Pierre-Paul Broca has been referred to as brilliant neurologist, surgeon and anthropologist, a child prodigy, and a man well ahead of his time. Broca became early a professor of surgical pathology at the University of Paris and a well known medical researcher in many areas. He held degrees in mathematics, literature, and physics. His early scientific work focused on the histology of cartilage and bone, the treatment of aneurisms, infant mortality, and cancer pathology. Also a wonderful brain anatomist, he made contributions to understanding the limbic system. Broca was also responsible for his discovery of the speech centre, known today as Broca's area.
He studied the brain of aphasic patients, which were people who were unable to talk. The most well known person he studied was the first patient at the Bicetre Hospital named "Tan" who had a neurosyphilitic lesion in one side of the brain which controlled speech. On April 4, 1861, at a meeting of the Societe d' Anthropologie, Broca sat in the audience as Ernest Aubertin presented a paper discussing several case studies to argue the craniological site for cerebral localization to articulate language. Aubertin was the student and son-in-law of Jean Baptiste Bouillaud, a powerful figure in scientific circles. He was a student of Gall's and a founding member of Societe Phrenologique. In 1825 Bouillaud published a paper that implied evidence to support Gall's view that articulated language lies in the anterior lobes of the brain. For forty years, this cerebral localization hypothesis was accepted as the basis of language articulation. At this talk, Aubertin stated that he would give up his belief in cerebral localization if even one case of speech loss could be produced without a frontal lesion (Mind, Brain, and Adaptation, 2000). Broca was intrigued and interested in this concept, so he decided to conduct an experiment and determine what he found. Within a week, M. Leborgne, famously referred to as "Tan", died from gangrene on Broca's surgical ward. Tan was a speechless and hemiplegic patient. Broca performed a detailed post-mortem examination on Tan's brain, and found a superficial lesion in the left frontal lobe. To support his findings, a similar post-mortem examination done a few weeks later confirmed that there was a similar lesion in this person also. This section in the brain, referred to as the left inferior frontal gyrus of the brain was then determined to be the centre for speech, today called Broca's area. This was one of the first discoveries of a separation of function between the left and right hemispheres of the brain. It was also one of the first indications that specific brain functions exist in particular locales in the brain, and that there is a connection between the anatomy of the brain and what the brain does (Sagan, 1979). Broca next saw an eighty four year old man named LeLong who had suddenly lost his speech. He conducted a post-mortem examination of his brain that showed a lesion in the left frontal lobe. The right side of his brain was perfectly normal in all of the patients he examined. In 1863 he described over twenty five aphasic patients who all had lesions in the left hemisphere. Broca went on to hypothesize that the left hemisphere develops more quickly than the right, and so it is more advanced. He also made important investigations of the limbic region, which is now known to involve human emotions.
People suffering from Broca's aphasia frequently exhibit agrammatism. Language performance is highly compromised and speech production is reduced to disjointed words so that morpho-syntax is very poor, with omission of function words and inflection. Clinical evidence has shown a better preservation of competence in comprehension and reading (both decodification tasks) with respect to speech or writing (codification). During reading tasks, repair strategies are usually adopted so that the patients make attempts to correct their errors. Troubles experienced by Broca's aphasics in controlling their phonological structure in both segmental ad suprasegmental levels reveal a deficit due to lesions in the left hemisphere. In particular, these patients are not able to regulate timing and F0 patterns over a rather extended prosodic domain, because their speech programming is constrained to small units of speech (see Danly et al., 1979; Danly & Shapiro, 1982; Gandour et al., 1989).
More relevant is the issue related to hemisphere specialization: left-hemisphere dominance is currently assumed for ‘core' (i.e. representational) linguistic functions in right-handed adults (Caplan, 1987). In this domain, an fMRI study (Schirmer et al., 2001) has recently demonstrated how prosody may be processed by both the hemispheres. The prosodic aspects (in particular, speech timing) strictly related to the linguistic structure are performed by the left hemisphere, whereas the emotive and affective prosody is related to the right hemisphere. As a result, Broca's area seems to be involved in prosody inasmuch it conveys linguistic information, although there may be other areas in the brain with overlapping functions.
Broca's aphasic patients show some recurrent phonological features:
non-fluency, i.e. slow and laboured speech
agrammatism or telegraphic speech
par aphasias, i.e. target words replaced by phonetically similar words
In particular, speech output by Broca's aphasics has been often described as dysprosodic. Although the clinical use of this linguistic term is ambiguous, as referring to all aspects of prosody, it seems to have been adopted with primary reference to a remarkable deficit in F0 programming. The most relevant features recoverable in literature are:
- impairment of melodic modulation;
- isochrony of syllables;
- alteration of speech timing.
The neurological symptoms of Broca's aphasia are hemiplegic and hemi paresis of the right side of the body and also apraxia of the limbs on the right side of the body.
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