n y p r o o f were needed.

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The final integration t h a t precedes voluntary action must therefore take place in the higher brain stem. This integration m a y be called eentreneephalie 9. This word indicates only t h a t the essential p a r t of integration is carried out in centrally placed ganglionic circuits. Nothing more! The integration results in inhibition as well as activation. Volunt a r y activity is carried out in accordance with t h a t p a r t of the sensory input to which one pays attention. The selected data enter consciousness. The other information is ignored. During the patterning of the message, there m a y well be the conscious use of m e m o r y and of reason. This, then, is a special mechanism for the mind. I t is not a place. I t is a communicating system within the brain. This is the mechanism t h a t is switched off in sleep, as W. R. Hess has shown. I t is arrested b y brainstem injury. Although all parts of the cerebral cortex m a y make a contribution to its action when called upon, the essential p a r t of the mechanism is subeortical. This mechanism must be active if messages are to enter central integration and if they are to depart. I t is, as Hippocrates put it, "messenger to the mind." B u t there is more t h a n t h a t to the special mechanism of the mind. I t s action accompanies consciousness and, in it, a complete record or engram is preserved. Reference back to Fig. 3 shows t h a t there are psychical responses t h a t follow cortical stimulation a s well as those of movement and sensation. After speech is established in one side of the child's brain, or the other, stimulation of the speech areas produces only interferenceaphasia. This is a negative response. B u t stimulation of the remaining interpretive cortex, as mapped out in Fig. 5, can produce a positive response - - automatic recall of all t h a t passed through the individual's awareness in some previous strip of time. This includes the things seen and heard, and all t h a t was passing through the patient's mind at t h a t time. I f music is heard, it is only one occasion of hearing t h a t returns, not the generalized m e m o r y of a song. W h a t the patient ignored then, is absent now. W h a t he chose to p a y attention to, appears in consciousness again. This positive response, like the sensory and motor responses, must be produced b y activation of a secondary ganglionic station, as shown in Fig. 3. One m a y assume t h a t the secondary station is in the higher brainstem at a distance from the surgeon's electrode which was placed on the temporal cortex. The conclusion, in any case, is this : There is a specialized, partially-separable brain-mechanism whose action corresponds with what goes through the mind. There is, then, a continuous thread of facilitation t h a t runs through the mechanism, a thread of lowered resistance to passage of impulses. This facilitation is instantly established and permanent. Thus, it is quite 9 Penfield, W. : Centrencephalic integrating system. Brain 81, 231--234 (1958).

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/sensoPy

Fig. 5. Lateral surfaces of the posterior parts of both hemispheres of a human adult. On the dominant side, local interference-aphasia is produced by a stimulating electrode in the areas marked "speech." Active responses, produced by an electrode on other parts of this interpretive cortex, are of two types - - experiential or interpretive. The area marked "space orientation" on the nondominant side (right) was outlined by study of the results of cortical excision. Complete removal produces apraxia and agnosia in contradistinction to the aphasia produced by destruction of the homologous area on the dominant hemisphere

different in this respect from facilitation in the cerebral cortex which lasts only a few minutes 1°. So m u c h for electrode-activation of the mechanism t h a t corresponds with mind activity. The mechanism can be separately paralyzed too, not b y the electrode of Fritseh and Hitzig b u t b y the focal electrical discharge produced in an epileptogenic lesion in certain types of epilepsy. During an a t t a c k of petit real absence there is interference in the same w a y t h a t aphasia is produced during a discharge in gray m a t t e r of the speech mechanism. During the petit mal attack, only consciousness is gone a n d no m e m o r y record is made. F o r t h a t reason, Jasper and I have called the "petit real attacks centrencephalic seizures to indicate where t h a t g r a y m a t t e r is located in which the epileptogenic discharge is occurring. I n a temporal lobe seizure, a u t o m a t i s m m a y also be produced b y discharge arising in one amygdaloid area and spreading to central gray m a t t e r 11. This produces an absence of the mind t h a t m a y resemble t h a t seen in petit real. Something similar develops when a sleep-walker leaves his bed. I n the epileptic automatisms, the brain's mechanism of the mind is arrested, due to discharge in the gray m a t t e r of one of its ganglionic 10 Penfield, W., Welch, K.: Instability of response to stimulation of the sensorimotor cortex of man. J. Physiol. (Lend.) 109, 358---365 (1949). 11 Feindel, W., Penfield, W.: Localization of discharge in temporal lobe automatism. Arch. Neurol. Psychiat. (Chic.) 72, 605---630 (1954).

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stations in the higher brain-stem. I n sleep, the mechanism is somehow switched off b y a more normal process. Conclusion

Finally, the brain does function as an integrated whole in one sense. B u t there are semi-separable mechanisms within t h a t integration. We m u s t continue to study them. This is the way of progress t h a t was begun for us b y Fritsch and Hitzig, and Charcot and Jackson. As scientists, we should reserve judgment as to the ultimate nature of things. Meantime we can only use the language of dualism, and speak thus of the mind and the brain. There is no other medium of analytical discussion. The ancient riddle of how brain and mlnd do interact is still unsolved. But, we begin to understand the brain, f f n o t the mind. The mind receives messages. I t seems to direct brain action in the focussing of attention and in voluntary activity. There is a special mechanism for the mind. I t can be activated from a distance b y an electrode on the interpretive cortex. The mechanism is sometimes arrested b y epileptic discharge in centrally placed gray matter. During this activation, consciousness is not lost. During this arrest, consciousness is lost and since other mechanisms continue without control from the mind's mechanism, the individual becomes an automaton. Fritseh and Hitzig had stumbled upon the truth. The brain does function, as they said, b y "isolated mechanical means." And we can now perceive the outline of a further truth: The mind is matched b y a specific corresponding mechanism in the brain. H u m a n behaviour is determined b y interaction of brain and mind. W. Penfield, M.D. Honorary Consultant Montreal l~eurological Institute Montreal, Canada