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During the 1850s Paul Broca (1824-1880) became an important and respected member of the French scientific establishment, sufficient to overcome noteworthy political obstacles and to found the Société d'Anthropologie in 1859 and remain its secretary until his death (Schiller 1979). In a series of papers published between 1861 and 1866 employing the clinico-pathological correlation technique to analyze a loss of speech (aphemia), Broca persuaded a majority of his colleagues that there was a relatively circumscribed center, located in the posterior and inferior convolutions of the left frontal lobe, that was responsible for speech (langage articulé). His conclusions have been enshrined in the eponyms Broca's Area and Broca's APHASIA. Whether or not Broca's conclusions constituted a scientific discovery, and whether or not he merits priority in this matter, has been debated ever since (Moutier 1908; Souques 1928; Schiller 1979; Joynt and Benton 1964; Young 1970; Whitaker and Selnes 1975; Henderson 1986; Cubelli and Montagna 1994; Eling 1994; Whitaker 1996). What is not in doubt is that cognitive neuroscience irrevocably changed after the publication of Broca's papers; the cortical localization of language, and by implication other cognitive functions, was now a serious, testable scientific hypothesis.
Broca's sources of knowledge about brain, intelligence, and language functions included François Leuret and Louis P. Gratiolet (1839-1857) and Gratiolet (1854), in which the history of cerebral localization was well described. Gratiolet, a member of the anthropology society, argued from comparative anatomy the importance of the frontal lobes. Bouillaud, who had been influenced by Gall, argued for language localization in the frontal lobe on clinical evidence. Broca knew Bouillaud personally, had been to his house, and even had considered studying internal medicine with him (Schiller 1979: 172). In early 1861 meetings of the anthropology society, Auburtin led a discussion on the question of localizing mental functions to distinct parts of the brain, specifically on localizing speech to the frontal lobe. Broca participated in that debate (1861a), and his April 1861 report noted the relevance of case Leborgne, alias "tan" (1861b). He chose the older, more prestigious anatomical society as the venue for publishing this case (1861c), stating his belief in cerebral localization in the convolutions, outlining his views regarding regional structural differences of the convolutions (prefiguring cytoarchitectonics) and suggesting that Leborgne's left frontal lesion and loss of speech furnished evidence in support of these views. Broca's second case of loss of speech, patient Lelong, was also published in the same bulletin (1861d); he expressed surprise that the lesion was in the same place as in the previous case -- left posterior frontal lobe -- and again noted the compatibility with the theory of localization.
The role of the left versus the right hemisphere in language officially arose in 1863 when Gustave Dax deposited for review a report that his father, Marc Dax, had presented to the Montpellier medical society in 1836. In this report the clinico-pathological correlations of forty cases of aphasia suggested that language function resided in the left hemisphere. While the existence of the 1836 Marc Dax mémoire is not absolutely proven, the version written by his son Gustave Dax existed on 24 March 1863, when it was deposited for review (it was published in 1865). The record also shows that Broca's own publication suggesting the special role of the left hemisphere did not appear until 2 April 1863. The priority issue, Dax or Broca, is ably discussed by Schiller (1979), Joynt and Benton (1964), and Cubelli and Montagna (1994); what is not in dispute is that by 1865 the lateralization of language had become an empirical question.
Broca's work was one more part of the ongoing debate on cerebral localization initiated by Gall and Bouillaud in the early nineteenth century; "What Broca seems to have contributed was a demonstration of this localization at a time when the scientific community was prepared to take the issue seriously" (Young 1970: 134-135). Less often appreciated is the fact that every component of Broca's analysis had been published before, between 1824 and 1849. In 1824, Alexander Hood, an obscure Scottish general practitioner who believed in phrenological doctrine, published a case of what would later be called Broca's Aphasia. Hood distinguished between the motor control of the vocal tract musculature, speech output control, and lexical-semantic representation, albeit not in those terms, and assigned each a different left frontal lobe locus. Bouillaud (1825), discussing cases presented earlier by Francois Lallemand, clearly presented classic clinico-pathological correlation techniques as applied to expressive language. Marc Dax observed (1836/1863) that Lallemand's case histories documented that aphasia-producing lesions were in the left hemisphere. The historical question is to explain why Paul Broca in the 1860s was suddenly able to focus neuroscience on brain localization and lateralization of language.
One must acknowledge that Gall's craniology (Spurzheim's phrenology) had stigmatized research on cerebral localization. The doctrine of (brain) symmetry, persuasively articulated by Xavier Bichat at the beginning of the century, posed a major theoretical hurdle. Jean-Pierre Flourens (1794-1867), an influential member of France's scientific establishment, opposed the cortical localization of cognitive functions. Finally, language was considered as verbal expression, as speech or as an output function primarily motoric in nature. What we today recognize as language comprehension fell under the rubric of intelligence or general intellectual functions. Much of the clinical evidence that had been marshaled against Bouillaud came from patients with posterior left hemisphere lesions who manifested aphasia; with no theoretical construct of language comprehension such data could only be interpreted as counter-evidence. The same arguments were offered against Broca, of course. It was the work of Theodor Meynert (1867), Henry Charlton Bastian (1869), and finally Carl Wernicke (1874) on disorders of comprehension that completed the model of language localization, thus setting the stage for the development of modern neurolinguistics and creating a historical niche for Paul Broca.
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Copyright © 1999 Massachusetts Institute of Technology