The French anatomist, anthropologist, and surgeon Pierre Paul Broca (1824-1880) is best remembered for his descriptions of two patients who had lost the ability to speak after sustaining damage to the left frontal lobe of the brain. Broca’s observations of these patients, and the conclusions he reached after his post-mortem examinations, would lead to major advances in the understanding of the brain, and laid the foundations for modern neuropsychology.
In 1859, Broca founded the Societe d’Anthropologie de Paris. Two years later, several heated debates had arisen there: one was about the relationship between brain size, race and intelligence, and the other about the localization of cerebral function. In the latter, one of the main proponents of the localization theory was Franz Joseph Gall (1758-1828), the founder of phrenology. Gall and others believed that the faculty of articulate speech resided in the anterior lobes of the brain, but most members of the scientific community were cautious; some argued that Phineas Gage provided strong evidence against the theory that speech was localized to the anterior lobes. Gage, a railroad worker, had suffered severe frontal lobe damage in 1848 when a tamping iron was propelled through his skull, but had retained his ability to speak after the injury.
Another supporter of localization theory was Ernest Aubertin (1825-1893), who presented his data to the Societe on April 4th, 1861. Aubertin’s father-in-law, Jean-Baptiste Bouillaud (1796-1881), a supporter of Gall, had noted a link between aphasia and the frontal lobes in 1825, and offered 500 francs to anyone who could produce an aphasic patient without a frontal lobe region. Aubertin had seen dozens of aphasic patients with frontal lobe damage, and continued to advocate Bouillaud. An association between frontal lobe damage, aphasia and paralysis of the right side of the body had also been extensively documented in the 1830s by the French neurologist Marc Dax (1771-1837), but, for some unknown reason, he did not publish or present his results; they only came to light when his son published them in 1865. At the Societe, Aubertin lay down the gauntlet to Broca: he stated that if he, Broca, or anyone else were to find an aphasic patient without a lesion in the frontal cortex, he would renounce his views. Broca, who had until then seemed somewhat indifferent to the debate on localization of function, suddenly took interest.
A few days after Aubertin’s presentation, Broca encountered his first aphasic patient, a man named Leborgne. Broca was then working at the Bicetre Hospital in the southern suburbs of Paris. Leborgne had been admitted to the hospital at the age of 21, unable to speak for some time, but otherwise able-bodied and intelligent. About 10 years after his admission, Leborgne began to lose the movements of his right arm; the paralysis subsequently spread to the right leg, after which he became permanently bed-ridden. In April, Leborgne developed a gangrenous inflammation, and was transferred to the hospital’s surgeons, where Broca encountered him for the first time. Leborgne died on April 17th, 1861, just 6 days after Broca first met him. Nevertheless, this first case study became Broca’s most famous one. Upon Leborgne’s death, Broca removed his brain and examined it; he found a large lesion in the frontal lobe of the left hemisphere, just as Aubertin had predicted, and determined that it had been caused by syphilis. The next day, Broca presented Leborgne’s brain, the results of his examination, and a description of his symptoms at the Societe d’Anthropologie:
He could no longer produce but a single syllable, which he usually repeated twice in succession; regardless of the question asked him, he always responded: tan, tan, combined with varied expressive gestures. This is why, throughout the hospital, he is known only by the name Tan…[at autopsy it was found that] most of the other frontal convolutions were entirely destroyed. The result of this destruction of the cerebral substance was a large cavity, capable of holding a chicken egg, and filled with serous fluid. The softness had spread up to the ascending fold of the parietal lobe, and down to the marginal fold of the temporal-sphenoidal lobe; finally, in the depths, [it spread to] the region of the insula and the extraventricular nucleus of the striate body; it was the lesion of this last organ which was responsible for the paralysis of the movement of the two limbs of the right side. However…the original seat of the softness is the middle part of the frontal lobe of the left hemisphere; it is there than one find the most extensive lesions – the most advanced and the oldest.
Broca’s presentation of Leborgne’s brain to the Societe had provided the first solid anatomical proof of the localization of cerebral function. And, later that year, he was sent a second patient with symptoms similar to those of Leborgne. This patient, named Lelong, was an 84-year-old male who had suffered a stroke one year earlier; in consequence, he was capable of uttering only five words: ‘oui’, ‘non’, ‘toi’, ‘toujours’ and ‘Lelo’ (meaning, respectively, ‘yes’, ‘no’, ‘always’, a mispronunciation of ‘trois’, meaning ‘three’, which he used to represent any number, and a mispronunciation of his own name). Upon examination, Broca found that the lesion in Lelong’s brain was in approximately the same region as Legorne’s. At a meeting of the Societe d’Anatomie, Broca stated that “the lesion occupied exactly the same seat as with the first – immediately behind the middle third, opposite the insula and precisely on the same side.” Broca subsequently examined the brains of a number of other patients with speech disturbances, and found that they too had suffered lesions of the third convolution of the left frontal lobe. Together, these patients provided Broca with confirmation that “the integrity of the third frontal convolution (and perhaps of the second) seems indispensable to the exercize of the faculty of articulate language.”
Broca became one of the most vocal supporters of the localization theory, but stressed that his localization of speech differed from that of the phrenologists. Regarding Phineas Gage and other such cases that seemed to contradict the localization theory, Broca theorized that it was only in most right-handed people that speech was localized to the left hemisphere. In left-handed people, it may reside in the right hemisphere. Broca further suggested that the right hemisphere could take over the function of speech if the left hemisphere was damaged at an early age. Eventually, the scientific and medical communities came to accept that speech was localized in the frontal cortex, and it may have been because of Broca’s status – a distinguished scientist and physician, and founder and secretary of the Societe d’Anthropologie – that they did so. Thereafter, Broca referred to the third convolution of the left frontal lobe – the posterior inferior frontal gyrus in modern terminology – as the circonvolution du langage. He believed that his patients were capable of understanding everything that was said to them, and referred to the loss of speech he had observed in them as ‘aphemia’. Later, the pioneering Scottish neurophysiologist David Ferrier would call that region of the brain Broca’s convolution, and the speech deficit that occurred as a result to damage of the area would be renamed ‘aphasia’ by Armand Trousseau in 1864. Broca’s convolution eventually came to be known as Broca’s area, and the language deficit associated with it came to be known as Broca’s aphasia.
Photographs showing lateral views of the brains of Leborgne (left) and Lelong (right). Broca preserved the organs by immersing them in alcohol; he then donated them to the Musée Dupuytren in Paris.
It is now widely accepted by modern neurologists that Broca’s area is one of at least two speech centres located on the lateral surface of the left hemisphere. Broca’s area is thought to be involved primarily in the production of speech; it is found immediately anterior to, and can be considered as a part of, the primary motor cortex. Broca’s area controls muscles in the mouth and larynx required for vocalization; hence, Broca’s aphasia is sometimes called motor aphasia. (The other speech centre is called Wernicke’s area; clinical studies show that damage to this area results in an inability to understand speech. Wernicke’s area is therefore involved in the comprehension of language. It is located further back, in the superior temporal lobe of the left hemisphere, and is connected to Broca’s area by a tract of nerve fibres called the superior longitudinal fasciculus.)
These long-held assumptions about the location and function of Broca’s area are the basis of hundreds of clinical studies. The symptoms of Broca’s aphasia include difficulty in finding the right words and articulating them properly, and problems with repeating and producing sentences with complex grammatical structures. Neurologists normally ascribe all these symptoms to damage to Broca’s area. In numerous neuroimaging studies, activation of Broca’s area is taken as strong evidence that the speech centres are being recruited during performance of a task, but recent evidence obtained from studies of language impaired patients suggest that other regions of the brain are also involved in speech production.
However, the findings of several studies carried out in recent years suggest that these assumptions are an oversimplification, and that the relationship between Broca’s area and Broca’s aphasia is more ambiguous than it was previously thought to be. For example, studies of lesions of speech-impaired patients show that Broca’s aphasia often occurs as a result of damage to surrounding frontal cortex, underlying white matter, or even deeper below the brain’s surface, in the insula or basal ganglia. Also, observations of language-impaired patients show that damage to Broca’s area results in only a temporary disruption of speech: patients with new lesions in that area are often mute for several weeks following injury, but the ability to speak soon returns. By contrast, Leborgne, Lelong and other patients examined by Broca suffered from severe and persistent aphasia. Together, these findings suggest that Broca’s area is not the only brain region involved in speech production.
Now, a neuroimaging study of Leborgne’s and Lelong’s brains, published earlier this year in the journal Brain, further suggests that neuroscientists need to re-evaluate their ideas about Broca’s area, or, at least, need to reconsider the nomenclature they use when describing the location of Broca’s area. Nina Dronkers, of the VA Northern California Health System in Martinez, and her colleagues, collected the Leborgne’s and Lelong’s brains from the Musee Dupuytren in Paris, and transported them to the neuroradiology service at the Centre Hospitalier National d’Opthalmologie des Quinze-Vingt. There, Dronkers and her group re-examined the brains using high resolution magnetic resonance imaging (MRI). Although two neuroimaging studies have recently been performed on Leborgne’s brain, Lelong’s brain has remained unexamined, since the nineteenth century, in the Paris museum.
This re-examination revealed that, in both Leborgne and Lelong, the most extensive damage is not in the part of the frontal lobe most often designated as Broca’s, but rather in the region just anterior to it – thus, the area considered by Broca to be crucial for speech atriculation is not the same as the region that is today called Broca’s area. Further, in both Leborgne’s and Lelong’s brains, the damage extended far deeper than the lateral surface of the frontal lobe than Broca’s reports suggested, and it is probable that these deeper lesions contributed to the speech deficits that the patients presented with. But Dronkers stresses that the findings do not in any way detract from Broca’s outstanding work. Broca had in fact noted that Leborgne’s legions extended posterior to the third convolution of the frontal lobe, but suggested that this damage had occurred after the onset of Leborgne’s aphasia, and that it was unrelated to the speech disturbances. During his examinations, Broca had actually chosen not to dissect the brains, so could only assess the superficial damage, and only inferred the extent of the damage to deeper structures. “Fortunately,” writes Dronkers, “Broca had the foresight in preserving these historic brains and, in some ways, Leborgne and Lelong can speak to us more eloquently now than they could over 140 years ago.”