Despite these early views, the doctrine of functional localization proper -- the notion that specific mental processes are correlated with discrete regions of the brain -- and the attempt to establish localization by means of empirical observation were essentially 19th century achievements. The first critical steps toward those ends can be traced to the work of Franz Josef Gall (1758- 1828).
Gall [see figure 13] was born in Baden and studied medicine at Strasbourg and Vienna, where he received his degree in 1785. Impressed as a child by apparent correlations between unusual talents in his friends and striking variations in facial or cranial appearance, Gall set out to evolve a new cranioscopic method of localizing mental faculties. His first public lectures on cranioscopy date from around 1796. Unfortunately, his lectures almost immediately aroused opposition on the grounds of his presumed materialism, and in 1805, he was forced to leave Vienna. After two years of travel, he arrived in Paris accompanied by his colleague, Johann Gaspar Spurzheim (1776-1832). In 1810, Gall and Spurzheim published the first volume of the Anatomie et physiologie du système nerveux en général , Gall's most important contribution to neuroanatomy and the first major statement of his cranioscopy.
The essence of Gall's method of localization lay in correlating variations in character with variations in external craniological signs. The validity of this approach depended on three critical assumptions: that the size and shape of the cranium reflected the size and shape of the underlying portions of the cerebrum, that mental abilities were innate and fixed, and that the relative level of development of an innate ability was a reflection of the inherited size of its cerebral organ. On these assumptions, an observed correlation between a particularly well-developed ability and a particularly prominent area of the cranium could be interpreted as evidence of the functional localization of that ability in the correlative portion of the cerebrum.
While Gall's correlational approach was eventually abandoned in favor of experiment, his conception of fixed, innate faculties replaced by a dynamic, evolutionary view of mental development, and his pivotal assumption concerning the relationship of brain to cranial conformation rejected, it would be a serious error to underestimate his importance in the history of functional localization. Gall's assumptions may have been flawed and his followers may have taken his ideas to dogmatic extremes; but there was nothing wrong with his scientific logic or with the rigorous empiricism of his attempt to correlate observable talents with what he believed to be observable indices of the brain.
Indeed, it was Gall who lay the foundations for the biologically based, functional psychology that was soon to follow. In postulating a set of innate, mental traits inherited through the form of the cerebral organ, he moved away from the extreme tabula rasa view of sensationalists such as Condillac [see 30]. For the normative and exclusively intellectual faculties of the sensationalists, Gall attempted to substitute faculties defined in terms of everyday activities of daily life that were adaptive in the surrounding environment and that varied among individuals and between species. For speculation concerning both the classification of functions and appropriate anatomical units, he substituted objective observation.
Even Gall's most persistent opponent, Marie-Jean-Pierre Flourens (1794- 1867), was willing to admit that it was Gall who, by virtue of marshalling detailed evidence of correlation between variation in function and presumed variation in the brain, first fully established the view that brain serves as the organ of mind. In almost all other respects, however, Flourens was highly critical of Gall. Something of a child prodigy, Flourens enrolled at the famed Faculté de Médecine at Montpellier when he was only 15 years old and received his medical degree before he had turned 20. Shortly thereafter, while Gall was at the height of his career in Paris, Flourens himself moved to the capital. On the basis of his 1824 Recherches expérimentales sur les propriétés et les fonctions du système nerveux , he was elected to membership and eventually to the office of Perpetual Secretary of the Académie des Sciences, rising to become one of France's most influential scientific figures.
In Recherches expérimentales [see figure 14], Flourens provided the first experimental demonstration of localization of function in the brain. While previous researchers had lesioned the brain through a trephined aperture that made it impossible to localize damage or to track hemorrhage with any accuracy, Flourens completely uncovered and isolated that portion of the brain to be removed. Taking care to minimize operative trauma and post- operative complications, he employed ablation to localize a motor center in the medulla oblongata and stability and motor coordination in the cerebellum. Although his treatment of sensation was still rather confused in 1824, by the time the second edition of the Recherches expérimentales (1842) appeared, Flourens had articulated a clear distinction between sensation and perception (treating perception as the appreciation of the meaning of a sensation) and localized sensory function in several related sub-cortical structures.
With respect to the cerebrum, however, the results were quite different. A successive slicing through the hemispheres produced diffuse damage to all of the higher mental functions -- to perception, intellect, and will -- with the amount of damage varying only with the extent and not the location of the lesion. If adequate tissue remained, function might be restored; but total ablation led to a permanent loss of function. From these results, Flourens concluded that while sensory-motor functions are differentiated and localized sub-cortically, higher mental functions such as perception, volition, and intellect are spread throughout the cerebrum, operating together as a single factor with the entire cerebrum functioning in a unitary fashion as their "exclusive seat."
Unfortunately, however, as Gall (1822/1825) himself observed, Flourens's procedure "mutilates all the organs at once, weakens them all, extirpates them all at the same time" (ENG: VI, pp. 165-166). Ablation by successive slices was not a method well suited to the discovery of cortical localization. Joined to a strongly held philosophical belief in a unitary soul and an indivisible mind and an uncritical willingness to generalize results from lower organisms to humans, Flourens's results led him to attack Gall's efforts at localization and to formulate a theory of cerebral homogeneity that, in effect, anticipated Lashley's (1929) much later concept of mass-action and cortical equipotentiality. Having extended the sensory-motor distinction up the neuraxis from the spinal roots of Bell and Magendie [see 33], Flourens stopped short of the cerebral hemispheres. From his perspective, the cerebrum was the organ of a unitary mind, and, by implication, it could not therefore be functionally differentiated.
Before the cortex could come to be construed in sensory-motor terms, the intellectual ground had to be prepared and the technical means developed. The intellectual requirements for this achievement involved the abandonment of a fixed faculty approach to mind in favor of a balanced sensory-motor, evolutionary associationism and an appreciation of the functional implications of brain disease. The technical requirement was the development of a technique for electrical exploration of the surface of the cortex. The intellectual advances came through the respective psychologies of Alexander Bain and Herbert Spencer and the neuropathological discoveries of Pierre Paul Broca. The technical advance, involving development and use of electrical stimulation, was first employed by Gustav Fritsch and Eduard Hitzig.
Alexander Bain (1818-1903) [see figure 15] was born, educated, and died in Aberdeen, Scotland. After receiving the M.A. degree from Marischal College in 1840, he joined the faculty in mental and moral philosophy. In 1860 he was elected to the chair of logic at the newly created University of Aberdeen where he remained until his retirement. During these years, Bain wrote a rarely read but interesting critique of phrenology, On the Study of Character, Including an Estimate of Phrenology (1861), and a valuable survey of mind/body views, Mind and Body. The Theories of Their Relation (1873). It is, however, to his general psychology that we must look for his most important contribution to the intellectual climate from which the first specific demonstrations of the cortical localization of sensory-motor function arose. This contribution consisted of the sensory-motor associationism which he worked out in The Senses and the Intellect and The Emotions and the Will , first published in 1855 and 1859 respectively and revised in four editions through 1894/1899.
Bain's work marked a turning point in the history of associationist psychology. Before Bain, the associationists' empiricist commitment to experience as the primary or only source of knowledge [see 27-30] led to the neglect of movement and action in favor of the analysis of sensation. Even when motion was explicitly included in associationist accounts, as for example in the case of Thomas Brown [see 34], it was the sensory side of movement, the "muscle sense," rather than adaptive action that claimed attention. Bain, drawing heavily on Müller [see 38], brought the new physiology of movement into conjunction with an associationist account of mind. As Young (1970) has summarized Bain's view:
"'Action is a more intimate and inseparable property of our constitution than any of our sensations, and in fact enters as a component part into every one of the senses, giving them the character of compounds ...' (Bain, 1868, p. 59) ... Spontaneous movements are a feature of nervous activity prior to and independent of sensations. The acquired linkages of spontaneous movements with the pleasure and pains consequent upon them, educate the organism so that its formerly random movements ... (are) adapted to ends or purposes. Bain defines volition as this compound of spontaneous movements and feelings. The coordination of motor impulses into definite purposive movements results from the association of ideas with them" (p. 115).
Within association psychology, these were revolutionary ideas. Together with the evolutionary conceptions of Spencer, they paved the way for the later functionalist psychology of adaptive behavior; and, as we shall see, they provided the intellectual context for a sensory-motor account of the physiological basis of higher mental functions. Ironically, however, this was a step that Bain himself was completely unable to take. Impressed, as those before him had been, with the lack of irritability exhibited by the cortex when pricked or cut, Bain drew the traditionally sharp distinction "between the hemispheres and the whole of the ganglia and centres lying beneath them" (pp. 53-54). Whatever the function of the cerebrum, it was clear to Bain that it could not be sensory-motor.
In 1855, the same year in which Bain published The Senses and the Intellect, another even more revolutionary work appeared in England. The Principles of Psychology  by Herbert Spencer (1820-1903) offered students of the brain an evolutionary associationism and a related concept of cerebral localization that gave impetus and direction to the work of John Hughlings Jackson and through Jackson to that of David Ferrier.
Spencer [see figure 16] was born in Derby, England and was largely self- taught. At the age of 17, he took up railway engineering but left that occupation in 1848 to work first as an editor and then as a free-lance writer and reviewer. In An Autobiography (1904), Spencer tells us that, at age 11 or 12, he attended lectures by Spurzheim that for many years made him a believer in phrenology. Indeed, as late as 1846, before his growing scepticism regarding phrenology led him to abandon the project, Spencer had designed a cephalograph [see figure 17] for the purpose of achieving more reliable cranial measurement.
In 1850, as a result of a burgeoning friendship with George Henry Lewes, Spencer began to read Lewes's A Biographical History of Philosophy (1845/1846). Within a short time, he found himself so absorbed in the topic that he decided to make a contribution of his own to philosophy in the form of an introduction to psychology. In 1855, Spencer's Principles of Psychology appeared. It is a complex and difficult book, hardly an introduction to the topic; and, like Bain's The Senses and the Intellect, it too marked a turning point in the history of psychology. While Bain had married movement to the sensations of associationism and arrived at the first fully balanced sensory- motor associational view, Spencer went even further and grounded psychology in evolutionary biology.
In particular, Spencer stressed three basic evolutionary principles that transformed his view of mind and brain into one to which the cortical localization of function was a simple logical corollary. In so doing, he lay the groundwork for Hughlings Jackson's evolutionary conception of the nervous system and extension of the sensory-motor organizational hypothesis to the cerebrum. Spencer's key principles were adaptation, continuity, and development.
Like Gall, Spencer viewed psychology as a biological science of adaptation. "All those activities, bodily and mental, which constitute our ordinary idea of life ... (as well as) those processes of growth by which the organism is brought into general fitness for those activities" (p. 375) consist simply of "the continuous adjustment of internal relations to external relations" (p. 374). Neither the associations among internal ideas, for example, nor the relations among external events, but the increasing adjustment of inner to outer relations must lie at the heart of psychology. Indeed, for Spencer, mental phenomena are defined as adaptations, "incidents of the correspondence between the organism and its environment" (p. 584).
Like adaptation, continuity and development were also focal ideas for Spencer. Development consists of a change from homogeneity to heterogeneity, from relative unity and indivisibility to differentiation and complexity. According to the principle of continuity, life and its circumstances exist at all levels of complexity and correspondence. The level of life varies continuously with the degree of correspondence; no radical demarcations separate one level from the next. Thus, mental and physical life are simply species of life in general, and that which we call mind evolves continuously from physical life -- reflexes from irritations, instincts from compounded reflexes, and conscious life and higher mental processes from instincts -- co-existing at varied levels of complexity.
The implications of these evolutionary conceptions for the hypothesis of cortical localization of function are clear. The brain is the most highly developed physical system we know and the cortex is the most developed level of the brain. As such, it must be heterogeneous, differentiated, and complex. Furthermore, if the cortex is a continuous development from sub- cortical structures, the sensory-motor principles that govern sub-cortical localization must hold in the cortex as well. Finally, if higher mental processes are the end product of a continuous process of development from the simplest irritation through reflexes and instincts, there is no justification for drawing a sharp distinction between mind and body. The mind/body dichotomy that for two centuries had supported the notion that the cerebrum, functioning as the seat of higher mental processes, must function according to principles radically different from those descriptive of sub-cerebral nervous function, had to be abandoned.
While these ideas were to be worked out more fully by Hughlings Jackson, it is quite clear that even in 1855 Spencer was well aware of the implications of his concepts of continuity and development for cerebral localization. In the Principles, he wrote that "no physiologist who calmly considers the question in connection with the general truths of his science, can long resist the conviction that different parts of the cerebrum subserve different kinds of mental action. Localization of function is the law of all organization whatever ... every bundle of nerve-fibres and every ganglion, has a special duty ... Can it be, then, that in the great hemispheric ganglion alone, this specialization of duty does not hold?" (pp. 607-608).
With the ground prepared by the sensory-motor associationism of Bain and the evolutionary psychophysiology of Spencer, all that was needed in order to overcome the last obstacle to extension of the sensory-motor view to the cortex was the impetus provided by striking research findings and new experimental techniques. In the period between 1861 and 1876, Broca, and Fritsch and Hitzig, provided the first critical findings and techniques; Jackson, heavily influenced by Spencer and Bain, provided the extension of the sensory-motor paradigm to the cortex; and Ferrier, influenced by Bain and Jackson, provided the experimental capstone to the classical doctrine of cortical localization.
Paul Broca (1824-1880) [see figure 18] was born in the township of Sainte-Foy-La-Grande in the Dordogne region of France and studied medicine at the Hôtel Dieu in Paris. A lifelong interest in physical anthropology led to his becoming one of the original members of the Société d'Anthropologie and a founder of the Revue d'anthropologie and the Department of Anthropology at the University of Paris. On the 4th of April, 1861, at a meeting of the Société d'Anthropologie, Broca sat in the audience as Ernest Aubertin presented a paper citing several striking case studies to argue the craniological case for cerebral localization of articulate language.
Aubertin was the student and son-in-law of Jean Baptiste Bouillaud, a powerful and distinguished figure in Parisian scientific circles, himself a student of Gall and founding member of the Société Phrénologique. As early as 1825, Bouillaud had published a paper that employed clinical evidence to support Gall's view that the faculty of articulate language resides in the anterior lobes of the brain. For almost 40 years, in the face of considerable opposition, Bouillaud had succeeded in keeping the cerebral localization hypothesis alive. Thus, Aubertin was merely carrying on in his father-in-law's tradition when he promised to give up his belief in cerebral localization if even a single case of speech loss could be produced without a frontal lesion.
Intrigued, Broca decided to take up Aubertin's challenge. Within a week, a M. Leborgne ("Tan"), a speechless, hemiplegic patient died from gangrene on Broca's surgical ward. In the "Remarques sur le siége de la faculté du langage articulé, suivies d'une observation d'aphemie (perte de la parole)," published in 1861 in the Bulletins de la société anatomique de Paris, Broca presented a detailed account of his post-mortem examination of Tan's brain. What he had found, of course, was a superficial lesion in the left frontal lobe, a finding confirmed a few weeks later by another case in which post-mortem examination revealed a similar lesion.
While neither the conception of a faculty of articulate language nor even the notion of its localization in the anterior portion of the brain were especially novel in 1861, what Broca provided was a research finding that galvanized scientific opinion on the localization hypothesis. The detail of Broca's account, the fact that he had gone specifically in search of evidence for the patients' speech loss rather than employing cases post hoc as support for localization, his use of the pathological rather than the craniological method, his focus on the convolutional topography of the cerebral hemispheres, and, perhaps most importantly, the fact that the time was ripe for such a demonstration, all contributed to the instantaneous sensation created by Broca's findings. Now all that was needed was a technique for the experimental exploration of the surface of the hemispheres, and this technique was contributed jointly by Gustav Theodor Fritsch (1838-1927) and Eduard Hitzig (1838-1907).
In 1870, in the Archiv für Anatomie, Physiologie, und wissenschaftliche Medicin, Fritsch and Hitzig published a classic paper that not only provided the first experimental evidence of cortical localization of function but, at a single stroke, swept away the age old objection to localization based on the idea that the hemispheres fail to exhibit irritability. Employing galvanic stimulation of the cerebrum in the dog, Fritsch and Hitzig provided conclusive evidence that circumscribed areas of the cortex are involved in movements of the contralateral limbs and that ablation of these same areas leads to weakness in these limbs. Their findings established electrophysiology as a preferred method for the experimental exploration of cortical localization of function and demonstrated the participation of the hemispheres in motor function.
At approximately the same time in England, John Hughlings Jackson (1835-1911) was converging from a different direction on a sensory-motor view of hemispheric function. Hughlings Jackson [see figure 19] was born in Providence Green, Green Hammerton, Yorkshire, England. He began the study of medicine as an apprentice in York and completed his education at the Medical School of St. Bartholomew's Hospital in London and the University of St. Andrews. Among several hospital appointments, perhaps his most important was as physician to the National Hospital for the Paralysed and Epileptic, Queen Square. His contributions to neurology and psychology are scattered throughout papers appearing in a variety of journals between 1861 and 1909. Many of the more important papers have been gathered together in the two volume Selected Writings of John Hughlings Jackson, edited by James Taylor (1931/1932).
While Jackson's specific contributions to our understanding of the etiology, course, and treatment of neurological disorders ranging from aphasia and chorea to epilepsy and vertigo were of exceptional importance, it is his evolutionary conception of the localization of sensory-motor function in the cerebrum that was most influential for psychology. This conception was, of course, developed under the inspiration of Spencer. As Young (1970) describes it, "Spencer's principles of continuity and evolution provided Jackson with a single, consistent set of variables for specifying the physiological and psychological elements of which experience, thought, and behaviour are composed: sensations (or impressions) and motions. All complex mental phenomena are made up of these simple elements -- from the simplest reflex to the most sublime thoughts and emotions. All functions and faculties can be explained in these terms" (p. 199).
Jackson's paper, "On the anatomical & physiological localisation of movements in the brain," serialized in the Lancet in 1873, is representative of a series of papers during this period that reflect the sensory-motor conception. In an interesting and revealing preface to an 1875 pamphlet, Clinical and Physiological Researches on the Nervous System , which reprints the 1873 paper, Jackson describes the background for the hypothesis as it developed in his own work, almost as though he is endeavoring to establish his priority. Fond as always of quoting himself, Jackson reprints a footnote from an 1870 paper, "The study of convulsions," that summarizes his views:
"It is asserted by some that the cerebrum is the organ of mind, and that it is not a motor organ. Some think the cerebrum is to be likened to an instrumentalist, and the motor centres to the instrument -- one part is for ideas, and the other for movements. It may, then, be asked, How can discharge of part of a mental organ produce motor symptoms only? ... But of what 'substance' can the organ of mind be composed, unless of processes representing movements and impressions ...? Are we to believe that the hemisphere is built on a plan fundamentally different from that of the motor tract? ... Surely the conclusion is irresistible, that 'mental' symptoms ... must all be due to lack, or to disorderly development, of sensori-motor processes" (p. xi-xii).
Thus, by the early 1870s, Jackson had fully articulated a general conception of the functional organization of the nervous system. In the words of Young (1970), this "constituted the last stage in the integration of the association psychology with sensory-motor physiology ... (and) involved an explicit rejection of ... work which had hindered a unified view: the faculty formulation of Broca, and the unwillingness of Flourens, Magendie, Müller, and others to treat the organ of mind -- the highest centres -- on consistently physiological terms" (p. 206). In Jackson's work, the theoretical analysis of cerebral localization reached the full extent of its 19th century development. In the systematic, experimental investigations of his friend and colleague, David Ferrier (1843-1928), this analysis was strikingly confirmed.
Ferrier [see figure 20] was born and educated in Aberdeen, Scotland where he studied under Alexander Bain. At Bain's urging, he journeyed to Heidelberg in 1864 to study psychology. During that period, Heidelberg was home to both Helmholtz and Wundt. Indeed Wundt had only recently (1862) completed the Beiträge zur Theorie der Sinneswahrnehmung [see 40] that contains the first programmatic statement of his physiological psychology and Ferrier must certainly have encountered Wundt's views.
On his return, Ferrier completed his medical training at the University of Edinburgh and served, for a short time, as assistant to Thomas Laycock, who had been the first (see Laycock, 1860 for a priority claim) to articulate the concept of "unconscious cerebration." Among other appointments, Ferrier, like Jackson, served as physician to the National Hospital, Queen Square. Influenced as Jackson had been by Bain and Spencer, Ferrier set out to test Jackson's notion that sensory-motor functions must be represented in an organized fashion in the cortex and to extend Fritsch and Hitzig's experimental localization of motor cortex in the dog. Employing very carefully controlled ablations and faradic stimulation of the brain, an advance over the galvanic techniques available to Fritsch and Hitzig, Ferrier succeeded in mapping sensory and motor areas across a wide range of species [see figure 21]. His first paper, "Experimental researches in cerebral physiology and pathology," appeared in 1873 in the West Riding Lunatic Asylum Medical Reports; but it was the impact of the cumulated cross-species research brought together in 1876 in The Functions of the Brain  that served to confirm the installation of sensory-motor analysis as the dominant paradigm for explanation in both physiology and psychology.
Wozniak, Robert H. "Mind and Body: Rene Déscartes to William James"
Bryn Mawr College, Serendip 1995
Originally published in 1992 at Bethesda, MD & Washington, DC by the National Library of Medicine and the American Psychological Association.
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