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The Broca's contribution to our knowledge of localization of speech production

In current times of successful monitoring of newly discovered neurophysiological cortico-cortical connections between the Broca's area and orofaryngeal motor cortex (Greenlee et al.) and Broca's area and the Wernicke's auditory field (Matsumoto et al.) in the dominant hemisphere or vice versa, it is interesting to look back and remind ourselves how Broca’s discovery, became the cornerstone of our contemporary knowledge in cerebral localization beginning with the speech centre. On the basis of Galvani’s experiments, Volta discovered the electrical pile in 1800 and a decade later, Rolando wrote about the electrical nature of the complex nerve-muscle. Broca, in the 2nd half of the 19th century, was of course, not familiar with the scientific (electrophysiological) methodology of our age as hemispheres back then were divided into cerebral lobes (Gratiolet). But Broca happened to live in an opportune time when a very controversial, but fruitful, discussion was developing among scientists, who were beginning to ask themselves on the location of the speech centre. Surprisingly enough, the unconventional chief of the Hôpital de la Charité in Paris, Bouillaud, offered 500 francs to whoever could demonstrate that speech disorders were not related to the frontal lobe. Bouillaud and Aubertin, his son in law, were named Gall’s “blind followers”, the founder of pseudoscience phrenology. Flourens, Bonaparte’s secretary of science and education, concluded, after investigating Gall’s theories, that the brain functioned as a whole– a holistic view as there ‘were no circumscribed functionally specialized cortical centers”. Such ‘erroneous’ conclusion, presented by the greatest authority of that time, became the scientific doctrine, which lasted for half a century until it was disapproved by Broca’s discovery. Broca was appointed surgeon in Bicêtre Hospital in January the 1st 1861. He was 37 years of age then. Three months later, on the 4th of April 1861, in front of the Anthropological Society of Paris, Auburtin described an articulatory organ and a cerebral centre that he believed resided in the left frontal lobe. Auburtin’s claim was based entirely on clinical (Galls and Bouillaud’s) observations. Broca obviously heard Auburtin’s claims and was intrigued by the topic. Shortly thereafter, Broca published his paper in the Bulletin de la Société Anthropologique in which he related the destruction of the left frontal lobe to aphasia. Leborgne, also know as ‘Tan’, the patient who made Broca famous, was admitted to the hospital in 1840 when he was 30 years old. Tan died on April 17th 1861 (21 years after admission!) because of the widespread gangrene in the hip region. The following day, Broca presented the autopsy findings (macroscopic and without brain cuts!?) before the society and suggested that a softening of Tan’s brain in the third left frontal convolution was responsible for his speech disturbance. The next aphasic patient was M. Lelong. In Broca’s words, “The integrity of the third frontal convolution seems indispensable to the exercise of the faculty of articulate language.” Broca himself, although not fully aware of the historical importance, made the first step towards cerebral localization in spite of strong opposition (Flourens, Marie etc) by the establishment. Thereafter in 1870 Fritsch and Hitzig referred on the electrical irritability of the nervous tissue in animals, and Bartholow in man. In 1874, Wernicke published his book Der aphasische Symptomencomplex“, describing sensory aphasia. Ferrier, together with Jalo (neurosurgeon), drew up the localization map in the monkey. Lichtheim described the importance of conductive fibers and came up with the connection theory between hearing and speaking. Dejerine pointed out in 1891/92 the importance of the pathways connecting visual cortex with Wernicke's area (alexia, dyslexia) – the problem of seeing and reading words. Foerster, and later his pupil Penfield, together with Jasper, Rasmussen and Boldrey, performed electrical cortical stimulation in awaken patients during numerous neurosurgical procedures, came up with the cortical map with motor and sensory homunculus in the central region. Geschwind (language theory) and other investigators (Amounts) eventually made numerous contributions to the field (citoarhitectonic, genetic, connections etc.). In the modern light of the mirror neurons’ theory (Rizolatti-Arbib) and useful imitation in language development (“within our grasp”) (Jacoboni), and the idea that the Broca’s area, or its small part, represents a kind of “supramodal hierarchical processor” (not existing in other species) that controls the motor and premotor cortex for speech production, one can just admire Broca’s determination when proclaiming “nous parlons avec le hemisphere gauche.” occurred prior to Fritsch and Hitzig, Bartholow, Wernicke, Dejerine, Ferrier, Penfield- Rasmussen’s works on cerebral localization and, above all, before the idea of handedness/hemispheric dominance. It is astonishing for a researcher as Broca, who was not equipped with modern electrophysiological armamentarium, to realize such a discovery with a simple clinico-pathological correlation.

Broca; motor speech area; aphasia; history; cerebral localization

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