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THEORIES OF BRAIN LOCALIZATION
FROM FLOURENS TO LASHLEY
by
BARBARA TIZARD
Introduction A history of theories of localization of function in the brain can be found
more or less briefly outlined in Boring (I929 and^ I950) and Lashley^ (I929).
Both writers point out that all such theories can be^ broadly divided^ into two
types-localization theories, which hold^ that^ specific functions^ are^ controlled
by specific parts of the brain, and^ field^ theories,^ which^ hold^ that the^ brain
acts as a single functional unit.^ It is^ said^ that,^ historically,^ a^ swing^ of the pen-
dulum tends to occur between these^ two^ positions. At^ one^ period^ the^ majority
of informed opinion holds^ a^ localization theory,^ but^ a^ generation^ later this
tends to be considered distinctly unorthodox.
Too much can be made of this^ distinction.^ Localization^ and^ field theories,^ as
defined above, have not^ been^ held^ since the^ time of Gall. The^ first^ achievement
of Flourens, usually regarded as^ the^ founder^ of field^ theory,^ was^ to^ show^ that
the different parts of^ the^ brain^ have^ specific functions:^ he claimed that^ only
the hemispheres act^ as^ a^ single functional^ unit.^ Later^ field theorists further
restricted this claim. Nevertheless, the distinction between localization theorists
and field theorists is broadly valid. The purpose of this article is to examine the
factors responsible for the 'swing of the pendulum', that is, for the development
and general acceptance of successive theories.
Two factors are shown to be important. The development of a new theory
of localization depends partly on the development of new and more refined
techniques of investigation, and partly on the nature of current psychological
preconceptions. This is because such a theory must involve assumptions about
psychological processes and brain function, and the^ models^ of^ brain^ function
are themselves determined by psychological preconceptions. In^ the^ past these
assumptions have been explicit. It is argued that the^ implicit assumptions of
contemporary localization theory could usefully be^ examined, and^ brought
into line with contemporary psychology.
L Flourens' Field Theory
Theories of localization of function^ can^ be^ traced back^ as^ far^ as^ Aristotle,
but the work of Pierre^ Flourens^ (1794-I867) was^ the first^ to^ be based^ on
experiment, and Flourens^ is^ today^ recognized^ as^ the^ founder^ of^ the^ modern
field theory of brain function.
He was undoubtedly a^ great physiologist. His^ experiments were^ systematic,
his observations were^ always^ repeated,^ and^ they^ were^ made^ on^ a^ number of
subjects. Using the methods of extirpation and^ stimulation^ he^ was^ the^ first
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Theories of Brain Localizationfrom Flourens to Lashley
to show experimentally that different parts of the nervous system have different
functions. He concluded that the function of the spinal cord is conduction, that movement is controlled by the cerebellum, the vital functions by the medulla, and perception, memory, and will by the hemispheres. In 1824 he put forward the first scientifically based theory of equipotentiality
within the hemispheres.
All sensations, all perceptions, and all volition occupy concurrently the same seat in these organs. The faculty of sensation, perception, and volition is then essentially one faculty.
He was the first to (^) state the principles of (^) equivalence of structure and (^) of mass action.
As long as not too much of the lobes is removed, they may in due time regain the exercise of their functions. Passing certain limits, however, the animal regains them only imperfectly, and passing these new limits it does not regain them at all. Finally, if one sensation comes back, all come back. If one faculty reappears, they all reappear.... This shows that each of these organs is only a single organ.
Again, like later field theorists, he emphasized the integration of the nervous
system.
In (^) the last analysis ... all the essential and various parts of the nervous system have specific properties, proper functions, distinct effects, and^ in^ spite of^ this marvellous^ diversity they constitute nevertheless a^ unified system. When one point in the^ nervous^ system becomes excited, it excites all others; one point irritated, irritates all. There is^ community of reaction. Unity is the great reigning principle (Flourens, 1824).
All this, of course, constitutes a field theory of brain function more thorough-
going than any held since. No one today would be prepared to support the
proposition that there is no localization of sensory function in the cortex, and
that 'if one (sense) comes back, all come back'. Indeed, as will be shown,
there was a good deal of evidence to the contrary available at^ the^ time. Never-
theless, Flourens' theories were at once generally accepted and remained
orthodox doctrine for over forty years. There were two^ important reasons for
this. Firstly, the techniques of stimulation and extirpation were too crudely
developed to reveal much localization of function, and the^ knowledge of^ neuro-
anatomy then available too limited. The only parts of the brain^ distinguished
were medulla, corpora quadrigemina, cerebellum, and^ the^ hemispheres; it was not known in^ what way, if^ any, grey and white^ matter^ differed^ in^ function.
In the following experiment, for^ example, on^ which^ Flourens^ based his^ principle
of equipotentiality, it is certain that he must have extirpated more than the
hemispheres, and that^ septic and oedematous^ processes must^ have^ resulted^ in
generalized damage of an unknown extent. He removed, 'layer by layer',
different parts of both cerebral lobes of a pigeon, and found that^ the^ animal's
sight weakened with^ each^ new^ extirpation until it^ was^ totally lost, and that
'from the moment that sight was gone, hearing was gone too; and with it went
all intellectual and sensory faculties'.
'
Theories ofBrain Localizationfrom Flourens to Lashley
anatomist, phrenology was as speculative a doctrine as the orthodox theory of
the sensorium. It had tremendous popular appeal but it was bitterly attacked
by most scientists and philosophers as irreverent and materialistic because
incompatible with the concept of brain as a sensorium. Flourens' work was
hailed as a convincing experimental refutation of this heresy, and a validation
of orthodox concepts.
Consequently the observations that were incompatible with equipotentiality
of the cortex were disregarded. Bell (I 774-I842) had argued that the fact that
separate nerve tracts lead to separate parts of the cortex indicates that these
have distinct functions. It was pointed out by some that the insane (^) are not
usually blind and deaf. The experiments of Fransois Pourfour de Petit were
forgotten. This eighteenth-century French surgeon had adduced strong evidence
that the control of movements of one side of the body is localized in the hemi-
sphere of the other side. Contralateral hemiplegia was at the time ascribed to
loss of fluid from the contralateral ventricle, which moved into the wounded
ventricle to replace its lost fluid, with a resultant loss of power on the contra-
lateral side. Petit opened the skull of an officer who had died from a rapier
thrust beneath his right orbit, and who before death had sustained a complete
left hemiplegia; he found pus pouring from a right anterior abscess, but nothing
amiss in either ventricle. After a number of similar post-mortem observations
he decided to operate on dogs, destroying various parts of their brain through
a trephine hole, noting their loss of power, and then examining their brains.
He observed^ that^ paralysis of the opposite side always ensued, and dissection
led him to the discovery of the decussation of the pyramids (Rawson, I927).
III. A new concept of brain
It has been argued above that, for an empirically based theory of specificity
to develop, more refined techniques would be needed than were available to
Flourens, and, for such a theory to be generally accepted, the orthodox concept
of brain would have to be abandoned. The latter change occurred first. The
essential preliminary to the more detailed assumptions of localization theory
was an attempt to account for the workings of the nervous system in purely
physical terms. The earlier semi-scholastic conception ofthe brain as a sensorium
where mind interacted with body, the nerves being passive conductors of animal
spirits, was replaced by an explicit determination to 'constitute physiology on a
chemico-physical foundation' (Helmholtz, I847, quoted in Boring). In I
du Bois Reymond demonstrated the electrical nature of the nervous impulse
and in^ I850 Helmholtz measured its speed. During the next decade reaction
times began to^ be measured. No wonder that Muller hesitated to accept these
discoveries with their implication that the nervous system is wholly orderly and
physical.
During this period, too, it was discovered that the grey matter of the brain
is cellular, that the white matter is fibrous, and that the fibres begin and end
in the grey cells. The contemporary model of the brain, based on these
observations and the new (^) preconceptions, is described (^) by the (^) psychologist,
'
Barbara (^) Tizard
Alexander Bain (I8I8-I903), in his book, The Senses and the Intellect, I855. He
states in his (^) preface:
Conceiving that the time has now come when many of the startling discoveries of Physiolo- gists relative to the nervous system should find a recognised place in the Science of Mind, I have devoted a separate chapter to the Physiology of the Brain and Nerves.
In this chapter he compares the nervous system to a telegraph system, with
a general terminus, the brain, from which wires proceed to (^) substations, from
which further wires proceed. The function of the nerves is solely to transmit
impulses. The brain is also compared to a voltaic battery.
The brain is not a sensorium where impressions are poured in and stored up. A stimulus or sensation acting on the brain exhausts itself in the production of a number of transmitted currents or influences.... The revival of the impression is the setting of the currents anew.... No currents, no mind (Bain, 1855).
Later, he expounds Flourens' doctrine of equipotentiality, combining this
with the concept of the brain as a voltaic cell. Nevertheless, the change in
attitude to cerebral functioning which was essential for a revision of Flourens'
doctrine had occurred. 'No currents, no mind' is an assumption of startlingly
materialist implications, compared with Muller's theory of twenty years earlier.
IV. The era of localization theory
The first outright opponent of the principle of homogeneity was Broca
(I824-80). It is interesting that Broca was a pupil of Bouillaud, Professor of
Clinical Medicine at La Charite, one of the few academic champions of
phrenology. Bouillant had offered a sum ofmoney to anyone who could produce
the brain of an individual who had lost his speech, and in whom the anterior
lobes presented no lesions. Broca found at the autopsy of a man whom he had
recently examined and discovered to have no defect except inability to speak,
a lesion at the base of the third frontal convolution of the left hemisphere. He
announced in^ i86i^ that this^ was the^ centre for speech, and drew broader
conclusions.
I believe in the principle of localisation ... the totality of the convolutions does not con- stitute a single organ, but many organs or many groups oforgans, and there are in the cerebrum large discrete regions corresponding to large discrete mental functions (Broca, I86i).
This (^) generalization was based on rather (^) inadequate evidence, since, as Marie
showed later, of Broca's two original patients one had further lesions involving
Wernicke's zone, and the second had a generalized cerebral wasting. He does
not seem to have developed a theory significantly different from Gall's, and he
would probably have attracted little attention had the (^) opposition to Flourens not then become general. I
Barbara (^) Tizard
the hypothesis of circumscribed centres for special functions is^ untenable,^ and that^ there^ is no area of the cortex exclusively concerned with sight, hearing, smell, taste,^ touch^ ... or the higher fimctions.
V. The assumptions of nineteenth-century localization theory
Goltz, however, was in an^ unpopular minority,^ and^ it^ seems^ reasonable^ to
conclude that the physiologists of^ the^ last^ quarter of^ the^ nineteenth^ century
interpreted their^ results as^ indicating^ the^ existence^ of^ local centres because^ of a
prior conviction about the nature of the^ brain.^ An^ analytic trend^ was^ general
in scientific thought^ at^ that time.^ The^ cell^ theory,^ originated^ by^ Schleiden,^ was
developed by Virchow, Professor^ of^ Anatomy in Berlin.^ In I858^ he^ suggested
that a^ disease^ originates within^ a^ single^ cell, and is propagated^ by^ malignant cell formation.
Every animal [he wrote] is a^ sum of vital units, each^ of^ which^ possesses^ the^ full^ charac- teristics of life.... The composition of the major organism, the so-called individual,^ must^ be likened to a kind ofsocial arrangement or society, in^ which a^ number of^ separate^ existences^ are dependent upon one another, in such a^ way, however, that^ each individual^ possesses its^ own peculiar activity and carries out its own powers (Virchow, 1858).
This emphasis on the discrete and diverse functions of the cells was echoed by
the contemporary stress in psychology on the elementary particles of thought-
ideas. Mental processes were almost universally understood at this time in
terms of more and more complex associations of elementary ideas. The aim of
Associationism, in fact, was
to construct a^ psychology without^ a^ soul,^ by^ taking^ discrete^ ideas,^ and^ showing^ how,^ by^ their cohesions, such things as reminiscences, perceptions, emotions, volitions,^ passions,^ theories, and all the other furnishings of^ an^ individual's^ mind^ can^ be^ engendered^ (James,^ I891).
Hence the assumption by physiologists that they should look for the elementary
structures of the brain corresponding to its elementary functions.
The hypothesis generally held in the 'seventies, then, long before there was
much evidence to substantiate it, was that^ the^ cortex^ is^ the^ surface of^ projection
for every muscle and every sensitive^ point in^ the^ body. These different cortical
cells were held to represent the^ elementary ideas of sensation and motion^ of
which all mental^ processes are^ composed.^ The fibres between^ the cells^ represent
the association between^ ideas, hence there^ was^ thought^ to^ be^ a^ complete^ and
neat parallelism between^ brain processes^ and^ mental^ processes.
It is^ important^ to^ note^ the difference between^ the^ localization theory^ held
by physiologists of^ this^ period and^ the older^ phrenologists.^ The difference
depends on the development in the assumptions about^ mind^ and^ brain described
above. The later localizers held^ that^ elementary motor^ and^ sensory^ functions
were localized, but^ not^ the^ higher mental^ functions,^ still less^ traits^ such^ as
'hopefulness'. Some,^ for^ example,^ Ferrier,^ argued^ on^ mainly^ deductive^ grounds
that intelligence is dependent on the frontal^ lobes.^ Psychology, the^ argument
I
Theories of Brain Localization from Flourens to Lashley
ran, has shown that all the higher thought processes can be explained in terms
of the association of ideas, together with the power of attention. Intellectual
attention involves implicit head and eye movements, and hence depends on
the frontal lobes, which Ferrier had shown to be the centre for these movements
(i886).
Other physiologists, unable to confirm Ferrier's experimental findings,
adapted different theories. Munk, for example, argued that
intelligence has its seat everywhere in the cortex of the brain (^) and in no part in particular. Any lesion of the cerebral cortex whatsoever alters (^) intelligence, all (^) the more severely the more extensive the lesion, and this is (^) always due to the loss of its groups of images or representations, simple or complex, which had their (^) foundations in (^) the perceptions that belong to the injured cortical area (Munk, (^) -1890).
Thus, experimental observations similar to Flourens'-that intelligence does
not depend on any one part of the brain, and that the greater the lesion, the
greater the mental loss-were differently interpreted because of Munk's
different preconceptions about the brain and mental functioning. Instead of
concluding, like Flourens, that 'the faculties of perceiving, understanding, and
willing constitute a single function', he claimed that intelligence results from
co-ordination of a great many differently located elementary functions. Here
is a particularly clear illustration of the way in which assumptions about mental
processes have influenced the interpretation of findings in this field.
Later, however, it came to be generally accepted that the frontal lobes and
certain posterior parts of the brain were 'silent', and not projection areas. In
these areas the higher mental processes were said to be localized. Flechsig, the
originator of this theory, considered that the function of these areas was to
associate together the impressions received from the adjacent sensory and motor
areas. The frontal lobes, for example, lying between the olfactory and tactile
areas, combined the perceptions and memory traces of these areas. Flechsig was
primarily an anatomist, and the experimental investigation of the theory was
mainly the work of Bianchi, the last of this great school of physiologists. He
argued that
intelligence emanates from the (^) play of (^) sensory images ... and of infinite combinations of these and other images not sensory in character. I believe it is (^) permissible to (^) suppose that this vast co-ordination... has its seat in an (^) organ distinct from the organs of (^) perception (Bianchi, I922).
This organ he located in the frontal lobes, which until very recently have
continued to hold this (^) distinction. There was no question at (^) any time (^) during this
period, however, of a specific localization of traits akin to phrenology. Such a
doctrine was quite inconsistent with Associationist psychology, which held that
any complex function was the result of an interaction between many simple
functions, localized in various parts of the brain.
The influence of psychology on physiology at this period was remarkable.
Observations were scanty, and the main (^) emphasis in (^) discussing residual defect
'
Theories ofBrain Localizationfrom Flourens to Lashley
trials as the first learning. He performed control experiments, cutting the dura mater only, excising only one frontal lobe, and excising other lobes of the
brain (Franz, I907). The basic advances in methodology had been made-
that is, the use ofobjective tests that could be quantitatively scored, the procedure
of training, operating, then retraining, and the use of experimental control. To these Lashley (I929) added the use of enough animals to allow for statistical
analysis of results, and the attempt to assess the extent of lesion by post-mortem
examination.
Running fifty rats through mazes before and after cortical lesion, Lashley
found that the amount of impairment was roughly proportional to the extent
of cerebral lesion, and that the same amount of impairment in maze learning
is produced by equal amounts of destruction in any of the^ principal^ regions of
the cortex. From these observations he deduced first the Principle of Equipo-
tentiality, that the rat's cortex functions as a unit in maze learning and no one
part of it has special significance, and, secondly, the Law of Mass Action, that
the more cortex is available, the more rapid and accurate the learning. The
degree of deterioration after injury is closely related to the complexity of the
maze. These principles closely resemble Flourens', but Lashley restricted^ their
application. Not every habit in the^ rat^ is^ governed^ by these^ principles. Brightness
discrimination was disturbed only by lesions of the visual^ cortex, and^ he^ con-
cluded that it is only the more^ complex^ functions which^ are^ not^ localized.^ He
rejected the suggestion that his results might be due to the statistical effects of
different sensory losses, and insisted^ that 'the^ more^ complex^ functions^ ...^ are
largely carried^ out^ in^ independence^ of^ structural^ differentiation'^ (I929).
Lashley's findings met^ with^ a^ rather^ uncritical^ acceptance,^ at^ least^ among
psychologists. Hunter and Pavlov, however, suggested a different interpretation
of his results. There is, they pointed out, a good deal of evidence that maze
learning is dependent on sensory cues. Ifone sensory centre were destroyed, the
rat would utilize cues from another, so that, whilst no one lesion would destroy
the habit, it would be diminished roughly in proportion to the amount of
cerebral tissue destroyed, as fewer sensory cues were available (Hunter, I930;
Pavlov, I 94 I).
Lashley supported his conclusion that maze learning is dependent on some
unitary function ofthe cortex rather than on sensory cues by control experiments.
He showed that learning is unaffected by section of the kinaesthetic paths, by
enucleation of the eyes, or by removal of the occipital cortex from rats^ already
blinded before training. The evidence here is, however, conflicting. Other
experiments have shown that lesions of the dorsal spinal tracts^ have^ little effect
on behaviour cued to proprioceptive stimulation, which^ they argue are^ routed
round the lesion (Ghiselli, I936; Brown, I942). Finley (1941) removed^ about
I0 per cent of the rat's cortex, keeping within the striate area, and found that
in the dark these rats learnt mazes as well as normal rats, presumably by other
cues. Pickett (I942) trained blind^ rats^ in^ a^ kinaesthetic^ maze, and^ found^ that,
whilst anterior lesions produced some loss ofthe habit, there was little deteriora-
tion following striate lesions. These conflicting results cannot be reconciled
I4I
Barbara (^) Tizard
without further experiment, but it is clear that different hypotheses can be put
forward to^ account^ for the^ findings^ on^ which Lashley based his^ principles of
equipotentiality and^ mass^ action.
VII. Lashley's^ assumptions
There can be little doubt that Lashley, like his predecessors, was influenced
both in designing and interpreting his experiments by his prior conception of
brain action. He explicitly rejected the reflex, analytic model of the^ brain,
built up in the last half of the nineteenth century. He^ denied that^ integration
can be expressed in terms ofconnexions between specific^ neurones,^ and asserted
that brain function is not a summation ofdiverse functions, but^ a^ non-specialized
dynamic function of the tissue as a whole. He offered a^ tentative^ theory^ of brain
action, based on potential differences. A given ratio of^ stimulus intensities^ at
two peripheral points may, he suggested, establish^ a^ potential^ difference
between two corresponding areas in the cortex, resulting in a^ polarization^ of
the cortical field, essentially the same for different points within^ the^ areas.^ The
excitability of the final motor path would depend on^ the relative^ excitability
of the two areas (Lashley, I929).
This was the first attempt to give a physiological content^ to the^ principle^ of
'action commune'. Lashley was the first psychologist working with^ problems^ of
brain damage to interpret cortical dynamics in^ terms^ of^ field^ theory,^ and^ to
abandon Associationism.
In this he was largely influenced by Gestalt^ psychology.^ Wertheimer,^ the
founder ofGestalt psychology, had made an^ attack^ in^1912 on^ what^ he^ considered
the fundamental scientific assumption^ of^ his^ day,^ that^ scientific^ method^ must
be analytic. He argued that^ the^ scientists^ should^ not^ proceed^ by^ dividing^ a
whole into its elements, and^ discovering^ the laws^ of the^ elements.^ Instead,^ he
stated:
There are wholes, the behaviour of which is not determined by^ that of^ their^ individual elements, but the part-processes are themselves determined by the intinsic^ nature^ of the whole (Ellis, 1938).
Hence it is useless to study the^ elements,^ since the^ properties^ of^ the^ whole^ are
'emergent' and do not inhere^ in the^ parts.^ The^ organization^ of^ the^ whole^ was
described by the Gestalt school^ in terms^ offield^ forces,^ by^ analogy with^ magnetic
and electrical fields. The^ principle^ of^ Isomorphism^ was^ also^ enunciated,^ that the form of brain^ events^ is similar^ to^ the^ form^ of mental events, and^ should^ be
studied by the same principles.
Gestalt psychology, therefore, implied not only a^ rejection of^ Associationist
psychology, but also of the nineteenth-century theory^ of brain action.^ It^ is
significant that^ Lashley^ advanced only^ psychological^ evidence^ against^ the
doctrine of localization of function-his own experiments, Gestalt^ experiments
on perception, and clinical data. Just as Ferrier^ and^ his^ contemporaries^ had
quite consciously looked in^ the brain^ for the^ structural^ basis^ of^ association,^ so
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Barbara (^) Tizard
distinct structural unit, because of structural or axonographic characteristics, mediates a distinct function whose nature can be revealed by stimulation, or
the effects of clinical or experimental ablation, or preferably both. The effect of
these two sets of assumptions amounts to an implicit doctrine of psychic centres, the mapping out of psychological entities on the cortex. In other words, Associationism has been discarded in favour oftrait-analysis, but the^ nineteenth- century model of the brain has been retained. Fulton, for example, has argued that the lessening of aggression after cingulectomy reveals the^ localization^ of
'emotional expression' in the 'visceral brain'. Neurosurgeons have attempted to
alter personality in specific ways by lesions of specific parts of^ the^ frontal lobes. This is, however, physiological and psychological evidence that the classical model of the brain as an organ of independent centres controlling different functions is inadequate. Large areas of the brain appear to be implicated in most psychological functions (Meyer, I956; Tizard, 1958). The psychological
entities which have been so readily localized (for example, ability to abstract,
arithmetical ability) probably involve many complex processes which may be
differentially impaired. These changing assumptions should be reflected in the
field of brain physiology, where, as in the past, they can be expected to lead
to new departures in research.
REFERENCES BAIN, A. (^) (i855), The^ Senses and the^ Intellect, London. BIANCHI, L. (1922), The Mechanism of the Brain and the Function^ of^ the Frontal^ Lobes, Edinburgh. BORING, E. G. (1929), A History of Experimental Psychology, New York. BROCA, C. (i86i), Bull. Soc. anat., 2me ser., 6, 330-57. BROWN, C. W. (1942), 'Spinal lesions and distance discrimination', J.^ comp.^ Psychol., 33, 305-14. ELLIS, W. D., ed. (I938), A Source Book of Gestalt Psychology, New York. FERRIER, D. (I876), The Functions of the Brain, London. Ist. ed. FERRIER, D. (I886), The Functions of the Brain. London. 2nd. ed. FINLEY, C. B. (^) (i94i), 'Equivalent losses in accuracy of response after central and after peripheral sense deprivation,'. comp. Neurol., 74, 203-37. FLOURENS, P. (I824), 'Exprimental Researches on the properties and functions of the nervous system in the vertebrate animal'. Trans. Wayne Dennis (I948), Readings in the History of Experimental Psychology. FRANZ, S. I.^ (1907), 'On^ the^ functions^ of^ the^ cerebrum;^ the^ frontal^ lobes',^ Arch.^ Psychol., N.Y., I, I-64. GHISELLI, E. E. (1936), 'The effects of lesions in the spinal cord on the ability of^ the^ rat to discriminate differences in inclined planes', J. comp. Psychol., 22, 319. GOLTZ, F. (I882), Abstract in Brain, 4, (^) 554. HUNTER, W. S. (1930), 'A Consideration of^ Lashley's theory of the^ equipotentiality of cerebral action', J. gen. Psychol. 3, 455-68. JAMES, W. (I89I), The^ Principles of Psychology, London. LASHLEY, K.^ S.^ (I929), Brain^ Mechanisms^ and^ Intelligence,^ Chicago. MEYER, V. (1957), 'Critique of Psychological Approaches to Brain Damage', J. ment.^ Sci., I03, 80-I 0. '
Theories of Brain Localizationfrom Flourens to Lashley MULLER, J. (^) (1838), Elements of Physiology. Trans. W. Baly, London. MUNK, H. (I890), Ueber die Functionen der Grosserhirnrinde. PAVLOV, I. P. (^) (i94i), Lectures on Conditioned (^) Reflexes, vol. II, London. PICKETT, J. M. (1952), 'Non-equipotential cortical function in maze learning', Amer. (^) J. Psychol., 65, 177. RAWSON, N. R. (1927), 'Early Steps in Cerebral localisation', Newcastle med. J. reprint. TIZARD, B. (1958), 'The Psychological Effects of Frontal Lesions,' Acta Psychiat. Neurol. Scand., 33, 232-50. VIRCHOW, R. (^) (I858), Cellular-pathologie, Berlin.
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